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Unread 16-01-2012, 20:42
ToddF's Avatar
ToddF ToddF is offline
mechanical engineer
AKA: Todd Ferrante
FRC #2363 (Triple Helix)
Team Role: Mentor
 
Join Date: Apr 2011
Rookie Year: 2011
Location: Newport News, VA
Posts: 593
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Team 2363 double wheeled shooter prototype

Video here: http://www.youtube.com/watch?v=neqyzZ1SM2w

We hooked up the drive motor two ways. First, the CIMple box output shaft directly drove the the wheels. This produced shots similar to those from the single wheeled prototype. (http://www.chiefdelphi.com/forums/sh...hreadid=100266) Then we used chain driven sprockets to speed the output. This produced the shots in the video.

We didn't make any baskets because pointing the shooter directly at the backboard caused the shots to bounce off before they reached the apex of the trajectory arc. Our room doesn't have the headroom for us to tilt the shooter back far enough to arc the shots into the hoop. The shooter was ~16 feet from the backboard.

Some numbers...
when direct driven by the CIMple box:
- CIM motor free speed 5310 RPM
- CIMple gbx reduction 4.67:1
- pitching wheel speed 1137 PM
- pitching wheel tangential speed 39.7 ft/sec
- ball center speed 39.7 ft/sec

with sprockets driving the wheels:
- CIM motor free speed 5310 RPM
- CIMple gbx reduction 4.67:1
- gbx output shaft speed 1137 PM
- chain drive speed multiplier = 40 teeth/15 teeth = 2.67
- pitching wheel speed 3032 RPM
- pitching wheel tangential speed 105.9 ft/sec
- ball center speed 105.9 ft/sec

Calculations assume:
- motor running at free speed (not true because of inefficiencies in the transmission)
- ball leaves the pitching wheel traveling at the tangential speed of the wheel (may or may not be true depending on the friction between the wheel and ball)

Ideal calculations give a good rule of thumb for comparing various transmission designs. We would have saved ourselves a ton of time if we only had a shaft coupler to direct connect the CIM output shaft to the wheel shaft.

Next we'll hook up a motor controller to see how reducing the motor speed affects the shots. We may also go outside to see how far we can make baskets, at full motor power, given adequate headroom. Then, it's on to the catapult prototype.
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Last edited by ToddF : 16-01-2012 at 20:47.
 


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