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TMM's TT02 / TT02B Garage

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Thought I’d finally start this thread as I’m currently building another one from scratch, and it would be a good opportunity to share some tips along the way for building these cheap plastic bathtubs-on-wheels to cope with decent power, handle decently and be reliable. I hope that this might be a good primer for someone to make the leap from just following the kit instructions to being able to fit parts designed for other cars (or questionably fitting aftermarket parts!) and do their own mods.

Questions such as “how much power can the TT02 actually handle?”, “what upgrades are worthwhile?”, “how do I stop <insert part of the drivetrain here> slipping/breaking”, “what is ‘shimming’ and how do I do it on my TT02?” and “how do I work out what pinion/spur gear ratio to use?” will be answered in due course.

So first a background of how I came to be a fan of the TT02. The first TT02 I bought was a TT02D. It was my first ‘hobby grade’ RC car. I knew I wanted a drift car, and wanted a kit instead of ready-to-run so the TT02D seemed to fit the bill. After building it and running it, I soon got bored of the 50/50 style of drifting.  First thing I tried was removing the front diff but that just resulted in endless spinning out due to the mediocre steering lock that the stock TT02 has (and lack of driving talent). Then I discovered counter-steer or ‘CS’ drift setups - soon after I was learning about one-way and locked/’spool’ differentials, and working out how to modify the TT02 to adjust camber, caster, ackermann, kingpin inclination and get more lock like the expensive RC drift chassis’ had. Also along the way I bought a lot of blue aluminium hopups since blue aluminium parts are cool :P

After seeing some speedrun videos, I decided that was the next thing for a TT02 to accomplish and bought a second chassis, a TT02RR, since I didn’t want to dismantle my drift setup. My logic was that if I broke any part on either car I could probably just temporarily rob parts off the other car so I didn’t have to wait for replacements to arrive. This as it turns out, this is the strong point of the TT02 – it’s a jack of all trades that can basically do anything – drift, rally, touring, speedrun – you can have a whole lineup of them and share parts if/when they break, or just have one of them and convert it to do something else when you get bored of it.

Anyway, so the TT02RR was my first car with a LiPo battery and brushless motor – in this case a 7.5t motor and 2S LiPo (go big or home home, right?). Somehow I decided that a 64dp 82t spur and 46t pinion would fit so that’s what went in to it, which turned out to be fairly decent starting point for speedruns. With this setup the car easily did 75km/h and some spectacular high speed crashes ensued. Nothing ever actually broke, although I bent various turn buckles, a couple of metal dogbone axles, lost count of the number of crunchy bearings replaced and kerbed every millimeter of the wheels by driving wrong side up.  I learnt a bit about the importance of diff oils/spools and suspension setup for stability. Eventually I lowered the gear ratio as far as possible (by clearancing the gear cover) fitting a 60t spur and 69t pinion. The car could hit 100km/h over a 100m stretch of road but I could only do a few runs back to back before the motor got too hot. At this point it ended up sitting on a shelf since I didn’t feel it could go any faster unless I got a new motor, or ventured far away to find a longer smooth road and risk burning up my motor.
ZE8B14h.jpg

The ‘drift’ car meanwhile got a set of rally block tyres installed and the suspension stroke and ride height was increased as much as possible using some cheap aftermarket long shocks and custom parts. I put a 21.5t brushless motor in, then upgraded the Tamiya ESC to the same 120A Trackstar one as my other car so I could run a 3S battery. Swaybars from an XV-01 chassis were retrofitted. I managed to make it much more capable off-road but it still wasn't enough to run properly on longer grass and it rolled easily when going over jumps.
ezVC2Or.jpg

HIQkf6w.jpg
Qh78uRD.jpg

The 21.5t on 3S was pretty powerful but of course more power is always better. So the 7.5t motor ended up in it, still on 3S of course, even though it’s not recommended for the motor. I figure if theres a 3.5t motor in the same motor series rated at 705Watts on 2S and my 7.5t motor is rated at 410Watts on 2S, then on 3S it will be 410*(3/2)^2 = 922Watts. Well, that’s not a great deal more than 705Watts so with appropriate gearing and cooling it should be fine, right? My ESC says it’s good for >5.5T on 3S for ‘on-road’ and >8.5T on 3S for ‘off road’ – that’s a bit ambiguous but I’ll assume it’ll be fine. And it is fine :). I put slick rubber tyres on the car, lowered it a bit made the rear sway bar extremely stiff and now it does high speed 4WD powerslides/drifts - I'll have to shoot a video of that but in the mean time here it is on plastic tyres:

So that brings us up to date. I want to build a car that is more capable off road, can run on grass and handle some small jumps, so I bought this:

ySldLIJ.jpg

TT02B, Neo Scorcher (the best looking one ;)). The aim is to swap the fast bits from the 7.5t/3S car into this and do similar upgrades where parts are not compatible (suspension/driveshafts). The on road TT02 will then be converted back to 21.5t/2S with a CS drift setup - I’ll document that one in this thread too.


So, on with the TT02B build! If the build seems a bit out of order, it's because it is. I'm not following the manual to the letter and some steps will be held up waiting for parts. 

