Hi! We are currently in the process of designing a shooter for out 2020 robot. Our current prototype is a hooded shooter that has a 8-compliant wheel drum that is powered by a 775 motor with a 4:1 that we put on an Andymark flyer gearbox at 2.5. We only have about a 1/2" of compression, which could be causing a problem.
As we have tested our shooter we have burned out 3 775 motors and a 775pro, and when it does work it does not shoot into the goal.
Currently we are trying to mathematically calculate the RPM needed from a motor so we can get the speed up. However, the equations we are googling do not seem to be accurate. Does anyone have a way of calcualting the need RPM for a shooter? or better yet a idea of the issue we are having in our shooter?
@Secretspy97 we don’t quite understand it either. We have the motors programmed through a Victor and every time we have burned out a motor it hasn’t even been at its full speed.
you can check for the rpm by putting encoder on the shaft and converting the native units to rpm. I know the quad encoders will give you encoder ticks per 100ms and you can easily convert that to rpm. Or you can get the rpm reader(I forget the actual name for it) but this works well too. (edit: tachometer is what it’s called).
I mean, yes, but they also run at a different output power and will have noncomparable test results. They may also stall and burn out easier, so you should always use a consistent motor for testing, rather than any random 775 sized motor that you have laying around in the shop.
Since you are going with 775’s right now I have a few suggestions based on my teams findings, it should be noted that using other motors can provide similar or better performance.
Around 2.5" of compression
Total reduction between 2-3:1 w/ 775pros and 4" wheels
While 1x 775pro will get the job done, 2 will help provide better/more consistent results. + quicker spin up time.
Coregated plastic is a wonderful surface for the inside of hooded shooters this year because of how the power cell “slips” on it.
You can use encoders to measure and control RPM’s
Also quick question which compliant wheels are you using?
Well, if we want find the exact RPM for the shooter, we can math out the speed using physics. Given the height, distance, and angle, we can calculate the initial velocity. With initial velocity, we can work backward for the actual flywheel speed. The flywheel will transfer the rotational energy to the ball with most of it getting translated to linear motion of the ball. But make sure to keep in count of the friction of the hood as it moves along the wheel of the shooter. At the end of this you should be able to find how much RPM you need to spin your ball.
There’s a chance there’s a lot of drag in your system which is causing the motors to burn out. If you can’t spin your shooter by hand and have it spin for a second or two after you let it go, it’s probably got too much drag. Check that your gearboxes are greased, your bearings aren’t binding, etc.
Also if you want to calculate the RPM needed for a certain shot, I have this nifty calculator: Flywheel Calculator
It actually will probably increase speed since you get more friction and the ball will get pulled by the motor more(I dont know how to explain it properly)
My team has been testing a dual 1:1 neo shooter with a 4" wheel and 1" of compression, and we noticed that any less than 1" allows the balls to slip and they lose velocity.
Sounds like the motor is stalling somehow (the 775s don’t handle stalling well), check for vibrations that could be jamming up your gearbox. We had an issue with one of our prototypes that vibrated so hard it bound up a versaplanetary.
Secondly, we literally doubled our distance from 1" to 2" compression.
How many motors are you running on the shooter, and have you verified they’re all running the same direction?
Also, the BaneBots 775 and AndyMark RS775-125 are very different motors than the 775Pro and 775 Redlines. The latter two can be safely mixed, but any other combination of different motors will likely cause something to burn out because they’re trying to run different speeds.
@euph2137 we are using a variation, only because we don’t have that many in or shop. On the outside we have 4 of the green 35a, and then 2 of the red 40a, and in the center to of the black 60a.