Flywheel RPM High but Disk not Shooting Far

Hello Vex Forum. I’m trying to create a flywheel to launch the disk. Right now, our rpm levels are excellent. It can sustain around 400+ for around 1 minute and a half. Our team also used two wheels to increase the moment of inertia of the wheels as well as a linear puncher to increase our initial velocity, but despite all this, our team could barely shoot from the autonomous line. I’m thinking that it could possibly be due to the lack of compression. Any thoughts?

400 rpm is WAYY too low. You need at least 3000 rpm to launch the disc.

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400 rpm is pretty low for a flywheel. The lowest I have seen is 3000.

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Can you send us a picture of your flywheel? 400+ is not a very fast speed (assuming you’re in rpm) and most teams use 3000, 3600 or 4200.

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Sorry, I am stupid. That was the motor rpm. We used a gear ratio of 7:1 so the final rpm should be 3000 rpm+. Its max should be around 3220 RPM.

If that’s the case I’d say you should try making the space the disc goes through smaller. Also, can you send a picture of your current one so we can help better?

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If you have high RPM and the disk still isn’t going far, your issue is likely compression. What type of wheels are you using, and how much distance is between your wheel and the hood. To have effective energy transfer on a flywheel, you need it to be tighter then you’d think. Also if you’re using a 600rpm cartridge and are at 400 rpm it’s likely that you have a lot of friction in your system, and that could be part of your issue.

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Assuming you’re using a blue motor, which should yields 600 RPM, but 400 RPM means that it’s working only at around 66% of what it should’ve. This may be indicates excessive friction. Do you have a picture of your flywheel?

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Do you mean friction between the gears? How can we solve this problem? I’ll try to send a photo, but I’m not near my robot right now sry.

No, there might be vibration issues, misalignment, or just rubbing against axles or something.

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It could be in the gears, but likely it’s something like a misaligned bearing. Try taking the motor off and spinning the axle, you should be able to freespin it with little to no effort. From there you can change things until you find the culprit. Once you tackle the friction issue you have to work on making sure the distance between the disk and the wall isn’t too large, as that is likely the largest contributor to your range issue.

You’ve told the motor to turn @ 400 rpm, but are guessing that it’s happening. Query the motor and display the rpm to the brain as well as watts & temp.

We actually told it to run at 600 rpm, but it can only spin up to around 450 rpm. Given the extra weight we added was around 350ish grams, that’s probably why. The weight is pretty darn heavy.

Compression could definitely be a contributing factor… we have found a good way to test for the best spacing is to put different amounts of metal plate on the flat side opposing the flywheel and seeing what number is best, then put poly on it at roughly the same distance as the metal plates were at.

This process is also a good addition to your notebook… high graph potential.

does it spin to 600 rpm without the weight?

If I am reading your posts correctly, this is a big red flag… if you are trying for 600 and only getting 450.

You are likely looking at a combination of frictional losses and balance issues.

This is probably separate from the launch shortcomings but must be addressed as it will overheat the motor in short order.

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So for launch shortcomings, we should probably readjust compression, but the bigger problem is with the motor rpm? I was just thinking because of how heavy the weight was, it was rotating more slowly. Ill try to show a picture, by tomorrow. Sorry for the lack of info.

The mass of the flywheel affects acceleration, how long it takes to speed up/slow down when a given force (motor or disc) is applied to it.

The final rpm is limited by mainly by friction (shafts, bearings, gears, etc) and wind resistance.

For comparison, a WELL build flywheel will hold 600 rpm (motor) and 3,000 rpm (flywheel) while using around 1.5-2.5 watts of power, regardless of mass. Check your watts… post your findings.

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Do you mean friction between the gears? How can we solve this problem?

A certain amount of friction is unavoidable. To keep it at a minimum I would:

  1. use gears that are in good condition… no bad teeth or gouges
  2. check shafts for straightness. this means CHECK them with a straightedge. note: new shafts can, and often are, bent.
  3. sand shafts lightly to remove surface corrosion
  4. check bearings, make sure they are not ‘notchy’
  5. do not overtighten bearings
  6. keep shafts short and well supported, long shafts will flex which will amplify vibrations
  7. if you use bearings, i would clean the grease from them using electronic spray cleaner (or some safe solvent). the grease slows them down. grease makes them last longer… but you won’t wear them out… they are designed for tens of thousands of hours of operation.
  8. technically you could polish the gear teeth using polishing compound, a rubber tip, and a dremel… but your time is better spent elsewhere
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