View Full Version : Best motor/gearing option to drive a shooter?
clandry94
08-01-2013, 23:04
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?
nathan_hui
08-01-2013, 23:25
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.
Dominator1619
08-01-2013, 23:33
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.
From what i've roughly calculated that would give around a 2,000 rpm output.
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?
What's your wheel diameter?
Theoretical frisbee exit speed in mph (no slipping) is given by
pi*d*s/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.
clandry94
10-01-2013, 01:36
Is consistency important to you? If you run it at free speed, there's no headroom for speed control.
What's your wheel diameter?
Theoretical frisbee exit speed in mph (no slipping) is given by
pi*d*s/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?
JohnSchneider
10-01-2013, 01:40
Is this exit speed in feet per second?
I believe he has it listed in miles per hour. Just do some unit conversions.
clandry94
10-01-2013, 09:00
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.
Andrew Lawrence
10-01-2013, 09:13
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:
Is this exit speed in feet per second?
answer:
Theoretical frisbee exit speed in mph (no slipping) is given by...
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.
Not saying you're wrong, but where did you get the 8000 rpm number from ?
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.
5200 rpm CIM geared at 1.5:1 => 7800 rpm. He rounded that up.
Who said they are running it at full voltage ?
ehochstein
10-01-2013, 10:46
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 ?
Aren Siekmeier
10-01-2013, 12:30
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.
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.
Did you gather any data (that you'd be willing to share) during this testing?
Aren Siekmeier
10-01-2013, 12:42
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:
http://www.chiefdelphi.com/forums/showpost.php?p=1212312&postcount=55
FWIW, World's record for fastest frisbee throw was 74 mph in 1988 (citation: YouTube video from Guiness Book of Worlds' Records TV show)
Aren Siekmeier
10-01-2013, 13:17
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...
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.
http://www.chiefdelphi.com/forums/showpost.php?p=1211078&postcount=36
Aren Siekmeier
11-01-2013, 00:23
Yesterday we were running our shooter at ~4000 ft/min (about 45mph). As far as we can tell there is no slip on the belt, so this should mean a frisbee exit speed of 2000 ft/min, or 22.5 mph. Shooting from ~130" from the wall and ~30" off the floor, we were able to hit a spot on the wall a foot or two below the 3pt goal (at the farthest) with excellent consistency, all within a few inches of each other. We are happy with the consistency and the shooter design, so we are working on getting it up to speed and making a few other improvements. We would like to shoot about twice as fast, for a nice level shot.
As far as we can tell there is no slip on the belt
How could you tell ? Did you take video and slow it down like 2073 (http://www.chiefdelphi.com/forums/showpost.php?p=1212312&postcount=55) did ?
Is consistency important to you? If you run it at free speed, there's no headroom for speed control.
This makes sense to me, but I couldn't explain to a mentor why you wouldn't want to run the motor at its free speed. Why wouldn't it be consistent at its free speed? Is it just because there isn't much torque at that speed, so the motor might slow down more when it shoots a frisbee?
nathan_hui
12-01-2013, 11:42
Free speed means 100% power. If you slow down and all of a sudden need more torque, uh oh. You can't get 110% power (unlike a nuclear submarine). That's what the headroom for speed control is. "Space" for more power, if and when you need it.
This makes sense to me, but I couldn't explain to a mentor why you wouldn't want to run the motor at its free speed. Why wouldn't it be consistent at its free speed? Is it just because there isn't much torque at that speed, so the motor might slow down more when it shoots a frisbee?
If you run it open-loop at full voltage, three things happen:
1) The actual speed you get varies greatly as the battery voltage changes
2) It takes a long time for the motor to spin up to free speed
3) When the motor slows down due to a frisbee passing through, the motor doesn't have much torque at that high speed and so it takes longer to recover
Gearing your shooter wheel motor so that you can get the desired wheel speed when the motor is running at less than free speed*, and using some sort of closed-loop control of speed, solves all three of the above problems. A bang-bang controller is very easy to implement and works well for this application.
* ideally at 50%
Free speed means 100% power.
No it doesn't. It means 100% voltage.
100% power (mqx power) occurs at 100% voltage and half free speed.
