I’m looking for some advice after our shooter motor started smoking today.
Our current setup: 2 4" AM Stealth Wheel Flywheels with about 1/8" compression. We are running a MiniCIM through a VersaPlanetary encoder (but no gear reduction) then to a 3:1 chain reduction to the flywheel.
We tuned it in so the max height of the ball is about 3-4 feet above the HE goal. We’re running PID and were able to get very consistent results at about 1 balls/second. We were having good success and the motor was getting hot, but not hot enough for me to worry. I need to double check with coding, but as far as I know, we are not running our motor at max speed so the PID should have room to adjust after each shot.
We then mounted our motor onto our robot and attended a practice competition (thank you 2338). Due to it’s location, it ended up encased in a very small space enclosed with Lexan. After testing extensively (still at 1 balls/second), it performed great, but it was now hot enough for me to worry.
At practice today, we added our indexer motor and sped up the rate to about 2-3 balls/second). We also added a CIM Cooler to try and help out. The balls still seemed to shoot the same, but at the end of it, our motor was smoking.
We’ve gone about cutting several holes into the space to increase the airflow. But, I’m unconvinced that this will fix the problem. How much of an issue is the sauna we inadvertently created? If it’s not that, any advice on how to go about testing this ideas? Looking into several other posts, I note that 775s are very popular, but we had shied away from them since we hadn’t used them before.
Obviously we have 1 day until Stop Build so we are likely going to pull our shooter off the robot and use it as our allowance.
How long is your MiniCIM running at a go? CIM-class motors aren’t known for long running times without a chance to cool down. A match is one thing, 20 minutes straight is another.
Past that, I’d also make sure things are running freely. Disconnect the motor and give the shooter wheel a spin; any binding you feel is only going to make the loads on the motor higher. (We smoked a 775pro before overhauling our conveyor and shooter to take more load out of the system.)
And statement of the probably-obvious: the MiniCIM you’re describing needs to be removed from service now.
You can also track how much current your mini cim setup is using without any code changes with the driver station log.
As long as your power distribution panel is properly attached to the CAN bus on your robo rio you can click the little gear icon in the driver station (http://imgur.com/a/xbDH8) and select ‘view log file’ to get at a super handy charting tool that tracks the current utilization of every device wired through the PDP.
Mini CIMs don’t stall until about 90 amps, but they can get awfully hot before that. If you had an idea of how much current was required for your application, you can get a sense of what motor speed and torque is required for your application, and you may be able to select a more appropriate motor/gearing.
Just to make sure that I understand correctly, can I run through a hypothetical? If we were to get a reading of approximately 50 amps, then given the specs that would indicate that the MiniCIM is running at about 3000 RPM in order to get our desired shooting results? Because this is not the ideal efficiency for a MiniCIM, I should then either change my gearing to get the MiniCIM RPM at about 5000 to match its peak efficiency while leaving the RPM of the flywheel unchanged OR switch to a new motor that is more efficient at 3000 RPM.
To expand on your example, at 50 amps, you’d be running at roughly 2.5-3k RPM and also generating approximately .8 Nm of torque. If you were to re-gear it to say a 6:1 then you would expect ‘roughly’ .4 Nm of torque, at say 4.3k RPM, and your actual output wheel would be spinning slightly slower at ~716 RPM compared to its previous 916 but only using ~25 amps of current and likely perform better.
There are some other questions as well, for instance is your shooter a well performing fly wheel, in that does it actual retain a large amount of energy after the motor has stopped spinning and mostly power the ‘ball’ from its stored energy reserve, or is it more the torque of the motor that’s applying force through the wheel in to the ball that’s powering your shot.
4 inch stealth wheels don’t really make a great ‘fly wheel’ in that they don’t have very much rotational inertia, so what you’re seeing isn’t a motor building up power in a spinning wheel, and then that wheel flinging a ball, but rather a motor gripping a ball with a wheel, and the motor flinging the ball.