Steering

Hi,

I'm looking for some guidance on steering. I have a 6 wheel vehicle with 4 steering motors. I'm using an Arduino Mega.

Where do I go to look for the calculations to do the corner steering? I have an analog joystick and I can calculate the magnitude of the vector and the angle from zero. (I've got diff drive working)

I need to calculate the angular rate for each wheel I think and the angle for each steering motor. How do I go from magnitude vector and angle from zero(not turning radius) to wheel speeds and angles?

Like this nifty little rover:

Show us a picture of the vehicle and describe the steering in more detail.

Wheel slippage in differential drive robots is a severely complicating factor for steering calculations, and a lot depends on what steps you have taken to minimize that.

It's a little 3D print rover kit-very much like the one in the link I posted, just not as fancy.

I'm just looking for some general guidance, pointing in the right direction as I don't know what questions to ask to even get numbers for some of this stuff.

What values do I need to accomplish 4 wheel steering? Do I need angular rates and steering angle for each steered wheel?

Is there a specific method to go from vehicle angle and turn radius to angular rates and steering angle? Is there a good way to go from analog joystick values to vehicle speed and turning radius? I can calculate the magnitude of the joystick vector and the angle from the zero line.

You mention slip. Since its a kit, I doubt I'll have too much info on that, other than vehicle dimensions. If we assume no slip, for ease of calculations, what equations do I use? If I want to incorporate slip, where can I find those equations?

I'm hoping to figure out a lot of this-just really need a place to start.

Google will provide lots of basic material on differential steering.

This paper is good for understanding differential steering with a two-wheel drive, where wheel slippage is not such a serious problem, but the server seems to be off line.

One example for 4 wheel drives: http://www.rakeshmondal.info/4-Wheel-Drive-Robot-Design

I think nowadays many people don't even try to calculate body orientation from wheel motion. It is easier and perhaps even more accurate to use a 9 degree-of-freedom IMU like the BNO055 to measure it. Adafruit 9-DOF Absolute Orientation IMU Fusion Breakout - BNO055 : ID 2472 : $34.95 : Adafruit Industries, Unique & fun DIY electronics and kits

I don't think I want differential steering. I thought differential steering was steering by varying wheel speed(tank drive), not by using steering motors. I can do this already. I want to be able to use 4 independent steering motors with 6 drive motors. What is this called?

I've tried to google for steering with steering motors but I have no found anything for calculations that is not differential drive. How do I calculate the angle for the steering motors?

You want to put Four Wheel Steering on a 6 wheel rover.

This is not hard at all. All you need to do is mirror your front wheels.

Not hard if you have Ackermann steering, but we don't know what the OP has.

He has four motors each of which is mounted in its own steerable block. Each block controlled bu its own motor.

Mark

Good to know! Just a little trigonometry.

If the distance from the front to the centre wheels is the same as from the centre wheels to the rear wheels then I reckon the same angle is appropriate for front and rear steering.

For more sophistication one might try to rotate the wheels on the outside of the turn a little less because they follow a wider radius than the inner wheels. Personally I wouldn't bother unless there was some problem.

The way rubber tyres interact with the ground during steering is quite complex and there will be some natural side-to-side compensation.

...R