More EHB stuff

While I really didn't have the time today, I decided to do a little work on EHB.

I finished designing the battery box:

I used SolidWorks' sheet metal tools to design it. It's contoured to fit my deck. I plan on waterjetting it out of 1/16" 6061 aluminum. The battery packs are 4s1p 5000mAh Zippys.

I also did a pretty detailed mass calculation. It comes out to about 35lbs...which is annoying because I was shooting for < 30lbs. The motors are ~13lbs, and the batteries and battery box are ~5lbs. Unfortunately, the four kelly controllers weigh in at ~7lbs. Add in the deck and the trucks, and I get ~32lbs. Grrr...

So at this point, I have 2 options: Keep the current heavy configuration, or give in and make it 2WD (soo not as cool...). 2WD will save me about 9lbs, which brings the total down to ~26lbs.

I guess another option would be to suspend work on EHB and start LiteBoard. Though that would mean my $500+ investment in EHB parts would just be sitting around until LiteBoard is done...

We'll see what happens. Heck knows, at the rate things are going (I'm swamped), neither may get done by the time I graduate.

Update

Well...not much has happened. I've been swamped (work, classes, DBF, etc...).

I got my hands on a pair of Ground Industries Bionic Spring trucks...arguably the best trucks out there (too bad GI seems to be going out of business).

I also bought a bunch of metal stock (for hub motors and battery box). EHB will happen eventually...just not as fast as I'd originally hoped...so no, you can't ride it yet.

EHB updates

I shrunk the innerside bearing in the CAD. I decided that a 1x2x.5 inch bearing is a little lot ridiculous, so I downsized it to a 25x37x7mm bearing (which happens to have about the same load carrying capacity as the 12x28x8 stock bearings). This shrunk the size of the width of the motor by about 4mm, freed up some space around the coils inside, and shaved a few ounces off the estimated weight of the motors, which is hovering right around 1kg each...less than half the weight of ELB's motors (5lbs each!).

Another advantage of shrinking the motor by this much is that it allows me to use MBS Matrix trucks (in addition to the Bionic trucks I currently plan on using). They have the same size axles, except the 1/2" section on the Matrix trucks is 3mm shorter than on the Bionics. If I end up breaking the Bionics, and Ground Industries really does go out of business, then I'll have an alternative. I could also just buy Matrix Wides, which have an axle even longer than the Bionics, but smaller motors are more covert :) . There's actually another difference between the MBS and GI trucks... the GI axles are held to much tighter tolerances than the MBS ones. In fact, much of GI's machining seems to be of higher quality than MBS's. Too bad they seem to be going out of business.

Unlike ELB, I'm trying very hard with EHB to design for flexibility. ELB's motors were designed only to work with the MBS skate-style trucks, only to have polyurethane strip tires (I got lucky and found an alternative), designed never to be opened once they're closed, etc... I'm addressing all of these and other issues with EHB's motors.

Despite the cost, and previous conclusions, I'm leaning towards having the rotors waterjet cut by Big Blue Saw. It'll be about $260 for twelve 1/4" thick rotors, which seems absolutely insane to me. I re-ran the numbers, though, and if I was getting paid for the time I'd spend cutting (along with material and operating costs), it actually about evens out. In other words, waterjetting is expensive unless you have free access to one.

The other large expense will be the motor controllers. I really wish I had time to learn how to design brushless PM motor controllers, but there's no way in heck it'd be cost efficient for me to do so.  I'm thinking 4 Kelly KBS controllers, which is ~ $320 with the water proofing option. OUCH.

As you can probably tell, I did a preliminary cost estimate. The total cost for EHB is looking to be about $1600 (not counting labor of course). That's a shit ton of money. I already have $345 invested in it (stators and board).

I had a realization: 2 motors will be a lot cheaper than 4. Probably not half, because the 2 motors will have to be larger, but at least 30% cheaper...I'll keep that in mind for V3. Of course, with two motors, I lose 4WD, which is necessary for the wintery conditions I hoped to drive ELB in and hope to drive EHB in.

Classes start in a week.

Win!

The ELB successfully ran for the first time yesterday, after a year and a half of work. WOHOO!!!!

