Our team has decided to build an X drive for defense and accuracy in autonomous, but would like the robot to still move quickly in driver control. What do think the best gear ratio would be, considering that we will have a bit of weight on the robot and 3.25" wheels?
I’ve heard that gearing the motors for high speed works well with 3.25" wheels. As to the external ratio itself, I’m not sure. Depends on the weight.
Some might say that this is unnecessary, if u keep our robot under 10-11 pounds, turbo gearing with 3.25 works extremely well…
High speed motors should work with 3.25" wheels which is what I have currently with my X-Drive. We have never experienced any browning out issues when pushing things under the fence but that is probably because our robot is extremely light. With a heavier robot though you may experience some browning issues but that would probably only occur when pushing things under the fence.
For some comparison: http://robosource.net/files/public/Direct%20Drive%20Ratios.pdf
I know you are talking about having 3.25 inch wheels, but we have found that high speed on 4 inch or turbo on 2.75 inch works really well.
With “a bit of weight” that you’ve mentioned, high speed should work well without burning out. If your robot is light- to mid- weight, I’d go for turbo. I assume you’re using 3.25 inch wheels because you don’t have 4 inch wheels. If you do have 4 inch wheels, I’d stop you in your tracks and almost order you to use them. 
P.S. For this year’s challenge, ** DO NOT GO WITH TORQUE DRIVE **. If you do, you are insane. Watch any Starstruck match video to see why.
Is there any benefit to using a single piston to make a shifting tank-X drive if we already have a pneumatic claw? I would think that the speed and torque benefits would be substantial.
My team has had luck with 3.25" wheels and turbo motors. Our robot weighed 14 pounds. Recently we changed to a tank drive to achieve higher programming and autonomous scores.
@VRC 929X Gearing on an X drive is going to be pretty hard, but if you can do it, i would recommend a 2:1 ratio. Depending on torque, speed, or turbo, do whatever you guys feel like is right. We’re changing our drive to a 2:1 ratio, but we have a tank drive. If you can, I would really like to hear how the X gearing works.
I have a CAD for that… Although it takes 2 pistons. Anything less is honestly unreasonable.
Why do you prefer the 4" wheels? I always suggest the smallest wheels possible because they weigh less and take up much less room. Where do you see the advantages of larger wheels?
@Rick TYler idk about them but I will never use 2.75" omnis again after last year. There is so much unnecessary friction with those wheels because of the rollers’ poor spacing.
The 3.25 omnis are actually the lightest–
2.75" Double-Roller Omni-Directional Wheels: 0.154 lbs (70 grams)
3.25" Omni-Directional Wheels: 0.132 lbs (60 grams)
4" Omni-Directional Wheels: 0.232 lbs (105 grams)
we plan on using the 3.25" wheels because they are lighter and have the smoothest rollers. Our initial plan was to gear them for turbo, but our concern was that they would stall under typical driving situations, not necessarily pushing.
Thanks, everyone!