My activities this term

Dear readers,

You may have noticed that the Electric Longboard project pace has slowed down significantly since the summer. This is due to the following activities:

1. Fall term Classes. I'm taking the Aero/Astro Core class(es) called Unified, which is basically one GIANT 48 unit bootcamp course covering thermo, fluids, structures, and signals/systems. This is in addition to other classes, including an advanced composites course (16.202) and German 2.

2. Research. I'm starting a UROP (undergraduate research opportunities program) in the Space Propulsion Lab. I'm working with a senior on a new kind of L.E.O. ion thruster. VERY cool.

3. Rocket Team. The MIT Rocket Team is doing NASA's University Student Launch Initiative (USLI) this year.

4. Design/Build/Fly. I'm doing DBF again. This is always a huge time commitment. Last year, while it only counted as a 6 unit UROP, I spent probably 18 units worth of time or more on it.


5. House Manager for my fraternity. Takes LOTs of time and effort.

Yeah....I'm busy. So I'll fit the ELB in when I can.

9/20/10 Update

ELB: The motors are in the process of getting internal Hall effect sensors. The method seems to be working well, so I plan on doing it to all of them, reassembling temporarily with the semi-busted polycarbonate hubcaps, testing/calibrating, then replacing the hubcaps with aluminum ones. The aluminum stock is in, so I should be able to start machining those soon.

eXKateCD: It is now the eXKateDB (exkate drill batteries). Let me explain. Someone (no idea who) came into the lab, saw it under the desk, probably tried to play with it, and left the Lipos plugged in. This drained the ENTIRE pack down to about 1V...yeah, Lipos don't like that; they're dead.

Wall of Shame.

So while we wait for $160 worth of new batteries to come, I rigged this up:

 2 18V drill batteries in series. Not pretty, but no noticeable power loss, which is nice. Plus, we don't have to worry about these being drained all the way down (NiCD's actually like that). Our plan to prevent this from happening again is to have a keyed battery selector and hiding the key. I never wanted to have to do the 4 hours worth of soldering, etc. that it took to put the original Lipos in again, so I definitely don't want to have to do it a third time.


That's all for now.

9/5/10 Motor Update

Good news: I took the sensor board out and tested it with a small magnet. The sensors were fine, they just weren't close enough to the magnets/coils. So I'm going to stick them in the slots of the stator and get rid of the sensor board. Even though they won't have the same angular separation as on the board, it will be a combination of slots that works, such as A(sensor)aAB(sensor)bBC(sensor)cCAaABbBCcC. I'm pretty sure I did a previous post on calculating hall effect sensor positions, or it's in my design review for this project, so look that up if you want to know where to place hall effect sensors. Anyways, this means that the sensor board cannot be adjusted, which is nice to have if you want to mess with timing. Oh well.

picture added 8/20/11

picture added 8/20/11

Bad news: Chips of the polycarbonate hub caps/spacers fell out. However, it wasn't the total disintegration I thought it would be. In fact, it's salvageable, so I may just put them back together the way they were. (I'll at least do one to test the sensors in the slots idea.) On the other hand, sidewalk cracks and other bumps might finish the disintegration process, which would be really bad while riding.

Another option is to make new hubcaps/spacers out of aluminum, but it wouldn't be see-through anymore. :(
I could waterjet new polycarb spacers and hubcaps, but I really don't want to deal with that again. Especially because it'll be impossible to get rid of every little molecule of loctite.

Another option is to shove the rotor into an aluminum pipe and make aluminum hub caps for the pipe, eliminating the spacers. Something like this:

I got this idea from Charles if you can't tell.

Cool. The cylinder in the background is the tire.

The holes are filled with glued or pressed-in polycarbonate disks. I really like the way this looks, and I think it'll be much stronger than the current design (though the current design is plenty strong...). The larger diameter will give a slightly higher topspeed. One draw back with this is that the outer edge of the hub cap is now an important surface and has to be a very close fit for weather-proofing. In fact, the hubcap-outer tube interfaces would probably have to be sealed with silicon. Drilling radial holes is no easy task, and getting it apart would also be a pain.

