TXT racing

[vodka 35]

I've been thinking about it for a while: I'd like to set up a "competition" monster, something like a TRF project. Nothing really new, but I do not like projects where the only original tamiya item is a sticker.

I would like to start from a txt-1 and use Tamiya hopup where possible, this is my idea:

• servo on standard axle guard (like original Tamiya design) front and rear
• sway bar
• hex screw
• 2 27t motors and brushed tamiya esc 106BK
• txt-2 plastics parts (battery tray etc)
• txt-1 body (I love the Agrios body, but the original txt-1 is more iconic)
• clod wheels

Main questions: 

• for increased wheelbase and lower ride height I wan't use traxxas drive shaft (or similar) so machining a longer tamiya shaft or adapt universal or something else?
• 8 oil damper (like txt-2) or cantilever? (cantilever is sexy, but txt2 style damper is better I think)
• wich servo? the tamiya one is very weak...

Suggestions? Hints? 

[Mad Ax 9312]

I've never raced a stock TXT-1, and I didn't run mine in stock trim for long before I broke it up for parts, but back then it was all about height and ground clearance, these days racing trucks are run lower the ground.  With that in mind, and provided you want to bias towards racing, the stock axle guard might be fine.

I rebuilt mine into a race-oriented rig last year but haven't had the chance to run it in anger yet, besides a few runs on gravel and some jumps in the garden.  I definitely need a swaybar (piano wire seems to be the way to go unless you have a better idea already).

27T motors will be OK for starters but you could consider 3S with a HW 880 ESC.  I run mine with two Etronix 19T Sport Tuned motors which have been OK so far.

Servos - I recently switched to Power HD 20Kg servos with solid horns.  Steering seems to be good, haven't had any big impacts yet (I had an impact with a different servo late last year which snapped the plastic horn).  They're pretty cheap and sturdy.

Driveshafts - IME you can't really cut corners here.  There are some cheap shafts out there but they're cheap for a reason.  Traxxas are recommended because they're good.  I'm using some cheap Cross RC shafts but will probably have to switch to Traxxas soon as they are already showing signs of wear despite little use.

IIRC neither the transmission outdrives nor the axle inputs have holes in them, so they rely on one or two grubs being done up tight.  IME they never stay on.  I carefully drilled mine in a drill press to accept a, Axial pass-through grub pin.

Shocks - I kept the cantilever on mine but fitting much stiffer shocks, as in standard form it is too soft for racing.  The beauty of the cantilever setup is you can get your spring rate and damping dialled in and still change the ride height later, by adjusting the pushrod length.  With a conventional upright coilover you are often compromising something when you adjust the right height.  (Generally a 1:1 coilover setup has an adjustable spring perch to set the spring rate and a separate thread on the shock body to set the ride height - RC shocks don't have this.)

IIRC if you are fitting Clod wheels you will also need the Clod drive stubs and the grey drive hubs that fit between hex and wheel, as the TXT wheel is both wider and has different lugs on the back.

One final thing I did on mine was to invert the transmission.  This brings the weight right down.  Sure, the motors are now underneath and up front and in line to hit any obstacles - indeed my cans are already scratched from running on rough gravel - but this is less of an issue on a race-inspired setup.  I will probably build a sump guard for mine.  I had to drill one extra hole in each chassis plate to get the transmission where I wanted it.

[MadInventor 3884]

I've not raced TXT's either, but have run one for a long time.

If you're going racing I would stick with the stock wheels. They have larger drive lugs than the clod wheels and are more robust if you're putting lots of power in. 

The stock axle guard frames are brittle and are spares are like unicorn horn now. Try and obtain some aftermarket aluminium ones if you can.

I use traxxas drive shafts as well. Without wishing to contradict @Mad Ax (Perhaps you're thinking about Juggernaut 2 shafts?), the stock TXT axle input shafts come with a pin hole drilled through them, as does the gearbox output shaft (I've been searching for input shafts to replace my Juggernaut 2 5mm shafts).

