Electric Razor: Construction

So I kind of never made a post on the machining and construction of the rest of the scooter (other than the motor), even though it came (chronologically) before the motor testing. Instead of making a bunch of separate posts, I am just going to dump it all here in one post.

The scooter body is made out of a rectangular extrusion, with a hollow that runs down the center. Unfortunately, it is not large enough to accommodate the Li-PO cells that I wanted to use. So the scooter had to have a little reverse-gastric-bypass machining. The extrusion makes for a nice deck, and has all the bolt holes to connect to the folding/steering assembly, so I did not want to loose all of it. But the bottom had to go. Using a 1/2 inch end mill I cut out most of the bottom of the aluminum extrusion that makes up the body/deck.

Machining out the bottom on the mill

The body is made out of some relatively-easy-to-machine aluminum so cutting out the bottom was pretty easy. The deck had to be clamped down by the edges of the deck since that was the only sturdy feature that wasn’t going to get cut away and wouldn’t collapse under the clamping forces. Here is the finished product.

It's SO shiny

The next order of business was to make the underside cover for the battery compartment. It is made from a section of 2″ x 3″ x 1/8″ rectangular aluminum tube with one side cut off to allow it to slip over the edges of the scooter body. The legs of the “U-channel” are about 3/8″ longer than the legs of the body extrusion, thus expanding the under-deck space providing enough room for the battery pack, and associated electronics. I used a slitting saw to cut off the bottom of the rectangular tubing. I could have used an end mill, but I had really been wanting to use the slitting saw for something (justify random tool purchase), and as I found out, they produce really nice surface finishes.


Power feed is awesome

Now I needed a way of joining the deck extrusion with the battery box extension. There was one problems with this, the inside width of the aluminum tube was about .4″ larger than the outside width of the deck extrusion. If one were to simply drill some hols and bolt the 2 together¬† the aluminum would buckle without some sort of support or spacer placed in-between. The solution was to make “shims” that would take up the extra space and allow the bolts to develop sufficient clamping force to hold the 2 together. On the front end, the shims consisted of aluminum bars, milled down, and drilled with through holes to let the bolts pass through. The clamping force came from some auxiliary bolts that go into the backing plate that the folding bracket mounting bolts thread into.

On the back end the spacer comes in the form of the mounting “legs” of the motor support forks. Since the motor was significantly larger than the stock rear wheel, 2 mounting forks had to be fabricated to hold the motor. The plan was to machine them out of aluminum bar, with a long thin “tang” that would be clamped between the battery box and the body extrusion, and a hole to accept the motor support shaft. A slit was cut and a cross hole was drilled and taped to allow the fork to clamp down on the motor shaft and secure it in place. Holes passing through the support forks, the original body extrusion, and the battery box extension allowed bolts to pass through and clamp the whole assembly together.

Some "gang" machining - has nothing to do with organized crime


A REAL use for a slitting saw


The completed motor support forks

After all this machining was done, the scooter was essentially finished… except for one key component; THE CONTROLLER. And so began the saga of brushless aiplane ESC’s. It went something like this:

1. The cheap non-name one from china, which would start the motor, but never got out of start up mode, and so would shut down in a matter of seconds, thinking the motor was stalled.

2. Shane’s Turnigy Sentilon, which started and ran the motor just fine, but was not mine and so could not be installed.

3. The Turnigy Superbrian, which started and ran the motor fine, but would not get out of start up mode when installed on the scooter, due to the higher loads of the scooter+human it was pushing.

4. Finally, a shipment of Turnigy Sentilon’s arrived at HobbyKing, now I can buy one for myself.

Here you can see the general wiring schema, shown here with the HK way-to-smart-for-its-own-good superbrain.

So about a week later, the Sentilon arrived, and I lashed the electrical system back together,  for a test run. After about an hour of troubleshooting the servo tester, I was able to get in a few test runs. They were spotty at best, with crappy acceleration, difficulty starting, as well as being super-bumpy due to the seam on the glued on rubber strip that was acting as a tire. A loose signal cable, as well as spotty performance from the servo tester ended testing for the night. A few days latter with a new servo tester and well connected signal cables, I went out on another test run, only to discover the motor had develoed several shorts and that 2 of the magnets had come un-glued and where dragging on the stator, so the motor was taken out of commission for repairs.

I am coming to understand the limitations of sensorless control, and am starting to seriously consider switching to sensored control, most likely utilizing a custom built controller, centered around the UCC3626, an integrated, sensored, brushless motor controller chip, which handles hall sensor commutation, over current protection, start-up sequencing, etc.

With that I will leave you with a few images.


Well, that’s it for now, more on motors, controllers, and various electric stuff later.