Wednesday, December 16, 2015

Three Pound Prototype Robot

Although my middle school combat robotics class has been both successful and fun for many years now I have been tinkering with the idea of a technology upgrade.  In part to keep it more interesting. And in part because we can.  Electronics in particular have gotten so much more affordable recently.

But anything I would do would have to fit the spirit of the class, which is cheap and fun.  It would also have to be within the dubious skill set of middle school students.  And would have to be feasible within the somewhat cramped confines of our Machines Behaving Badly combat arena.

So eliminating any elements that would be too complex, too expensive or perhaps too speedy for a confined space, what's left?

Some of the Minions who come over to help with the event suggested this motor, widely available on ebay.

They claim to put out 1000 rpm at 12 volts and come well recommended for durability.  But still, at about ten bucks including shipping, they are not quite the bargain of our hacked servo drive systems. Or at least they did not look to be, then I found a bag of 18 similar motors that I ordered years ago and never got around to using.  I should clean the workshop more often.

428 rpm at 9 volts sounds good, we will actually be running at 9.6. Assuming two per robot, if I toss in the ones I already have we are down to an affordable price per machine.

I made some hubs out of plastic squares from the surplus store.  Just tighten that little set screw...

Motors with attached hubs/styrofoam wheels going on.  I am using cheap and easy cable ties and hot glue here, but there are nice mounting screws on the front of the motors.

And...the finished product.

If you are keeping track of such matters, that is a standard 9.6 volt RC car battery.  I don't doubt that the system could handle more voltage but these are cheap and sufficient.  That is a standard Futaba FM 75mhz receiver, it runs with the free Vex transmitters I have been using.  The green board is an older model Scorpion speed controller.  This could be the rate limiting problem for us.  I have to do some ebay prowling and tinkering, but most of the ultra cheap speed controllers have suspect reliability.  And even the cheapest equivalents to the above unit are around 35 bucks.  Of course it is quite possible to swap speed controllers from one machine to another for a season or two as we build up stock.

On to the testing.

Speedy enough?
Yep.  The controls are a bit glitchy due to a conflict between the on board mixer of the transmitter arguing with that of the speed controller, but that is fixable.

How about pushing power?
If you can push a tool box around you can push another three pound robot.  Keep in mind that the box has a lot of friction from its surface area and that my tossed together robot does not have anything on the wheels to enhance traction.

So, lets pass judgment on the prototype.  We need to make it fit the budget which at present is about 20 dollars a machine.  If I scale the class size back from 24 to 20, and toss in the 9 robots worth of motors I already have, then assume I can get some kind of bulk deal somewhere, I figure motors will be around 200 dollars.  The cheapest speed controllers that look up to the job are about 35 each.  If we swap from one machine to the next, lets say we need six.  I might be able to shave a bit off the cost there as I plan to shop a few of the cheaper "mystery electronics" controllers from ebay.

Other costs should be fairly minor.  We will need more 9.6 volt batteries but our stock is good there as is our "in event" charging capacity.  Wheels, hubs, electrical connectors all are minor issues.

The prototype as shown above is only 1 pound 9 ounces so there is room for armor, weaponry, decor, etc.

One problem I note is that this is a little too easy.  Tossing together Proto3 took an hour or so of tinkering.  My charge is to keep the kids engaged for six or seven sessions of two hours each.

Another option I have considered is reviving the earlier dual path event, having one and three pound machines in their own brackets of course.  To that end I also tinkered with a Proto1 robot.......

1 comment:

The Old Man said...

Ain't your first rodeo....