It’s getting EVEN CLOSER! Holy crap, it might actually MOVE soon! I took the opportunity of a convenient gap in the schedule to get some more work done. The motor and drive (okay, so it’s one unit) is mounted, and pretty much now the only thing missing is electronics. And the battery bay – because despite my best machining abilities, things still take a while.
The motor mounting & structural & electronics bay mounting rails. These are waterjet-cut out of a sheet of 2024 aluminum. In fact, it’s the same sheet I had TB4.5SP1‘s wedges made from.
There are either 2 or 6 mounting points for the assembly, depending on how ambitious I feel. The quarter inch hole in the center of each beam clear 1/4″ screws to mount the motor between two of them (I cut four, in case I somehow fuck up twice). The 3/16″ slot at the front of each beam latch under the bolt which holds the brake fender in place. Overall, the assembly should only need those two (four) mounts, but I also have 4-40-tappable holes in a rectangular arrangement if I feel the need.
The small chunks are the mounting ears I designed for the supplemental battery pack.
Additionally, I GIANT LAZER’d some acrylic endcaps for the supplemental battery pack.
WHAT? CHARLES USE ACRYLIC?! WHAT HAS COLLEGE DONE TO HIM!?
Well, it’s not a particularly structural application, and plus the Media Lab laser cutter does not have a proper ventilation system for handling the cyanide gas that burning polycarbonate can produce. Also, the waterjet would have left a nasty draft and clouded the edges.
So why not. It’ll glow better.
Additional machining was require for each frame rail thing. First, the mounting hole had to be counterbored 1/8″ deep at 1/2″ diameter to accomodate the motor. I could have done without this, but extending the motor shaft gave me a critical few more millimeters to run the wires out without squeezing them. Here, on the right side, the counterbore is “extended” outwards away from the wheel. The three motor wires will sit in the hollow until they pass in front of the wheel.
Compare to the left, which only needs the dimple to seat the motor shaft.
Next, each rail had to get a chamfer machined on its outside-facing edges. The interior of the Razor scooter’s chassis extrusion has a radius of about 2mm. I cannot duplicate this precisely, so a messy one-size-fits-all chamfer takes care of it.
Because I had no dovetail orÂ real chamfer cutters, I milled these chamfers with a countersink.
That was exciting.
Next, the back end of the chassis extrusion had to be opened up to ~42mm wide, from the 33mm stock. The width of the motor is 40mm, and I did want some play on each side.
And hey, it’s mounted. I had to shave down the waterjet edge draft on the rails before they fit properly, but that was trivial to do on the mill. The motor slips into place and bolts down with no fuss. Best of all, it’s smooth.
Really smooth. I took the thing for a quick test cruise, unpowered of course, down the hallway. It makes the same obnoxious 3-phase PMDC motor sound, amplified n-fold by the waveguide-shaped chassis.
Here, the brake has been removed along with its retaining bolt, which would normally cross the gap and mate with the latch shape in the frame rails.
While the machines were warm, I turned a new standoff & wheelie bar for the back end. I could have just shaved down the stock one a bit, but I left it back at my dorm room.
It took about as long to find a piece of 1/2″ aluminum, shave it down to 11.5mm, drill and thread both ends, and throw it on there, as it would have for me to go back to campus, dig it up, and return, only to throw it on the lathe anyway.
So here it is, sitting amongst my random stuff pile. I need to design and build the electronics bay (internal) and the supplemental battery pack (external), then wire stuff up. Oh, and order two more 4AH cells from Maxamps.
I did ride it the whole way back (yes, with no brake… who needs ‘em anyway?), and threw some durability tests at it in the form of bunny hopping off sidewalks, wheelieing, skid-stops, and purposefully riding over stone-paved paths and cracks. Nothing has let loose yet.
At this point, I can make a duct tape test rig similar to what I did with Beta 1. Maybe I should do that just so I don’t have to get my hopes up…