Belt or gear for swerve?

#1

What are the advantages and disadvantages of using a 2910 style belt for steering or a 1323 style gear?

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#2

From what I know, a gear is going to have more backlash than a belt/ chain. You can tension a belt or chain to reduce slop, where gears will always have a little bit of backlash. Chain and belts have the advantage of having more teeth engaged at a time, giving it more strength do.

But gears do have the advantage have just having less parts and less weight. And really, the backlash is minimal if the C-C is correct.

Pulleys have the advantage of being able to machine easier. It’s very hard to make a gear like what Vex sells on a mill, but 2910 does all their parts on a mill.

I’m not an expert, but just from what I know, these could be some factors.

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#3

We used a belt for turning the module for the first time this year. On our practice robot, we had some trouble with the belt slipping around the small pulley. This was primarily due to:

  1. Mounting screws backing out coupled with a plastic module created enough flex when changing directions to allow the belt to slip.
  2. A weak rotation motor causing really high amounts of wheel scrub/drag on the other module on that end.

We will probably do it again. We learned a lot from this season. We didn’t see those issues out of the competition robot. It was better cared for and didn’t get the abuse the practice bot did.

#4

In the design belts can be more flexible than gears. You can increase the c-c distance of a belted system without changing the ratio.

#5

We like belts - used for steering starting in 2017 (gears before in 2014, 2015) to help reduce backlash - this year we did have some issues with belt slippage that we did not see in previous two years - and we are still sorting out root cause. But we still believe it is very helpful to reduce steering backlash - though would like to know how 1323 managed such awesome tracking this year…

We also changed to belts from gears on our drive side (from bevels to wheels) this year and loved the quietness and smoothness - no slippage issues there and also liked moving to the higher DP bevels from AM vs the Vexpro ones. (we use miter gears up to now vs the 3:1 or 2:1 side bevels).

#6

Typically teams that are using a big central gear for steering are using a vex gear and machining the features they need into it. The large pulley in 2910/SDS modules is machined from a piece of 4" aluminum round bar. The material cost for the big pulley should be about 1/4 as much as the cost of a big vex gear. If you are looking to 3D print the part, a toothed pulley will be less sketchy because the belt is engaging on many teeth where as a gear concentrates the stress on one or two teeth at a time.

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