Search This Blog

Saturday, July 23, 2011

T-minus 4 weeks

I can't believe the summer is 2/3 over. Between working at Aurora, this longboard, designing the next longboard, rocket team, house managing (work week is in 4 weeks O.o ) , designing a laser light show, planning classes, etc... I've been insanely busy with projects. It almost feels like school, minus the little voice in the back of my yelling at me to start my psets.

Anyways, progress report.
All controllers working: check.
All motors working: check.
All essential electronics in box: check.

That means it's time to glue tires! Last time I mentioned a suggestion I got about how to fix my shearing problem when wrapping the tires around the rims. Well...

It works! I tried various ways to clamp the angle, but eventually gave up; the glue is too slick for clamping. However, it was plenty strong for butt-joints, even unclamped. Thus, I hammered in the rest of the motors' steel alignment pins, tightened the screws down, wiped off the motors with rubbing alcohol, and starting gluing on tires.

Steps for gluing on polyurethane sheets/strips to round objects:
1. Acquire a couple packages of 3M Scotch-Weld Urethane Adhesive DB-640.
2. Acquire some plungers from used tubes of epoxy (the cheap double plunger kind). This prevents you from having to buy 3M's overpriced cartridge gun.
3. Acquire a bunch of hose clamps/ low profile zip ties (low profile because they're easier to pull on).
4. Tools: An electric driver or screwdriver, a point-ish glue application device (sharpened stick), rubbing alcohol, paper towels, disposable GLOVES (you'll see why this in caps in a second), something to mix the 2-part glue in.
5. I'm assuming you already have the shape of polyurethane you need cut (bandsaws and hacksaws work well for harder urethanes). Test wrap around part to make sure it'll fit.
6. Wipe off the part with alcohol.
7. Mix up some glue and spread a thin film over the part. Don't use a thick film or it will squeeze out all over the place when you tighten the hose clamps.
8. Spread some glue on the joint ends
9. Carefully wrap the urethane around part and hold with one hand while slipping hose clamps on/over it one by one with the other hand.
10. Grab driver and tighten hose clamps until they're sorta snug (not all the way).
11. Your urethane has probably moved around by now, so reposition it.
12. Continue successively tightening hose clamps until they're all tight.
13. Wipe up excess glue with paper towels/alcohol.
14. Wait 24 hours for it to cure.

This glue is INCREDIBLY messy. Like, 10x worse than the messiest epoxy I've every used, so wear gloves. I didn't wear gloves and got it all over my hands. Alcohol seemed to get some of it off, but not all. It's a really weird feeling: it seems to have increased my hands' coefficient of static friction, without affecting the coefficient of sliding friction, and without being sticky to the touch. Very odd sensation...

The mess. The other side was even worse.

Mostly clean.

I only did one wheel today as a test. I'll see how it turns out tomorrow evening.

Left to do:
1.  Finish gluing on tires (4 hours)
2. Figure out/make new package for hand controller (3 hours)
3. Re-time and program motor controllers (6 hours)
4. Finish mounting motor controllers (45 minutes)
5. Test drive (1 hour)
6. Install fans (5 hours)
7. Install lights (20 hours) (optional)
8. Waterproofing (4 hours + drying time)

Estimated work time left on project: ~44 hours (including lights). I'd call it 90% done at this point. Wohoo!

Now presenting the ELB-Heavy
ELB-Heavy will be an electric longboard powered by four custom 500W brushless sensored electric hubmotors and controllers. These new motors will incorporate all of the lessons I've learned so far to make a much lighter, faster, and more robust electric propulsion system.

You can see the coils through the polycarbonate if you zoom in.

 One of the goals of this board is to make the motors much more covert. I believe this hub motor design does that nicely. It even uses half the stock hub.

Things to note: red fiberglass stator protector (like BWD), stock outer-side hubcap, wheel restrained by stock nut, stock axle, stock bolt holes, rotor laminations.
Things to note: hole for valve-stem, massive 1" inner-side bearing, through-hub holes for wire routing, odd bolt patterns (actually a 7 hole pattern for steel alignment pins that stop at the seal disk, and the stock hub's 4 bolt pattern).
The polycarbonate seal disk has its own thin bearing. The axle really does step like looks like they take 1/2" steel stock and turn it down to 12mm for 36mm of the axle.

The donor board is a brand new Ground Industries (which might unfortunately being going out of business, if rumors prove true) "Patrol" that I got off of ebay for a steal ($140 shipped). I replaced the off-road tires with some MBS street tires. I'm using the board to ride around Cambridge/MIT while I finish ELB. Speaking of this board...I have a set of brand new GI foot bindings and like-new Bionic Trucks (with sets of T4 and T1 cubes) that I'd like to sell if anyone is interested.

Sorry for all the fuzzy cell phone shots. I still haven't gotten in the habit of carrying around my camera with me.

Motor Specifications
Power: 500W
Operating current: 18A
Poles: 14
Slots: 12
Phases: 3
Windings/phase: 84
Winding style: AacCBbaACcbB (dLRK)
Stator: 0.75in x 70mm, 0.2mm M19 silicon steel laminations (by Scorpion)
Rotor: Three 0.25in laminations of  waterjetted low-carbon steel
Magnets: 28 3/4x1/4x1/8" N40 NdFeB bar magnets
Air-gap: 0.9-ish mm
O.D. : 92.1mm
Width: 54mm
Estimated torque (FEMM): ~3.15 Nm.

Other Specs
Controllers: ??
Battery: 8S LiPo (or possibly 9S LiFePo4)
Estimate top speed: 30mph
Tires: Pneumatic 200x50

FEMM simulation. Lots of saturation...oh well.

So, if you've been following ELB from the beginning, then you may have noticed that these motors produce the same amount of torque (in FEMM) as the ELB's motors (ELB was at 3.1Nm in FEMM and ~2.9Nm in real life). Here is my reasoning for this: ELB ended up with twice the amount of  torque I'd ever really need at 10A, and I'm doubling the current for these motors. However, I'm also doubling radius and halving the stator width. Therefore, 2 x 2 x 1/2 x 1/2 = 1 . It's very hand wavey, but I think it should get me reasonable torque numbers. Worse comes to worse, I can always drive them at more current (18A is pretty low as far as PEV's go).

I haven't picked a motor controller yet. Hey shane...want a test bed for your new sensorless controllers? haha

I decided to go with bar magnets this time (instead of custom arc magnets) because of the sky-rocketing price of neodymium. There will be 2 magnets per pole as a first order simulation of an arc (an angle).

I guess one question to ask is, why make a "Heavy" version? The basic answer is that Cambridge streets are awful...and having pneumatic tires is amazing because of that. And Cambridge streets get 3x worse in the winter (which is half the year), so an electric board that can have off-road tires, drive through slush, and you can pick up and take to class is a nice thing to have. Ironically, this one will likely be lighter than the original ELB...

I don't think I'll be able to get started on it this summer, but we'll see.

No comments:

Post a Comment