Middle school needs help still.

Middle school team still having issues getting fly wheel design to shoot ball full court. Here are pics of their design. Any suggestions? they have taken off the top wheel. Aligned the bottom one to be in middle of ball. Added rubber bands for grip and to decrease the space between them to get more friction on ball. Motors are high speed set to max (127).



You are missing the pics.

Sorry forgot to attach.

Four motors in the gear box have different gearing… From casual inspection, the motors work against each other… What gear ration do you want in the gear box?

Not quite sure what you mean. The motors are turning the the gears the same way. One motor is set to reverse. If they were working against each other then they would never spin the wheels. The wheels spin but are only shooting about 4 feet. If I understand. I think they are aiming for 7:1 gear ratio. I am not that good with figuring gear ratio with compound gears. The drive gear is a 7:1 (84:12) which then turns the top gear which is a (64:12) or I believe 5.33:1. So I am not sure if this is the correct ratio.


It seems the ball compression may be an issue. Do the wheels touch the ball enough? Too much? Having 4 wheels may not be good, either. I haven’t tried that but it seems that there may be more unnecessary resistance.

At first there was not enough and the wheels were just nudging the ball through. We found that the spacing between the high and low wheel was not right. The Kids decided to go to the 2 wheel design to simplify things. They added the rubber bands to lessen the space between them to compress the balls. I will have them take some bands off and see if that works. Does the gearing look ok to produce enough speed?

It looks like you are trying to drive both the 84 tooth gear and the 12 tooth pinion in the bottom part. This results in the motors not providing power as expected because of how much faster the pinion is spinning in comparison to the 84 tooth gear. To fix this, you would need to add another 84 tooth gear attached to the other already driven 84 tooth gear and power that gear, replacing the motor on the pinion.

The gear ratio is a 49:1 (84:12 * 84:12 = 7:1 * 7:1 = 49:1), which is way higher than necessary for a double flywheel. My middle school team uses a 15:1 (60:12 * 36:12 = 15:1) gear ratio and can shoot way further than necessary.

Ok so if they cut down the gear ratio. Do they only run this with 2 motors then. Motors on the 60:12 which will then turn the 36:12?


Sorry. When the kids changed out the to dual fly wheel they did lower it to a 60:12 on the upper gear. Still is 35:1 if my calculation is correct. Could it be that the wheels are compressing too much on the ball. or still not enough?


@mwang17: Okay after reading your post many times, do they need to add another gear of the same size to the upper 84 tooth gear and drive that one with the motor instead. So one motor driving the small pinion which is driving the upper 84. Another motor driving another 84 on the upper 84?


Maybe you should also look into closing the space between the each wheel, as in, chuck the spacers between each 4" wheel. It’ll help with compression and giving you a better shot.

You want the driving motors to have the same gearing … This will supplement the power to drive the flywheels… So all drive motors will be 84 tooth if that is what you want driving your gearbox … The size of your gears on the driving motor and number of motors will determine the amount of time your flywheel will need to get back up to speed, which ultimately determine how many shots you will be able to make.

This. I didn’t look closely at the gearing the first time aroubd, but your one motor has a 7:1 ratio to the axle that the other motor it drives. It is basically doing nothing.

What he’s saying is that you have one motor running the 84-tooth gear and another motor running the 12-tooth gear.This doesn’t work because one motor is trying to run significantly faster than the other motor (exactly 7x). Assuming the bottom set of gears is still connected and the motors all have the same internal gearing; what’s happening is that the motor on the 84-tooth gear is attempting to move the motor on the 12-tooth gear faster than it can physically move.

For example, if you have all those motors on hi-speed and at max power, your motor on the 84-tooth gear is running at 160 rpm, and is trying to move the 12-tooth gear, but the motor on it cannot safely exceed 160 rpm with its internal gearing.

Middle school is difficult when it comes to understanding gears. They seeing subsystems that seem to work, but have trouble figuring out why they work. VEX has links to gearing under their curriculum partner links, AutoDesk and RobotMatter. Plenty of other material if you google. What seems to be hindering this implementation is the notion that driving motors should b link with the same gears, otherwise one motor will try to outrun the other due to the different gear ratio. This of course depends how the motors are geared internally.

There are a few things that I think might help. I couldn’t tell from your picture if you had 4 or 2 motors, but if you only have 2 i would suggest 4. In addition, I would suggest a ratio of at least 25:1 in your gearing. For your build I would suggest a 5:1 gear ratio connected to a 3:1. This, in addition to your high speed motors, should give you a ratio of 30:1. If it won’t fire properly, you might need to go to low speed motors with higher gearing. If you’re going to the competition on the 6th or the 13th I can explain things better, if that didn’t make sense.

Your motors are trying to turn at different speeds. When a motor is driving a big gear, another is driving a small gear, and the two gears are meshed, the two motors are fighting each other, resulting in really low efficiency. Instead, move the motor on the 12 tooth gear to the same axle (motor to motor axle) as the other one on the larger (60/84 tooth, whichever it is) gear.

Hi guys this is heavy metals dad. Check Steve’s phone for a message, I left my number. If you could call me, we can walk you through the issue over the phone rather than on here where it could be confusing.
Thanks, William.

I learned understand gear ratios my first day. I think it depends on who taught you and how you look at it.