# Best motor/gearing option to drive a shooter?

Using a linear shooting system what would be the best way to drive those motors? By looking at Andymark I noticed the Double Doozy assembly http://www.andymark.com/product-p/am-0629.htm for the AM 9015 motors and then the http://www.andymark.com/product-p/am-0449.htm gearbox. From what i’ve roughly calculated that would give around a 2,000 rpm output. Would this be enough to launch a frisbee a reasonable distance?

You won’t know for sure until you slap the thing together and toss a frisbee. Also, a “reasonable distance” might be anything from 2 feet to 40 feet. It depends on what “reasonable” is to you. Check your game strategy.

That truly depends on how far and what goals you are aiming for. Just to give you an idea, watch the robot in 3 days video about their linear shooter. They are using a CIM geared up to roughly 8,000 RPM (if I’m remembering correctly they are gear up about 1.5:1 and a CIM standard is around 5,200 RPM). You also have to consider the pressure you are applying to a disc and how much that affects the speed of your shooter. I would suggest looking through all the legal motors that you don’t plan on using for other things and see what you can find. A good place to start can be the BaneBots motors. Many of those motors have a very high RPM output and have many options to how you can apply them for your needs.

Is consistency important to you? If you run it at free speed, there’s no headroom for speed control.

Would this be enough to launch a frisbee a reasonable distance?

Theoretical frisbee exit speed in mph (no slipping) is given by

pids/2112

“d” is wheel diameter in inches.

“s” is wheel speed in rpm

If there is slippage between the wheel and frisbee, the exit speed will be lower.

If there is slippage between the chute and frisbee, the exit speed will be higher.

Is this exit speed in feet per second?

I believe he has it listed in miles per hour. Just do some unit conversions.

That would give an 8,000rpm, 8inch wheel (exactly like robot in 3 days) and exit speed of 95 MPH. Seems a tad fast for a frisbee exit speed.

Just to throw it out there, the MiniCim actually spins faster than the CIM motor (free speed 6200 rpm, compared to the CIM motor’s 5310).

question:

Not saying you’re wrong, but where did you get the 8000 rpm number from ?

5200 rpm CIM geared at 1.5:1 => 7800 rpm. He rounded that up.

Who said they are running it at full voltage ?

Before we can answer the question of the best motor/gearing option, we need to determine the ideal exit speed.

*Does anyone have any data (actual measurements) for the following?

1. what effect do different shooter wheel speeds have on frisbee flight path (e.g. height at the target distance) ?

2. how much does your shooter wheel slow down when a frisbee passes through it ?

Your best bet to determine any of this is to put together something with a launch speed in the desired ballpark and test the desired shot. Then you don’t need any math beyond knowing how things scale. We have run all of our tests off of a UPS (uninterruptible power supply) so that we can adjust the voltage to get the desired launch speed. Knowing this speed makes it much easier to design the final mechanism, and we haven’t needed any frisbee flight models, only repeated testing.

Of course, we are not simulating any shooter spin down with a UPS, but as already mentioned, leaving headroom for speed control should take care of this.

Did you gather any data (that you’d be willing to share) during this testing?

Not that I have access to at the moment. When I get into the shop this afternoon I’ll see what I can dig up.

*This post has some useful qualitative observations:

FWIW, World’s record for fastest frisbee throw was 74 mph in 1988 (citation: YouTube video from Guiness Book of Worlds’ Records TV show)

Note that with any no-slip one-sided design, the tip will have to be going twice as fast as the desired exit velocity, since half of the imparted velocity must go into spin. So even if we only need a 70mph launch, the shooter would need to be going 140mph.

Add in a second side, however, and that changes entirely…