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.

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?

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.

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!

Interesting, but a couple clarifications.

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) :slight_smile: This is probably fine for “short” shots, but might limit your range.

Like Korbin says, last night we were just fooling around with this design for the first time. But we were getting distances of about 30 feet easily. We need to measure the exit speed, it might be excessive.


Yes, we’re direct driving the 8 inch wheel with the big CIM. I wonder where you get your 4x estimate? Here’s the calculation as I see it:

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.


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.


good work … our motors only got up to around 1800rpms … were not sure why, but we’re moving on to other ideas

  • JERY!!!

This raises a good question. On one of our prototype launchers, we’ve geared the Bigcim to spin a single wheel at a surface rate of 24 m/sec (twice the 12 m/sec limit). We are trying to get a high-speed camera so that we can directly measure the muzzle velocity of the ball, but so far we haven’t been able to. I’ve been wondering how much velocity will be imparted to the Poof ball by the wheel. The upper limit on this prototype is 12 m/sec, but we haven’t found out what the true speed is. Does anyone with better testing gear have any suggestions on how much the typical wheel underperforms theory? (We are using a pair of 8-inch Skyway wheels in the prototype – low mass.)

Has anyone tried a traffic radar on the ball? Does it register?

Don’t have specific data for you. We’re still trying to decide how to measure speed too.

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.


FYI: We bought solid tires for that wheel from Skyway 2 years ago. If you decide to use that wheel, you may want to see if they are still available.

They are… we baught 10 from them :slight_smile: FYI!

  • JERY!!!

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.

looks cool, how do you pickup the balls though? or is this just a proto type that won’t be on the robot

this arm mounts on the back of the robot and we have a roller pick up balls in the front. this is part of the reason for the shape, it loads by gravity feed from the bottom, but shoots out the side like a hook shot it does not take up a lot of space with the angle necessary for shooting out the top (in odor not to be blocked). this is not so much a prototype as a mold for a fiberglass version later. the frame it is in is the real thing though.

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?

That’s brilliant! I was toying with the idea of a ballistic pendululum, but with all the rotational energy aproximations it wouldn’t be accurate. Your idea is much more elegant. The only problem though, is you’d need a pretty nice camera for the shutter speed to be precise. Luckily we’ve got one. :smiley:

Another untested idea that we’ve thought of possibly using would be to hook up two light sensors or beam sensors a set distance apart and measure the time it takes from when the ball breaks the first beam to when it breaks the second. It would require somewhere to mount it for testing and would take a little programming, but with this shooter you could just mount the sensors in the sides of the upshaft facing inwards. Of course that’s just an idea.

I look forward to seeing this thing working at Duel in the Desert.

We tried a snowblower idea once… that failed. We know why, but yours is better.

yes, an idea we briefly went over was disrupting shooters with a blower. but we threw that out for a lot of reasons

Is there a Duel in the Desert this year? We haven’t heard anything about it.