We have designed and created a flywheel shooter prototype to test wheel materials, compression, RPMs, etc. We are running into a significant problem. Every time we spin up the flywheel at a reasonably rapid rate, (anything greater than 2.5v/second), it trips a 40amp breaker and shuts down.
The power train currently consists of 2 775 pros geared to a 4" Colson, and an overall gear ratio of
2.4:1 (2.4 rotations of the motor for every rotation of the flywheel). The gearing is achieved through a 4:1 Versaplanetary followed by a 36t:60t pulley. According to JVN Design Calculator, if you model the system as a 2in arm with a weight of 0.76lbs (which I am sure is not the correct way to model the system), the system should only be pulling a maximum of 7.42 amps, which is significantly less than the 40+ amps the system must be pulling.
Interestingly, I am able to spin up the flywheel without a problem when I set the ramp rate to anything over 5 seconds (ramp rate being input as seconds from neutral to full power, meaning that 5 seconds converts to 2.4volts/second). The problem with this is that I am unable to effectively use a velocity control loop at this ramp rate, since the system isn’t able to accelerate fast enough to maintain an RPM.
Something must be fundamentally wrong in my system, since I know for a fact teams have pulled off significantly more aggressive ratios with far more aggressive ramp rates without a problem in the past. For example, in 2016, according to their 2016 Technical Binder 254 had a 30:19 ratio (1.57:1, far less reduction than our 2.4:1), and according to their code release, they used a ramp rate of 36v/second. In a more recent (and not 254) example, from this year’s Bison Robotics Ri3D shooter with just one 775pro,
I currently don’t have access to our workspace, so I can’t take any pictures, but will be more than happy to post pictures after 3pm. Some things to note:
- We are using an old PDM (blue PDP) for this prototype
- The system is being run on TalonSRXs on the last 2019 update
- We tried powering the system with a brand new battery probed at 13.2v, and a dead battery probed at 11.9v, problem persisted in both scenarios.
- The belts are tensioned properly, not overly tight or loose.
- The wheel spins freely and easily by hand when not powered.
I’m losing my mind over here. Any ideas?