Centrifugal Enforcer Build Report - Part 1

"You are mine to toy with!"
Franjean, Willow (1988)

I'd been wanting to build a helicoptor, or Hazard style Kinetic Energy spinner for quite some time. The original design of what became Tangled Marionette was originally slated to be an EV spinner, but it was painfully clear early on that there wouldn't be weight for that. Well, a year later, with a slightly lighter surplus pancake motor and some experience in construction for the 13 pound weight class, I set out once again to build a "Hobbyweight" robot with real knock-out potential.


Here's the basic idea. Building off of the knowledge base of Walmart Cordless Handiworks drills, pioneered largely by Team Cosmos I chose four of the gearmotors, and a 2.4lb pancake motor from Sciplus.com. The pancake motor is originally a Radiator fan motor from a truck, as near as we can tell, and runs OK at 7.2v and gets down right exciting at 14.4v.
First problem was figuring a way to mount the Handiworks to the chassis. So I started with some 3/8" High Density Polyetheline and milled them into square blocks. I shopped around for a discount source of HDPE and found that it was actually cheaper to buy cutting boards on sale at Ikea and cut them up than it was to buy raw plastic from any of the local suppliers. A 12" x 9" x 3/8" slab of HDPE cost me $2.95, if I recall correctly.
Once the blocks were square I marked them for center and used a 1-1/8" Hole saw to cut a hole that was a perfect fit for the motor can of the Handiworks drill/gearbox combo. Here I'm laying out to get the final wheelbase with the weapon motor, drive motors, weapon batteries, and the Intellispeed 12T Hobby ESCs I was using. The batteries are these trick CP-1300SCR NiCds from Robot Power Solutions. They're a 1/2-height sub-c that weighs just 35g per cell.
After determining the wheelbase I started on the 6063 Extruded Aluminum channel stock for the side rails. Tangled Marionette Mk1 was 3" tall, and Mk2 was 2.5" tall. With Centrifugal Enforcer I'm pushing even further and building the entire robot in a chassis that's only 2" tall. This 1/2" x 2" Extruded Channel comes in 16ft lengths from Industrial Metal Supply
After drilling an access hole for the threaded output shaft of the Handiworks gearbox, I attach the nose of the gearbox to the rail by tapping the two holes on the front to 6-32 and affixing button-head cap screws. Thanks again to the guys at Team Cosmos for all the help with tips on using these motors.
3mm carbon fiber sheet in a "stressed skin" arrangement, like a race car, uses the side rails, the motor mounts, and front and rear panels as structural members. When all the fasteners were in place, I could actually stand on top of the 7 pound assembly (no weapon, batteries, etc.) and it would take my 220+lb weight without any trouble.
I didn't want my precious new Battlepacks flopping around inside the machine so I worked up these snazzy tie-down strips out of nylon. They keep the batteries tight to the rail and yet were very easy to remove to change out batteries, etc. without having to string new zip-ties, etc. Incidently, I had to mill 3 small reliefs in each side of the extruded channel to fit the tops of the cells. The cells were nestled in nice and tight right between the angled portions of the channel.
Similar clamps were used on the Intellispeed 12T ESCs. This method allowed me to still reach the calibration button on the speed control but kept them safely secured. You can also see that I've converted the power lines to Anderson 45A Power Pole genderless connectors for easy tie-ins to the batteries, etc.
I hoped to have enough weight to put a "feed ramp" hinged wedge on the front of the bot. Here's the hinge affixed to some of the 2mm Carbon Fiber I had left over from Tangled Marionette.
After a little experimenting I found that #8 sheet metal screws into a small pilot hole made the best method for affixing the motor mounts and other 3/8" thick HDPE pieces to the base and top plates. You can also see the radio receiver in place here.
I got the idea of using the super-light Dave Brown "Lite Flite" foam wheels from the Infernolab Wheel Comparison Guide and similar wheels on last year's 12-pound opponent "Kram", built by Kelly Small. I had some custom aluminum hubs spun by friend Randy Rabb and drilled some washers to match. Then, after cutting the cheesy plastic hubs away I enlarged the center holes by heating a piece of 3/4" brass tubing until red-hot and burning it through the foam.
It made one hell of a stinky smoky mess in my garage, and the wife was sort of miffed, but the result was an EXTREMELY lightweight 3" wheel. In the end this foam was almost too soft to use as I had some handling problems when turning (the foam kept rolling over during the "scrub" part of the turn), but they were LIGHT. The hub threads onto the output shaft of the Handiworks (3/8"-24 thread) and is affixed with a left-hand 10-32 screw that threads into the barrel of the output shaft.
By way of comparison I also found and tried these other model aircraft landing gear wheels. They have a built in Aluminum hub that could be bored at tapped out to fit the Handiworks gearbox, but they were nearly twice as heavy as the Lite-flite wheels above. (And yet they were still 1/2 the weight of a comparibly sized colson wheel, so I guess they're not THAT bad.) But I was fighting for every ounce so I used the foam wheels for most of the BotBash competition.

On to Build Report Part 2

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