4000 RPM Flywheel

I am having trouble with a middle school team that I am mentoring, they have a double flywheel with 2 motors on each side with gears, 25:1, finally connecting to 2 stacked 4" wheels. The motors that we are using are put into High Speed and we are mounting this at roughly 30 degrees. b
We have problems with stalling; however, each side of the flywheel, 2 motors on each side, are mounted in separate circuits. The left set of motors are in port 8 and port 9. While the right set of motors are in pins 2 and 3. This helps with distributing the current but there are still problems with the entire thing stalling.
Also when the motors stall out of the two motors only one of them gets warm

Gear Ratio:

(2) 60 tooth gears connect each of the High Speed motors

On one of the 60 tooth shafts there is another 6 y0 tooth gear attaching to a 12 tooth gear

Lastly the final 12 tooth gear is attached to a 60 tooth gear which also has a 12 tooth high strength gear.

Potential Problems:

Friction due to the amount of gears

To great of a gear ratio, maybe lowering the speed

That gearing ratio is insanely high. You are doing the right thing in distributing your motors amongst the two thermal fuses found in the cortex; however, you should definitely decrease that ratio.

Yes, you are correct, high speed motors driving 25:1 gears (1.6*25:1 = 40:1 total gear ratio) is way too high for the dual flywheel. You could drive a single 5" flywheel with 25:1 gear ratio.

Many people having success running dual 5" flywheels with 15:1 total ratio. So you, probably, need to have something like 18:1 total or ~(10…12):1 external to high speed motor.

You are, likely, stalling because there is too much friction amplified by your gear ratio and because part of the torque needs to go into accelerating your flywheels.

Also, make sure that all of your motors are geared the same and well lubricated. Without load each motor should run at 104-110% of the nominal speed.

After you reduce the gear ratio and friction, you may need to implement some sort of speed control to increase power gradually, both to reduce PTC current to prevent them tripping and stalling and to protect motor gears from the shock.

If at all possible i would suggest staying away from lubricant. I do believe it is possible to build efficient double flywheels without the use of lubricant and it will make your life so much easier at competition. I have seen some teams use turbo motors and a 1:7 ratio, not sure if it will work for you but I suppose it is worth a shot.

It might be possible to build a good launcher without lubricant and, depending on lubricant, it could avoid a lot of mess.

However, I was referring to lubricating internal motor gears. It could make difference of the same motor having idle speed of 95 RPMs unlubricated and 110 RPMs lubricated. This would mean that there is a non-negligible portion of the motor’s output power is lost to friction and, most likely, destroying internal motor gears in the process.

Externally to the motor, I would agree that lubricating any axle rotating slower than 1000 RPM is, probably, not worth the mess. Anything over 2000 RPM I would definitely lubricate. And in between those numbers you need to experiment and see if it makes the difference. We use white lithium grease on the two fastest axles in our flywheel and it seems to help a lot.

I see what you mean and that makes a lot of sense, we have had motor gears rip themselves apart before.

we use a 21:1 gear ratio, with the exact same set up with motors and wheels and everything as you do. it works well for us, but we have spent hours hunting down sources of friction. this is what I suggest you do.
look any where shaft collars touch metal or bearing flats. specifically somewhere you might have made the shaft collars too tight.
also look where ever shafts pass through metal or bearing flats

A couple other places to check for friction…how far apart are the flywheels? also consider replacing the HS 12 tooth gears with LS 12 tooth gears.

This is what we have, works excellent.

Like i have said many times, a 15:1 with high speed motors and 4" wheels works great with dual flywheels, the 7:1 with turbo motors and 5" wheels also works great.


Have you tried 4" wheels with the 7:1 turbo gear ratio? How much compression have you used?


7:1 with 4" wheels? How much compression? Angle?

I use 25:1 with a dual flywheel but I use normal unmodified motors. I do use 6 of them, but it doesn’t ever stall with 4 unless I do something stupid and put my hand in the flywheel. This is theoretical 2500 RPM. however this is enough to launch the ball significantly more than the length of a field. (Our angle is roughly the same as yours). You guys are overkilling it. I would change to normal motors.

has anyone tried 15:1 with turbo?

That’s higher than you need, since my team uses 35:3 (~11.67:1) with turbo motors. Maybe try speed motors? That is a little bit lower than my team’s (24:1 vs. 28:1), but we usually need about 50-60 power, depending on battery level (even with our bad, half capacity batteries that we need to fix).

This is basically a complex gear ratio of 84:60 and 84:12 along with the turbo motors?

What is the angle and the amount of compression that you have?

The 35:3 is strictly external. It is 60:12 to 84:36. The turbo motors are factored in later (it ends up being about 28:1). We use a 45° angle, since Vex makes 45° mounting brackets, and using them means the hood can’t slowly tilt backward over the course of a tournament (or several). We have basically no compression, and our hood is polycarbonate wrapped in friction padding. This lets hard balls push the backplate ever so slightly backward, so that they are compressed less than soft balls and the flywheel needs to “spend” less momentum. The already minuscule amount of compression means that the balls have almost identical trajectories, and our flywheel is very consistent. Now if we can just get our fire rate to about double what it is now (.75 - 1 ball per second), we might stand a chance at State.


sounds very nice, thanks for the details

Would you be able to send a couple of pictures thanks so much

Apparently, all of the pictures I have of our flywheel are corrupted, or something else is preventing them from being uploaded. I can upload other pictures just fine, so I will retake them on Tuesday, when we regain access to the robot.

Edit: If anybody thinks it’s a problem with the way iPads and this forum interact (I don’t think it is), I’m getting an error saying “Error uploading image.jpg: ‘undefined’”

I get this will some pictures also even though I know for a fact they are not corrupted