Hi, my team is attempting to build a flywheel, and we are having issues with it causing rapid vibration throughout the robot. Our current setup for it is one 200 RPM motor geared 7:1. For now, the flywheel does shoot triballs across the barrier consistently, but it can obviously be improved on, and the shaking also does make us worry about vibrations causing some attachments to become loose throughout the robot,
The only recordings I have were a bit rushed as I was getting ready to leave, but here is one of the flywheel at full speed: Vibrating Flywheel
What I believe the main causes might be are our bracing for the base of the flywheel, as well as the flywheel seeming to rotate inconsistently. Here is a video of the flywheel at low speed, showing the inconsistent rotation: Inconsistent Rotation
The flywheel & shaft assembly seem to have pretty low friction, there is a good amount of freespin, especially when the motor is detached.
Our goal is to be able to use a 600 RPM cartridge, and get the flywheel to spin consistently at 3000+ RPM. We previously used a 600 RPM cartridge, but it was only able to reach a speed of 300 RPM, most likely due to these vibration issues. We are settling with the 200 RPM motor for now because the extra torque is able to overcome these issues enough to get the triballs over the barrier, while lasting much longer before overheating (about 5-6 minutes)
Any help or ideas would be appreciated, and I will be able to show more detailed videos and photos tomorrow.
The best way to find out would probably be to balance the flex wheel on your finder to find the centre of mass. If this isn’t in the centre of the flex wheel this is probably the issue.
Since you probably don’t want to shave the weight off the sides of the flex wheel, my advice is to make sure every part of the rotating flywheel is as symmetrical around the axle as possible.
Vibrations are almost always caused by mass imbalances across your flywheel. Without getting too deep into moment of inertia and center of gravity (COG) calculations, the COG of your combined flywheel setup is not in line with the axis of rotation( the shaft). From the slow rotation video, it looks like you are only using 2 points of contact to secure your flex wheels which is forcing them into an ovular shape. This technically can rotate without vibrations around its center point. However, you have stacked two of them together out of alignment. What you have kind of represents the static imbalance example of this demonstration. As far as solutions go, you are going to want to devise a mounting solution that keeps the flex wheels as circular as possible. There are many examples of flex wheel mounting plates on this forum or you could try and make your own. The more points of contact the better. Also, each wheel needs to be symmetric to the other when they are mounted on the shaft to further reduce vibrations. Also, you can greatly reduce vibrations by adding more support angles to your flywheel structure. This will help the vibrations not be as pronounced as the mass of the rest of the robot will be able to dampen the vibration. Think
Yes, I am using only 2 attachment points on each of my flex wheels. They are misaligned ovals, which definitely makes a lot of sense. I will change my mounting technique to the one I mentioned above, which should keep both flex wheels circular and aligned. I’ll also try to add some more support angles, probably with triangle bracing. Thank you both for the help, I’ll update whenever I make these changes.
Thank you for the help, my method of attaching the flywheel to the shaft was not symmetrical in one way. I believe the center of mass is in the middle of the entire flywheel assembly, I screwed both flex wheels to a 60T gear in-between. However, because the gear was in-between, I only used 2 screws for each flex wheel, but in different holes from each other. I’ll be able to show what I mean better with pictures, but I think this is very likely the issue. I’ll switch my method of attaching to flywheels by using 2 60T gears on the outside of both, so that all my attachments can be symmetrical with 4 screws for each flex wheel.
Another thing you can do is make sure the shaft the flywheel is on is perfectly straight. From personal experience, even a slightly bent shaft can cause the flywheel to vibrate a lot at such high speeds.
Also… the ball bearings do help if you are able to get some.
You are shooting for a certain speed… but how do you know you are achieving it? Query the motor and see what rpm it’s actually turning. If it’ never reaching desired rpm… then you will see better launches by not gearing up as much. Also… I’d keep a close eye on motor temp and watt usage. Anything much over 5 watts sustained will lead to RAPID motor heating.
You can put the flywheel on a hinge, make it inertia deployed.
Be careful when making a flywheel. Our flywheel’s axle snapped in half while it was spinning at max rpm and the flywheel nearly hit a team member.
that shouldn’t be an issue as long as you use HS axles. HS axles also fit into ball-bearings without an adapter which you can mount in a 3x C-channel easily and are great for reducing friction/inconsistencies caused by normal plastic bearings.
Update: The issue was the 2 flex wheels not being aligned. I ended up only using one flex wheel as I ran out of space, but I made sure everything was attached symmetrically and there are no more vibration issues. Thank you for the help!