pic: Octocanum Module

[Ari423]

Originally Posted by GeeTwo

You shouldn't need 2" - Bimba does have 1.5" cylinders in both square and round pancake styles. Remember that force goes up as the square of the diameter, so 1.5" provides twice the force of a 1.0625" cylinder (to within 1%).

I knew I didn't need a 2" cylinder, but it was the smallest I was able to find that would work when I posted. But speak and it shall be so. I went back and checked, and this time I found the 1.5" pancake cylinder. I will probably end up using that one.

Originally Posted by GeeTwo

You could pivot on the mecanum, which would make the cantilevered wheel the traction wheel which has a 42 tooth sprocket, if I did my math correctly. This would be easy to mount sprocket to wheel on a dead axle. This solution would also require a change in gear ratio of your gearbox - in the direction that it will probably get simpler and lighter. This would also make high-speed mecanum your "default" drive if the pressure goes out, which may be a good or bad thing depending on your game strategy/style.

One of the big perks of octocanum for me is built-in mecanum suspension. I wanted to pivot on the traction wheel so we wouldn't have to worry about uneven loading. I agree that switching them would make it easy to do a dead axle, but that would take away a major advantage in my opinion. Would it be advantageous to add more bolts, a piece of churro, or some other cross brace between the wheels to better connect the plates instead of going to dead axle?

[GeeTwo]

Originally Posted by Ari423

One of the big perks of octocanum for me is built-in mecanum suspension. I wanted to pivot on the traction wheel so we wouldn't have to worry about uneven loading.

I don't see how the air suspension would compensate for uneven loading. Air (especially if allowed to flow among the cylinders, or vent when over-pressured) does not behave like springs do in this case. If you have uneven loading such that the weight on any one wheel is greater than what the air can carry, that one will drop until the traction wheels touch the carpet and compensate. At lesser inequality I believe it will lift the lightest corner relative to the others, but if you have a low CoG it will take a lot of lift to effectively move the robot's CoG to the geometric center and equalize the weight carried by each wheel.

[Ari423]

Originally Posted by GeeTwo

I don't see how the air suspension would compensate for uneven loading. Air (especially if allowed to flow among the cylinders, or vent when over-pressured) does not behave like springs do in this case. If you have uneven loading such that the weight on any one wheel is greater than what the air can carry, that one will drop until the traction wheels touch the carpet and compensate. At lesser inequality I believe it will lift the lightest corner relative to the others, but if you have a low CoG it will take a lot of lift to effectively move the robot's CoG to the geometric center and equalize the weight carried by each wheel.

I was under the impression that if the mecanums were pneumatically actuated, you could tune the pressure so that the cylinders would have some give. Then the heavier wheels would compress the springs, and all four wheels would still have the same ground contact. Am I wrong?

[GeeTwo]

Originally Posted by Ari423

I was under the impression that if the mecanums were pneumatically actuated, you could tune the pressure so that the cylinders would have some give. Then the heavier wheels would compress the springs, and all four wheels would still have the same ground contact. Am I wrong?

Based on my dry-erase figuring (not experience), the air suspension will help keep all four wheels on the floor/carpet as you go over minor bumps and dips. It will not do much to equalize the weight carried by each wheel due to differences between center of gravity and center of geometry.

[Hugh Meyer]

Originally Posted by Ari423

I was under the impression that if the mecanums were pneumatically actuated, you could tune the pressure so that the cylinders would have some give. Then the heavier wheels would compress the springs, and all four wheels would still have the same ground contact. Am I wrong?

Yes, you are correct. If you supply air to all four wheels and adjust the pressure so the cylinders are not bottomed out all four wheels will maintain equal pressure and contact with the ground as the system travels over uneven surfaces. This is indeed a great feature of your design. This helps steering because if one wheel floats, as a ridged system would, the robot will not steer correctly.

You may need to pivot the cylinder to compensate for the radius as the assembly articulates. Otherwise it will likely jam.

Keep up the great work!

-Hugh