Help needed with four wheel steer
 

Hi all,

I recently purchased an extended wheelbase TLT as an almost-finished project on a bit of a whim (I have several other R/Cs including an x-crawler but fancied a bit of a scaler).

I've made a few changes like swapping the weak Tamiya axle links for much stronger spare steering links from my Revo, and have mounted them above the carriers to increase clearance, hence everything is now on collars on M3 screws rather than ball joints. I've purchased a Rastar Land Rover Discovery and my plan is to put the shell from that on to this as, if I've done my measurements correctly, it should be close to a scale fit.

After realising how little steering angle there is I decided to convert to 4WS as I had the spare parts. Problem is I am experiencing a truck that seems to want to go in any direction other than straight when a bit of throttle is applied!

I should say this is still quite a nippy TLT with the standard Tamiya silver can and ESC in it, and I want to keep it that way if possible as I want a sort-of crossover vehicle, not too slow.

Admission time: the 4WS is running via dual channel 1s on a Traxxas receiver. I know a 3ch set-up would be best, but I'm a bit short on funds for this one so I'm trying to make do with existing spare 2ch parts I had including a Losi Tx which usefully, given the narrow steering angle, has rate adjustment. This is also why front servo horn is at 6 o'clock, but rear horn is at 12.

I would like to keep the 4WS but even though I have tried my best to line up the axles perfectly on the bench, it seems to want to pull off when I put the gas down - usually to the right, but I have noticed it will go to the left too. The chassis seems to keep sagging after a turn, rather than return to upright, and I'm now wondering if this is a suspension involvement issue rather than a steering alignment issue?

There are some photos below, any set-up comments are appreciated (the lipo and electrics are in testing positions atm, probably not in final places)

Front of the truck;

http://i.imgur.com/1GrnlPA.jpg

Rear of the truck;

http://i.imgur.com/yUrULDM.jpg

Rear quarter view;

http://i.imgur.com/uaET3hl.jpg

Re: Help needed with four wheel steer
 

I would guess your problem to be your servos. The Futaba S3003 only has 57oz of torque. It sounds like when the throttle is applied, the rear servo can't hold the wheels straight. Everything else looks fine and that would be the only thing I can think of. Are you using one of these since you don't have a 3-channel radio...?
http://www2.gpmd.com/image/t/tram2046.jpg

Edit: I would also lower it some. It also seems that your pinion angle is a little steep. For rear steering, you want your kingpins to be closer to straight up and down.

The servos are not strong enough....and like in the post above,I would lower that beast....you must be experiencing binding right?

Re: Help needed with four wheel steer
 

Well, problem solved with a bit of pre-load on the shocks after all that. D'oh.

The compromise is slightly weaker articulation performance but I will live with that as this is not an out-and-out crawler.

The front servo isn't great, but it's what came with it. The "Tower Pro" is a cheapo I bought from China - I got a pair for less than £15 shipped which is a bit nuts. I was expecting them to be pretty awful especially when I saw Jang's comments on UltimateRC about these things but I kinda just needed a cheap servo to get my old e-maxx towing truck going (it tows my x-crawler on a trailer which always goes down well with onlookers) after the Cirrus in there finally died after ten years...

I was kinda amazed when it was actually pretty good. My e-maxx runs big Cen MGT wheels and tyres and this servo will dry steer them no probs. The gearing is a little rough and I dunno how it will last of course, but they seem to have a fair bit of torque at least.

Having one left over for the TLT was a bonus, I actually think this servo should be at the front now, as that's where the stronger of the two should be, right?

Having the rear steering arm that high isn't great, but I dunno how else to do 4WS on 2ch without one horn at 180 degrees to the other? Simple answer is yeah, I don't want to buy any more radio gear I'm afraid. No money!

It's not too bad, it's not binding, but then there isn't much steering angle on these narrow little TLT axles, which is why I went 4WS when I could. No way would this work on my x-crawler.

Re: Help needed with four wheel steer
 

You need to lower it first off. You need stronger servoes and a bec to run the servoes. You need to get rid of the battery connector and go deans to deans without the tamiya connector. Thats just what I see right off. Oh and you need to flip that other servo horn down. It is pushing down more than anything not side to side. You will lose strength from even a good servo at that angle.

Re: Help needed with four wheel steer
 

You could bend the rear steer arm to help.

Re: Help needed with four wheel steer
 

Longer term I will maybe switch to something like an HPI sc-15 with a drag brake. Maybe. Gonna see how I use the truck first. For now it's a TEU-101BK esc with a silver can motor - deans to deans isn't critical imo.

As I say, running two servos on the same channel, not much I can do with the rear arm. Bent link sounds interesting but I'd need a longer threaded shaft - say I could get hold of one how would you bend it to help the servo?

Re: Help needed with four wheel steer
 

You will need to put about a 30 degree bend on it so it will kinda look like a really short hi clearance link. You might want something a little stronger than all thread though since it will bend easy. Basically it will cause the force to go more to the side to side instead of down. If I come across a pic I will post it up.

Re: Help needed with four wheel steer
 

it seems from the pic you have some axle clocking to it, if that´s the case then that also affects your steering angle

Re: Help needed with four wheel steer
 

Yeah, there's a fair bit of clocking. Original owner used TNX steering links (I think) as chassis links. The issue then though is the dog bones. They are pretty limited in flexibility of the axles, and assuming lowering the stance, clocking back the axles, and longer links, they would no longer be long enough. Could switch to a universal joint and I'd have a crawler, but I'd still need to sort the battery, and anyway that's kinda changing the whole thing then. Also with any longer a wheelbase the turning circle would be too great again imo, even with 4WS, so it's kinda self-limiting.

Thing is I don't think the TLT is a serious crawler anyway with it's belt-drive and top-heavy construction. There are other issues from the stock configuration like the axle shock mounts being at an angle - see the pics above. I do like the elegance of the belt-driven design and Tamiya quality though. The Rastar 1/14th scale Land Rover Discovery body is a close-to-scale fit as it is now, so I'm going to fit LEDs to that, find a way to mount it, and make this a scale-ish fun truck that can off-road a bit, and is a bit of a conversation piece. I am kinda of the opinion that's the realistic limit of the TLT-1's potential.

I still like that bent link idea though, I actually found a metre of M3 threaded shaft I bought a while ago so I will try to make something.

Re: Help needed with four wheel steer
 

If you shorten just the upper links that should help the clocking issue he was talking about. That with lowering it should still keep your wheelbase about the same."thumbsup"

Re: Help needed with four wheel steer
 

Can't do it - the dog bones won't take the angle :-(