Breaking and Fixing the Mars BLDC Brushless Motor

Here’s the short version: Because we are cheap, my friend picked up a Mars “Brushless Etek” BLDC motor from Ebay user “megadan” who has been selling these motors for about half price, with the catch that they are shipped with an odd and difficult to deal with shaft adapter (I’m starting to get used to this reality of cheap and surplus motors)

The first plan we had for removing the shaft sleeve adapter was to cut the end off then hold it in a vise and use a pin to beat the motor shaft out from inside it.

Cutting the end of the adapter was uneventful, so we found a pin and started hammering on the shaft. Seeing no movement we beat on the shaft pretty good. Then I noticed the motor had bound up and wouldn’t spin anymore.

Turned out the hammering caused two magnets to come unattached from the rotor plate. You can see the left magnet in the photo protrudes further from the rotor than the right magnet, it has stuck solidly against the stator. Still no movement in the shaft adapter.

The next day I figured out a better plan for removing the shaft adapter- I used a dremel cutting disc to cut a slot in the sleeve right above the keyway, using the keyway as a relief to cut through the sleeve without cutting into the shaft. The adapter sleeve was held on the shaft purely through friction, no internal keyway. Given the tightness of the fit I would guess it was an interference fit assembled with thermal expansion. After slitting the sleeve I ground out the motor-side of the sleeve in the corner that the dremel cutting disc was unable to reach. I pounded a screwdriver into the slot and the sleeve slid right off. With careful grinding and cutting I managed on only nick the motor case and shaft.

So now, an adapter-less but seized motor. Time to disassemble. But how? There’s just one screw on the outside of the motor that holds it together. Other than that it is held together by the axial magnetic force of the rotor -> stator and the friction fit of the shaft through the rear bearing. There are three metric (M5?) tapped holes in the rear case that can be used to attach some sort of puller rig.

This can only end badly

I bolted the front case to the welding layout table (conveniently spaced holes) and whipped together a plate to bolt to the puller-holes out of some scrap. A 2×4, bottle jack and some bolts and nuts complete the picture. And yes, this is surely a Miller-recommended usage of the Dynasty welder cart.

Spoiler: it ends up working— Read the rest of this post »

Posted on June 16, 2010 at 12:45 am by Henry · Permalink · 2 Comments
In: Electric Alt-Kart, Little Fixes

The Most Advanced Scotch Tape Dispenser. In The World.

It’s absolute overkill. Over a pound of 6061 aluminum, every part CNC machined and yes, it’s just a scotch tape dispenser. This is the creation of the Advanced CNC class at Laney College as taught by Bob Rice. I programmed and machined all the parts from drawings using MasterCAM, a Chevalier toolroom mill and a Haas SL lathe. All the threads were single-point cut and threaded holes rigid tapped. Every part required at least two operations, every face is machined.

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Posted on June 3, 2010 at 11:09 am by Henry · Permalink · 41 Comments
In: Machining, Photo Journo

Full Speed Ahead

I’m really looking forward to driving this one. Of course it will be electric. Yes, a steering wheel is on the shopping list.

Posted on June 2, 2010 at 9:59 pm by Henry · Permalink · 3 Comments
In: Electric Alt-Kart

One Step Closer: New DC/DC

In the seemingly never-ending parade of not-quite dialed in and failed components preventing the EV Miata from being able to be a car instead of a project the latest issue arose with the DC/DC converter. After spending a couple days working on the stupid battery balancing system, thinking it had a better chance of being finished than ever before, I went to go take the car for a drive. You can instantly tell if the DC/DC is online or not with the sound of the vacuum pump, if the DC/DC is running the pump runs much faster than if it’s not. It wasn’t. I scoped the connections out and realized that the DC SSR that was supposed to switch power to the DC/DC had failed closed and that the fuse was blown. I tried a spare fuse, which instantly blew. Then I tried a spare 25A fuse up from 12, which also blew instantly. Yuss- $20 of fuses blown in 5 minutes.

I was using a IOTA DLS55 as a DC/DC converter- so I tried plugging it into AC power- no circuit breaker popping, and 13.8v output. What the fuck. Not really wanting to try to troubleshoot the cause of the problem, and leery of the general suitability of the IOTA to vehicular DC/DC duty anyways I decided to replace it.

After shopping around I decided that the isolated 675W DC/DC from Belktronics was the best replacement, features and cost wise. I really wanted a 12v enable input so that I could skip worrying about switching the HV input, given the patterns of long periods of disuse this car gets I like to be able to disconnect all loads from the battery. Several chinese DC/DCs have come on the market lately with similar pricing to the Belktronics, some with enable inputs as well. The “product support” line at Cloud electric was unable to confirm if the enable input was on the 12v side, as a HV side enable input would be much less useful.

After confirming it would do what I want over Email, I ordered the Belktronics converter with remote enable and soft start options. I consider the fact that you can actually get in touch with the guy who designed and builds the Belktronics converter a selling point over the Chinese one, I have a feeling if it broke you would be pretty much without recourse, particularly considering the generally under-capitalized support-averse nature of EV part dealers.