We begin with the bathtub chassis, propeller shaft, prop joints and spur gear The prop shaft is an aluminium one from Eagle Racing, with steel prop joints - I'm using this for no other reason than because I already had it sitting unused. If you're on a budget the standard plastic propshaft and joints are probably fine even for this power - upgrade them only if they break. For the spur gear I've opted for the TT02 high speed gear set, which we only need the blue aluminium bits from - the 68t spur gear that comes with the HS gear set gets tossed away and a 48dp 78t RW Racing gear is mounted. I had found previously with 7.5t/3S combo and 64dp gears that adjusting them to a tight mesh was critical to prevent the pinion/spur gears jumping teeth. With the bigger wheels and grass running on the TT02B I'll inevitably have to run a higher final drive ratio (smaller pinion / bigger spur) which results in even higher torque handled by the gears, and even higher probability of jumping teeth on 64dp gears so I decided to go to coarser 48dp gears. From some rough calculations I figured 82t and 78t spurs, 20t and 18t pinions would give me evenly spaced ratios in the ballpark of what I think I need (FDR=~10 to 12) and should fit. The reasoning behind that FDR was that between 7 and 8 worked well for that motor setup on my on-road car, so accounting for the difference in wheel diameter (+30%) and then perhaps a little bit more because of the extra drag of running on grass and we're in the FDR = 10-12 range. I guess we'll find out if that logic holds when I finally run it. It turns out that the 82t spur is too big to fit, so I've installed the 78t which just barely fits. As always, where ever a metal screw goes into metal, blue Loctite (#243) is used, so the screws holding the spur to the blue aluminium high speed mount get some to prevent them rattling loose. In hindsight, the standard 70t spur and 17t pinion should work perfectly, but i hate the sound that 0.6mod gears make -_-. The 64dp RW racing gears are precisely machined and very quiet, so I hope these 48dp gears follow suit.
DeV5QCB.jpg

Next comes the assembly of the diffs. This seems to be the first thing that everyone blames when a TT02 starts making bad noises after getting a brushless upgrade - "it can't take high power because it has plastic diffs". I don't believe that the material of the diffs is to blame. You see on the tree it says 'PA-GF', which means glass fibre reinforced nylon, a light weight and very tough plastic. The only flaw I believe is not the choice of material but rather that they are injection moulded gears instead of machined from a solid block of material. They can take significant power as long as extra attention is given to adjusting the mesh of the diff pinion and crown gears so they don't jump teeth under high torque loading - I'll cover this later.
LP6bnV9.jpg

All the gears are cut from the tree with side cutters and then any remaining sprues are sanded smooth with 600grit sandpaper - if you avoid doing this your gears might not run as smoothly as possible.
vG7xTO2.jpg

AW grease lubricates the spider gears on the crosspin
FFWzMzX.jpghw8rAZz.jpg

More AW is applied here on this out drive gear and all the spider gears where they run against the differential casing 
xtX5QjV.jpgxgjyky7.jpg

At this point we decide how tightly locked (limited-slip action) we want the diff to be. Below is how I assembled the rear diff and I'd consider this a loose to medium configuration.
eZjCnfj.jpg

Then the other outdrive gear goes on, with a small amount of AW and finally the diff is closed up by installing the crown gear / cover with 4 screws. You want those screws to be tight, but not so tight that it warps the crown gear. You can place the diff (with bearings installed) in the chassis and slowly turn it, noting the gap between the gear and the chassis near the pinion gear that drives it. If the gap to the chassis widens at one point as the gear is rotated, loosen the nearest screw 1/4 of the turn to see if that alleviates the warping. 

O0o2ks6.jpg

For the front diff I put a lot more AW grease on the teeth of the gears. I'd consider this a medium to tight locking action. I want the front to be tighter than the rear, because the front tyres are narrower and will have less weight on them, therefore the front is more prone to breaking traction. If the front diff is too loose, it'll just spin all the power away through whichever wheel has less traction. Maintaining some drive at least one front wheel (especially when the other is lifted in the air) will make the car easier to drive quickly by being less prone to oversteering.
2oOX9Qw.jpg

(to be continued in the next post...)



 

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Very interesting thread.  I'll be watching this one.  The drift bash video is really sweet, and I'm not much into drifting.  It looks really fun.  I just got a stock tt-02 used at my LHS, now I want to tinker with it.

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These next steps are the most critical for running a high power motor, involving shimming the differentials and spur gear. For the newbies out there, 'shimming' is just the process of taking up the slack in the fitment in two parts by installing a thin 'shim' in the gap. For shafts, washers are used to stop gears or bearings being able to slide up and down a shaft or two push two gears closer together. Shim washers differ from regular washers by being manufactured to tighter tolerances and (at least for rc cars) being thinner than usual. The outer diameter is usually not much bigger than the inner diameter, to prevent it fouling on the outer races of bearings.  RC cars usually only require shimming of shafts so the term 'shims' usually refers to shim washers but as you will see below, I also use some tape to shim parts other than shafts as well - you could use aluminium tape/foil, printer paper, whatever works for you. A TT02 needs shim washers with an inside diameter of 5mm in most places. Thicknesses of 0.1, 0.2 and 0.3mm are ideal. Most RC shops will sell you a shim kit with a variety of thicknesses. 
DbwGQlm.jpg


The first part to address is the rear propeller joint. 5mm ID shims are placed on the shaft between each bearing and the blue aluminium high speed gear mount (positions A and B below). The same can be done with the stock plastic spur gear if you don't have the HS gear set. Just keep adding shims until the spur gear and prop joint can no longer move fore and aft in the chassis or until the bearings no longer seat properly in the chassis, then remove a shim or two until everything seats and spins freely again. You should do this without the motor, propeller shaft or diff installed, as it'll be hard to tell how well it is working with the cogging/friction of those parts as you turn the prop joint. I think I ended up with 0.2-0.4mm total of shims in each location. If you can, use multiple shims (e.g. 3x0.1mm instead of one 0.3mm) as this will make the later steps easier.
bIkJhIw.jpg

