TXT-1 - First Try...Again! (Build Thread)

[bsrboy]

2 years ago I bought a TXT-1...after 6 months I sold it to race 1/10th carpet oval...then the track closed in the middle of the season. I always regretted selling the TXT before truly figuring it out. Now I've got a 2nd chance!

Picked this one up off craigslist for $350, here's what I got:

EVX speed controller
2 "huge" silver can motors (I had no idea what I was buying...)
2 JR high torque servos

The original rims were gone so I got a set of Clodbuster tires and rims.

 

[bsrboy]

The first step was taking the truck apart...these were the motors in the truck (that's a Trinity 27T stock motor next to it for comparison...)

They were some 600-size super-silver-can motors. Not surprisingly, the guy told me "when you get on the gas the truck makes a popping noise sometimes..."

I could only guess what the noise was.

 

[bsrboy]

Once I got the main transmission apart I realized a few things...one motor wasn't driving the truck because the pinion lost its set screw. I think this prevented further damage before I bought it. Just had to clean the cases, oil the bearings, and put it back together with slightly more tame motors.

HPI GT550 motors with 15 tooth pinions went in (I have 17 tooth pinions in reserve...hehe)

 

[bsrboy]

After the transmission went back together, my differential parts showed up. That was tonights project. (All the previous posts took place over the last week or so).

Unfortunately, the two oversized motors must have tag-teamed the truck for at least a little while, because both spiders had all 3 legs snapped off them and the teeth of the bevel gears were starting to roll over. Nice...I wanted to rebuild my diffs anyway.

Here's a hot tip - after you rebuild your differentials, fill them with 3000 or 2000 weight oil and use a drill to turn one axle shaft at a time (hold the differential and pinch the other axle shaft to provide resistance). From the factory the gears don't mesh well - after 10-15 seconds of run-in time per axle, per direction, the diffs felt much much smoother.

 

[bsrboy]

Took the time tonight to make sure my electronics all worked (they did) and to tune my radio (Futaba 3PDF). I'll use my channel 3 switch to drive the rear wheels to one of 3 positions (full left, centered, full right). This will be the first truck I've had that will do donuts AND crab walk. I'm pumped!

 

[bsrboy]

And lastly - if I've learned anything, its to buy up spare parts while you can. I cleaned Tower Hobbies AND Tamiya America's shelves out!

 

[bsrboy]

Ok, now I'm up to date. Here's what I'm waiting on...

1. New bevel gears
2. Ball bearing set
3. Revo suspension link-ends
4. Parma "Monster Jam" decals

Once it comes time to build the truck, I'm planning to deviate a little from the stock TXT-1. The biggest issue I had with my old TXT was the body roll. I'm hoping that by going to vertical shocks and using the stock sway bars I'll be able to fix 90% of it.

The last TXT I had was "quick" (not fast) with two 19T LRP motors and a 7 cell pack. I'm expecting the GT550 motors with 14.4V to have MUCH more rip. I can't wait to drive this thing.

Thanks for reading!

 

[scottgir]

Those "super" silver can motors are probably drill motors. That's what they look like.

 

[JKRacing37]

Wow that motor is huge! Bigger than a 600 series, for sure.

Looks like Revo drive shafts are installed as well. Looks like you had a good find!

 

[bsrboy]

Definitely a good find. Overall I'm happy - despite having to put diff gears in it. I've got enough spare parts to drive it until I retire! (I'm 26).

More to come as soon as my bearings show up - then I'll get the axles together and start mocking up the suspension!

 

[Supreme Reign]

Awesome!! I love Jugg/TXT build-ups. I don't know how you guys do it. I could never sell one of mine.

 

[TXT-2.0]

good start and good idea to ditch the cantalevers i have very little torque twist on my trucks once i went vertical shocks and sway bars :tmb

 

[Ball Racing]

Sway bars are the answer to twist.
Cantilevers never cause twist ,

they just apply more leverage to your existing spring- oil combo, because of longer travel.
When you lose the cants, you are losing suspension travel, and the same spring applies more tension because of the lack of leverage.

 

[TXT-2.0]

^^ thanks Daniel i definitely learned something form that :tmb

 

[bsrboy]

I agree with your logic, but I disagree with the final statement. It's been my experience (with my first TXT-1) that the cantilever system introduced "slop" in the suspension (link-to-cantilever, cantilever to chassis, cantilever to shock). As a result, it took nearly no force to lean the chassis ~5-10 degrees off vertical. Add in the twist from the drivetrain and you have a truck that always leaned. Since I don't feel like re-designing the cantilever system (yet) I'm going to try vertical shocks for the initial build. The sway bars will remain (and hopefully get beefed up).

That said, I will need to address the limited-travel problem, but I'm not worried about that.

More to come - tonight I'll be tinkering.

 

[joe]

...Cantilevers never cause twist...

but they sure dont help! seems they allow it to happen more, even though they dont cause it to happen.
:bang

i noticed that just removing the cants on an otherwise stock TXT, the torque twist was diminished.
then switching to better, shorter, and stiffer shocks it was even better.
with some adjustment to the rear corner, it was almost gone.
:tmb

 

[HawnMT]

I see what everyone is saying and there some truth to all of it but I'm going to attenpt to pull it all together, I'm no expert but I have some experience also in this area from crawling to bashing to racing.

First off, Ball is right in saying cantis do not CAUSE torque twist. And Joe is right by saying they allow it to happen more. And bsrboy is right that slop plays a part.....I know that was real "Miss America" of me...

Torque twist, as it's name implies, is a product of the torque of the driveshafts(motors,transmission) trying to spin the axles like propellers. That is why on a TXT the front driver's side rises and the opposite end drops(in essence it's rising towards the chassis but the result is the chassis drops towards it) What stops this is the links, shocks, and the ground. But what ends up happening because of the suspension is what we see as Torque Twist.

So when we run a "softer" suspension, whether it be through cantillevers, link mounting, or just really soft shocks, we see the effects of torque twist much more, which is what Ball and Joe were saying, and the same can be said for "slop." Now the answer for a longtime has been to run thicker oil or stiffer springs especially in the two corners lifting up. I never did like that answer because it created an unbalanced suspension that only addressed the truck when it was accelerating but was detrimental when jumping and turning. And while stiffer swaybars are indeed the answer, they're the last part of the equation because they simply counter the effects of the torque twist that is already there. The first thing to do is minimize torque twist in the first place....

To do that can get complicated because a lot of things affect torque twist. But since most guys aren't designing full up chassis' and can't redesign axles and transmissions, I'm going to focus only on one area, weight. The best thing you can do is lower the weight of the truck. By that I mean lighten up the truck as much as possible and then whatever you left with get it to sit as low in the chassis as you can get it.

When you have a lot of weight, like in a dual battery/dual 550 motor setup, and that weight all sits up at the top of the chassis, you have an upside down pendulum effect. That heavy weight up high swinging around makes the truck unstable(which also makes it flip in turns) so it actually multiplies the effects of torque twist making it much harder to control. By lowering the weight you lower the effects considerably.

 

[william g]

moving the placement of rear links up or down on the chassis can help, or hinder the twist/lean of acceleration. However you have to be carefull of your drivesaft pinion angles changing as they travel

 

[Muddigger Racin]

So when switching to vertical shocks on a stock TXT where do you mount them where they wont hit the tires?

 

[joe]

^
there are a few different options and configurations.
if you look at builds from HawnMT, TXT-2.0, and from me, youll see a few.
im sure there are others, but those are a few i know of for sure that have moved the shocks and still used a stock chassis.
basically, the bottom attaches close to where the canti rods were, and the top moves around.