Gear ratio recommendations with bag motor

My team and I need some assistance / recommendations on what gear ratio we should use on our ball accumulator / magazine to advance the power cells from our intake up to the shooter. Our team is a low budget team so we can not afford to purchase a bunch of pulleys and belts to test what would work. Maybe we are thinking wrong and we need to purchase versaplanatary gearboxes instead just to advance the power cells.

We will be using bag motors and sensors to have the power cells advance through “zones”. Plan is to use one bag motor per zone. Each zone had urethane belting turning on a shaft to advance the power cells from one zone towards another.

I’m going to suggest you take a look at my design spreadsheet to help you make that decision. With the mechanism ratio calculator you can input the motor you’re using (BAG), the pulley radius, the load on the pulley (a bit more than the weight of the ball is a decent guess), and the speed you want the belt to travel at, and the calculator will tell you what gear ratio to choose as well as a number of other useful statistics about your mechanism.


First, you should determine what surface speed should be for each surface that comes into contact with the game piece. Then use the design spreadsheet that @AriMB created.


Our team is also going to do a similar thing, and we also are using bag motors, but more for bringing our intake up and down. We personally used 1:1 from roller to gearbox, and then using a 9015 motor, used 100:1 reduction. It’s small and light, and does the job. Using 100:1 on a bag motor should be fine too, but you can calculate your gear ratio quite easily. Just divide your free speed by your target rpm, and try to get to the nearest radio by stacking ratios. Ex. We have a motor that spins 14k free speed. We want it to go 200 rpm at 50 percent. So that 7k. 7000/200 is 35. We then use a 5:1 versa gearbox and a 7:1 gearbox. For intake and conveyor stuff for the balls, 200 is pretty ideal too.

Thanks for the insight and design spreadsheet.

Please note that the diameter of the rollers that @Burritoman is using may be different from the diameter of the rollers that @WStech has available so some adjustments to the reduction ratios may be necessary.