Big wheels keep snapping off

[chemieglennie]

I've been trying to add the big wheels to my Eve lander, but during testing they keep snapping off. The turning forces seem to snap them off whenever I try to turn no matter how many struts I add.

The lander is quite heavy, about 70t.

Is there a trick to using them or can someone suggest some good wheels from a mod.

Thanks in advance for any help.

[ScottyDoesKnow]

I probably won't be able to answer your question, but I'd recommend putting up some pictures of your current design.

[Kasuha]

Pictures would definitely help.

Also you may have too few wheels for the mass, or you might have center of mass too high.

[chemieglennie]

I've been working on lowering the centre of mass. The picture shows the 6 wheeled version. I also had a 4 wheeled version that did the same thing.

The wheels are attached to decouplers. Whenever I try to turn the wheels snap off of the decouplers. It's a bit better with struts but nowhere near stable enough to take to Eve.

I've tried adding girders in the picture with more struts but it still happens.

It seems to be a problem with the way the wheels "turn". They turn the rover by rolling in opposite directions on each side, kind of like tank tracks. The twisting force from this just snaps them off.

[Kasuha]

If your rover has six wheels, try disabling steering on the middle pair.

And check if you have all other tweakables on default, i.e. not inverted steering or disabled motor anywhere. Because I don't think wheels should roll in opposite directions.

Edit: ah, they do, actually. I don't use them often so I did not remember these wheels steer differently. Then you maybe should just give your rover some forward momentum first.

Edited March 18, 2014 by Kasuha

[Nurph]

Mabye try less struts? With the big wheels I found that giving the attachment point room to flex resulted in less breaking.

[Aragosnat]

Question? Are you turning while moving or are you coming to a complete stop then turning?

[chemieglennie]

I've been testing on the launchpad which means slow sharp turns. I'll try and give it a run on more open ground.

With regards to struts I started with none and gradually added more. More struts seems to help quite a lot, but I want to know it's really stable before I attempt a mountain climb on Eve.

[Voculus]

As others have said, use fewer struts. It'll allow for flexing before failure, and will look a lot nicer. Also, try disabling steering on the front and rear sets of wheels. Let the center wheels do the tank-steering.

[MarvinKitFox]

Try attaching your wheels to structural members, not directly to tanks?

A wheel-girder bond is much stronger than a wheel-tank join, especially when the join surface is so much narrower that the wheel's attachment plate. (as yours is..)

OTOH, my imput may be of limited value, I usually have Joint Reinforcement active, which very much changes the rules for structural members.

[LordFjord]

I've been working on lowering the centre of mass. The picture shows the 6 wheeled version. I also had a 4 wheeled version that did the same thing.

The wheels are attached to decouplers. Whenever I try to turn the wheels snap off of the decouplers. It's a bit better with struts but nowhere near stable enough to take to Eve.

I've tried adding girders in the picture with more struts but it still happens.

It seems to be a problem with the way the wheels "turn". They turn the rover by rolling in opposite directions on each side, kind of like tank tracks. The twisting force from this just snaps them off.

I can confirm that there is something fishy with the big rover wheels. I had steering and motors enabled for all wheels.

Especially when turning while accelerating, they gain higher speeds than when accelerating without steering. This usually results in the wheel breaking.

For example, on my Eve rover (meanwhile a poor abandoned derelict):

Going straight ahead usually goes fine, accelerating while making small turns results in increased top speed, but the gears are more prone to breaking.

On flat ground this results in a 2-5m/s speed difference, which is noticeable.

I also noticed the same on my Mun rover:

On steeper ground, it could not climb when going straight, but when mixing that with small fast left-right steering, it could climb up also steep crater slopes.

When overdoing it, the gears broke.

Might be something similar as with winglets/infiniglide - or the classical FPS slide-run bug.

Anyway, regarding your rover:

I never had trouble with the wheels falling off. They are remarkably stable. They may bend like hell, the gears may break, but they never ever broke off their attachment. In my cases this was either directly to a big fueltank or to struts.

I guess its not the gears but probably the decouplers breaking.

[chemieglennie]

Just did some testing on Kerbin around the launchpad and it works fine. It appears the grass is "slippery" enough to allow it to turn without a problem. There must be too much grip on the launchpad which breaks the joints.

Went along at about 12m/s on flat ground at 3 times warp. It will also turn on the spot now.

Next test is on Eve. I'll use hyperedit to put me in Eve orbit to test parachutes etc, then hopefully a driving test.

[Voculus]

If you're using Hyperedit for testing, you can also simply copy the Eve parameters onto Kerbin. It makes it very easy to do, and is also easy to revert back to default.

[chemieglennie]

Thanks, I didn't know that about hyperedit. Might be useful. I haven't used it much before. Just installed to test Eve landers because I got bored of wasting time flying them there and watching them fail many, many times.

I just use it to set a 100km orbit around Eve and then zero my orbital velocity when I want to land to test parachutes etc.

Anyway did this and the lander/rover works pretty well. Had to add some more parachutes.

Also had to add some landing legs and associated girders. It doesn't like landing on it's wheels at all!

So I landed drove around a bit. Got to 5000m height. Did a successful test launch with 400m/s dv left

Now just have to build a launcher and send it "for real"....

Drogue chutes deployed

All chutes deployed

Driving up a mountain on Eve!!!