View Full Version : "Pitching Machine" motors
fortinj1354
10-01-2012, 17:06
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
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
Do you need help with the math to find out how much energy it takes to get a basketball X feet?
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
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.
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 (http://engunneer.com/content/blog/first-2012-ball-trajectory-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.
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
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?
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. (http://www.team811.com/photo/main.php?g2_view=core.ShowItem&g2_itemId=2087) Can't find one "proving" the distance, but the turned faces are an indication.
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. (http://www.team811.com/photo/main.php?g2_view=core.ShowItem&g2_itemId=2087) 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
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
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?
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.
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
Thanks for all the help, guys
EricLeifermann
10-01-2012, 20:45
You can get backspin with just 1 wheel...
Ninja_Bait
10-01-2012, 20:50
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.
Oh, check out this post (http://www.chiefdelphi.com/forums/showthread.php?t=99696) that has a spreadsheet to calculate velocities, angles, etc. and try reading this thread (http://www.chiefdelphi.com/forums/showthread.php?t=99561) that has stuff with torque, speed, and motors in it that address the questions on the OP.
You can get backspin with just 1 wheel...
Yes, but that results in less ball energy at the same launch speed. There's the extra friction given by the cowling and the lack of energy from a second wheel. If you're aiming to hit a goal from a distance with any accuracy, you'll need to have more energy in your system to hit from ~20' or more than a single CIM or similar motor can supply.
Also, this (http://www.chiefdelphi.com/forums/showpost.php?p=1102024&postcount=15).
Some examples of that would be nice ^^
Well, it was a bit of trick question. Using a sort of flywheel setup, a system could have any amount of energy as long as the flywheel fit in weight and size requirements.
This gets difficult for me to explain without a whiteboard for drawings in front of me, but here is my best shot:
What you really want to find out is if you can get a ball moving fast enough to go the distance.
The speed at which you need can be solved with basic high school physics using motion formulas. Enlist a student or physics teacher at your school if this isn't making sense. This is often taught as "projectile motion" in the classroom.
After you have found the speed you need, gear the shooter to spin at this speed, and off you go.
Other things to consider on a shooter:
-How much you compress the ball
-Weight of flywheel (heavier will keep it from slowing down on shots as much because it will have a higher moment of inertia)
-Gripping material (KoP wheels from this year have not wielded good results for me either)
-Time and distance of contact (remember force times distance)
-Spin
Best of luck!
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.
Doesnt that all depend on how much backspin you want? Elaborate please.
Doesnt that all depend on how much backspin you want? Elaborate please.
If you have 2 rollers spinning in opposite directions (clockwise and counter-clockwise) with the higher roller spinning slightly slower than the bottom one, you'll get backspin because the 2 rollers both give energy to the ball. If you had just the bottom roller and a hood, you'd still get backspin, but that's because of the friction of the hood keeping the top of the ball from spinning as easily. So basically two rollers are better than one + hood because of more power given to the ball and less power needed (you don't need to overcome friction).
Ninja_Bait
11-01-2012, 22:12
Doesnt that all depend on how much backspin you want? Elaborate please.
It's time for a free-body diagram explanation.
Bottom roller + hood:
Two forces: the force from the wheel and the force of friction from the hood. both work together to create backspin; friction works against the wheel to create forward acceleration.
Top and Bottom roller:
Two forces: The wheels work against each other, with the bottom wheel applying more torque to create backspin; the wheels work together to create forward acceleration.
So yes, there is a backspin consideration involved here - more backspin would be easier to get out of a hooded shooter. However, the wheel is forced to do more work, so you lose more momentum between shots, and can't shoot as far.
EricLeifermann
11-01-2012, 22:19
It's time for a free-body diagram explanation.
Bottom roller + hood:
Two forces: the force from the wheel and the force of friction from the hood. both work together to create backspin; friction works against the wheel to create forward acceleration.
Top and Bottom roller:
Two forces: The wheels work against each other, with the bottom wheel applying more torque to create backspin; the wheels work together to create forward acceleration.
So yes, there is a backspin consideration involved here - more backspin would be easier to get out of a hooded shooter. However, the wheel is forced to do more work, so you lose more momentum between shots, and can't shoot as far.
Have you seen some of the shooters from 2006 with only 1 wheel? They could shoot pretty far, the only thing keeping them from shooting as far as they could was the speed limit the had that year...
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