Let me apologize in advance for the shitty pictures...still using my cellphone camera.

But back up a day:

I modified the pistol grip AM r/c car controller I bought off of ebay to be more useful for controlling a longboard. In otherwords, I took it to a bandsaw:

Unscrewed.

Random PCB that didn't have anything connected to it...

The control board.

post-bandsaw action

Post dremel action. That bit is amazing for carving plastic. The white shiny stuff on the right is just bad lighting.

It fits perfectly!

Wired up.

I only needed 5 AA's to power the board, so I cut the other 3 off.

I also cut out small delrin plates to cover up all of the holes in the controller, but didn't put them on yet in case we needed access to the transmitter board (which we did).

I needed to finish pressing on the scooter tires next. I used the exact same process as last time.

I made a boo-boo milling this one, and a approximately 20 degree arc ended up too large in diameter. I just pressed a piece of aluminum in the gap after I put the tire on.

It looks awesome.

Re-wired.

After a few hours of shane being awesome and tinkering with software...

IT RUNS!!!!!!!!!!

All four motors spinning.

The thing is a beast. It sounds almost like a jet turbine spinning up. Unfortunately, there is a lot of mechanical friction, especially in one of the wheels (too tight of a press fit on the large bearing), which results in about 300W total at full speed no load. So the mechanical/electrical/magnetic losses are eating about 2/5 hp at full throttle, which sucks.Probably a combination of machining errors, press-fit errors, and really cruddy bearings (VXB's cheapest bearings).

Lessons learned up to this point:

• Scooter wheels make awesome looking tires.
• Mechanical accuracy is essential for efficiency. 
• Shitty bearings are shitty.
• Two motors is probably more efficient despite increased current/windings necessary to maintain torque.
• Find a better way to have charge leads and battery disconnects outside. The current setup is wayy to sketchy. *This is the part that I am totally at a loss on and could use advice.*

Here is a video of it running:
 
Things to listen for: the awesome spin-up, the horrible sounds of the shitty bearings, the slipping of the hubs on the axles (the "cogging") , the battery box rattling like a shopping cart.
Things to watch for: The magnets taped to our feet. The really cruddy turning. You can see attempts to turn; the board is even all the way rolled at points, but you can see that the risers are giving way and the trucks aren't torquing.



We definitely got the breaking right, haha. Thanks to Shane for taking video!

Post run.

You can tell by the wear patterns on the tires that the axles are slightly swept.

Results:

The steering sucks....bad. Like 15 ft turning radius bad, which was really disappointing because I'm so used to the awesome trucks on my current longboard/mountainboard thing. Part of it is the trucks, I think. But the majority of the problem is coming from the giant stack of risers you can see in the above picture. The risers are there for 3 reasons.
1. Vibration/shock absorbtion. Mountainboards usually rely on the deck springyness to absorb shocks, but I bolted a 1/4" aluminum battery box to the bottom, which makes it super stiff.
2. 2 of the risers on each side are angled, which gives me an extra 15ish degrees of truck tilt, which should aid steering.
3. They raise the ground clearance under the battery box enough in order to turn. Without them, the battery box will scrape the ground. And I can't mount larger tires without significant ($ and time) overhaul.

The last reason is the most detrimental...it means that I really need that much riser.  But why are they a bad thing? Well, when I lean out to turn, the deck rolls, causing a torque on the trucks, which causes them to pivot. The rubber (which makes for a very flimsy/flexible mount to the deck), just flexes in the opposite direction, instead of forcing the trucks around into the turn. I totally should have (but didn't) foreseen that.

Another problem came up: Even with the axle set screws as tight as I could make them, the hubs were still slipping around the axles.

There's also a weird control issue. While the transmitter is transmitting a slight breaking command at the neutral point, and 3 of the 4 motors are listening, one of the motors actually accelerates at neutral. We have no idea why. The same motor also oscillates while it's doing this.

It's also blatantly obvious that it's wired too much for torque and not enough for speed.