The next step is to install the rear differential pinion gear. I find that this gear often fits too loosely on the shaft. The OD of the shaft and ID of the gear are usually a good match, but the flats of the shaft and gear almost always have some slop, especially on cars that have already been run and the bad fitment has wallowed out the inside of the plastic gear somewhat. To solve this, I put a piece (or two) of kapton tape (polyimide tape) over the flats of the shaft to shim the gaps. The tape should only cover the flats and end of the shaft - if it extends on to the cylindrical part of the shaft it could prevent the gear running true.
 R2usFkO.jpg

Next, the diff is installed with bearings. Sometimes you will need to shim the diff itself to prevent it moving left and right in the chassis. This can be achieved with 8mm ID shims placed between the bearing and the plastic diff casing (position C above). I've never needed to do this with the stock plastic diffs, but have had to do it for a few aftermarket diffs. To lubricate the gears I just use the yellow grease that comes with the kit. (the bronze bushings in the photo were only used here temporarily for mock up as was waiting for more ball bearings to arrive)
oV1UOEa.jpg

Now we will address the fitment between the differential pinion gear and the diff crown gear. The differential top cover and spur gear covers have to be installed and tightened down for us to evaluate the mesh between the gears. Interestingly the diff cover is different to the road going TT02 with an extra lip which should better prevent dust ingress (below): Unfortunately, this cover seems to be a worse fit than the regular TT02 cover and all 3 bearings were a loose fit with the outer races able to spin. I solved this by putting a few strips of kapton tape (first photo in this post) on the top of each bearing which when sandwiched by the diff cover tightly hold the bearings in place. If the tape was ever to work it's way loose and get sucked into the gears it should be thin enough and soft enough not to do any damage.
nHPJ5HG.jpg

With the covers installed the mesh of the differential pinion and crown gears can be evaluated by holding the two diff outdrives stationary and turning the propeller joint. There should be almost no slack between the gears - the propeller joint should not be able to rock back and forward more than 1/2 a tooth when the diff is held stationary. If it can, the fitment is too loose and can be tightened by moving shims from position B to position A. If you can feel notchyness of the gear teeth when you freely rotate the parts then it's too tight and shims need to be moved from A to B. You'll want to continue turning the prop joint many times as the same teeth on each gear only meet again every 5 turns of the diff or every 13 turns of the pinion - it might seem ok within 1 turn but if you keep rotating it you might find a tight/notchy spot as certain teeth on each gear mesh together.
Since rearranging the shims on the prop joint requires the gear covers to be removed and then reinstalled to recheck the fit, care needs to be taken to prevent stripping the screws which are threaded into the plastic chassis. I had to remove and reinstall the covers probably 10 times to get the fit perfect. When reinstalling the screws, unlike the first time installing them (which requires the force of a 200lb gorilla), they should screw back in easily. If you rotate the screws counter-clockwise until you feel a click and they drop down slightly you've found the old threads and can then drive it in. You should be able to drive them all the way back in and tighten them while gripping the screwdriver between only 2 fingers, like so:
ghO78UT.jpg

If it takes more force then that you're probably cutting a new set of threads. Cutting multiple sets of threads or trying to really crank them down when they bottom out is how you end up with stripped threads. 

Next we will fit the prop shaft. I put an o-ring in front prop joint cup which ensures the shaft is captive (it can't move forwards or backwards far enough to fall out of either cup). Putting o-rings in both joints resulted in too tight of a fit as the bearings on both prop joints became slightly preloaded which will make the bearings prematurely wear out. Instead, I put a piece of open cell foam in the rear joint. This prevents the prop shaft jingling about and provides little to no preload on the bearings.
oMtGLqr.jpg

Finally, bearings and a front diff pinion gear can be installed on the front prop joint with kapton tape just as was done for the rear. The front differential is also installed, same as the rear. For the front prop joint, since there is no spur gear assembly between the two bearings, the only place that can be shimmed is between the front most bearing and the diff pinion gear. Placing shims there will tighten up the mesh with the front diff. The thickness of shims required will depend on how much preload the prop shaft is providing since it will push the entire front prop joint forward towards the diff. The mesh must be evaluated only with the front diff cover and plastic prop joint bearing retainer in place, as well as the prop shaft and rear prop joint to provide any preload. I found that the fitment was already perfect if even on the slightly tight side of things, so I didn't add any shims up front.

If you ever change the bearings on either prop joint, the prop joints themselves, diffs, the high speed gear mount or standard spur, or the chassis itself, you have to go through all the above again as the tolerance of the new parts may be different to the old ones therefore requiring different thickness shims. 

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This is cool B) you're making me want to start new TT02 project!