Here's a combination of the above two options:

 Aluminum hubcaps with polycarbonate inserts in the outer-side one. Keeps the current bolt pattern. Scraps the useless o-ring seal (explained in an earlier post). This allows partial see-through without the draw backs of polycarbonate (can't loctite, not as stiff).

I'm leaning towards the last one.

Sigh...

Bad news. A bunch of my sensors aren't functioning. This means I'll have to break the motors open and either a. fix broken wire connections, b. reposition the sensors, or c. both.

That doesn't seem that bad, except the polycarbonate hubcaps have spiderweb cracks from the loctite and parts of them might disintegrate...which would be very bad. It would pretty much mean a redesign of the motor casings.

Since I don't really have time for the next few weeks to work on it directly, I've started designing custom LED lights for it.

That's all for now

eXKateCD

The build log is this Instructable. Feel free to ask questions about it in comments here or there.




Other projects included:

• Overhaulin' this custom built Segway
• Making a Quadrotor from scratch (an instructable should be up soon, so please don't ask me about it)
• Pong from scratch (and by scratch, I mean wires, LED's, and microcontrollers. I didn't work on it, so again, please don't ask me about it)

Here are some pics of those projects and of the Edgerton Center Summer 2010 Engineering and Design Class in general:

Parts of the quadcopter

Believe it or not, the quadcopter actually flew.

Pong from scratch. Tilting the controllers causes the paddle to move.

The old segway.

Clear deck

Oh yeah, LED's

The eXKateCD team

Class photo

Shane's summary is here.

Done for the Summer

Here are all the polycarb parts laid out in order (insert rotor in middle):

The waterjet didn't cut as cleanly as the lathe (duh), thus the cloudy white appearance. You can also sorta see in the 3/8" (left) spacer how nasty the small thru-holes are. I undersized all the holes in my waterjet drawing because I knew it couldn't cut them perfectly and I was planning on drilling them out later. Instead of cutting nice straight holes, though, it kinda just bubbled up inside and threw up some plastic out the otherside. Next time I need small holes cut in a piece I'm waterjetting I'll do the holes on a mill.

Anyways, here are all the polycarb parts stacked up. The waterjetted ones need to be drilled and cleaned up a bit, but that wasn't too bad.

Next came skid plate work. I cut the basic size with a band saw, used a leveling surface and gauge to score lines parallel to the factory edges at the length/width I wanted, and then used a belt sander to even it all out. Then I marked all the screw hole locations.

Next came drilling. I used a drill press because I was too lazy to set up a mill. I ended up off by a tiny bit on a few of them, so I just took an endmill and routed out the holes a little in the right direction. Then I countersunk the holes.

Countersinking

Fully assembled battery box. The extra skidplate lip was intentional.

It turns out I was a little off (max. 3/16") on the curves in the CAD drawing I used for cutting out the sides:

Oh well, that can easily be filled with Blue RTV.

The next things that needed to be done were gluing/wiring the hall effect sensor boards:

Win for polycarbonate.

I used epoxy to glue down the hall effect sensors, so I scored the surface. You can also see where I scratched in the 12 degree angles for spacing.

4 motors, 4 boards.

Since each sensor had a power, ground, and phase pin, I could wire all the powers and grounds together and only have 5 wires to deal with. I did this by first bending the pins as in the picture below, and cutting to short pieces of solid copper wire:

Then I soldered all the power pins to the bar:

And all the ground pins to the next bar:

Then I just soldered on the wires:

See the Blue RTV (aka. smurf blood) in my nails?

All 4 wired. The old first one is above.

Next came inserting all the stators into the rotors:

Then putting on the bearings and hall boards.

Cool reflection of the coils in the bearing.

I needed to glue the 1/16" in-board hubcap bearing retainer plates to the inner-board hubcaps. I though that super glue would work...

Well, it worked. But it turned cloudy and purplish when it dried. Oh well, at least I got them on there.

