Watcha Doin’? (Competition Belt Sanderz)


That’s how it started.  Which was just way too easy.

About 5 years ago or so they had this thing called the New England Belt Sander Racing Association, right?  It comes and goes, and it went, right after I’d built the prototype of my ultralight sander and crashed it tested it.  Here’s the evidence:

Then the races got cancelled for that year, then moved to another place which wasn’t as fun, so I never rebuilt it and didn’t do anything with it, and just kept on building my motorcycles.  In the process I learned a lot about motors and things.  Then I hear they’re resurrecting them.  Then I found some stuff at the dump.  Then I did this thing.


Nothing so wrong should be so easy.

So here’s the deal.  There’s a Modified class that has one rule: it must be driven by sandpaper.  It’s always seemed to me that the typical belt sander arrangement has a lot of friction, and what could be better than the traditional dragster configuration?  I ask you.  So that’s what led me down this road.

But, there’s Physics.  Your power is coming from the wall.  120V, at maybe 20A.  Then it goes down a long pipe called an extension cord, right?  So even the biggest, baddest, most efficient setup is going to be limited to 20A.  Unless you do something a little different.  And this is a little different.  Credit where due, A123 and DeWalt teamed up with an A123 powered sander that did pretty well until the board caught on fire.  But still, they were running an itsy-bitsy belt sander motor.

I happen to have the ETEK sitting around, looking for a Special Purpose.  It’s a 10KW motor, just to refresh your memory, and can be overvolted to 96V pretty safely.  (The track is 75′ long, and the run time is maybe 2 sec. for a slow sander.) I have a handful of RC lipo hanging around, and a few contactors.  Right?  See where this is going?  If I can carry 96V on board and dump directly to the motor, I’m probably feeding it 200A or so.  Just to do a little math, using the motor RPM at 96V and direct gearing, with 100% traction you’re looking at doing the 75′ run in about .6 sec.

What could possibly go wrong?

Of course, you’re not going to get 100% traction, in fact, most sanders spin for the first 20 feet or so.  I’m assuming I can turn it off effectively, and that the lipo won’t burst into flames.  I’m also assuming that 50lbs + of belt sander sketchyness at 125 ft/sec or so will eventually come to a stop, hopefully without causing structural damage to the building we’re in. (For reference, the muzzle velocity of a black powder gun is around 390ft/sec.)  Nevermind itself.  Don’t even think about the fact that I don’t have a welder and the frame is brazed with that little Bernz-O-Matic rig I have.  Just don’t think about that.

So here’s the “build”, and I use that term loosely.  The ETEK with a 48V contactor, fed by a 120VAC power supply outputting 48VDC.  This is so you can run it like any other sander, dragging the extension cord and actuated by the starting switch on the track.  I have to put a 250W halogen light on the PS outputs to load it enough to turn off in a second or so, rather than taking a few seconds to dump the capacitors, which adds another level of sketchyness to an already entirely sketchy scenario.  The contactor should hold up OK, but we’ll find out really quick.  There’s a decent chance the contacts will fuse under load.  Naturally I’ll test this mess out with low voltage first, right?  Of course.  Safety first!

Here’s the photo album:

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The race is Nov 1, and I have the jackshaft on order from Go Kart Supply, my new favorite supplier.  In Thrust We Trust.  If it don’t tell you something that I’m buying parts for a competition belt sander from a kart supply shop, there’s nothing I can say.  But I am.

I actually think I’m going to have to build an ad-hoc track to test this little bitch.  Kidding aside, I really want to know what this is going to look like before I bring it to an event full of drunk guys with powertools in a wood-frame building, right?  At least some vague notion of what to expect.

Video coming soon, I hope.

In the meantime here’s the Rocketboom video by Steve Garfield from the first year I ran it – 2007.  Coincidentally the first year I became obsessed with building an electric motorcycle…  Note: THE RED LINE OF DEATH.

Along the way I found this video of my second year, Doom2:


2 responses to “Watcha Doin’? (Competition Belt Sanderz)

  1. You gonna put a wheelie bar on that thing? Or maybe 36 grit ‘slicks’ and a cinder block or two for traction….. I’ll bet it could dig a nice hole at launch!

    • I’m going to wait on a wheelie bar until I see how it does with full voltage, but yeah, maybe. I did find some 3″ wide 36 grit which fit the tread a lot better – should be coming in this week.


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