More tea please.

Less random conjecture and more evidence please.

A message on the Student Robotics mailing list had cast some doubt as to whether it would be possible for teams to launch balls from a robot. Jeff and I strongly disagreed with this pure conjecture. Having been involved previously with building a ball launcher for a FIRST robot, we knew that it was possible (video here) with much larger balls than SR is going to be using.

But we felt that further conjecture about the situation wouldn’t have helped. Just after I’d digested what the mailing list post had said Jeff and I started hacking up a demonstration device from stuff that we’d got lying around the place.

We built a launcher from a battery-powered drill, a random wheel Jeff had lying around, a coach bolt, numerous wood screws and a few bits of wood. The most complex part involved was a turned insert for adapting the wheel’s hole to the coach bolt diameter. The result of this build was a little disappointing:

Can’t see the video? Click here

After considering the situation for a few minutes, we decided that this didn’t sufficiently demonstrate that balls could be launched. We could either increase the wheel diameter or increase the rotational speed. Since we didn’t have a bigger wheel available and Jeff had got a suitable motor from a printer, we changed the motor. This involved putting the wheel on bearings made from chopping board and coupling the motor to the shaft with plastic tubing:

Demo Ball Launcher Prototype 2

We connected this motor up to my power supply. This motor had previously been pulled from a printer so we were unaware of its specs. Sticking 36V into it from my bench PSU worked pretty well. The performance with the faster motor was much improved:

Can’t see the video? Click here

We pointed it upwards to find out how far up it would go. Unfortunately, our measurement system became saturated:

Can’t see the video? Click here

We made a point of timing how long it took us to do this prototyping: 4 hours and 49 minutes. That’s two prototypes and dinner. Not bad, considering that we got a definite answer about whether one can build a ball launcher. There are a few more photos and videos on Flickr.

Once again, the value of actually getting one’s hands dirty and actually building something has been demonstrated.

P.S. I’m back from Iceland, but more on that later…

Posted at 3:48 am on Saturday 30th August 2008

5 responses to “Less random conjecture and more evidence please.”

  1. Justyn says:

    Hi, you know in the Planet Student robotics feed the embedded videos don’t show up (at least in my Google Reader feed). They do in the feed direct from xGoat though.

    If only glancing quickly at the post it is not obvious that there are missing videos at all.

  2. rob says:

    Hello. python-feedparser, which is used by Planet, strips out embed, object and param tags. So, I’ve injected links under the videos.


  3. Peter says:

    Awesome Rob
    loving the launcher
    by the way the video links are broken – they point to http://xgoat.com/wp/2008/08/30/less-random-conjectureless-random-conjecture/ instead of here

  4. Justyn says:

    Can’t you add custom exceptions for embedded flash from “trusted” sites, ie youtube, vimeo and flickr?

  5. rob says:

    Cheers Pete. I have fixed the links.

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