July 29, 2013

Bot Blast Recap

So, Bot Blast happened, and it wasn't a complete failure.

Actually it was, but it was a highly entertaining failure.  In the week hours before we left for PA, Jaguar and Dane also managed to whip together some little antweights.  I finished a little early, so I did some weapon testing on Jaguar's in-progress bot.

Here's the trio of last minute bots.  Mine on the left, Dane's stepper motor powered Del-Ran Bumble in the middle, and Jaguar's Speed Bump on the right.

Picture credit to Charles
My first match was against Dust-Pandemonium, a dustpan shaped robot with a blender-like attachment in the middle of the pan.  It became immediately apparent that my robot was just way too slow.  I just could not move fast enough to do much of anything.  My opponent even had some sharp corners and exposed wheels that my recessed spinning drum could have easily bit into, but he outmaneuvered me by a mile.  Fortunately, his weapon was more for show than destruction, so all it did was put some scratches on my steel drum and carbon fiber armor.

My second match was against Fire Arrow,  a simple but very effective wedge robot.  It was much faster than mine, and even more importantly, had a really impressive driver.  Neither bot took any damage, but I was outclassed, and voted the loser by the judges.

The competition was double-elimination, so I was out.  Maybe next time I'll start more than five days before the event.

July 20, 2013

One-Week Battlebot Blitz

Sometime in the early hours on Monday morning this week,  I decided to join Charles, Dane and Jamison on an adventure to Bot Blast 2013.  Problem:  I do not have a battlebot.  So I had roughly five days to build up a 1 pound battlebot from scratch.    I came up with the rough design for a robot with spinning drum weapon, and then just built the drum so I had something to design around.

The drum was made from some steel tubing.  It's driven by a small brushless motor I scrounged via a press fit aluminum hub:

I scrounged some tiny gearmotors and grabbed one of my spare quadrotor batteries:

Starting to look like a robot

I turned some very shiny wheels out of 2" aluminum round stock.  The tires are made from short segments of bicycle inner tube.

As a backup defense mechanism, I made the non-attacking side of the robot wedge-shaped.  The tip of the wedge was milled from aluminum, using some very sketchy clamping techniques:

The rest of the robot's shell is carbon fiber.  Because of the robot's wedge-shape, I named it "A Glorified Doorstop."  When it fails miserably as a robot, you know how I'll use it.

To actually hold all the parts inside the shell, I laser cut a Delrin frame.  The motors are press fit into 3D printed mounts, and the drum rotates around a pair of low-profile bearings on the outside of the drum.  I put the bearings on the outside, because I could not spare the weight for an axle about which the drum could rotate.

The Delrin pieces were edge tapped and screwed to the carbon fiber.

So the spinning drum could catch opposing robots, I added some flat head socket cap screws around it. They thread into an aluminum nut strip on the inside of the drum.

Electronics were pretty straight forward.  An RC receiver feeds signals to a Turnigy Plush 6A brushless controller for the weapon motor, and two VEX 29 controllers for the DC drive motors.  For some unknown reason, I was unable to get the drive controllers working on a 3S LiPo pack (11.1V), so the robot is painfully slow.  I think the issue is probably with the brushless controller (which provides 5V to the receiver), since it's really only meant for 2S batteries.

And some pretty pictures:

An event report will follow.  If only its destructive abilities matched its good looks...

July 12, 2013

The Rebirth of the All-Terrain Scooter

The all-terrain electric scooter has lived a sad and broken life.  A combination of design flaws and user stupidity have caused it to burn through more CIM's than I would like to share, and since the Great Blizzard Snow Storm of this year, the scooter has been folded up in a corner with all three motors in some state of broken.

The basic problem with the scooter was that I wanted both more torque and a higher top speed than 3 CIM's were really capable of producing.  Combined with a motor controller that would happily feed the motors over 100 amps until the battery went flat meant that the motors got really toasty, especially at low speeds or on any sort of hill.

I came up with two basic plans of attack for reviving the scooter carcass:
  1. Rewind the original shorted 80-100 motor from the tricycle for operation at 60 volts, and buy the most powerful Kelly KBS motor controller.
  2. Find some giant DC motor(s) to swap in for the CIMs.  Preferably one or more short magmotor.
Since I did not want the 72V 200A peak brushed controller on the scooter to go to waste, the second option was more appealing.  I checked ebay for magmotors on a regular basis for a few weeks, but found nothing for sale below ~$225 per motor.  Eventually I tried lowballing the seller, and somehow came away with 2 Magmotor S28-200's for 27% of the original asking price.

While waiting for the new motors to arrive, I stripped down the scooter.  I found lots of things that were either beginning to break or were simply too painful to look at to continue using.  The fork fit both these descriptions, as the its aluminum plates were beginning to bend, and it was a real hack job in the first place.  The plate that held the idler sprocket on the high-tension side of the chain was warped from the torque of the motors.  When I got down to the bare frame, I found that the aluminum extrusion the original kick scooter frame was actually slightly bent where the suspension attached.    So, rather than sinking time (and fancy new motors) into a scooter frame that would probably break repeatedly, I plan on rebuilding the scooter pretty much from the ground up.

I will be using the same electronics plus the two new magmotors.  Some of the original gears and sprockets will be used, as will the hubs of the original wheels the original head tube and folding mechanism and handlebars.

In the spirit of the original scooter (and because I'm lazy and don't want this to take all summer) I am not really designing much before hand.  I am certainly not CADing out the entire thing, although I am fairly carefully planning things that require some degree of precision (like the gearbox).  So, when I'm done, this should be an interesting comparison of what I can whip up with a hacksaw and drill and what I can whip up with a mill, lathe, semi-infinite aluminum, and a year of hanging around MITERS.  

Enough text, and more pictures.
Some large aluminum U-channel makes a frame that is much easier to attach things to than the old weird extrusion shape was.  Also, since it's open underneath, the battery pack will be able to fit in a single-pack-thick arrangement, giving another inch and a half of clearance.  The controller also fits in nicely.

I beheaded the old scooter for it's head tube and folding mechanism, and bolted that assembly onto the U-channel with a gratuitous number of 1/4-20 bolts:

There happened to be a pair of whees at MITERS that used the same size hub as my original wheels, but the tires were 14" in diameter rather than 12.5", and had rounded rather than flat tread.  I swapped one of the new tires onto the old back wheel hub, and just used the entire new front wheel.  here's a comparison of the old vs new wheels:

Because the original for was terrible, and also not suited for a slightly larger wheel, I built a completely new one.  The fork crown came from some old moped/motorcycle contraption.  For no reason other than that I think they look cool, I made it a single swing arm fork - the wheel is only supported on one side, not both. Like the Cannondale Lefty forks, but with a leading link suspension design, rather than a telescoping tube.

The fork is supported by this massive chunk of 2" square aluminum stock, turned to round and clamped into the fork crowns:

The wheel is held by this steel axle.  One end is threaded, for a bolt to axially retain the wheel.

And here's the (mostly) finished fork.  The spring/damper was also an old moped part.  The swingarm itself was machined from some more 2" square stock.

The axle is clamped to the swingarm.

With a wheel attached.  The combination of slightly larger wheels than before as well as a spread out battery pack will give this something like a foot of clearance.

Don't miss the next episode, in which I turn an aluminum brick into a dual-Mag-gearbox!