My team has recently switched to a flywheel design, ditching our inefficient double catapult. We have a working design, but what we are finding is that the 2 V5 motors we have placed on the flywheel are heating up, and the power output becomes insufficient for us to shoot well. Currently, we have a 12:60:12:60 (or 1:5:1:5) gear ratio and we are also using a weighted gear for rotational inertia. So my question is a big one: what can we improve? I’ve seen some designs that use ratchets on their flywheels, but I am concerned that the problem lies in our gear ratio or our power distribution, and using a ratchet won’t really help that. I have included some photos of our robot below. It shoots very well for the first 1 or 2 shots but begins to struggle after the flywheel has been turned on for a while. We’ve never built a flywheel before so we’d love to know what is going on. Any tiny piece of advice could help.
Thank you all for your help! Every little thing helps us improve.
For starters: you don’t really need high strength gears on your flywheel, especially unlubricated (tons of friction). Depending on your V5 insert, your gear ratio is good. If you’re on a 100rpm insert, it’s probably not enough, and a 200rpm insert might be too fast. Generally you want your flywheel to be anywhere from like 2800-4000 rpm freespeed. With a 200rpm default V5 insert, I would recommend something like 15:1 (60:12:36:12) or similar. Minimize the number of gears, as each additional one causes more friction. Never have more than two bearings per axle (this is pertinent at the top)
There needs to be more bracing to hold the whole system securely and should be composed primarily of c-channels as they have more than one point of rigid contact. We had similar issues and we improved our flywheel by adding multiple bracing points and using low strength gears as they reduce friction to a great extent. We also used white lithium grease on the axles to reduce friction even more. The weighted gear is not really necessary.
Some people are saying that using low strength gears will help, but I disagree. In my opinion, the high strength gears make it possible to use aggressive velocity control loops on the flywheel. What I would check is the friction. You also definitely don’t need two V5 motors to run your flywheel. We run a 15:1 gear ratio with a single 200 rpm motor and don’t have any stalling problems. If you have the extra motors and want to use them on the flywheel, build the flywheel and make it work well with just one motor. Then, you can add the extra motor just as a bonus. That’s how you get the best build quality.
You want to make sure that you have basically no friction on the flywheel system, use grease on the gears and inside bearing flats, and ensure that every axle is perfectly straight. The slightest bends can cause enormous problems on a flywheel. Also add some support to the system. I like to have at least two pieces going across the whole system to add some support.
The other thing I would change is the gear ratio. If you have a 100 rpm motor, it’s too low. If you have a 200 rpm motor, it’s way too high. As @MayorMonty stated, you want a ratio that will get you between 2800 and 4000. I prefer 3000 because that has worked really well for us.
We have the same gearing setup that you have with two motors, but it doesn’t over heat until you shoot 15-20 shots, so it shouldn’t be the gearing, I would check for friction and make sure every time something that spins is touching metal, that you put a Teflon washer there.
On a side note, does you flywheel shoot from the bottom of the wheel. If it does, that is very interesting, and I would love to see a video of it working.
I remember when ours did that – we had the same exact gear ratio and a single 200 RPM V5. It would slow down and speed up arbitrarily, never exceeding 80 input RPM. Once we switched it out for a 100 RPM torque motor, it seemed to work fine.
But we scrapped that whole robot, including the flywheel, so I’m not a great source of advice.
Are you using torque settings right now, or normal?
I’ve also heard of teams using a lesser ratio (1:5 or 1:15 or something) on a 600 RPM motor(s).
Like many other have said, using a 1:15 gear ratio with 200 rpm V5 motors will work better for you. We previously had a 1:25 ratio, and my team and I immediately noticed that the motor was heating up and no spinning at full speed. Especially with those two traction wheels, I would recommend you lower the ratio to slow down the flywheel. My team has a very compact low-strength gearbox for our flywheel, and it has worked beautifully.
Thanks so much! This actually fixed our issue, in addition to removing the weighted gear. We also used a lot of WD40 which worked out for us in the end. Also, yes, our robot does shoot from the bottom of the wheel. I will attach a gif of it working at high speed (before calibration). Sorry, the gif isn’t fantastic, but it shows how far it can shoot.
I wonder what rationale led to the unorthodox underhand shot? Surely you intake from the other side, meaning you’d have to turn around to grab balls, then turn back around to shoot, rather than the meta of intaking and shooting from the same side. Just wondering.