A month later the DC/DC was built and shipped. I installed it and it appears to work exactly as I would expect and hope. It’s a bit smaller than the IOTA but similar weight. It’s in a sealed box, should fare better under the hood than the IOTA. I’m not a huge fan of the recessed faston terminals but I think they well do the job just fine.

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Posted on June 1, 2010 at 1:18 pm by Henry · Permalink · One Comment
In: EV Miata

More Faux-Regen: Because I Just Had To Push It

Last time I faux-regen’d on the bike I hit -4.9A, or about 120w. Today, with a bigger hill…

That’s fifteen amps back into the battery. At least 350w. But how?

Yeah, 35mph is how. I could feel a slight drag on the bike when I opened the throttle, less drag with it closed. As I expected.

And yeah, that’s faster than I’ve ever been on the bike, or any bike. I couldn’t hardly see from the tears getting blown around in my eyes. The force of wind against my chest was pretty impressive. I think I’ll keep it under 30 in the future.

It seems to begin to Faux-regen at about 28mph. 30 gives you about 5A. I should really pick up a real regen controller 🙂

Posted on May 21, 2010 at 10:21 am by Henry · Permalink · One Comment
In: Electric Poly-V Bike

TTXGP in the USA: Round 1 Infineon Raceway May 16, 2010

I had the privilege of attending the first ever US TTXGP All-electric motorcycle road race on Sunday May 16th at Infineon Raceway. I arrived with uncertain expectations about the nature of the race- I was impressed by the innovation and variation in the bikes and the determination of the teams. Here are the results in place order, with my photographs and technical observations and impressions:

First Place: Zero/Agni

Coming from their victory at the 2009 Isle of Man TTXGP Zero/Agni put up a formidable and balanced showing. The combination of an excellent rider, a good-handling bike with a balance of power, battery capacity and thermal management allowed them a handy victory.

The large rectangular Molicel battery pack is mounted oblique in the frame. With the composite fairing installed the rider appears to rest almost flat on top of it. Molicel supplies batteries for Zero’s production bikes.

Looks like an analog balancing system. I don’t believe I’ve see this system before.

Dual Agni Lynch motors coupled directly with a steel shaft with sprocket. Adequate power, good cooling from outboard mounting and ram-air scoops taken from the production bike.

The Zero/Agni team ran a very clean and uneventful race. Their bike clearly balances proven reliability and performance.

Read on for the rest of the competitors- Read the rest of this post »

Posted on May 18, 2010 at 11:32 pm by Henry · Permalink · One Comment
In: Photo Journo, Racing

How It Came To Be- The Big-Ass Billet Pulley

Once I decided to run a single stage poly-v belt reduction on the e-bike instead of a two-stage timing belt/chain reduction on the advice of Bob Schneeveis I set about figuring out how I was going to come by a foot diameter rear pulley for the bike, preferably a really sweet one, in line with my recent attempts to do things as minimally shittily as possible.

I thought about machining one out of plastic which proved to be practically as expensive or more than solid aluminum, or attaching an octogon of bar stock pieces to the edge of a sheet of aluminum, then turning it to make it round. When I described this plan to my machine shop teacher Louis he looked at me funny and said, “Why not use a single piece of aluminum?”. He then proceeded to find me a spare piece of .800 thick aluminum from the stock pile- “use this!” It started as a piece of an industrial fixture that was donated to the department and had previously been face cut and drilled in a few places- I trimmed and layed out around those spots.

So I pulled out the biggest rotary table I could find and started the longest week I have yet spent in the machine shop-

After fixturing, cutting the outside edge, inside bore and bolt circle. The large holes are to be used to plunge the end mill through.

Many many more pictures after the break– Read the rest of this post »

Posted on May 9, 2010 at 8:09 pm by Henry · Permalink · 4 Comments
In: Electric Poly-V Bike, Machining, Photo Journo

Finding the E-Bike’s limits

A common question asked in these parts when I am describing the power and speed capabilities of the electric bike is “Well, can it scale Marin?”. Marin is an extremely steep street, notoriously and constantly steep- it goes from bottom to the top of the same hill I climbed last time, just in less than half the distance. I usually replied that I thought probably not- and now I can confirm- no Marin for this e-bike.

I didn’t actually take it up Marin today, but took it up a similarly challenging street, Centennial Way, on the South side of the UCB campus. Just above the Botanical Gardens the bike suddenly lost power. No connectors had come undone and the Cycle Analyst reported an idle energy usage of 3w, instead of the usual 6w. I figured the controller had either blown up or shut down, a suspicion reinforced by the extremely high temperature of the controller and motor case. The electric motor drive is a direct-drive single speed affair which affords good acceleration and a comfortable 20mph top speed on the flat, as well as good hill-climbing assist up to a limit. Climbing the big hill on the less steep street Spruce I was able to maintain a speed above 13 or 15mph and the motor did fine. On Centennial, with lower speeds and higher torque and current the controller overheated.

I also tried climbing solely on electric power- by this time the motor and controller were already hot and the batteries a bit soft,  unsurprisingly the bike slowed to a stop without pedal assist. It pulled about 650 watts at 22v at stall and was not able to move again without pedaling.

