Torque twist/HELP PLEEEEEEEEEEASE!!!!!!!!

[Reflection]

I'm getting really agravated here. My first attempt at building a crawler,I used carbon fiber for my chassis plates. Heres my first attempt........



It worked fairly well,but not acceptable. It had some torque twist. I figured some was cuz the Savage shocks were laid over at 45* and some of my weight was above the tops of the tires. I wanted to build a new chassis to lower things down and stand my shock stright up. Sorry,no pics of my new chassis yet,this rough MS paint picture will have to do.




The green box simulates my motor and reduction on one side of the chassis and battery on the other.

The orange boxes are the RX and EVX

The red,where the link mounts are and shock mounts are is made of 1/16" sheet metal. The rest of the chassis is made of 1/8" solid rod.

When sitting flat on the garage floor the chassis and links look exactly like their painted. The Savage shocks lack 1/4" from being bottomed out sitting at rest. I'm running black springs(stiffest you can get,I think) and 60 weight oil in the shocks also.

I'm pretty mad about this,I went through all the trouble to build a new chassis for 1-to lower things down and 2- to stand the shocks straight up. I thought for sure this would help,if anything it made it worse. I tried to skimp on material to save weight up high. Does ANYONE have ANY ideas?

[Plays_with_Toys]

Your shocks are mounted to your links. This is going to make the shocks "softer" because thereis more leverage acting on them from the links. Try and move the shocks further down the links if you can. Though they will be angled, they will be a little stronger on the axle.

[toyofast]

Are your links mounted at the same point on the chassis? If so, try relocating the upper links. Try to get your links more parrallel with each other.

Also, ditch the Savage shocks. IMO they are not helpfull when crawling. You either have to make really tall and long shock towers to mount them or adjust your ride height so tall that you just turn the truck into a show truck.

Toss on some shorter shocks(4" or slightly larger 1/8 scale buggy style). Stiffen up the shock weight and maybe even the spring rate.

Also, try to get your batteries off the chassis. Batteries on the chassis of a shafty is the killer... less weight on the chassis and less amount of chassis twist/roll.


If you want to make minor changes start with the link placement first. Then move onto shock oil weight/spring rate. See where that takes you.

[Reflection]

Although it would be alot of work making new mounts,I will probly try that. Thanks,that makes alot of sence

One thing I was thinking about while in the shower,well after the wife got out anyway. Softer springs and stiffer oil. The way I'm thinking,although I may be WAY off,the stiffer springs want to push up harder. Therefore making it easier to lift one side. A softer spring wouldn't push up as hard,would this help?,I dunno.

I went from 30 weight oil to 60 weight and didn't notice much change. Is there THAT much difference between 60 and 80 weight? I wouldn't think so but might be worth a few bucks to try it.

On a side note:

I remember seeing a rig(can't remember whos,I think it was from down undah)anyway,he was running aluminum threaded shocks. He had one front spring tightened all the way up and the other side all the way down. The rear axle was done the same way but opposite sides. Was this done to help counteract with torque twist? Seems like it might help. Could even try it with softer springs placed at opposite corners and stiff springs at the other corners.

What do you all think?

[toyofast]

Okay...

Try this really quick, charge up a pack and rather than putting it on the chassis like you normaly do, zip-tie it to your front axle... run around for a few minutes and see what happens.


I really think you should change your link setup on the chassis as well. Just raise you upper links up the same distance apart as the link ends are on the axles... did that make sense? I'm drugged up from meds right now so things are not coming out like how they should

[DirkDigler]

There is so much stroke on the savage shocks that I ended up making sway bars. this helped out more than anything, controlling the long dampers. My biggest problem was the unloading shocks wanted to twist the rig over when articulating in off camber situations. The sway bars fixed that problem.
As for the torque twist, I just think you are going to suffer from it no matter what if you continue with the savage shocks. You could mess with your link geometery but that will only go so far. Try and "middle of the road" long shock, like the Xfactor shock. They are longer than a maxx shock but shorter than the savage shocks. I'll bet just changing the shock will net you the best results.

[DirkDigler]

oh yeah! I'll bet that 10 pound body ain't helpin anything!!!

[kyle]

You need more anti squat on one side to balance it out. Raise the upper link on the side it twists to.

[Reflection]

Thank you everyone,VERY much.

I will raise my uppers on the chassis mount a little first. I may just run by my LHS and see what shocks they have in stock. The only shocks I have other than the Savage are my factory Twin shocks. I think they are the same length as maxx shocks but not poss. Another thing I relized tonight after work,I might be able to move my motor,reduction and battery down another 3/4",might help a little. I could drop it down a bunch more. Doing that though means my tranny hangs below the chassis and my driveshafts are below the links. The driveshafts don't really bother me much,they are steel and can take some beating and draging. The tranny though would be a huge anchor,I would think.

Oh yeah,that 10 lb body,it's in the trash can. It had SOOOOOOO many cracks it was literally barely holding itself together. I've got a XXX Crowd Pleazer on it now

[SR5Dave]

Get a clod Steve. Get a clod.

[Reflection]

Let me think about it DaveNOPE!