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I had second thoughts about not shimming the diff spider gears, so here's that. 

it's hard to see here, but pressing the the outdrive gear all the way in, it  sits slightly lower than the face of the diff case
TOe5DUT.jpg

Additionally, there is a slight recess in the crown gear/cover. 
k5upejC.jpg

We need to fill that space so that under load the gears don't just push outwards, loosening the mesh and jumping teeth. Without shims big enough to put over the outdrive gear, the next best thing is to push all the spider gears inwards like so
7UA1OB4.jpg


This in turn will push the out drive gears outwards. A 3mm 0.5mm washer behind each spider gear seems to do the trick

M0BTLFu.jpg

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The lower suspension arms are installed, placing some 3mm shims between the arms and the chassis to remove slop
IYAF9cl.jpg

 

irTbvhV.jpg

 

Shock towers and upper arms are installed. The smooth portion of the step screws are too long which result in the upper arms being able to flap around. Granted, they don't strictly need to support the hub in that axis (if a turnbuckle upper arm is used, it doesn't) but I'll take what I can get! I used 4mm washers to account for this. On the rear inners the washer goes between the tower and the arm. On the outer rear and both ends of the front arms the washers sit between the arm and the head of the screw. 
H2PO4os.jpg

The nylon shock towers are extremely flexible. These will be upgraded in the near future.
VdRK5xq.jpg 

yjzDdBc.jpg

I gave the famous rusty suspension hinge pins a polish 
4Q86ZSF.jpg

before installing the hubs with some minor shimming
q2ygwRo.jpg  5gcWIYf.jpg

Grub screws are removed from the Yeah Racing universal shafts. All threads are thoroughly cleaned of oil and then Loctited back in place, making sure that the pivot pin (which the grub screw retains) is perfectly centred. 

UvQFPGd.jpg

The universal shafts are installed into the hub with bearings, drive pins, hex adapter, the wheel and tightened down with the wheel nut. In the picture below the plastic hub sits between the bearings. When you tighten the wheel the hex adapter bottoms out on the drive pin and the surface on the hex adapter labelled B rides on the outer wheel bearing when the wheel is being pushed towards the centre of the chassis. When the wheel is being pulled outwards the driveshaft pushes against the inner wheel bearing. The drive pin should not touch the bearing ever. I add shims at position A until there is minimal side to side movement (<0.1mm) but the bearings still spin freely.

Ey0ZUmE.jpg

Speaking of wheels, oddly they don't come with foams, nor does the instruction manual recommend gluing them. The wheels also don't have breather holes so if you squeezed the tyre in it would stay sucked in :huh:. I drilled two 0.75mm breather holes in each wheel, and assembled them with 1/10 touring car foams (which were perfect for the front, a little small for the rear). It took a LOT of effort to get the tyres on to the wheels. Even though the tyres fit so tightly that I'd doubt they'd debead, I still glued them to prevent dirt and stones getting in there.

The shocks were built with the standard 400cst oil although I suspect I will want to put a much thicker oil in later, probably 1000cst or more. These are the 'cheap' CVA shocks which have a metal piston integrated into the shaft. Instead of holes in the piston there are two flats on the piston which allow oil to flow around. The manual suggests installing a plastic spacer to limit compression on the front shock. I'm not sure why because at full compression without it, the piston just barely contacts the rubber bladder. I left the spacer out. I also pushed the piston almost all the way in when installing the cap to achieve minimal rebound.
aZvbOZI.jpg

I gave the rear shock shafts a bit of a polish before assembly as unlike the front shafts they had a rough finish. This will make them work more smoothly and help prevent dirt getting trapped between the seals and the shaft, which will score the shaft and make them leak.
YyWlyKa.jpg

The rear shocks did require the plastic spacer as the piston otherwise touches the rubber bladder about 5-6mm before bottoming out - I figure that might cause a hydraulic lock condition and suck the bladder into the bore so I played it safe and used the spacer.
yVqdIgh.jpg

I installed all the shocks on 5mm steel ball joints instead of the included step screws.

S8oe9Oa.jpg

The rear shock tower can flex a lot under compression

GiMj3DZ.jpg

Because of this, the suspension could compress so much that the driveshafts became over-angled. I put the plastic compression spacers that came with the front shocks onto the rear shocks, in addition to the spacers already installed. Compression is now limited to a safe amount. Also installed the thickest clip-on spring collars/spacers as I felt the rear suspension would be too soft - I'll know for sure and adjust it again when the motor/electronics/battery is in.
OKOTll0.jpg

The front works out just right without spacers
2D1CDbK.jpg

That completes the chassis, sans steering parts and motor/electronics. It'll have to wait until I give my road car one last run for those parts :)
5sCXS1h.jpg


Size comparison with an on-road TT02:
bskRNXz.jpg

I actually want to raise the ride height to use more of the shocks travel and help grass running. It can't be done with the stock parts, but an upgraded shock tower with extra holes should sort that out. Longer shocks would also work.

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Also painted the shell. Used PS-59 dark metallic blue instead of the recommended PS-16 metallic blue. Backed with PS-5 black to provide some scratch resistance and make it completely opaque (PS-59 is a bit translucent). I debated whether I should attempt to paint the cab white or just use the white stickers. Ended up painting the whole shell blue and just using the stickers.

I had a spare spoiler from a failed attempt at making an under-shell dust cover for my on-road TT02 out of a Dual Ridge shell, so I cut that out to look at home on the Neo Scorcher so I can use it as a spare. If you're trying to keep dirt out of the bathtub of your on-road TT02 you're better off making some XV-01 style mud guards (or retrofitting the XV-01 parts). The buggy shell doesn't fit tightly enough clear the wheels since they are a lot closer to the tub compared to an actual TT02B. Even if you do get it to fit the wheels will just fire dirt through the hole for the steering arms, and up the gaps either side of the chassis. TT02B wheels are far enough away from the chassis that dirt shouldn't end up thrown into the bathtub. When the front wheels are at full lock some might get in underneath the shell, but most should be thrown at the outside of the shell.
 iV6E4OK.jpg

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I had a lightbulb moment and remembered a cheap hack I'd done before to extend the length of a shock shaft. I could use that here to raise the ride height to how I wanted it, and solve the issue of the rear suspension compression without having to limit the overall stroke of the shock.

