[WIP] HELP steering slop normal? Trial truck axle

[MangaNOID]

I'm putting this up as a WIP as I must be the worst axel maker! this so far has been maybe 20 hours or more, over the last couple months so any tips or pointers greatly received.

im trying to make an axel for my very modified MOG...

 

 

...that has good turning circle, slow precise steering, maybe a manual diff lock if there is space and suspension that somewhat resembles real movement. By that I mean if one wheel goes over an object, that shock absorber will compress leaving the vehicle chassis mostly unmoved. 

After the PNEUnimog...although it worked somewhat as a trial truck (it went over stuff) I may as well have had lift arm suspension and the steering was total understeer from the portal axels scrub radius (if that's what it's called)

So I am trying CLAAS hubs instead of portal hubs to try limit scrub radius. I've built the portal axel double height cog bit solid into the axel for more ground clearance.

I've spent ages trying to develop Ackerman steering. I think I have it. Or at least the result of it but how the heck do I operate it.

I am trying to hook up smal LA for slower steering. Although I would like 4WS and LAs can easily go out of sinc if there is 2. 

 I feel like I'm being over pedantic to try and get the perfect axel. But that's my project and I can't seem to move on until I'm happy.

What has annoyed me and prompted this WIP is that I was testing the Ackerman setup with only RWD hooked up and it turned in 1200mm but with 4WD it was 3 times that on a solid surface house floor. WTH! Maybe it will be different on loose surface. 

This is the template I have so far.

 

 

 

Edited August 11, 2017 by MangaNOID

[Imanol BB]

I dont think that this axle you are making is bad, i actually like it, maybe you could change those 16t gears for 12t and 20t, so you will have more torque, about the steering system, if you want to achieve 4WS, you should use one motor for the front steering and one for the rear, like most of the crawler vehicles.

[brickless_kiwi]

You do not have diffs in your axle hence it will crab steer with such a huge turning radius 

[MangaNOID]

Thanks Imanol bb. swapping cogs will happen! It's a low priority at the moment 

 

I'm not sure about crab steer, kiwi but you are right that locked diffs and 4wd are not a friend of tight turning circles.

This is a new steering setup with Ackerman. It had a real tight turning circle. But so tight the hubs won't turn with those 2 pin CV type shafts! 

 

A: my expectations of Lego mechanicals are too high.

B: I'm useless.

 

[suffocation]

CV joints and tight turning circles just don't mesh

If your priority is minimising scrub radius with portal axles then you can use Nicjasno's solution:

 

I built it and it works pretty well - the only downside is the limited steering lock. Since you've got more width to work with, maybe you can adjust it to use U-joints and thus get tighter steering.

 

[HorcikDesigns]

CV joints in wheels in trial truck will not survive. I am sorry to say that.

 If your truck has more than 1kg of weight (and according to Class tires it will), you'd better use portal axles - prefabricated, or brick-built, because they minimize the stress in the U- , or CV- joint (in case of Nicjasno's solution.

[MangaNOID]

Thanks for the input, suffocation and horcikdesigns.

I think this firmly seals the coffin on this axle (I learnt to spell) it's a light vehicle but probably not that light.

maybe I'll go finish that one man crabbing boat that has no technical functions...

[suffocation]

Hi @MangaNOID, I built this axle for a truck I'm working on. It's partly inspired by your work and @Oliver 79's yellow truck. It features portal hub reduction without portal hubs (if that makes any sense ), limited tyre scrub, Ackermann steering and multilink suspension. There's plenty of room for improvement, so maybe you can use it as a starting point to come up with your own, much better axle

(sorry about the atrocious pics).

[MangaNOID]

that looks alright!

have you tested it in vehicle?

I'm actually kinda happy with the axle i have its getting quite structurally robust with minimal parts its just the steering that I cant enjoy, as the rack and pinion setup is so loose and as its 5 studs above the hub connecting points it makes it even more loose with the 'leaning' tolerance at steering lock. i could gear it so the rack sits lower but then the more gears in pace the looser it will be.