Possible Solutions:
1. Not care and move on to V2 - HeavyBoard. Leave ELB 90% complete
2. Fix/finish ELB. This involves machining a stiff plastic riser to replace the rubber ones (which might not even fix the turning issue), grinding flat spots in the axles for the set screws to set, fixing the weird control issues (not sure if possible), implementing the field oriented control, adding a fan circulation system, adding lights, waterproofing...probably another 60 hours worth of work for a board that won't be very comfortable to ride.

While it would be nice to finish ELB, after spending thousands of dollars and so many hundreds of hours working on it, it's probably a better move practically to leave it alone and start V2. On this note, I'll part with ELB for $3000 (controllers and battery charger not included) if anyone is interested, haha.

Lessons learned:

• Folded sheet aluminum battery box. Lighter and more flexible.
• Don't use skateboard style trucks on a mountainboard.
• Avoid massive risers if possible.
• Figure out a better hub-to-axle interface.
• Follow all lessons learned from ELB on V2.

Christmas in August

I got some presents (from myself)!

First, a pistol-grip controller:

It's in way to good of shape for what I'm planning on doing to it. I'm planning on gutting it/hacking it apart and using it to replace the Wii Nunchuck controller I put together a few weeks ago. I also got a couple of 2 channel receivers with it...not sure what I'll do with those.

Second, I got the scorpion stators in!

They shipped them DHL Express, which was nice.

They even included fiberglass end plates and coil protector sheets. But how do the stators look?

Pretty good. The laminations are not perfectly aligned, but they're close. The result is a slightly larger maximum diameter of 70.15mm, instead of 70mm. Many of the dimensions were off by about .05mm, which is probably about the accuracy of the stamp tooling.

I believe the wire was installed to keep them from breaking apart during shipment.

Too bad they didn't cut them slightly oversized. I'll have to use the wire protector sheets. The double key slot is a nice feature.

Both 70mm x 50mm stators. I plan on cutting them down to four 70mm x 0.75in .

Not bad for $200 with shipping. 

The next step is to update the CAD files with the exact dimensions, but that'll have to wait until after I finish ELB. Only 2 weeks left O.o .

Money pains

Just checked Big Blue Saw for water jet cutting costs. My rotors will cost almost $17 a piece for regular cutting and over $20/piece for low-taper cutting...and that's without the bolt holes, which add another $6/part (and cutting 24 out of 1/8" makes the prices worse). I'd have to do the bolt holes on the mill anyways, because of the waterjet's taper, so I took those out. At first, I thought this was insanely expensive. Then I realized that if I did my own waterjetting, it would probably take 4 minutes/part, and at $3/minutes, that's $12/part in just cutting costs. Add $5/part in steel, and that's the same price as Big Blue Saw. Wow, waterjetting is expensive.

In contrast, I can turn four 3/4" long rotors out of steel tube for $65 and a few hours. But I won't have the nice magnet notches.

Waterjetting Pros: Very handy little magnet notches that conform to the magnet geometry. No effort on my part.
Waterjetting Cons: $200+ dollars. Over triple the cost of turning rotors. I have to put 12 parts in a mill instead of 4.

Turning Pros: Cheap: $65. I only have to put 4 parts in a mill afterwards (instead of 12).
Turning Cons: I have to spend probably 3-4 hours turning (even if I take time off work to do this, it's still cheaper than waterjetting). No little magnet notches, so add an hour to magnet gluing time.

I'm fairly certain I can glue the magnets in the right place without the notches (I've done it before). And I REALLY don't want to spend $200 on the rotors, when I'm already spending $220 on the stators. I'll sleep on it.

But speaking of stators. The stators I'm getting are from Scorpion Power Systems . They started out by producing lower cost brushless outrunner motors for the R/C aircraft market, but are now expanding to larger motors and wind generators. They're currently developing the "65" (65mm) and "85" series motors. You can purchase the 65mm stators from GoBrushless.com (they are the ones I used in ELB). Apparently they're developing a 70mm and 130mm line, too, or at least the R&D guy I talked to suggested that by letting me purchase a couple stators from them. So far, they are the only source I know of for stators in the famed "70mm-130mm" gap (where copier motors and turnigy motor stators are on one end, and alternators and ceiling fans are on the other end).

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 that...it 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.