The Alien Torch
The alien torch- finally documented! After practically a year, I’ve finally put up the photos/descriptions I was planning for the Alien Torch! What is the alien torch? You may have seen the thumbnail on the homepage recently– Now, for your visual pleasure, check out all the photos here!
This is my first try at the “static project page” which the re-design of the site several months ago was geared towards- let me know what you think!
In: Art and Design, Machining
BAS Alternator- Part 2
The Plot Thickens…
I worked on the alternator again this morning, I decided it was time to remove the pulley and get the case open, one way or another. I beat on the pulley with a hammer some more, put some penetrating oil on it, pried at it, and just as I was about to fire up the angle grinder to destructively remove it I decided I’d give it a few more concerted whacks with the hammer, just since I was going to destroy it anyways… and pop! the tapered bushing flew out and the pulley was free.
First impression: This is not like any other alternator I’ve seen before…
Let’s see what’s going on here.
Stator looks pretty normal, looks like it’s wound with the same wire in the same method as a regular alternator.
The rotor, on the other hand… first off it’s got eight pole pairs, as opposed to the usual six. Secondly… what’s that in between the claw teeth?
Little ferrite bar magnets, in fact!!
Now, a couple comparison photos, comparing a standard GM parts bin ’90s Delco Remy alternator (I believe it was used on a northstar cadillac) to the BAS alternator. Stators:
Rotors:
Notable, aside from the different number of pole pairs and the magnets are the lesser gaps between the claw teeth, and the smaller angle of taper- the BAS alternator teeth are closer to rectangular than the the standard teeth are. I don’t know what this all means, but I would hazard a guess that these changes will improve the efficiency of the machine.
Coooool! Now I need to come up with a commutation sensor and controller, and some way to get a sprocket on the shaft. I’m glad I did not have to destroy the original pulley. Given the knowledge that it’s running 8 pole pairs the Austria Microsystems AS5134 won’t work (6 pairs max), maybe the CUI AMT303 is still an option.
In: Electric Vehicles
GM BAS Alternator
A little background: GM has two lines of hybrid vehicles, large full size truck “Two Mode” systems, which are a little bit like a Prius torque-split bred with an automated manual, with a few extra clutches and planetary sets thrown in for good measure, and the decidedly underwhelming “BAS” belt-alternator-starter mild hybrid/start-stop system. The BAS system was found on the “Green Line” Saturn Vue and Aura, as well as on the Chevrolet Malibu Hybrid, starting in 2007. A new higher powered system has been announced for 2012. The Malibu hybrid did not sell well and was soon made available only to fleet sales.
The system uses a motor/generator packaged very similarly to a standard alternator, with a special high-tension 7-rib ribbed V belt drive to the crankshaft. A standard starter motor is used to turn over the engine when cold, once the system is active the a modest amount of regen and assist, as well as start/stop operation is run through the BAS unit. The most reasonable figures I could find for regen/assist capability were 5kw/2kw, respectively. The system runs with a 36V trunk mounted NiMh battery.
I have been hunting for a BAS Alternator for a while to see if it might be suitable for a installation on an EV, most likely a “big bicycle”- in the 100 lb/45mph range. I finally got an opportunity to snag one in my price range- I immediately went about dis-assembling it to try to determine if it is even worth putting on a bike- Spoiler: it’s got some immediately visible plusses and minuses, but I think it’s worth a try.
The BAS Alternator in the flesh. This example is from a 2009 Malibu Hybrid. I purchased it from an auto dismantler.
The rear-cover of the unit.
Phase wire junction box. The phase cables appear to be somewhere in the #2-#6 region. The wiring is very nice, all the connections are pretty robustly weather-sealed.
Position encoder, under the rear cover. I would hazard a guess that it’s a type of resolver or sin/cos style sensor, but I am not sure really.
The rear cover plate comes right off the alternator, carrying the sensor with it.
Revealing… BRUSHES. Dang! I was really hoping this might be a PM machine. Oh well, all is not necessarily lost. The sep-ex rotor is only one of the several factors that generally make alternators non-optimal motors, hopefully some of the other important factors are indeed better on this BAS alternator.
The laminations look really good- nice tall stack of what I guestimated at .3mm thick lams. Lams that thin aren’t cheap and may indicate that some cost and effort was made toward making this alternator more efficient than the average, which has lams more around 1mm thick.
That’s where my dissection finished- most alternators use the nut on the end of the shaft to retain the pulley- the torque on the pulley is always tending to tighten the nut- since the torque on the BAS alternator goes both ways, for regen and assist they clearly needed a more robust method of attaching the pulley- prompting the use of a tapered bushing, which unfortunately has no jacking screw holes or other obvious way to get it apart. I’m a bit stymied about what to do next. I’ve come up with three general options: Use the 7 rib pulley as is, onto a jackshaft for dual reduction, or direct. Hacking it off with a grinder, then figuring out something to replace it with, whether that be another taper bushing or keyed connection. Or, lastly maybe machining the pulley in situ for a flange that I can mount a sprocket on. Unfortunately I wasn’t able to get the case split apart with that pulley on there- so I was not able to get a look at the rotor or stator more clearly.
