March 4, 2013

Tricycle Shenanigans, Pre-CPW Stress Testing

The tricycle has actually been done for a few weeks now.  The two things stopping me from doing a final writeup are that I have still not gotten around to taking nice pictures of it, and until yesterday, I did have any good videos either.  In the acquisition of the video, some parts of the trike were broken, so now the pictures have to wait until everything is fixed and pretty again.  Here is as close to a final picture as I have right now:

Before doing any thorough testing, I remade the stem, which I broke just before TechFair.  The original stem was made from a block of aluminum that was a little bit too small.  I had to use thinner bolts than I would have liked to, and they were the super-shady kind of bolt MITERS probably purchased by clicking "sort by lowest price."  The fit around the handlebars was never ideal, so I had to crank the bolts especially tight to stop the bars from rotating.  I overtightened one of the shady bolts, and sheared it off inside the stem.  I may have been able to remove the left over bolt-stump, but the failure was a good excuse to make a new and better stem.

Here's the back end of the old stem, with embedded bolt:

I made the new one much better looking.  I started out by facing all six sides of a large chunk of aluminum, which used to be part of an even larger billet that found its way to MITERS from the CSAIL stock room.

To make the circular lip that holds down the headset bearings, I clamped the block to an indexing table:

Also using the indexing table, I milled a nice curved face into the front of the stem, à la Amy:

I drilled and countersunk all the holes on the mill, and cut the slots on the bandsaw.  All the corners were rounded on a belt sander, and then finished with some sandpaper by hand.  Also, this time around the headeset cap sits flush with the surface of the stem rather than sticking above everything.

And finally, here is some real footage of the trike in action!

Jaguar and I started out by taking it to the Kresge oval, but the path turned out to be too rough in places to sustain very high speeds.  On the way there from EC, we attempted some 2 person riding, to determine whether it would be possible to trike around with  prefrosh on the back during CPW.  This kind of worked.  The second person rides by standing on the back platform and leaning forward, holding onto the driver's shoulders.  This riding method caused two problems - one per foot.  If the rider's feet are hanging off the back of the platform, and they lean back, their heels put pressure on the things sticking out behind the metal:  The battery cover on the left, and the power switch on the right.  The acrylic battery case snapped into 3 pieces, and the power switch also broke.  I was able to duct-tape the switch together enough to keep it working, but it will need to be replaced.  I will probably remake the battery cover out of carbon fiber, since carbon fiber seems to be my answer to everything right now.  On the way back to EC via the Infinite Basement Corridor, we realized it was two thirty in the morning and no one would know/care if we rode around in the basement tunnels.  Due to their width and slippery floors, the tunnels around Stata are especially good for drifting.  This lead us to what may be the best (well, very early on Sunday mornings, at least) small electric vehicle racing grounds on campus:  the parking lot under the Stata Center.  The concrete surface makes for excellent traction.  It has regular pillars which would make setting up a race course easy, but it also has long straights all the way across its length and width.  There isn't enough space to max out the trike, but we easily got it into the upper 20's (estimate based on which gears we were in) on the straights.

Here it is in its ugly but still functioning state, pre Stata:

The night morning of riding ended when I accidentally pulled loose one of the leads to the hall effect sensor board loose while fiddling with the power switch.  

Some thoughts and observations:

-Some serious prefrosh-proofing would be required to make this a CPW event (e.g. no more acrylic or switches sticking out)
-Swappable battery packs are awesome.
-Even with the current limiting set to around 80% of maximum on the motor side, the controller still sometimes cuts out, especially if you gun the throttle right after shifting.  According to Shane, getting a Kelly with the high speed option would probably eliminate this problem.  To be fair, this is an awfully big motor to be driving with this controller
-MITERS Small EV Rallies in the Stata Garage need to become a thing.  All the pillars and other obstacles would make it pretty easy to set up a temporary racetrack.