Torque Twist

[Android]

This story began from the middle, so I'll just correct the mistake and write it from the start.
So in the beginning of this year postman brought me a Venom Creeper kit.
Right from the start I was planning to build a scaler, and decided to start with the creeper mostly because of it's price, good price/performance level, and lots of tech info and spare parts available.
I finished assembling it somewhere in the beginning of february - not much to write on that. After that I added some chassis rails - screwed some aluminium tubes to the original chassis, adjusted the wheelbase, relocated upper shock mounts, made inner fenders and floor from some plastic material, installed the original Venom crawler esc and 55t motor, which turned out very sluggish.
So, the rest of the story is depicted here.


I've finished assembling my venom creeper and also have rebuilt it into a scaler, and I have an issue with torque twist - it leans to one side when going forward, and to the opposite side when going backwards.
I've read the FAQ section and the suggestions on how to decrease TT, and I've moved the rear upper arms wider apart. It helped a little, but hasnt' cured the problem. I can not move them higher on the axle as it would decrease the suspension travel (the upper arms would hit the floor/frame).
Is there an ultimate way to eliminate the TT? I use the stock shocks without the inner spring. I've considered using only the inner springs without the outer ones, but i'm not sure if that could help. I'd also like to have the springs/shocks as soft as possible - so the rig behaves more realistic.
Also - do the SCX10, or creeper safari or any other stock scale-ish rigs suffer the TT, or is it just a creeper malady?
And one more question - in my opinion, if the front and rear driveshafts rotated in opposite direction, it would eliminate the TT - do the driveshafts rotate in the same direction on other RC rigs?

Thanks!

[Exocaged]

use the inner springs. They help a lot. I run the inner springs in my creeper and my bouncer.

[Docwolf]

link geometry will effect this a lot as will the springs.

[kart45]

My 'scaler' built from an RTR safari does this too... Anyone know of a substitution for the inner springs or do they need to be ordered from Venom?

[Exocaged]

IDK what spring would cross over for this but If we could get some measurements if someone has them out, we may be able to do some searching and come up with something. I kinda think about 1/4" X 1" but I am probably wrong on this. It's possible we may be able to find different spring ratings to do some fine tuning as well.

the measurements needed are wire diameter, overall diameter, overall length.

Something like this could be bought and cut to length.
http://www.reidsupply.com/sku/SSS-209/

[Android]

But how about other crawlers - scx10, for example - are they having bad TT too, or it's just the creeper that has the problem?

[Exocaged]

Everything with a live axle and a driveshaft has this, from ours to the Wraith to the Twin Hammers and even my new bouncer. You can change link geometry to try to counter act it but its there. Its also in real vehicles with live axles. It shows up worse on long travel soft suspension. I have a real offroad truck like many others on this forum, when I am pulling someone in a hard pull situation it shows torque twist. One way I am trying to counter it on our RC's is by running the internal springs, stiffer outer springs and some link geometry changes. Its not too bad. On my creeper I also moved the shocks out from the original top position to a more vertical position. This cuts down a bit on overall articulation but with locked axles it still pulls fine anywhere I put it.

[Android]

Ok, thanks!

I'll try my luck with the inner springs, then post some pics here.
I've already moved the springs to vertical position, but as they are very soft, TT shows badly.
I suppose I'll have to add some weight to the chassis for the rig to behave realistically.

[ratterd]

Originally Posted by Android

But how about other crawlers - scx10, for example - are they having bad TT too, or it's just the creeper that has the problem?

The ax10 RTR also had horrible TT.A heavyer shock oil (10-15wt)in the rear left shock will help somewhat.

[Rodeo]

You can also try turning the left rear spring tighter to help it out a little.

[Crawlerjedi]

I used a 50 weight oil and it almost takes care of it all. But I also put Wraith shocks on it because the stock venoms couldn't keep fluid in them

[Android]

Today I tried to fiddle with the shocks/springs.
At first I tried to put back the stock setup - inner springs preventing shocks from being pulled out, outer springs working against compression. That reduced the suspension travel significantly.
Then I removed the outer springs completely, and put the inner springs so that they work the other way - preventing shocks from compression. This way the suspension became very hard, and that also s*cks..
So I'm still not happy with the way suspension works.
I want to get the right hardness, to eliminate TT, but soft enough for the suspension to work nicely.
I think I'll try to buy some other shocks/springs - from Hot Racing - at 20$ per pair, they come with three different springs - soft, medium and hard.
I'll post my progress..

[Exocaged]

Although I haven't tried them in mine yet, I recently found some slightly stiffer, yet a bit shorter springs for internal use. When I am crawling I for one don't want an insane amount of articulation, just stability. I'm sure my creeper in its current form has a lot less articulation then yours does, but since its locked it will go anywhere. If these stiffer springs work out for a buddy who has a bone stock creeper I'll post up. Right now mine has the stiff ones up front and stock ones in back. His is the opposite of mine right now. By any chance, did you widen the front upper links at the axle too?

[Android]

I did widen the rear upper links, but that just made the rear wobble - rear axle wobbles from side to side, so I think I'll put them back to the stock position, maybe just a little bit wider and higher.
My creeper is a scaler'ish now, the shocks are mounted to the lower links, and are vertical, so they work a bit different from stock shocks, and the wheel travel is about 5-6cm now.

[Exocaged]

Is there any play in the link ends? Many run the tops almost straight and do just fine as the bottom links are triangulated quite a bit. Got any pics of this hosted somewhere? I'd like to see what you have.

[Android]

Yesterday I rearanged the rear links completely - the lower links are mounted to the chassis ~0,8 inch outwards - to the outer side of the frame, using longer screws and spacers. Upper links are mounted to the chassis closer to the centre - also using longer screws and spacers, and at the axle the lower links stayed in stock position, but upper links are made longer and attached to the where the shocks were mounted in stock position. Now the axle feels rock solid, no sideways play.
Also ordered Losi shocks yesterday - now I'll have to wait for them for three weeks or so - It's a long way from USA to my country, and the postman is not in a hurry usually
I'll post some pics later when I get home

[Exocaged]

dang man I didn't even see your location!!!

[Android]

At last I got time to upload some pics.
This is my bronco, on 2,2 stock wheels at the moment - was just trying them on. Anyway it will live on 1,9 wheels.


Here is the rear suspension - nuts instead of spacers is just temporary measure.


View of the underside


And the chassis from the top.


Bumpers and other bits will appear later - when I'll start the garage season (now its still freezing outside), don't want to have too big mess in the house.

[Exocaged]

On the rear suspension. I have a feeling as soon as one of the tires back there roots in you will at the least bend those extensions, even with proper spacers. I would move everything back to a more traditional 4-link design. Triangulate the top links back to the top center of the rear axle ( like factory ). Move the frame mounted lower links back close to the chassis sides. You want a slight spread out from the chassis back to the axle. I wouldn't run the set up you show on mine.

top links

chassis
\ /
top of axle

chassis
/ \
bottom of axle

[Android]

Thanks for the advice!
I'm waiting for the postman to bring me the 35t motor and Losi shocks - I'll test fit them, and then we'll see how it works. Anyway there are not many rocks in my country, and the rig is going to be used for trailing in forest or garden.