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-   -   "Pitching Machine" motors (http://www.chiefdelphi.com/forums/showthread.php?t=99732)

fortinj1354 10-01-2012 17:06
"Pitching Machine" motors
 
Has anyone had any good results shooting the balls a good distance accurately using any of the allowed motors other than the CIM motors? Do any of the other motors provide the required power to shoot at least half way across the field, or are we stuck having to use the CIM motors?

Mr. Pockets 10-01-2012 17:30
Re: "Pitching Machine" motors
 
My team was prototyping this using treaded wheels with a CIM attached to each. We maybe were getting two feet out of them. To be fair the set-up was far from optimal and we've still got to try fiddling with the gear ratios, but initial results aren't that impressive.

Edit: No we haven't tried anything other than CIMs, but even the CIMS were unimpressive

Jeffy 10-01-2012 18:16
Re: "Pitching Machine" motors
 
Do you need help with the math to find out how much energy it takes to get a basketball X feet?

Mk.32 10-01-2012 18:39
Re: "Pitching Machine" motors
 
Quote:
Originally Posted by Jeffy (Post 1101870)
Do you need help with the math to find out how much energy it takes to get a basketball X feet?
Some examples of that would be nice ^^

Mr. Pockets 10-01-2012 18:41
Re: "Pitching Machine" motors
 
Quote:
Originally Posted by Jeffy (Post 1101870)
Do you need help with the math to find out how much energy it takes to get a basketball X feet?
That would be very helpful.

Djur 10-01-2012 18:49
Re: "Pitching Machine" motors
 
Since Work = 1/2 * mv^2 (final velocity) - 1/2 * mv^2 (initial velocity) and Work = Force * Distance, you can find the force can be found if you know the other variables. Use this spreadsheet for specifics including angles and the velocities you need.

So say you're shooting from 6 meters (about midfield) at a 45 degree angle at the top hoop.

Code:
f * d = (mVf^2 - mVi^2) / 2

f * 6m = (0.32kg * (8.98 m/sec)^2 - 0.32 kg * (0 m/sec)^2) / 2

f = (0.32kg * (8.98 m/sec)^2 - 0.32 kg * (0 m/sec)^2) / 12 m
/* Plug into Google */

f = 2.15 Newtons
Now, that's the net force exerted on the ball at the launch velocity. Add sin(angle) * force of gravity and you'll need to shoot the ball with about 9.1 Newtons of force (2.05 pounds). Again, use the linked spreadsheet to determine your angle and velocity.

Ninja_Bait 10-01-2012 18:55
Re: "Pitching Machine" motors
 
If you took a momentum/impulse approach, do you think you would get the same answer, or would that add other factors in that this solution ignores?

Mr_I 10-01-2012 18:59
Re: "Pitching Machine" motors
 
As a side note: Back in the day ('07 to be precise), when we were trying to throw Poof balls, we were getting an amazing lack of distance, sometimes maybe reaching 6'. This would have been pitiful in competition.

On a whim we decreased the space between the spinning wheels, thus "squeezing" the balls more. Suddenly, we were exceeding 30' on a regular basis, without any other changes to the thrower.

Photo of work in progress. Can't find one "proving" the distance, but the turned faces are an indication.

Djur 10-01-2012 19:53
Re: "Pitching Machine" motors
 
Quote:
Originally Posted by Mr_I (Post 1101915)
As a side note: Back in the day ('07 to be precise), when we were trying to throw Poof balls, we were getting an amazing lack of distance, sometimes maybe reaching 6'. This would have been pitiful in competition.

On a whim we decreased the space between the spinning wheels, thus "squeezing" the balls more. Suddenly, we were exceeding 30' on a regular basis, without any other changes to the thrower.

Photo of work in progress. Can't find one "proving" the distance, but the turned faces are an indication.
Decreasing the space increases the linear momentum and decreases the angular momentum imparted to the ball. I think that squeezing this year's ball by ~3 inches total (i.e. 5" between wheels at their closest point) is a good starting point for experimentation to determine how to impart less spin to the ball (spin from each side cancels out, so that energy is wasted) and impart more linear speed (which does not cancel out).

EricLeifermann 10-01-2012 20:30
Re: "Pitching Machine" motors
 
Quote:
Originally Posted by Djur (Post 1101962)
Decreasing the space increases the linear momentum and decreases the angular momentum imparted to the ball. I think that squeezing this year's ball by ~3 inches total (i.e. 5" between wheels at their closest point) is a good starting point for experimentation to determine how to impart less spin to the ball (spin from each side cancels out, so that energy is wasted) and impart more linear speed (which does not cancel out).
You are going to want some backspin on the ball to make shots. There is a reason why NBA basketball players have good follow through, it puts backspin on the ball and aids the ball into the basket.

fortinj1354 10-01-2012 20:34
Re: "Pitching Machine" motors
 
Quote:
Originally Posted by EricLeifermann (Post 1101999)
You are going to want some backspin on the ball to make shots. There is a reason why NBA basketball players have good follow through, it puts backspin on the ball and aids the ball into the basket.
Is the best method of achieving this by having two spinning wheels and spinning one faster than the other?

Djur 10-01-2012 20:34
Re: "Pitching Machine" motors
 
Quote:
Originally Posted by EricLeifermann (Post 1101999)
You are going to want some backspin on the ball to make shots. There is a reason why NBA basketball players have good follow through, it puts backspin on the ball and aids the ball into the basket.
That's easy to do - place the wheels below the equator of the ball and this gives it backspin. You'll need a free rotating wheel or something similar on top of the ball to prevent it from shooting out at weird angles, though.


Quote:
Originally Posted by fortinj1354 (Post 1102005)
Is the best method of achieving this by having two spinning wheels and spinning one faster than the other?
That will work if you have the wheels vertically instead of horizontally with the top one spinning slower.

Mr. Pockets 10-01-2012 20:42
Re: "Pitching Machine" motors
 
Thanks for all the help, guys

EricLeifermann 10-01-2012 20:45
Re: "Pitching Machine" motors
 
You can get backspin with just 1 wheel...

Ninja_Bait 10-01-2012 20:50
Re: "Pitching Machine" motors
 
It's more efficient with two wheels instead of one wheel with a hood. The loss in momentum is divided over two wheels and the bottom wheel doesn't have to work against as much friction to launch the ball.


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