Well, it's sort of regen

I had descended a smaller hill earlier in the ride and taken the bike to higher speed than ever before- I held the throttle wide open and pedaled down the hill, hitting about 30mph. I noticed at the bottom of the hill that the Cycle Analyst had recorded a negative current flow during the decent- the controller is not set up for regen braking, but it continues commutating even when the motor EMF voltage is greater than the battery voltage- so an open throttle, presumably causing a full duty cycle PWM on this dumb controller means current flowing back to the battery. I was hoping to test this a bit better while descending the big hill but the controller didn’t cool enough to re-engage until I was already out of the hills, half-way back home. I would have expected opening the throttle at greater than 30 mph would result in some noticable drag from the motor charging- I was wondering what the “terminal velocity” would be on a steep hill with this sort of pseudo-regen. Maybe it’s just as well that I didn’t get the chance on account of my own safety on this crappy old 75lb bike with shitty brakes.

I spent most of the ride down the hill wondering if the controller would come back online and thinking about how I didn’t really mind an opportunity to justify picking up an controller anyways- it’d be pretty sweet to try out some real regen, or maybe some higher voltage hot-rodding. Now that it’s back working again I’ll have to go back to making up some good reason…

Since the sun has been shining the last couple weeks I’ve been charging the bike on pure solar electricity- when there’s plenty to go around I don’t feel bad burning it up through an inverter and a remarkably inefficient Soneil charger. I hear there are some hobby airplane chargers that will charge a 24v lead pack from a 12v source- that’d be ideal. Of course I’m also thinking seriously about dropping some money on LiFePO4 cells sometime soon. We’ll see 🙂

Posted on May 8, 2010 at 10:47 pm by Henry · Permalink · One Comment
In: Electric Poly-V Bike

An Electric Bike Future? Count Me In

Cars are great, cars are fun- but if you’re looking for ultimate efficiency it’s hard to beat a bicycle. Pedaled or powered a bike will get your butt across town using a tiny fraction of the energy practically any other conveyance would. Meet my latest project:

I’ve been working on the parts for this bike over the last couple months in the machine shop- I’ve changed my mind a couple times about how to put it together, but now that it’s together it’s working as well as I could have possibly expected. Let’s just take a look at the specs:

What does this all mean?

25wh/mile is approximately equivalent to 1500 miles per gallon efficiency.

I just returned from an 11.68 mile ride on the bike in the Berkeley hills. I ascended Spruce to Grizzly Peak then back down Centennial Drive to Oxford, then back to the flats via Monterrey. That’s over 1100 ft. elevation change. I made it up the hill in 15 minutes, averaging almost 15mph, pedaling hard but staying in my middle gear and not working so hard (in my out of shape condition) to really feel beat up. The extra 500-800 watts of assist climbing the hills makes a world of difference. It’s almost magical. Trips that I would normally just hop in the car for due to lazyness or time pressure suddenly become bike trips with the electric assist. Added to the fact that the bike is simply a joy to ride. The motor and belt drive are quiet, the bike feels secure and stable and the bike has enough power to make riding as lively or easy as you want. Having a trouble-free charging setup and ample instrumentation thanks to the Cycle Analyst makes riding stress-free as well.

The energy used during this ride?

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Posted on April 21, 2010 at 5:31 pm by Henry · Permalink · 6 Comments
In: Electric Poly-V Bike, Life and Times

A One Wheeler- the Uni-Pogo

Since this project was developed, built, tested and moved on-from all before I wrote anything about it I’ll tell its story:

I’ve been interested in the idea of super-compact, minimal urban transportation occasionally over the last few months. The idea of a mass transit “connector”, that’ll get you from your house to the train, then to work on the other side. A powered scooter of some sort that is compact enough to go anywhere you can. Instead of locking it outside the store, you just take it in in your shopping cart. Or put it under your desk at work. Because I think that an easy, quick way to get around like that would make transit work for a lot of people- faster than walking, easier and less sweaty than biking.

Of course- it’s got to be small. And that’s the trick. It’s really design something that’s small and light enough to carry around but stable and comfortable cruising at 12 or 15 mph and dealing with the usual bumps you encounter in the paved world. I started by imagining fold-able scooters, working out how a belt driven rear wheel, brakes, steering and battery could all fit and fold into a small briefcase like package. I realized just how complex all these things would be to actually build. And I got a little distracted- if you can make a small two wheeler, how about a one wheeler? And how about instead of the traditional unicycle form factor, make it scooter, or segway, or most aptly pogo stick style, with handlebars. I had great hopes for it- it was like a segway (which is pretty neat, I’ve ridden one) except better in every way. Lighter, smaller, narrower, more portable, less complex, more fun… I thought you could fix the main problem with the segway, its bulk and width by just ditching a wheel. I figured balancing on the thing shouldn’t be too hard, and remembered I had seen various home-built balancing scooters online, so I was confident I could get the balancing softare to work.

Read the rest of this post »

Posted on April 20, 2010 at 12:19 pm by Henry · Permalink · 4 Comments
In: Uni-Pogo, Urban Scooter