Re: motor for ball Shooter?
 

Does anyone have closeup pictures of a shooting prototype ?

How do you directly attach a CIM motor shaft to a 6 inch wheel (a picture would be sufficient as well) ?

Re: motor for ball Shooter?
 

I think there are some in our photo gallery. We used a transmission and a chain reduction on an 8" wheel. I think some reduction would be nice...we're planning on a 5" roller with 2.5:1 chain reduction on our first "real" shooter design.

Re: motor for ball Shooter?
 

If you do use a cim make sure to put a reduction on it. Going 5500 rpms (free speed) is too high. Make sure to put atleast a 3:1 reduction. That will increase stall torque for the motor. That way the wheel won't slow down after firing a wheel. Also a 2 inch thick wheel should be used.

If you use a Fp. Then dual it and use the planetary from Andymark into a spur gearbox. Making the output speed the same as a 3:1 CIM. Also, you could possibly hex a custom AL or plastic wheel and direct drive it.

This is what we will probably do. Also how much compression are most teams gonna apply to the ball. More compression = higher risk of hurting the ball?:ahh:

Re: motor for ball Shooter?
 

Your setup is very similar to what we have prototyped, but with less compression and a wider gap. That would probably explain the 30-35ft range as ours did not go quite as far.
How is your accuracy if you slow the motor speed for shorter distances to target?
Ours is quite accurate at the 15ft range, however, trying to make it into a trailer consistently while both our robot and the trailer moving with different orientations is another story.

I think a 1:1 CIM - shooter speed is fine without a reduction also.

Re: motor for ball Shooter?
 

If you have a wheel which has one of the 1.875" 6x #10 hole patterns (like all of the AndyMark, IFI, Skyway wheels), just take an aluminum hub of your choice (either make your own with a 8mm hole, or buy this one and ream out to 5/16" or O-drill hole*). Then take an 2mm broach (about $40 on McMaster - useful if you plan to do a lot of custom stuff with CIM motors), and broach the hub with a 2mm keyway. Attach CIM motor with 2mm machine key to the hub, and attach hub to the wheel.

Now this will cantilever the wheel off the motor, which may work for testing, but may not work well later on. To get past this, you can also make a shaft coupler than has two keyways (one 2mm, one 3/32" or 1/8") with the 2mm side bored to 8mm and the other end bored out to 3/8"-1/2"). Then use bearings or bushings on the shaft the motor is coupled to to support the wheels. If you are worried about keeping the shafts lined up, you can also use a Lovejoy connector here.

* Both 5/16" and O-drill are within 0.003" of 8mm, with 5/16" being undersized and O-drill being oversized. Or if you plan on making a lot of things adapt to the shaft of the CIM motor, just buy an 8mm drill bit, they're like $3-$5 on McMaster.

Re: motor for ball Shooter?
 

I will post pictures tonight of our setup. The material were using on our drum is going to remain a secret for the time being because we are finding it to be a real difference maker in the effectiveness of our design.

The quick story is 1 CIM, 1:1 reduction through a chain and sprocket to a 6" spinning drum approx. 4.5" wide.

Hahaha, you are on to us squirrel.

Picture coming later tonight, but we mounted the CIM inside of our prototype shooter box, behind the lexan arc the ball travels around. Then on the outside of the box we ran a chain from the CIM motor shaft to the shaft the spinning drum is mounted to.

The prototype we designed was made on a ShopBot (shopbottools.com). Its essentially just a CNC router. So we were able to cut nice arcs into the prototype. We put a bunch of arcs so we can slide a piece of lexan in and out (more compression and less compression) to tell us exactly what amount of compression worked the best. So far what we've seen is 7.5" to be the money zone.




For anyone who is interested...a quick video is posted here: http://www.youtube.com/watch?v=iAoDkzDBn2s

The video is pre-CIM. The shooter is just being driven off of our Dewalt cordless drill.

Hope it helps everyone get their shooters cranking!
-Brando

Re: motor for ball Shooter?
 

That's what we found, although we didn't use such an elegant method to discover this fact :)


For all of us reading this...thanks!

Re: motor for ball Shooter?
 

Thanks for the informative post. I can't wait to see pictures of your prototype.

Re: motor for ball Shooter?
 

Brandon - the key isn't how far you can shoot - even a small motor can do that if you give it time to get up to speed. The key is how quickly the motor gets back up to your shooting speed. THAT is what will determine how quickly you can feed your balls to your shooter and remain accurate.

The less gear reduction you have on your spinner (and the less powerful a motor), the more it will slow and the longer it will take to get back up to speed. There are tricks to combat that - putting weights around the outside of your rim will act like a flywheel and decrease the slowdown you get from shooting (it will equally increase the time it takes to accelerate back up to speed).

Do some testing and see how much the shooter slows as you feed balls at a good rate (2-4 a second).

Re: motor for ball Shooter?
 

Tom,
I am aware of these facts. We are not planning on shooting the ball 30 feet in a match ( I dont believe any team is ). What I was attempting to indicate was that with 1 CIM we can throw a ball however many feet at 1:1, thus we could then reduce the speed from that data point.

We have stacked 3 balls directly on top of each other and fed them through the shooter so 3 balls in probably something like 1/2 second, only to see them all land in the same exact location.

I understand your concern from my comment, I am just trying to clarify to you that I am aware of the points you brought up. My surprise came from the fact teams were using 2 CIMs in 3 or 4:1 reduction setups....it seemed extraneous to me.

Re: motor for ball Shooter?
 

The reduction may just be for the effective flywheel radius; my team isn't using a wheel to shoot but we are running CIMs through the kit ratio toughboxes because our shooter has an effective "wheel" radius of 14".

As for using 2 CIMs it may be a little overkill, but we think it can't hurt, they're not needed anywhere else on our robot right now. I think it will help with our design though, the faster we can get up to speed (from a dead stop as well as after firing a ball), the better.

Re: motor for ball Shooter?
 

I absolutely think if you have them you should integrate them. I also don't know your exact design (but I have a good idea). With a radius of 14", it makes sense to use 2 CIMs IF you have them. Good luck!!

Re: motor for ball Shooter?
 

The only reason to want to throw a ball -- accurately -- 30 feet is if you want to score all four of your empty cells into your two fueling stations in twelve seconds.

...but I only know of one team that's trying to do that. ;)

Patrick