Speed (Maybe).... TT-02 SR Build

[Keracticus Pots 200]

This thread is going to be a brief summary for the build of a TT02-SR chassis as a speed run car followed by the trials and tribulations of running the car. I’ve been inspired by the multiyear, multipart “Tamiyaclub Official Top 10 Fastest RC'ers” thread. I’ve even got an entry for a completely stock TL-01 near the bottom of one of the tables with an eye watering 16 MPH.

This all started with wanting a “different” on road car to run. I already had a Porsche RSR and loving all things VW and Porsche the Porsche 911 GT1 Street TA03R-S seemed to fit the bill as I’ve never had a belt drive car. But as a chassis, the battery compartment seemed a bit limiting. I wasn’t sure it could fit lipos, it definitely wouldn’t fit a tall 3S lipo and I didn’t like how exposed the battery would be. For me, another negative was being short wheelbase other standard wheelbase bodies wouldn’t fit nicely. As the eventual aim was always to get a speed run focused body I decided to explore the different chassis kits available.

Although I could probably stretch to one of the higher priced chassis, for that sort of outlay I know I’d be ****htened to crash it. I wasn’t previously aware of all the different TT-02 chassis kits and after a bit of deliberation ended up with the TT-02 SR. This seemed to offer a good balance of essential hops (bearings & CVAs), adjustability and other hops ups right off the bat.

 

There’s a load of good TT-02 stuff at the rcracer.com https://www.thercracer.com/2014/08/tamiya-tt02-guide-mods-tuning-and-tips.html and this was excellent to get an idea of the different TT-02 chassis kits and hop ups.

Link to the Tamiya product description https://www.tamiya.com/english/products/47439/index.htm

I got the kit from Tamico https://tamico.de/Tamiya-47439-TT-02-Type-SR-Chassis-Bausatz

KP

[Nikko85 3774]

Nice one, keep us posted.

[Keracticus Pots 200]

The first few stages was installing the centre drive shaft and spur gear followed by building up the diffs.

The following hop ups were installed at this stage:-

54500 - High Speed Gear Set

54501 - Aluminium Prop Shaft

5402 - Aluminium Prop Shaft Joints

The high speed gear set comes with a 68T spur. This will give a slight increase in top speed compared with the stock 70T spur.  More importantly it enables a whole range of different standard spur gears to be fitted. This enables a wide range of different pinion/spur combinations to be fitted. I got a 64T spur (51356) that I will be fitting later once up happy with the set up of the car.

The kit included a spool to lock the front diff and a fluid filled rear diff.

The googling I'd done suggested for speed runs a locked front diff was the way to go.  There was some difference of opinion for rear diffs - some said locked some just very stiff. I went with 1 million cst fluid. This only just meets the definition of fluid! and it took ages to "pour" into the diff.

KP 

 

[Keracticus Pots 200]

Next up was fitting the motor.

I don't want to break any records but wanted something as a start point that was reasonably priced and could be used in other future builds. I’ve got a DT-03 with a Robitronic Razer Ten combo with a 3000kv motor that I’m happy with (See note below) and decided to go with the Razer Ten 4600kv combo. For the rest of the power system I’ll start with the current pair of old batteries I’ve got; a 3500mAh NiMh & a 4200mAh 25C Lipo. This will certainly be fast enough for me to learn the car and how to drive in a straight line!

For this stage, as well as the Robitronic Razer Ten Combo with 4600kv motor & 60A ESC I fitted the following:-

Robinson Racing 22T, (25T & 28T) Pinions

Yeah Racing Aluminium Motor Mount

I fitted the 22T pinion. So to start I'll be running 22T pinion, 68T spur. 

Here's the point I realised I'm doing pretty rubbish for a build thread. The first post was pretty lacking in pictures. I get carried away enjoying the building and just forget to take pictures!

One area of doubt I've had was getting the gear mesh right.  With the adjustable motor mount the procedure was a bit of a faf. Fit motor to mount, don't tighten bolts, fit mount to chassis, set mesh, tighten top motor screw, remove motor mount, tighten bottom motor screw, refit mount to chassis. After doing this the next step is to fit the top cover for the gears.

