Friday, December 18, 2015

One Pound Prototype Robot

When I first started doing the middle school combat robotics course we had one and three pound weight categories.  This paralled the categories used in "official" competitions.  But the one pounders, known as ant weights, were never very exciting.  With that small a weight allowance you just could not build much beyond a simple pusher.  Or at least you had a very difficult time doing anything fancier such as adding a powered weapon.  So we have been all three pounders for several years now.

But things are changing.  As I started looking around at ways to move beyond simple hacked servos for robot drive I came across these:

Ebay has a ton of them for sale, with prices in the four or five dollar range once you factor in postage. So cheaper than a servo, but they still need something to control them.  A solution suggested itself...

Here is your basic - roughly one pound - robot.  Nothing more than a couple of  hacked servos, a battery and a radio receiver.  Not particularly zippy, but to be fair it seemed to have an excess of duct tape on one wheel that was catching...
video

I think we can do a little better than that.

Below are a pair of the bright yellow gearmotor/wheel combinations from China via the miracle of ebay.  The fact that they come with perfectly fitting wheels is a big help, fashioning sturdy, reliable hubs can be pesky and time consuming.



The little green circuit boards soldered on to the motors are my solution to the issue of control.  They are just the electronics pulled from servos.  Sure, why not?  I have a big box of them that have come to grief over the years of doing the event and they appear to have plenty of extra capacity.  So long as you run them at 6 volts they are unlikely to go up in smoke.  The slender wires act as sufficient resistance that I don't see any way to "over amp" them even if you did try to push an immobile object with them.

Here is the above platform with the servos swapped out for China Gear Motors.
video
Way faster.

As with my Proto3 robot a few thoughts on practicality.

Weight: above was, with battery, about one ounce under a pound.  There is room for improvement of course, the frame I borrowed had been heavily baptized with glue, and was larger than needed anyway.

Adaptability: OK.  I think enough weight could be spared to allow for either a four wheel version or a simple weapon running off the 6 volt drive battery.

Effectiveness:  It was not as effective a pusher as I would like, probably the gearing is set for speed over torque.  Four wheel drive would help a lot, and also make it easier to handle.

Challenge to Learning ratio: again I have to worry about making this too easy.  It was not at all difficult to toss this together in a few minutes.  Other than pulling the servo guts out and doing a little nimble soldering work, I don't see how the urchins would be kept occupied for very long.

Cost: feasible.

I am looking at several other options as well.  Some time into next year I may have to revisit this.


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