Re: Crab drive steering
 

EDIT: This is just a guess, but from what he said I think he means the type in figure 1. (Not A)

Re: Crab drive steering
 

What's "Type A" ??

Re: Crab drive steering
 

In our situation, because two wheels are linked, Ackerman angles cannot be achieved....so we're most like Figure 1. Because left and right drive are independent we do slow down the inside wheels with respect to turning angle.

A real monster truck is probably most like Figure 2.

Re: Crab drive steering
 

It might be useful to facilitate possible future discussion in other threads if you could assign a unique name to your steering method.

Did you determine the relationship between the steering angle and the skid-steer compensation empirically or by analysis?

Re: Crab drive steering
 

Our algorithm was purely empirical. We set up a linear relationship between angle and "detuning" of the inside wheels.

More important to me isn't that we have Quadrasteer (formerly Monster Truck)...it's that you can access tank, crab and Quadrasteer from the same steering setup. Our control scheme uses two sticks on a PS style gamepad.

Tank:
Left stick up/down is driver side throttle
Right stick up/down is pass side throttle

Quadrasteer:
Left stick up/down is all wheels throttle
Right stick left/right is steering

Crab/swerve:
Left stick up/down is all wheels throttle
Right stick left/right is all wheels steer angle

Each of these modes is access by holding a top or trigger button....I prefer to have it setup as momentary.

Re: Crab drive steering
 

I'd be curious to know how your empirically determined speed reduction compares to a rough analysis I just did. See attachments.

I assumed that the center of rotation of the vehicle will be halfway between the points A and B.

Multiply the "outer" wheel speed by the fraction at the end of the analysis to give the "inner" wheel speed. L is the vehicle wheelbase, W is the trackwidth, and Ø is the steering angle, clockwise from straight ahead.