Simply put a brass standoff on to the end of the shaft. An aluminium spacer and steel washer were added on to the shaft to cover some exposed threads and give a wide flat area for the spring perch to seat on to.
a7JUcKN.jpg

gEVjevf.jpg
 

The front shocks got the same treatment, albeit with a shorter brass standoff. I loaded up the car with an approximate amount of weight (battery, esc, motor and servo). The front shocks seemed too stiff (no droop at all) so I put in touring car springs with a bunch of collars/spacers to make up the length. Not pretty but seems to work.

Resting height front:
izdqgFb.jpg

Front droop:
iCPF0cY.jpg

Resting height rear:
bbPVH3A.jpg

Rear droop
ZAblMID.jpg

Side

KorBPCN.jpg

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Gave the TT02 one last bash before tearing it down. Got through most of a pack before a tyre had had enough

yPc8xZW.jpg

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Harvesting parts:
erUvlNr.jpg

Aluminium steering parts installed. I think these are Active Hobby brand if I remember correctly. If on a budget, retain the plastic steering parts but install metal ball joints and turnbuckles where possible - keep on top of servicing (clean and regrease every so often) and there won't be much slop.
The standard plastic tie rods are retained - not point upgrading them unless I want to adjust toe, or the ends wear out.

TtvbJBL.jpg Pdfv85A.jpg

Servo (Trackstar TS-411MG) is installed with a Tamiya #51000 servo saver and aluminium horn.  Rod ends and the ball end on the servo saver were replaced due to wear. You want the servo saver/horn to be close to vertical when the servo is centred. That will give you same speed and amount of steering when turning in either direction. In this photo I forgot to install the sponge on the chassis under the servo saver - you'll want that as it prevents rocks getting jammed between the chassis and saver.
7Y9VZQa.jpg

I also install some spacers to move the servo forward as it makes the turnbuckle straighter, resulting in slightly more steering force. It also moves weight forward in the chassis and leaves more room for the ESC.
fPaz6Zw.jpg

pVuxB8x.jpg

Next the motor is installed with the Yeah Racing adjustable motor mount. Adjusting the mesh between the gears goes something like this:
-Install the motor into the mount with the pinion installed. Bottom motor bolt semi-tight, top bolt loose. Use Loctite.
-Pivot the motor towards the pinion gear until there is just the tiniest amount of slop between the gears then tighten the top bolt semi-tight. If i hold the pinion gear stationary, I aim to be able to gently rock the spur gear back and forward about 1/10th of a tooth. For 64dp and this amount of motor power I have had to go just a little tighter - until there is no slop, but there isn't significant drag when the gears are turned.
-Slide the motor mount out of the chassis, tighten the bottom motor bolt gutentight, reinstall motor mount with two screws from bottom of chassis, with Loctite.
-Re-check mesh between gears. If it has changed you might be able to loosen the top bolt and lever the motor over with a big screwdriver, otherwise you have to loosen things off and try again.
-Tighten top motor bolt gutentight, install spur gear / motor cover.

Choice of pinion gear is dependant on how you drive, the terrain you drive on (hills, grass), and how much cooling the motor has (fan, or a physically larger motor = more cooling). The more time the car spends at full throttle and with the motor turning slowly, the hotter the motor and esc will get.
Besides cooling, I think of the choice of gearing as optimising the torque that is produced at the wheels for a given road speed. Torque = acceleration.
For instance, this motor on 3S will spin at around 60,000rpm without a load. Maximum power will occur at half that - 30,000rpm. I have a 18t pinion gear and 78t spur gear, and the TT02 diffs use a 15t pinion and 39t crown gear. Therefore the final drive ratio (FDR) is (78 / 18 * 39 / 15) = 11.27. For every 11.27 turns of the motor, the wheels turn once.
So if the motor produces maximum power while turning at 30,000rpm, the wheels will be turning at 30000/11.27 = 2662rpm. If the wheels are about 85mm diameter, then the road speed will be 2662*0.085*pi*60/1000 = 42km/h. Therefore, this choice of gears will produce the highest acceleration at 42km/h out of any other possible choice of gears, but other gear ratios will produce more acceleration at other speeds.
E.g. a smaller pinion / larger spur / higher FDR will produce more acceleration somewhere below 42km/h.
a larger pinion / smaller spur / lower FDR will produce more acceleration above 42km/h and therefore reach a higher top speed.

As a general rule of thumb, you don't want the motor to spend much time on full throttle and turning less than half of it's maximum rpm. Therefore we don't want the car to spend much time on full throttle with the wheels turning at less than 42km/h or things might get hot. If the car is going 20km/h but the wheels are turning at 50km/h then that's ok :)

DvBTgMy.jpg

ESC, receiver and 40mm motor fan installed. The things in the front two holes of the fan are noise isolation grommets used to quieten computer fans. I'm using them as they stick up a little and will prevent the body hitting the fan blades or choking the airflow.
Receiver is just a Flysky GT2 instead of the GT5 I usually use. If I find the need for a steering gyro I'll upgrade it to a GT5.
3YdYzbR.jpg

Extended battery posts to fit the tall 3S battery pack, made from two sets of battery posts. Just drill 2.5mm holes in each and join together with a long M3 set screw.

oTPPEUB.jpg

Foam installed in the battery tray to hold it securely
nGmmgVp.jpg

Ready to run

V8gQwKw.jpg

On the motor side the body sits how I want it to - almost flush with the bottom of the chassis at the front, and a little higher at the rear. On the other side battery hold down strap just barely touches the body so it sits higher. I think I can solve it but cutting the strengthening ribs down on the strap.
AzYtzHQ.jpg

 

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Good news and bad news. I did a drop test of the car from ~1ft and the suspension bottoms out and bounces way too easily, so I changed the front shock oil to 1500cst and rear shocks to 800cst. Going stiffer in the rear just introduced bounce from the tyres (they need bigger/stiffer foams) and shock tower flexing. I gave it a run on a grass oval and the choice of FDR seems good for grass running. Motor remained lukewarm, I could probably drop to an FDR of 10 or 9 if I want more speed.  The bad news is that it this is indeed too much torque for the plastic diff pinion as it started slipping after launching it (resulting in a wheelie :D) a few times on a faux grass cricket pitch. Rear diff pinion is turning into plastic shavings resulting in rounded over teeth:
JaKoBdy.jpg
It's hard to see, but there are also impressions where the flats of the prop joint have started to wallow out the hole in the pinion.

Front diff seems fine, probably because whenever there is massive torque produced the car is popping a wheelie (or almost popping a wheelie) so the front diff never sees much torque. I've ordered one set of GPM steel differential gears to put in the rear. I'll upgrade the front diff only if starts showing wear.

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This has been an interesting thread. When I built my TT02B's a few years ago I didn't notice all the slop as it was my first build in years, and now they are well used so there is a lot more than there used to be. One thing I found was the front u thing that holds the arms in bends. I drilled out the holes in the arms and sleeved them with brass tube which is working well. The u pin fits a standard sized brass tube which is at every hobby shop.

I also built a TT02D on friday and paid attention to the areas you pointed out, especially how you shimmed the diffs, and my one went together perfectly without needing shims. There is also minimal play in the arms which surprised me, but of course the first time it hits anything it will need shims. Even the TA07 needed shims until I bought the aluminium suspension blocks. Do you know if play develops in the drive shaft or should mine be good forever?

Great thread, I'm a fan of improving things without just throwing money at it!

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The TB01 rally diffs are steel and drop straight in but you would need to change to splined out drives. Also TT01 diffs will fit also but I don't know if they are steel.

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19 hours ago, TwistedxSlayer said:

The TB01 rally diffs are steel and drop straight in but you would need to change to splined out drives. Also TT01 diffs will fit also but I don't know if they are steel.

Good tip! Can get a TB01 A-parts bag which has two diffs for about the same price as one set of GPM gears. TT01 diffs are plastic with aluminium spider/outdrive gears if i'm not wrong.

19 hours ago, Jonathon Gillham said:

I also built a TT02D on friday and paid attention to the areas you pointed out, especially how you shimmed the diffs, and my one went together perfectly without needing shims. There is also minimal play in the arms which surprised me, but of course the first time it hits anything it will need shims. Even the TA07 needed shims until I bought the aluminium suspension blocks. Do you know if play develops in the drive shaft or should mine be good forever?

You'll get more play as things wear out - bearings becoming sloppy, gear teeth wearing down and especially if a bearing locks up solid and start spinning on the shaft it'll wear the shaft down. On sensible power (2S, <4000kv), and not crashing too much, it should take a long time for that to happen - tens or hundreds of battery packs. It might get a bit noisier over time due to wear on the gears and backlash.

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45 minutes ago, nbTMM said:

Good tip! Can get a TB01 A-parts bag which has two diffs for about the same price as one set of GPM gears. TT01 diffs are plastic with aluminium spider/outdrive gears if i'm not wrong.

 

I am running the GPM diff in the rear of my TT02B on stock dog bones with a TB01 diff upfront with hardened TT01 out drives and DF02 cvds. There is a whole build thread about it if you fancy reading it sometime. Just search Metallic Pink Neo Scorcher.  you'll find it. Lol

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Taking a break from the TT02B while I wait for some parts to arrive, so I started the drift build. I built this initially as a countersteer/'CS' setup where the rear wheels are over-driven and the front wheels are driven by a one-way diff. This sends drive to the front wheels only when the rear wheels spin a certain % faster than the front wheels, so it allows RWD behaviour up to a point. If the car slides past a certain angle or you floor the throttle you get 4WD which helps pull the car out of a drift and prevent spinning. Later I decided that this setup wasn't really what I wanted, but I'll show the build process anyway.

Inspecting wear on the stock rear diff from 3S running. There is some, the teeth of the pinion are partially rounded over but it still ran well like this.
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Chassis fully stripped
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I'd stripped out the threads around the motor mount before and installed brass M3 inserts. Some of these had pulled out a bit over time due to removing and reinstalling the spur gear cover - they can be pushed back in with a soldering iron at 200*C. 
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Chassis parts after cleaning with warm water, dish liquid and a paintbrush
Zpznv11.jpg

In the rear I used a steel geared eagle racing spool with 16t pinion and 25t crown gear, which gives a 66% overdrive compared to the standard 15/39t diff gears.
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The prop shaft needs to be modified to fit the Eagle pinion gear, as it uses a drive pin and an M3 bolt to hold it on to the end of the prop joint, instead of the flats which the stock gear uses. A spacer and a stack of shims position the diff pinion gear correctly. This isn't the best setup as everything presses down against the motor spur gear and its drive pin, which locks the spur solid on the joint. You don't really want this as some slop in the spur gear will allow for some misalignment between it and the motor pinion gear (which there will be some as it's a plastic chassis). The result of this is some additional noise from the gears, but it works OK. 