I like playing with my Shaftie to much

[MUD4FUN]

Hi raptorman, I too suffered really bad torque twist on my home built crawler when I first built it. I know everybody tells me that shaft driven trucks will all suffer this problem, for me it was unnacceptable. The torque would actually lift a wheel until the axle hit the bump stops, that was at near standstill with just minimum throttle.

I solved most of this with suggestions from both here and other forums.

First thing I did was to relocate the bottom shocks mountings further outboard, mine were mounted to the axle rather than to the links as in your case though. Once the lower mounts were moved outboard that solved quite a bit of the twist which was surprising. The shocks now sit angled slightly in towards the chassis at the top.

The upper mounting were also changed, I used cantilevers and I moved these so that the upper shock mounts made the shock sit just short of vertical. Bear in mind that I was making a scale looking chassis and shocks sat at extreme angles wouldn't look right.

The next thing I changed was the spring rates. I made the two diagonally opposed shocks much firmer by using spacers. These were on the corners that suffered the twist problems.

I then tried using anti roll bars from the 4 link arms to the chassis just as on the Tamiya TXT but I found that reduced articulation so I removed them. They didn't really make much difference to the twist anyway.

I then introduced a lower gear reduction unit of 3.5:1 which meant I could use tiny amounts of throttle to crawl over obstacles, this meant the torque twist was less noticeable.

However, the biggest difference was achieved by reducing the angles of the propshafts. I started out by having huge ground clearance under the chassis but I had to sacrifice some of it to lower the prop angles and that cut out 50% of my twist problem

I also tried mounting the motor transverse in the chassis and driving the props by bevel gears, this worked and cut out huge amounts of twist but was unworkable in a my scale ladder chassis although it might work for none scale crawlers. The loss of efficiency in the drivetrain is hardly a problem in a crawler running such vast torque at low revs anyway.

Good luck with your project and I hope you get your problem solved.

[Reflection]

Originally Posted by MUD4FUN

Hi raptorman, I too .................................................. ............................................
................................... alot of good ideas .....................................
.................................................. .............................Good luck with your project and I hope you get your problem solved.

WOW, thanks for the great info,good read. Don't know if I'll try all of them but thanks for the tips.

[Reflection]

O.K. Say I run a Twin shock on an angle,would they still out perform a Savage shock that was standing verticle? I know I may loose a little wheel travel but it's worth it if I can get rid of the twist,or at least com it down sum.

[TXTFUN]

Hi Raptorman,

I'm the Aussie guy with theTXT with the dual shock multi spring rate someone was talking about earlier and here's my theories and how I solved my probs.

The 1st thing I wasn't happy about was the leverage on the shock so I mounted them as close to the wheel as possible to reduce the leverage and give a more even shock travel per amount of wheel travel ratio but this reduced my travel by a fair bit so I changed the canty links for a 2nd set of shocks to get the wheel travel back up.

At first I ran it with limiting straps and 60 - 70% droop in the wheel travel but found that the torque just made the LHS unload and the chassis just lifted up untill that side was at full extension, so I changed my shock mounts so I was running my shocks at full extension again with fairly firm springs and all my wheel travel coming from compression.

I lowered my COG so it was closer to the point of pivot of the twist (where the links mount to the chassis) because I found once it started to twist the bulk of the weight would quickly be thrown past the centre line and make the twist worse. I did this by inverting the tranny so the motors are at the bottom and the driveshafts are at the top.

I ran the different spring rates to make the articulation more even from either aproach more than reducing twist. If you look close while you drive you'll notice if you aproach a step with the LH front it very easily flexes up and walks over it but with the RH front it tends to lift the whole front up flat until it gets to a point where it gets too heavy and the LH wheel drops back down and then you're right until you go on the flat again. I just used a softer spring in the front right so it flexed up easier to avoid this and make it smoother to drive, however if you do nothing else to reduce the initial twist I doubt this would help much it's more of a fine tuning thing than anything else.

I very much liked Kyle's idea of the asymmetrical 4 link with more anti squat on one side.... very ingenius.

I also refused to accept that shafties were doomed to flap a front wheel around in the air as the clods took out all the comps and with heaps of trial and error I proved them wrong and have a TXT as stable as a clod. I've missed the last couple of comps over here but I've taken out a 2nd place infront of about 12 clods and recon I've done enough tweaking to take home the gold soon.

Here's a pic from one of our comps, the truck in it is a Mud Cow clone clod but I managed to get up also without even lifting a wheel so it definately is possible to rid the twist, you just need to find the right setup.





Good luck with it.

[gasshead]

dude you wheel is off the ground, only by a little bit but its off the ground, so you didnt rid the torque twist completly, but its close

[Unholy]

Originally Posted by gasshead

dude you wheel is off the ground, only by a little bit but its off the ground, so you didnt rid the torque twist completly, but its close

Dig up old posts much?

[Grizzly4x4]

Originally Posted by gasshead

dude you wheel is off the ground, only by a little bit but its off the ground, so you didnt rid the torque twist completly, but its close

First of all that thread is 2 years old so I doubt if he still suffers from the same problem.

Second of all that pic is of a Clod which does not have torque twist since it has no driveshafts. He was only using the pic to reference the slope of the rock.

Good on you for reading old posts though.

[EeePee]

Holy crap.

[BENDER]

This is one of the threads in my cheap tricks sticky, it's good to see people reading them at least.