The Tamiya stock drive shafts are held on with 2 5mm grub screws in each end. (The old Juggernaut / Juggernaut 2 axle input shafts were 5mm and had no holes.). So the good news is that Traxxas REVO shafts will bolt straight to the axle input shaft, and in theory would bolt to gearbox outdrive as well, but the outdrive is too short, so you can either bodge the drive shaft on, or make a new bottom shaft. I would think very carefully before going to the effort of modifying tamiya shafts to support a longer wheelbase, they're made from really soft brass, including one of the pins that make up the UJ, and it all wears really badly once it starts to wear. Traxxas shafts are cheaper and better than the TXT-1 shafts. If you're tamiya shafts are new, I'd sell them and use the cash to get some traxxas drive shafts (Sorry Tamiya )

This is a REVO shaft fitted to the stock gearbox output shaft, with good luck and a bit of superglue holding the pin in. I later made a new bottom shaft that was longer to accommodate stock traxxas shaft end that has a threaded pin, which had a machined steel hex that was loctited to the shaft, and then drilled and pinned for good measure.

If you want to move further away from stock I made my own gearbox casing (using stock gears) to optimise the layout for one motor to lower the CoG as much as possible without having the motor below the output shafts. If nothing else, the underguard is very worthwhile.

 

 

 

 

[87lc2 2663]

Not much to add, @Mad Ax & @MadInventor covered it nicely.  I use the Traxxas Revo shafts and they are fantastic, hold up to 8th scale brushless with no issue.  As both said you want to get the center of gravity lower if you're going to race.  You can flip the trans, make your own case, or put an Emaxx trans in it.  You want the truck as low as you can get it, lower links parallel to the ground if possible.  As @Mad Ax said on power, 27t motors are fine, but you'll want to run 3S Lipo.  27t on 2S would be slow.  Best would be to go with a single 550 sized brushless system. 

Are you going to be racing this truck in a series or is this just for fun?  If just for fun then it should be a fun truck (love my TXTs), but if you're going to race in a spec series you really need to get the weight down, the stock chassis & axles are heavy.  If I were going to set up a race-TXT I would use an Agrios chassis without the aluminum side plates, nice and light.  I think it will be a fun project and hope it goes well.  No matter what it will definitley look cool and be all Tamiya, best of luck.  

[vodka 35]

Thanks for the hints, but the goal of this project is to build a racing monster (for fun) and I want to be sticky on tamiya parts, specially if the tamiya item exist.

@87lc2 The txt-2 chassis is nice and without side plates is light, but I have a txt-1 lightweight chassis: nice, lighth and blue. 

@Mad Ax I have found some cheap shaft on aliexpress and I undestrand your point of view, the Traxxas is cheap and good despite the design is the same.

@MadInventor I have seen your original post, very nice work, but I want to try something similar with Tamiya items, I want just give a try... if this drive me crazy and poor I buy a Traxxas shaft.

For the motors (due the esc) we have max 25t support (with 2s battery). I can manage 2 brushless motors with 2 esc, but for now is not necessary.

I read somewhere (clodtalk maybe) that someone managed to add a slipper clutch... this can be interestig. Hints here?

 

[87lc2 2663]

Yes, the blue chassis is nice and light, that should work well.  You dont need dual brushless, just run one and block off the other motor opening.  Running dual 25t motors on 2s is going to be slow, but if that's what the class specs not much you can do.  

I never saw a need for a slipper on the TXT as the transmission can handle the power just fine, not sure how much benefit you'd see there.  I usually lock the slipper tight on most vehicles anyway (SMT10, etc.)

[vodka 35]

For the drive shaft this is a solution: https://tamiyabase.com/articles/53-how-to/134-cc01-driveshaft-extention

cc01 is not abused like a txt, but it can works..

[MadInventor 3884]

5 hours ago, vodka said:

For the drive shaft this is a solution: https://tamiyabase.com/articles/53-how-to/134-cc01-driveshaft-extention

cc01 is not abused like a txt, but it can works..

The only problem that I can see with this for the TXT is that the steel shroud is also there to stop the brass that has the slot in it spreading or breaking off under load. Once you've cut through the steel outer shroud, it takes all the strength out of it. As you said, fine for the CC-01, but I'd be dubious about it's longevity in a TXT-1, particularly going to the rear axle.

For the CC-01, it's a very neat solution using stock parts if you have limited metalworking facilities.

[vodka 35]

Low friction damper set for TXT-1 are very hard to find (and I do not like txt-2 version, no blue no win), I need 2 box set, so why not build a TNX damper from scratch? Spare parts are few, but they are not that difficult to find on ebay or in some online stores.

[vodka 35]

On 2/20/2021 at 4:51 PM, 87lc2 said:

 You dont need dual brushless, just run one and block off the other motor opening.

I have a Tamiya 16T (around 2400kv) from the Levant or I can searching for the 8T (3000-4000kv)... a standard 540 is enough?

[vodka 35]

Difficult to find everything...  Project aborted, the items I found are now available in the forum.