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Up front i'm using a one-way diff for a HSP touring car with a set of plastic 42t/13t underdrive gears made by Active Hobby. The crown gear required the bolt pattern be redrilled for the rectangular pattern on the HSP diff center. The outdrives and bearings are from an Eagle Racing one-way. The combination of the under driven front diff and overdriven rear diff make the 'CS ratio' about 2:1. I.e. the front wheels aren't driven unless the rear wheels are spinning twice as fast. 
Xx3NIx6.jpg

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The standard plastic propshaft is used since it is fine for the low power

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For the motor i'm using a brushless Hobbywing Justock 21.5t. Gears are 64dp, 104t spur and 36t pinion. Together with the overdriven rear diff, the effective final drive ratio is about 4.5
6zLhrEq.jpg

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Since a CS drift car requires more steering to prevent spinning than a 50:50 drift car, the steering has to be set up for greater steering lock. The standard TT02 setup is not suitable for two reasons.

Firstly, it creates too much ackerman angle - i.e. when you steer to the right the right wheel turns a lot more than the left wheel. This creates a braking effect at the front of the car when drifting as one of the wheels isn't pointed in the direction that the car is travelling in. For 50:50 and CS cars with a small CS ratio this can be desirable as it promotes oversteer. For large ratio CS setups and rear wheel drive cars it's undesirable as the car will spin too easily. 

Secondly, when the inner wheel is turned, the angle between the steering hub and the tie rod becomes close to zero. Note how the red and pink lines are near 90degrees when pointed straight ahead, and near 0 degrees when on full lock:
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On full lock the steering has no control over the inner wheel and the hub will just flap around due to forces from the road. The tyre can rub the chassis resulting in an unintended braking effect and a spin.

The solution is to change the geometry of the steering arms. I'm using these extended ones from active hobby. Additionally I'm using some home made aluminium brackets on the hubs which move the tie rod mounting point outwards and allow the tie rods to be a more reasonable length. They also dial out the ackerman from the steering, in fact a little bit too much as now I have slight negative ackerman; when turning right the left wheel turns a bit more than the right wheel.
You can see how now the angle that the tie rods make with the hubs stays within about 45 and 90 degrees for all steering angles. When pointing straight ahead the angle is about 45 degrees so the straight line stability won't be as good as the standard steering, but it'll be much more solid and stable while drifting.
MY3am3r.jpg

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For suspension up front i'm using standard hubs, standard lower arms (with steel ball hopup), a 5mm ball end installed on to the top of the hub and aftermarket turnbuckle upper arms with a 5mm rod end installed. I rebuilt the kit CVA shocks with 3-hole pistons, 700cst oil and red (soft) springs from the 53163 spring set. I drilled a new hole in the lower arm so I could attach the shock to the arm further in than standard. This creates a really soft suspension with really long travel. I want the suspension to react as slowly as possible as this should make the car easier to drift, and won't be easily unsettled by bumps in the road
YMPZEKL.jpg
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Front driveshafts are a combination of 3Racing SAK-X27 double cardan shafts and Yeah Racing adjustable rod ends (to shorten them appropriately). These don't 'clatter' when on lock like universal shafts do because they are a true constant velocity joint. Additionally they can't fall out like the TG10 cups and metal dog bones can.
Top: TG10 cup, metal dog bone - standard parts from a TT02RR
Middle: yeah racing universal shaft
Bottom: double cardan shaft
FcLlaIH.jpg

The steering servo is just a cheap metal gear turnigy one: 12kg, 0.18s. Solid aluminium horn for zero slop (and because I don't care much for this servo :)). It's a slow servo, but faster is not always better for gyro assisted drifting. The slower the servo is, the more you can turn up the gain of your gyro (= more steering lock from gyro) without instability occurring.
rojljmh.jpg

The rear suspension has the same super soft long travel shock/arm setup as the front, but with yellow (medium) springs from the same set, due to the TT02 having a slightly rear-biased weight distribution. Driveshafts are the TG10 style with metal dogbones as came with the TT02RR
Hubs are some 3degree toe hubs (yeah racing iirc) that I cut and added M3 threads for 5mm balls to attach - not very well mind you, the balls need to be angled in to shorten the upper arms more and achieve more camber gain. Upper arms are from yeah racing's RWD conversion line, and the strut tower is a carbon one from Eagle racing - I don't recommend the latter, get the Tamiya brand one the fitment is a lot better.
gnu5JWb.jpg

Suspension flex is more like a 1:1 street car 
EbWwEn3.jpg

For electronics I'm just using a TBLE02S and 2S LiPo battery. NiMH had plenty of power, but LiPo voltages remain more constant from fully charged to empty, which helps since drifting is sensitive to throttle control. NiMH would have you barely touching the throttle on a full pack and having to floor it constantly when it was almost empty.
For the radio I'm using my Flysky/turnigy GT5 with inbuilt gyro. The GT5 gyro is a lot better than the cheap standalone GC301 gyro I tried previously. It steers much faster into a slide, but steers back to straight much more slowly. The result is that you can turn the gyro gain up way higher before the gyro becomes unstable (gyro starts swerving when trying to drive in a straight line). 
abDp0Em.jpg

After driving this setup I changed the front diff to this eagle racing one which has the same gear ratio as standard (39t/15t), therefore dropping the effective CS ratio from 2:1 to 1.66:1
With the 2:1 ratio I either didn't have enough steering lock or enough driving talent to catch the slides :P
vYmMEIx.jpg

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That is a brilliant read. I have never even thought about a tt-02 but now I am planning on picking one up. That blue chassis looks awesome. I think a drifter is on the cards.