The next thing I made were the o-ring seals. I cut some 1/16" o-ring cord stock to length and superglued the ends together in the groove. Then greased them. This worked great. Unfortunately, I'm not really sure how useful they'll be. A strip of urethane tire will be glued to the outer surface of the motor, sealing the interface between the hubcaps and spacers. If water gets under the tire, sure it won't get into the motor between the hubcaps and spacers, but the interface between the rotors and spacers won't have a seal...so it looks like the o-rings were kinda extraneous (they look cool though):

O-rings

 
Time to start assembling:

1st big problem: It turns out that the "1/2" inch sheet of polycarbonate I bought (and made the rear hubcaps out of) was closer to 7/16". This meant that the 1/2" wide in-board bearing had to stick out past the plane of the motor...which was now blocked by the superglued bearing retainer plates. Whoops...guess I shouldn't assume the thicknesses of my materials. grrr.... This meant I had to pry/chisel/sand/cut the stupid plates off:

Now they look even uglier.

Resistance is useless!

Back to assembling:

Do you see the 2nd big problem? It has to do with that double hole I painstakingly drilled because I broke off a tap in the original hole in the rotor. See the dark smudge in the left (second) hole? Yeah...I broke the screw off in it. WTF. That's irony if I've ever seen it. It's ok though; 4 screws should be fine.

Ok, how about the 3rd big problem? It's visible in the pic above, but I'll give you a hint with the next pic:

Polycarbonate and Loctite do NOT mix. I knew that loctite and acrylic didn't mix, but I had no idea about polycarb. I noticed these spiderweb cracks when I was halfway through the assembling the third motor. Better late than never, I guess... Yet another advantage to Charles' metal can methods. Any future hub motors I build will likely be some variation on his style. The motors should still be strong enough with the cracks because the screws are mostly providing compression, while the steel pins do most of the work.

Guess what's wrong now...

At this point, the 4th big problem popped up. 2 of the motors had full shorts. Ahhhhhhh. I checked them all before I assembled them! Dis-assembly and inspection revealed the same problem in the same place in both. Epoxy on a sharp edge had chipped away underneath a wire causing the wire short to the stator. Luckily it was in an accessible place. I cut the wires, slid some heat shrink on, and re-soldered. It only took 3 hours...
I really really dislike these stators now. Aside from taking 4-5 months for them to come, the epoxy coating really sucks. Using fiberglass insulating end plates (like on the BWD scooter) would have prevented the problem, and I'll likely use that method with any future motors I build.

Next, I did some work on the MC and soldered the sensor connectors on:

Then Shane and I  (mostly Shane) tried to match the motors to the controllers (takes a lot of trial and error with phase and sensor combinations). In comes big problem 5: Turns out one of the sensor wires in the first motor we tested has a bad connection...crap. I get to take it apart again...

Next came mounting the battery box to the deck. This required drilling 14 clearance holes for #10 screws in precise locations...on a curved deck. Yeah, I ended up drilling 1/4" holes as close to the right locations as I could get. It turned out well:

Drilled and countersunk.

I decided that securing the sideplates directly to the deck with screws was unnecessary. I figured the screws in the endplates would be plenty.

Screwed on.

Skid plate removed for electrical component locating.

And that's it for the summer. I got as far as I could, but I will have to continue in the fall.
Lessons learned:
1. Don't do small holes with a waterjet.
2. Measure all material...don't assume thicknesses.
3. Don't use superglue on polycarbonate if you want to see through it.
4. Loctite doesn't mix with polycarb or acrylic.
5. Use fiberglass endplates for stators when winding. Epoxy sucks.

Stuff left to do:
1. Figure out battery box wiring/component locations.
2. Mount/wire components in battery box.
3. Drill holes in battery box for various wires.
4. Fix motor sensor(s).
5. Finish motor testing.
6. Cut/Glue tires.
7. Replace truck bushings.
8. Seal/waterproof everything (with smurf blood).
9. Loctite
10. Lights.
(11. Lighter battery box?)

In the meantime, I will be writing an Instructable for the ExcateCD (a modified Excate longboard that actually works...as opposed to the stock Excates that really don't work). It was one of the projects of the Summer 2010 Edgerton Engineering and Design Class (video)....yes, I have been working on TWO electric longboards for the past month. I'll also likely write up a few things here about the class. I didn't so much under-estimate the amount of time it would take me to finish my longboard, as underestimate how much time being a teacher of the class would take.

Now I'll leave you with a couple pictures of Shane destroying/performing surgery on/obliterating a MOSFET with a sawzall: