Rovers: wheels per ton or any other rule of a thumb?

[juanml82]

I've dispatched rovers to Moho and Duna in my latest science career game and I'm finding out the Moho rover can't climb 15° slopes.

I guess the solution would have been moar wheels (it simply has four), but I wonder if there is a rule of a thumb or a way to calculate how many wheels a rover would need to climb specific slope angles in specific bodies. Kind of how TWR for different bodies can be calculated or how spaceplanes should have one rapier per 15 tons (I'm not sure if that's still the proper ratio for that, though), so I can plan ahead while building rovers for specific places

[FancyMouse]

The data isn't exposed in UI, I'm afraid, but if you go to wheels' .cfg files, you can get the info and calculate from there. The data you need includes:

ModuleWheelBase->radius - this is your wheel radius, let's call it r

ModuleWheelMotor->torqueCurve, first key, second value - this is your stationary wheel torque, let's call it T

T/r gives the force applied at the contact point of your wheel and ground.

On a hill, gravity has a component m*g*sin(theta) down the hill, where theta is the slope. You need your nT/r > m*g*sin(theta) in order to climb from stationary (obviously, n is the number of wheels running full motor, and g is local gravity).

 

Note however, torque isn't maximized at stationary. So you could climb with some initial speed while couldn't climb from standing still. I'm using stationary torque above just so that the rover doesn't need to find a flat place to do initial acceleration to climb. Feel free to use other values if those apply to your design.

[Sharpy]

- increase friction. Often the rover has a plenty torque, but slips faster than it climbs.

- pull Drive Limiter up. Be careful, because that really does increase torque - and can increase it so much your rover will flip due to wheelies.

 

The only point to add more wheels is if your rover jumps or wheels break too easily under the mass. They are mostly pointless when considering acceleration - Genuine lack of torque is almost never the case. Lack of traction (friction), limit on torque etc usually are the root of the problem.

Edited November 29, 2016 by Sharpy

[juanml82]

2 hours ago, Sharpy said:

- increase friction. Often the rover has a plenty torque, but slips faster than it climbs.

- pull Drive Limiter up. Be careful, because that really does increase torque - and can increase it so much your rover will flip due to wheelies.

 

The only point to add more wheels is if your rover jumps or wheels break too easily under the mass. They are mostly pointless when considering acceleration - Genuine lack of torque is almost never the case. Lack of traction (friction), limit on torque etc usually are the root of the problem.

Will try this and check @FancyMouse math later