Re: Motor Used for Shooting
 

Hands down, 775pro!

Re: Motor Used for Shooting
 

We made a prototype 2 wheeled shooter with 6 inch wheels and 2 mini-cims direct drive. For the final design we are going to switch over to the 775pro's with a 3:1 versa Planetary

Re: Motor Used for Shooting
 

Hm. I wonder why you would say that :rolleyes:

But in reality, I would have to agree. 775pros have been our best motor to shoot the balls.

Re: Motor Used for Shooting
 

Both sides of our shooter have an in-line versaplanetary encoder which allow us to control the speed of each wheel. Funny story, we remembered when we were setting different RPMs for testing that 4500 is the max for our setup because we set the system to 6000 and the when we measured our speed with a tachometer, it never got above that 4500. Hopefully that speed will be achievable with the new gearbox stages.

Re: Motor Used for Shooting
 

Not biased at all... :cool:

But in all seriousness we used it to test our 6" wheeled shooter and loved the performance. The power per weight is unmatched at this point in time.

We are using 3:1 versaplanetarys with 775pros on a greenhorn style 2 wheel horizontal variable angle shooter.

Cims and mini Cims do decent at 1:1 bags don't work at all unless you go for a 5:1 or higher gear ratio.

Re: Motor Used for Shooting
 

If you are operating the wheel at max motor speed there is no headroom to do closed-loop control.

So if you have a 775Pro geared at 3:1 and want to control the wheel speed at 6000 RPM you won't have a lot of battery voltage left to work with.

Re: Motor Used for Shooting
 

I'm not the one behind the controls for the robot, but I believe we're more interested in using the encoders for 1) making the two sides of the shooter differ by set amount to see how spin will affect trajectory and 2) monitoring when the flywheels get up to speed so that we can move the ball into the shooter the moment it's up to speed.

Re: Motor Used for Shooting
 

We're planning to pull our catapult with an AM PG71 (motor is a 9015), taken down another factor of 3.6 (at initial design) with sprockets and #25 chain. The encoder is already in place on the COTS assembly.

We'll probably use another PG-71 (no encoder, just limit switches) for our mechanism to lift the ball over the bumpers and into the launcher.

Roller pickup TBD.

Re: Motor Used for Shooting
 

I have seen you posting the same thing in a few other threads. I was wondering if you have a minute to explain/have a link to a thread that explains how operating voltage is tied to using control loops, to someone who knows very little about such things?

Re: Motor Used for Shooting
 

The control works by varying the voltage supplied to the motor. The motor controllers cannot put out a higher voltage than they take in from the battery. Without getting into PID theory, essentially if it's going too slow, the voltage is increased; if it's going too fast, the voltage is decreased. If you're running the motor at top speed (giving it full voltage), you can only adjust down. Far better to have your nominal operating speed at say 75% of top speed, especially later in the match when the battery voltage is reduced.

Re: Motor Used for Shooting
 

We have been using bb550 motors on versa planetary 3:1 gearboxes with a four inch wheel. It has been working great for us. We have used these motors in the past with great success and I am surprised i haven't seen anybody else using these motors.

Re: Motor Used for Shooting
 

Our team has tested both the miniCIMs and the CIM's. We are using two CIM's to "launch" the boulder. Good luck to all teams this year!

Re: Motor Used for Shooting
 

We're also looking at using a 775pro at a 3:1 but I'm having trouble figuring out how to attach a longer shaft to the VersaPlanetary Gearbox shaft.

I figure in order to gain efficiency it would be better to drive the shooter wheels directly from the gearbox, without adding a second set of gears, belt/pulley or sprocket/chain set-up. We don't have a lathe, so is our only option to not directly drive the shooter wheel?

Re: Motor Used for Shooting
 

For a shooter it really doesn't matter too much. The main thing that matters is your RPM and compression, I'm not convinced torque has a large impact on the shot as much as it has on spin up time / slow down after a ball is shot (which doesn't matter in this game). You want to get the wheels going at a specific repeatable speed to get an accurate shot - generally between 3000-8000 RPM with a 4" wheel(s) and depending on the distance / angle etc.

The advantage to a Mini CIM is that you can direct drive and be at around the right RPM, the disadvantage is that you can't really go any faster than free speed unless you gear up - which is silly. The Bag, 775, or 550 all have high free speeds and require some gearing down, but a versa planetary box makes that really easy. 550s are a little weird this year since you can't get them from VP or AM. Also consider packaging and where your motor / shooter will live inside the robot.