After fitting the top cover for the gears the mesh felt to have "tightened" up. I was judging this by feeling the backlash by turning the prop shaft joint. My guess was the adjustable motor mount was not seating perfectly in the chassis and/or the gear cover. Took it apart, checked, couldn't see a problem, reassembled, still a bit tight. Took it all apart again and set the mesh slightly loose, reassembled and the mesh felt OK. Now I'm far from an expert and am not 100% confident. Any top tips or similar experiences setting up the mesh using the Yeah Racing mount?

KP

(Note below - My DT-03 came as a combo from Tamico. At 106 Euros this was an absolute bargain that included the kit, bearings, CVAs and a Razer Ten motor/ESC combo.)

[Rvl 2 22]

On 12/9/2022 at 2:40 AM, Keracticus Pots said:

 Any top tips or similar experiences setting up the mesh using the Yeah Racing mount?

The Tamiya aluminum works very well with  68 and 64  and up to 26 pinion but when using a 28  can be picky. But the Yeah Racing has a problem , it is slightly out of alignment with larger pinions. I heard there is another maker that machines the slot but I haven’t bought it yet. 
I have  64/28 and 68/25 on my SR’s. Make sure the chassis slot and motor mount are totally clean

[Keracticus Pots 200]

On 12/11/2022 at 4:03 AM, Rvl 2 said:

Make sure the chassis slot and motor mount are totally clean

Thanks, next time I change the pinion I'll pay attention to the fit.

Next up was the suspension. The next few photos show the front suspension with the fibre damper mount and cardan drive shafts included in the kit.

I was intrigued by the cardan joint and had not heard this term before.  I've only got experience of low end RC cars and was aware of what are commonly referred to as CVs tend not to be constant velocity. A bit of googling and it would appear what we have here is a double cardan joint and is a true constant velocity joint.  https://en.wikipedia.org/wiki/Constant-velocity_joint#Double_Cardan I expect the subtle improvement in performance this offers will be wasted on me!

Rear suspension.

These photos show the different drive shaft arrangement for the rear with the type of driveshaft I'm more familiar with. I've not worked out why the double cardan drive shaft is only fitted at the front. Anybody understand the reason why? Do the TRFs come with double cardans at both ends?

The middle picture shows a close up of the rear suspension mount with the square plastic bushings.  A number of different plastic bushings are provided. These change the location of the end of the suspension shaft allowing toe and skid angles to be changed. I stuck with the default which is 2.5deg toe in and 0deg skid. 

While building up the suspension I used shims for the first time during a build. This noticeably reduced the slop.

KP

[Rvl 2 22]

The double cardan  really help when cornering ,  make sure you install the spring clips as per instructions. The first time I reversed them and lost the clips. The xv02 spool works very well and lightens up the front.

 

 

[Keracticus Pots 200]

I've been a bit slow with posting updates.

I got the car finished.

Kit dampers with 800cst oil & kit springs.

Kit bumper with forward body mounts vs the kit shock tower body mounts. This seemed like a good idea to reduce body flex at the front.

Final hop up was some bolt on hexes.

Next was the body.

KP

[Keracticus Pots 200]

This is the first time I'd fitted a body without pre-drilled mounting holes!

Measure twice, cut once.

I don't think I did a bad job with getting the body fore and aft position correct.  The big problem was getting the body low enough. In the photo below you can see the front of the body on the bumper.

The second problem was the body hitting the shock tower.

It's a bit hard to see in the photo above but the part of the shock tower hitting was where the kit body mounts screw in. As I was using the forward mounts I decided to modify the shock tower - so out with the hacksaw.

What can also be seen is where I reduced the height of the bumper mount. And also cut the bumper in half.

This resulted in an acceptable body fit.

The body I bought is a nominal 200mm wide body and it dwarfs the chassis with the 26mm wide foams.

I realised I haven't actually got any shots of the body mounted once I'd finished. I'll get on with that tomorrow.

KP

[Keracticus Pots 200]

First couple of runs were over Christmas. I was dying to run the car even though the road was not dry.

With a 22 pinion / 68 spur, max speed was 30mph. With a 22 pinion / 64 spur max speed was 35mph. This was a bigger jump than expected which I'm putting down to a partially discharged battery for the 22/68 runs.

