Steering design needed for unusual 4WD 4 wheel steering chassis

[Ralphius]

So the reason this chassis will be unusual is because instead of the wheels turning in parallel (ie linked by a track rod or rack\pinion), they will turn with diagonal opposed pairs together, ie. the front pair will both turn 45 degrees inwards towards each other, and the rear pair will turn 45 degrees inwards towards each other. This will allow zero radius turns on a 4WD chassis without the associated high torque requirements and required slip that is required of zero radius turns (contra-rotating) on a twin-tracked chassis.

A pair of photos may help illustrate this concept better:

  

Note this is NOT the model, it's simply to illustrate which way the wheels will turn. I'll probably re-use these wheels though.

Actual model will be approx 25 studs square, all 4 wheels will drive, with the left two on one PF-M motor and the right two on another PF-M motor. Steering is probably going to be a PF servo motor although I might go with the mini linear actuator and motor instead. Suspension will not be required as there's probably enough flex in a studless chassis to accommodate a single wheel going over a 15mm obstacle. Also, yes I'm aware that with this design the vehicle can either drive in a straight line, or turn on the spot, but not at the same time, and not turn in a curve like standard steering.

So my questions is, how on earth do I get the steering working while still having drive going through a UJ at each corner? I've had a quick look through the (massive) axle megathread but it all seems based on wheels turning in parallel or using special parts that I don't have. Ideas for mechanisms or info on similar models to mine greatly received!

Regards,
Ralph

 

 

 

[Carsten Svendsen]

Something like this?

[pagicence]

Take a look at NKubate's Jeep Hurricane. It has everything you need and more. It might give you some ideas. Official website LINK, YouTube

Edited April 26, 2019 by pagicence

[Ralphius]

That jeep model is seriously impressive! I doubt I'll get anything that looks nearly as good as that! I do note that the builder states "can not drive or steer smoothly, so rather than a playable model, this turned out to be more of a proof of concept". I'm hoping that by using multiple motors I'll be able to reduce the mechanical complexity compared to that one and end up with something that not only drives but has a fair bit of torque behind it as well.

2 hours ago, Carsten Svendsen said:

Something like this?

Thanks for that, I'd never thought of using an idler instead of a universal joint like that! Not sure how it could be steered, maybe attach an L shaped beam to the green bracket perhaps? How would those size gears stand up under the weight of a heavy model? Bit worried they would skip or break? (My previous model suffered from repeatedly shattering the gears inside the diff when it came to an incline)

[AndyCW]

The breaking gears in the differential and shattered universal joints can be partially alleviated by using portal hubs. 

Many of the official sets have used this approach

[Saberwing40k]

You know, for a model that is square, you might not need to have steering like this at all, but that's a different argument entirely. So is making steering hubs. you could use a set of mine linear actuators hooked up to each wheel to steer them that way.

Here's a vid of a model that does that: