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side shooter
Here are some sequential pictures of team 1011's side shooter. Seems to work well, and the top spin keeps the ball in its zenith longer to get a better chance of making the goal from the same angle and longer distances.
http://photodump.crush1011.org/index.../&pageStart=16 |
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Nice shooter. We tried that, too, but your's works better. Would you mind sharing the diameter of your wheel and how well the ball flies?
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Re: side shooter
the diameter of the wheel is 8.75 in. with a barley less than seven inches clearance for the ball, so very little squish, but we intend to use this heavy metal version as a mold for a very light fiberglass one, which reduce the clearance by about 1/8 in. right now the ball flies very well and floats at the top of its arc, but falls a little short. this is the first day making it fire so we don’t have any measurements yet, just having fun, but i will post data after we have tweaked it to work well.
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I was interested in hearing your distance numbers. We tried and gave up on that design because we couldn't get the range we wanted. We hypothesized that a lot of energy was being used in deforming the ball as it went around the curve. It didn't do really badly, just a little worse than a couple of other wheel styles we tried. (And it did better than our belt drive approach which we abandoned mostly for packaging reasons.) Good luck!
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Do you really direct drive an 8" wheel - seems like you would be getting surface speeds on the wheel of almost 4 times the max ball speed, so you are either losing a lot of energy in the energy transfer to the ball, or your exit velocity might be too high. I think you get backspin, not topspin, so you're shootin' a 9 iron, not a 3 wood (I'm not a good enough golfer to use a driver) :) This is probably fine for "short" shots, but might limit your range. |
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Bill |
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As a rough estimate, we assumed the wheel would present only minimal load on the motor once up to speed, so would be spinning at about 2400 RPM, near it's no-load speed. The speed at the edge of the wheel will be about (2400 rev/min) * (1/60 min/sec) * (8*3.14 in/rev) * (1/40 meter/inch) = 25 m/s With a single wheel system, the speed of the ball is half the edge speed of the wheel, assuming no slip. So we're pretty close to the 12 m/s limit right at the wheel, and there will be loss in the shooting track. I doubt we're over speed at all. You're right, this design is all about backspin. I'm not a golfer, but in tennis backspin slows down and lifts the ball, flattening out the curve and lengthening the range. This seems like all goodness. Bill |
Re: side shooter
congrats guys. team 1538 isn't getting enought intial speed on the dirrect drive prototype we've designed. we've tryed using this type of backwards launcher, thinking the backspin and curve would calm the ball down. but after many times running after the balls.... they were very strange launches. nothing consistant enough to use. at least with our crude designs.
anywyas good work ... our motors only got up to around 1800rpms ... were not sure why, but we're moving on to other ideas - JERY!!!!!!!!!!! |
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Has anyone tried a traffic radar on the ball? Does it register? |
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Our drive wheel is a 8" pneumatic skyway "tough wheel" from the kit a year or two ago, with the tire removed and the wheel slot filled with rubber bungies on edge and zip-tied in. This was a prototype, we're now removing the bungies and will replace it with some filler, maybe styrafoam, and cover with silicone. Don't like this idea a lot, but it's the one we have at the moment. However, we're hoping the ball gets up to near it's theoretcal full speed. We have the track wrapped around the wheel for about 80 degrees, with the spacing at about 6.75", so the ball stays in contact with the wheel for quite a long path. Hopefully it stops slipping and matches speed, although it will also slow down the motor/wheel so we'll have to measure what we ultimately come up with. We may add some flywheel weight to lessen the slowdown and get up to or near the 12 m/s sec goal. Here's an idea (untested) about measuring the ball speed. Rather than using a high speed camera, what about doing a time exposure of the ball flying by in front of some kind of yardstick, and measure the length of the blur? Another way, also using long exposure, would be a well timed strobe light so you get the ball stopped in one frame in two places, and measure that distance. You could use a 1/10th second exposure then the ball should move just over a meter at max speed. Bill |
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They are.... we baught 10 from them :) FYI! - JERY!!!!!! |
Re: side shooter
A possible answed to how to measure speed.
(Bearing in mind I haven't yet done it for this year but have done it with soccer balls being kicked etc) Veiner out of Portland has a program called LabPro. Works on PC or Mac and besides being able to use sensors like the TI CBL stuff it has a import movie componant that allows you to use any digital image (Any handheld works well) and then by analyzing the pictures frame by frame you can get velocities and accelerations pretty easily. Ask a physics teacher to see if they have the software. Its cheap (about 140) for what it does. I should have numbers by weeks end based on the software. |
Re: side shooter
looks cool, how do you pickup the balls though? or is this just a proto type that won't be on the robot
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