I'm now trying to fit the LA at the front of the axle for steering and settling for a small bit of toe out but getting a small amount of toe out from the front side of the axle seems hard.

never try to design an axle to fit a chassis.

 

 

 

oh, and I hope you can all accept that I put avocado in my fruit salad.  

Edited August 5, 2017 by MangaNOID

[1gor]

The only mistake that I see is this

[WIP] trial truck axel. Worlds worst at the moment.

so IMHO title should be like this

[WIP] trial truck axle. Worlds worst at the moment.

Edited August 6, 2017 by I_Igor
...axle not axel (with capital A it could be name)

[suffocation]

10 hours ago, MangaNOID said:

have you tested it in vehicle?

I've tested it on a ballast-loaded (3.5 kg total) 6x6 chassis. The turning radius, as expected, is a bit disappointing - but that's to be expected with CV joints. Other than that, it handles great and can take quite a pounding.

[MangaNOID]

9 hours ago, I_Igor said:

The only mistake that I see is this

[WIP] trial truck axel. Worlds worst at the moment.

so IMHO title should be like this

[WIP] trial truck axel. Worlds worst at the moment.

Well I think I know what you mean. 

I thought maybe you were going to say [WIP]trial truck axle. Getting better.

Oh well...

I may have a lead on the steering which is really my only annoyance. I've been putting the portal axle back together and hooked up ackerman steering on top which is pretty capable of LA operation on the front so I should be able to transfer this over to the other axle.

 

I know all this axle stuff may be trivial for you lot but I'm finding that I can make an axle easy and look good, but it won't operate properly. Hopefully getting there though.

Edited August 6, 2017 by MangaNOID

[MangaNOID]

A bit more progress. But on the portal hub axle setup.

I have slow steering hooked up without an LA. I used the rack and cog. It works really well, but there is slop in the rack so the wheels can bump steer a little still :(  the LA's stoped that happening. But there are compromises maybe if I can't get rid of the slop as the turning circle now is so good that I will stick to the portal hubs.

It's not Ackerman but I have toe out to help tight turning.

A few other small problems like if I oversteer the worm gear setup lifts off the following gear so you can't steer anymore.

Suspension travel is quite well balanced. Soft and good travel when one side is compressed but quite firm when both shocks and compressed holding the weight of the vehicle.

 

 

 

[MangaNOID]

I have only built 42042 and half of 8110 in my AFOL year so is this slop on the rack and cog setup normal?

if so does everyone just put up with?

 

 

 

 

 

 

 

 

 

 

 

 

Edited August 11, 2017 by MangaNOID

[suffocation]

The more gears, the more backlash. If you've got a servo, you can mount it directly on the axle.

(You could do the same with any other motor but would then need to gear down, leading to more complexity and backlash).

[AndyCW]

I know that the angled steering links help with ackerman, but they also induce slop.  I've found several things to reduce slop.

• Try to make the steering links parallel to the axle.
• Make the steering arm on the portal hub longer, but this reduces steering angle.
• Mount servo directly on axle

If you can put in some kingpin inclination and caster angle, then the slop won't be as noticeable because the wheels will 'want' to go straight ahead.

[MangaNOID]

14 hours ago, suffocation said:

The more gears, the more backlash. 

That's true but I put the worm gear driving the final cog that's on the rack to stop the feedback. Even holding that down tight does not stop the loose rack and cog.

11 hours ago, AndyCW said:

 

• Make the steering arm on the portal hub longer, but this reduces steering angle.

I thought that made sense at first but if I understand correctly you need the steering arm link as close to the wheel pivot point as possible to reduce the loose effect?

still that's a good point for me to work on! Mines 2 1/2 studs out. Input torque increases though I guess through the rack.

just tried this and it works a treat so i will have to buy a longer rack than the standard 8110 one to increase turn ability. thanks for the input!

Edited August 12, 2017 by MangaNOID