Is there a benefit to utilizing 4 independent CIM motor/drive wheels as opposed to syncing them with a belt/chain system? This is our first-year designing a custom chassis. Thank you
Unless you’re doing mecanum, linking them with a belt or chain is advantageous. When you accelerate, more weight is on the wheels you’re accelerating away from. This increases the traction (friction) you can get from that wheel, and decreases it at the other end. Linking the two with a belt or chain helps keep the light end from spinning on the carpet and delivers extra torque to the heavy end.
Last year we ran an H drive without belting or chaining the wheels together, it didn’t really hurt us, as long as you are careful with control of the wheels you should be fine, that being said others have found benefit to it, so it really depends on what you’re going for.
A secondary question, have you felt how the Omni wheels behave on the platform or done the geometry to ensure you don’t have dead zones up and down the ramp?
There’s also the nice advantage of having to only make two gearboxes instead of four.
Are all of your wheels omni wheels or just one set? If just one set, consider that your robot will no longer turn about its center. On the other hand, if you use all omni wheels, you might do a bit of slipping and sliding.
4 independent drive wheels means you need 4 gearboxes. Extra cost and weight.
belt/chain gives you more total traction because when any wheel starts to slip, the excess torque automatically goes to the chained/belted wheel with the higher traction (compare Scenario3 to Scenario5 here).
For Omni we went H-drive twice with pretty good success (RR/SW).
Four corner 6" … interior double 6" on a suspension which really helps but takes up some center space. Belts driving pairs on outer.
Works well very nimble in space… holds its ground too pretty well. that reqires 6 Cims two in center. The drivers like it.
We are putting omni wheels in the front and traction in the back similar to this chassis from vex except not a wcd. We basically were just wondering why they used a belt across, and specifically, if it hinders the capabilities and benefits of the omni-wheels https://content.vexrobotics.com/vexpro/pdf/217-8000-2+2.pdf
The belt doesn’t hinder the omnis. But, if you’re going to have a belt or a chain, then you have to think about where it’s going to go. And, there you have three choices: (i) inside the frame, (ii) inside the rail, (iii) outside the frame.
If you’re doing either (i) or (iii), then make sure that whatever shaft is driving your wheels (typically the output shaft of the gearbox) is long enough to accommodate the extra hardware. [And if you’re doing (ii), good luck. You’ll need it.]
Also, buy some of those Acetal spacers from Vex. Your traction and omni wheels are likely going to be different widths, so you’ll want something to make sure that things are all in the same plane.
If the wheels are different widths, you’ll need to accommodate this with spacers or different shaft lengths. However, having the wheels a half inch or so out of plane with each other shouldn’t make any noticeable difference, especially if the out-of-plane wheels are omnis. Any minor differences from some theoretical driving performance will become perfectly natural to your driver as fast as its specifics of acceleration and turning radius.