Our circular (90) degree shooter uses and AM pneumatic 7.5 inch wheel with a 32 tooth sprocket on it and a 25 tooth sprocket on the CIM. We have it set up so the wheel is hitting just above the widest diameter of the disk and just below the widest diameter of the tire with about 1/4 inch of compression and the tire at maybe 10psi. This ensures the disk does not ride up on the tire. This puppy will hit the top of a 10 foot door at 45 feet. up down variation is about 6 inches and side to side variation is almost nonexistent.
This is just with a plywood POC. You can read that as Proof of Concept or Piece of C&^%. Whatever. Still need to add a guide on the outer rail to keep the disk from riding up on that.
We have also tested a straight shooter bot so far it is not as consistent and much less powerful even with 2 wheel powered by separate CIMs.
Still plan on a little more testing here as I think it would be easier to incorporate to the robot.
Our circular (90) degree shooter...
You posted this identical post in three different threads.
http://www.chiefdelphi.com/forums/sh...46#post1213846
http://www.chiefdelphi.com/forums/sh...56#post1213856
It might be better to post it once and provide a link.
DonRotolo
12-01-2013, 19:22
Our circular (90) degree shooter uses and AM pneumatic 7.5 inch wheel with a 32 tooth sprocket on it and a 25 tooth sprocket on the CIM. Sounds like a direct drive to a 6" wheel would be the same.
At what motor speed did you log those shooting results?
You posted this identical post in three different threads.
http://www.chiefdelphi.com/forums/sh...46#post1213846
http://www.chiefdelphi.com/forums/sh...56#post1213856
It might be better to post it once and provide a link.
Sorry didn't think about the link idea.
I'll do better next time.
Thanks
At full battery voltage and no speed control.
Ya, it's primitive but it works. We will be looking into PID or bang bang later.
Sounds like a direct drive to a 6" wheel would be the same.
The larger diameter provides a slightly longer contact path.
Sorry didn't think about the link idea.
I'll do better next time.
Thanks
It's a great post though. The problem is, it's going to be difficult following the discussion. You've already got responses in two threads.
We were looking into gearing up our CIM motor to 6000-8000rpm and running an 8in pneumatic wheel. Originally we were looking to gear up a toughbox but after realizing that they only seel 12-14 teeth gears for CIM motors, we'll probably just use belts and sprockets
At full battery voltage and no speed control
We were looking into gearing up our CIM motor to 6000-8000rpm and running an 8in pneumatic wheel.
FYI, Team 2073 found that above a certain wheel speed, the frisbee exit velocity actually decreased.
http://www.chiefdelphi.com/forums/showpost.php?p=1212312&postcount=55
smclean1969
12-01-2013, 19:37
Something for the 8000 rpm, that's assuming free spin, which isn't accurate for a motor under load conditions. The CIM has to turn the wheel, so it's going to be something less than 8000. It won't be an amazing drop but 7000 - 7500 is probably more reasonable.
Something for the 8000 rpm, that's assuming free spin, which isn't accurate for a motor under load conditions. The CIM has to turn the wheel, so it's going to be something less than 8000. It won't be an amazing drop but 7000 - 7500 is probably more reasonable.
Could be a lot less than that if the wheel is generating vibration and windage.
Hint: measure the CIM current with a clamp-on ammeter. Then estimate the CIM speed from the voltage and current, as shown here (http://www.chiefdelphi.com/forums/showthread.php?p=1213520#post1213520).
FYI, Team 2073 found that above a certain wheel speed, the frisbee exit velocity actually decreased.
This is definitely interesting, though they're using (from what I can tell)
8" Plaction Wheel from AndyMark while we're using a rubber wheel which may be turned to better fit the frisbee so I guess we'll have to build the belt/sprocket mockup before we can really test what the effective speed is.
Who said they are running it at full voltage ?
http://www.chiefdelphi.com/forums/showpost.php?p=1214240&postcount=7
Could be a lot less than that if the wheel is generating vibration and windage.
Anybody planning to buy 8" pneumatic and run it at 8000 rpm read this thread:
http://www.chiefdelphi.com/forums/showthread.php?t=111118
MrRiedemanJACC
14-01-2013, 05:44
Is there anyone considering using dual banebot 550's to drive their shooter?
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