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What I don't like about the CS setup is that the throttle control isn't intuitive. At low throttle where the car is basically functioning as RWD, more throttle equals more oversteer. At higher throttle, more throttle equals less oversteer as the car reverts to a 4WD rally style drift with both front and rear wheels spinning significantly faster than the road speed. The other thing I don't like is that due to the CS ratio, the car seems to get 'locked on' to drifting around a circle that satisfies the CS ratio (front and rear wheels both having similar traction) and it is very difficult to widen the line that the car is taking without drastically changing the amount of throttle and therefore the speed of the car. You can see this in the following video when I was trying to drift a big oval around the two paint cans, it was really like connecting a series a equal radius arcs rather than drifting a continuous oval. I had some problems with the car getting 'stuck' in a slide also - I'd be on full lock and whatever I did with the throttle I couldn't get it to transition back the other way. I think part of this is due to having negative ackerman. It probably needs slightly positive ackerman so when the throttle is let off slightly it transitions into a slide going the other way.
I think CS works well for effortless sliding around in a big area but for drifting a track with pin point accuracy I think a RWD setup will work better, so that will be where this build is headed next.
 

 

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Buggy update.

Both diffs were upgraded to GPM steel gears. The rear diff was assembled with a minimal amount of AW grease so it is open/loose. The front diff was filled about 1/3 of the way with 1million cst oil and then up to half way with 100K cst oil to make it a little thinner than 1million. The only thing I don't like about these gears is that the ring/crown gear doesn't have the 4 tabs that key the gear to the housing like the standard plastic gear does, so the torque is transferred from the gear to the case by only the 4 small screws, and whatever friction is generated between the gear and casing. Nevertheless, it doesn't seem to be an issue.
mQbVDpK.jpg


I also changed the wheels to Proline Badlands SC 2.2/3.0". At ~113mm these are significantly larger than the standard ~85mm wheels, which increases ground clearance substantially. Being a higher profile tyre the suspension doesn't have to work so hard over rough ground either. 
 

5nQi6GW.jpg
The downside is of course that the rollout is increased substantially, as well as the wheels being heavier, and this drastically increases how hard the motor and ESC are worked. With the 7.5t (5100kv) motor on 3S and the timing wound all the way down (~5-10degrees = ~4000kv), boost timing disabled, the ESC would overheat after only a couple minutes of running in grass. I can't really increase the FDR since it's already just about at the maximum the TT02 chassis supports. The 48p 78t spur is as big as will fit. I have maybe another 1mm of adjustment room on the motor so perhaps I could change the pinion from 18t to 17t or *maybe* 16t but I think that would not improve things as much as I need. On 2S and boost timing, it ran great but I wanted a bit more power than that. I found a happy medium swapping the motor for a 13.5t (3040kv), running boost and 3S. This makes about 600W whereas the 7.5t on 3S is ~900W and on 7.5t on 2S ~400W. Speeds seem to be around 40kmh in 2" tall grass and 60kmh on asphalt. The limiting factor now seems to be motor temp rather than ESC temp. After half a pack at full noise in grass the motor was quite hot, I might still need to dial back the timing a little.

The other thing I've changed is the suspension. I opted for these '105mm' (95mm hole to hole) ZD Racing shocks. They are exactly the same length as the rear CVA shocks but have longer travel due to a longer body and shorter rod end. Of course, as with any cheap shocks they were not supplied filled correctly so I tore them down, inspected, refilled and bled them properly. 
WzUhIpZ.jpg

The oil that came out seemed about 200cst. The piston is a much tighter fit with the bore than a CVA shock, and the bore overall larger, so the oil doesn't need to be as thick.

The shafts had a slight 'turned' finish which caused a zipping sound as they moved in and out of the o-ring seals in the shock body. I gave them a once over with some metal polish to remove most of that finish - I didn't aim to get them perfect because I was worried about completely removing any plating on the shaft.
Left is as supplied, right is polished.
zoIivR9.jpg

 I refilled them with 350cst which gives quite firm damping - comparable to the CVAs with 800cst.

The front suspension was converted to use the same length shocks as the rear. Because the TT02 chassis is symmetrical front to rear, you can mount a rear shock tower to accomplish this, however due to the kickup in the lower front suspension arms, the mounting points for the upper suspension arms need to be higher on the front tower. Fortunately the carbon towers (hopup 54754) have enough material that you can simply align a front tower with a rear one and transfer the front holes to the rear part with a 3mm drill.
dMGHDl6.jpgcTQjh69.jpg

I'm just using a stock tower for the rear for now, until another carbon one arrives. If you cut down the 'stalks' that the top of the shocks mount to, as short as possible without the shock cap hitting the tower, it reduces the amount of flex in the shock tower to a minimum.
CRK73Ac.jpg

rr9LlNf.jpg

The springs that come with the ZD shocks turned out to be just about perfect for a TT02B. At the front I run no spring preload, and at the rear I have almost full preload due to the higher weight over the rear wheels.

One final tweak I've made is to drill some holes in the shell just in front of the A-pillars and put a zip tie through to slightly pinch the shell and make it fit tighter to the chassis. This is to increase clearance with the front wheels, since with the Proline wheels if the steering was turned to full lock and the body flapped around in just the right way the tyre could catch on the shell. It didn't damage anything but made a horrible noise. With the ziptie the shell can't flap around much anymore so the problem is solved.
GFipP57.jpgVyuHAU9.jpg

mMkaO1f.jpg

I'll shoot a video when it's not a roaring gale outside :) 

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