These runs were done without the body and before I'd made an undertray. In the picture you can just see my 1:1 car. Unfortunately I managed to crash into it and rip off a rear corner. Particularly disappointing as the body and an undertray (the width of the body and wider than the track) may have reduced the damage.

KP

 

Edited February 19, 2023 by Keracticus Pots
typo

[Keracticus Pots 200]

The thinner stock bumper, the undertray and some standoffs.

KP

 

[Keracticus Pots 200]

Today was finally good enough to attempt some painting.

Even though I was only planning on one colour, the body didn't come with any window masks. So it took a bit of time to mask up the windows and lights.

Judicious use of a hairdryer, a can of red and some smoke for the windows and lights and I'm pretty pleased with the result.

Then the best bit - peeling off the protective film!

Now on with some stickers.

(Badge not yet stuck on)

KP

 

 

[Keracticus Pots 200]

This has been a bit an on and off project but it's time for an update.

I recently treated myself to a new radio - a SkyRC Noble NB 4. This is a feature packed radio at a mid range price. One of the features is telemetry from the car back to the transmitter. A range of sensors are available to measure voltage, temperature, altitude and rpm. I fitted a couple of temperature sensors to the motor and ESC. Now I can see real time motor and ESC temps and can set up some max temp alarms.  For the power system and gear ratios I've currently been playing with temperatures were never really going to be a problem but I'm an Engineer and you can never have too much data!

Another feature of the new radio is the ability to set the "Channel Speed".  EG you can programme it such that if you rapidly pull full trigger, 0 to max ramps up over a user defined time.  This will be more useful when running bigger power systems where a having a smooth input of throttle is key to minimising wheelspin, current spikes and voltage sag. Combined with user defined throttle curves and throttle dead zones this gives a lot of flexibility.

Another area I've been playing with is getting the car to track straight.  The car is set up with ball raced steering linkages, 3 deg of rear toe in and about 1 to 2 deg of front toe out. I had trouble trimming the car, it seemed to wander around neutral.  To cut a long story short, I've tried 3 servos and replaced the servo saver with an alloy servo horn. The earlier servos I was using had more play/backlash around the neutral point. Combined with the mechanical nature of the backlash will be the accuracy of the sensors in the servo needed to maintain a commanded position both statically with no load and under load in use.  I've ended up with a servo and set up that's not too bad. But it may just be I'm gaining experience at 40+ mph.

As a slight aside, most will appreciate the specs for servos focus on torque values and angular speed. I haven't found any specs that detail either angular accuracy or some sort of measure of backlash.  I've been playing with cheapish servos and I expect that some of the higher priced brands are designed and built with tighter tolerances.

Steering gyros. There seem to be mixed views on steering gyros for speed running, ranging from "gyros are cheating" to "gyros are essential". My only experience of a gyro was recently with a drag slash. Box stock, cold tyres, full throttle, no gyro it was all over the place. With the gyro it was rock solid and straight as an arrow - I was amazed. So I wanted to try one. I fitted a SkyRC gyro. This was set up with the gyro gain adjustable on the fly using a third channel.  I'm still on the fence with the gyro but it's fun to experiment with!

 

The speeds I've currently got to are nothing to get excited about:-

45mph, 30T pinion, 64T spur, 2S CHNL 5600MAh 120C, Robitronic Razer Ten Combo with 4600kv motor & 60A ESC.

Next step is to see what combinations of 31T, 32T pinions and 63T spur will fit under the gear cover and then fit a 4.5R Speed Passion motor that was going cheap at Modelsport.

 

KP

 

[Keracticus Pots 200]

Photo of the car post run covered in dust and grime.

In the photo you can see the two temp sensors, the gyro and the SkyRC GPS mounted on the upper chassis plate.

The next photos show the road I'm running on - up to the usual standards of UK roads.

But on the plus side, on a Sunday (or Bank Holiday Monday) its pretty much traffic free, it doesn't have much of a crown to it and there are no cats eyes.

KP

 

[Keracticus Pots 200]

This photo shows the sacrificial under tray that has to deal with the road above has been properly sacrificed to the RC gods!

KP