Flywheel Becoming Slower

My team’s flywheel struggles to get the ball over the high bar and into the goal. Yesterday, when we finished making the flywheel, it was easily able to clear the bar. However, 20 minutes into testing on the day we finished building it, one of the motors got very hot and the flywheel slowed down. We replaced the motor, and it started doing fine again. Today, we adjusted the angle of our flywheel to try to replicate the strategy used in this video where the flywheel is at an almost vertical angle and the bot runs into the wall:

When we tried it, the flywheel gradually got slower the longer we tested. We put in fully charged batteries, and it didn’t change anything. We put the flywheel back at its original angle and it was sitll not shooting far. After waiting an hour and coming back, the results were the same. Do we need to change the motors constantly for the flywheel to work, or is there another solution? We might need to get new batteries, we’ve had the same few for a while. We have the same 1:15 gear ratio for the flywheel as @FRC973. Did you guys also have to change out motors frequently?
Thank you

From my experience with Turning Point in vrc, you’re probably overloading your motors. The motors only have so much torque and friction or the load might be too much for the motor to handle. The longer you overload the motors, the slower it gets. This would explain why your motors are slowing down. Long usage of a motor might result in the motor breaking. You can try to fix this by reducing friction in some way or reducing the gear ratio and adjusting the angle.

P.S. Is it one motor that slowing down and getting hot or both of them?

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You might want to let the motors cool down completely before using them again. Last year, I had the same problem with the motors not having enough strength to lift up the risers after long practices, and I just let them cool down before using them again.

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let the motors cool for a bit between uses
i think

Generally, the motors won’t damage themselves. Just don’t use them for a while. I do have a number of groups that are using the same gearing and not having those issues. What speed are you running them at? I have one group with a very efficient setup and they only need to run their motors at about 60%.

You really need to make sure that the flywheel gears are running as smoothly as possible. Make sure that only washers are next to the beams, etc… Also the teams use a flywheel weight and the seem to like them. It takes a little bit longer for them to spin up but they seem to have better results.

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No, I never changed out the motors. I did have to take breaks from practicing after about 30-45 minutes because the motors would get hot though. In my experience, the flywheel will slow down because of wither a low battery, hot motors, or both. While testing, one thing that can help is not spinning the motors up an excessive number of times. Another thing that is essential is to put your motors on coast, because it is bad for them when you try to bring them to a full stop from spinning at full speed.

Like @sankeydd I do not run my motors at 100% power. I run them at around 70 rpm, which is about 80% power. This allows me to run longer on warm motors and a low battery without causing a problem. It allows makes the motors spin at exactly the same speed, every single time (sometimes a more used motor will be less powerful than a new one, and that could skew your shot if you don’t regulate the motor speed).

I second this. We changed the shot to be more vertical in the last video for a few reasons, and one of the big reasons was to redo the gearbox and make there be much less friction. Another reason was to make a more accurate shot because with a more vertical shot, the more room for error there is (and flywheels have a lot of inconsistency, especially when you are trying to get 15+ balls in a match).

I have never used a flywheel weight because I don’t have one, and they’re kind of expensive, but I could see how they would improve your shot, and if you time it right, the fact that it takes an extra few seconds to spin up isn’t a problem.

I hope this helps and let me know if you have any more questions. Good luck!

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What are some things you guys did to reduce friction? We haven’t done anything except put the very thing washers between each gear and the beams.

The other main thing that we did besides putting washers in was to make the gearbox super rigid. This allows for very little play, and consequently very little friction. One key way we did this was by supporting the gears on both sides everywhere, so it was literally a box. We did this to the point where you had to take it apart to see the details of how it worked because there were so many pieces. One last thing that is kind of a given is to not use plastic shafts.

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This is one factor that is important, but be careful of build quality! You can build something super rigid, and yet still cause the structure not to line up properly for your shafts to spin freely. You can easily test this by decoupling the shaft from the motor and spinning the mechanism by hand, it should spin freely for a relatively long time. A definite sign of friction foe, is you spin it, and it stops quickly.

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In addition to the above suggestions - make sure your shaft is not bent, there is not too much compression between the structure encasing your mechanism making your washers behave like brake pads on car. Look at every interaction between each component and see if it is mechanically interacting with your fly wheel.

A well built flywheel is an impressive creation.

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Adding on to this, you need to make sure that your two sides supporting the axle are perfectly even with each other. If your supports aren’t directly across from each other, your axle will be slightly diagonal and you will gain a lot of friction. From my experience this is the single biggest cause of friction, especially on drives.

So i’d make sure there is plenty of structure (probably standoffs) between your two sides.

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Now that we have capped metal shafts, there is pretty much no reason to go with plastic.

Yeah that is true. I have borken my fair share of plastic shafts because I needed capped shafts and I put too much load on them. I just said that because not everyone (including myself) has capped metal shafts.

On the topic of shafts, I was wondering if anyone knew when the long metal shaft add-on pack would be available again? They’ve been out of stock for months, and I can’t even find the product on VEX’s product page anymore; I can only find it on RobotMesh. I understand that the 12" ones are still available, and you can cut those to length, but I was wondering about the pre-cut ones (that you get a much better deal on). Thanks!

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I made a hood flywheel and the flywheel only slows down when the battery is low.

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