So that’s where this investigation lies for now. I have an idea in the back of my mind of building a bike to go around this motor and racing it later in October… but that idea’s far from baked yet. I definitely think the BAS unit has some potential worth exploring.
CNC Bike Headlight – Part 3
Thinking about a proper name for this project- “Mega Beaminator”… what do you think?
Yesterday I finished running the 2nd operation on the “nose ring” lens retainer piece- as I mentioned last time I opened up the ID behind the threads just enough to make slight pressure on an o-ring dropped into the thread relief groove on the “light body” part, and added a 20 degree chamfer to ease the compression of that o-ring. Since school has started up at Laney it was top priority to get that part out of the machine, so that the CNC class can setup the machine.
I made it back to Bob’s house a couple weeks previous to finish machining the operation I had set up in his Matsuura, the inside cavity in the “Light body”. That went generally without incident, aside from breaking a 4-40 tap in the very first piece. It was clear why that had happened- inadequate coolant, bad tool-holder, non-optimal type of tap- after switching from a spiral flute tap in a drill chuck to a roll-form tap in a tap-holder the rest of the parts went perfectly without incident.
So now, just two more mill operations on the “light body” piece, then a simple 2 operation part- the LED mounting sub-plate that fits inside the “light body” – I mentioned last time that I was planning a handlebar mounting bracket based on o-rings or zip ties or hose clamps- I’m thinking that would be a good application for trying out 3d printing, either on Laney College’s Dimension printer, or through Shapeways (or both!). That way I can design a really goofy part without any concern for how many fixturing setups and special tools it would require to machine it. And making new design iterations if it doesn’t work at first will be much easier. That’ll be a fun challenge once all the machining is done.
Boosted/Busted
Since I last posted about running the Bike on a 12S LiPo setup (44.4 V Nom.) I did some work on the setup- I sewed up a bag for the four 6s packs with padding, and took it on my work commute last Wednesday. Things went well in the morning- cut my biking time in half- with average speed of 19+ mph, and only 3.6 AH used on the 10AH pack. I avoided flat tires and the extremely unlikely but terrifying scenario of a battery fire on BART.
I charged the pack at work using the Hyperion balance charger and on a 24VDC supply I was able to borrow from work. All was well.
Then, just before leaving work for the BART station- disaster! As a coworker was riding it around the parking lot it began making horrible scraping noises- it was clear that something in the front motor pulley had let go causing the pulley to scrape against the belt guard plate- something that had never happened before. There should be absolutely no movement in that pulley- I decided that I would investigate later- removed the belt and pedaled back to BART. What a disappointment!
On Saturday I finally got a chance to autopsy the motor shaft/shaft adapter situation- after blasting it with a propane torch to loosen the bearing locker I filled it with last time I put it together I was able to pull the shaft adapter apart- surprise!
The motor shaft sheared off right where it necks down to 8mm.- but also down into the cross-drill. I figure the side loading on the long shaft adapter, combined with the slight play inside it, must have caused the shaft to fatigue and break. The fact this happened after doubling the motor power input can’t have hurt either.
I decided to pull the rotor out to investigate how difficult shaft replacement would be.
It looks like the shaft is swedged into the rotor bell- the way that occurs to me to replace it would be boring a hole in the bottom of the rotor, with a bolt circle, then making up a shaft with a flange that fits the bored hole and bolt circle. It’d be nice to upgrade to a standard 1/2″ or 5/8″ shaft, but the bearings are 26 mm OD metric and there’s not really much meat on the bearing pockets to enlarge them. It’s possible to get smaller profile 26mm OD bearings with much larger inner dimensions, I’m not sure really if that’s an acceptable tradeoff- I’ll have to get some advise about that.
So, it comes down a question- is it worth it to rebuild?
In the interest of having a working ebike, and out of curiosity I did a little re-configure on the bike and installed the front-hub 9 Continent direct-drive motor I purchased from ebikes.ca a little while back-
Taking it on the “standard test-ride circuit” revealed some interesting aspects of the performance, useful to compare with the old Hi-Kol/Poly-V drive. Power and torque were quite similar, the cycle analyst recorded peak amperage of 10A lower with the 9C motor. The top no-load speed is about 37mph, wheras it was likely north of 40 with the Hi-Kol, my estimate, since the speed sensor is on the front. In my short testing I believe the efficiency of the 9C motor is better, but not by too much. Of course that depends entirely also on how you use the throttle. The 9C motor is quieter, but still makes a fair amount of noise.
Most notable is the difference in handling. I’m just going to say my initial assesment- heavy direct-drive hub motors suck when used in the front fork of a bike. The unsprung weight is distinctly noticeable and the handling is plagued by “torque steer” like effects. I’m concerned for the dropouts with the copious torque the motor is generating as well. I’d like to set a lower amperage limit, or get a smaller controller on it. I think that’d make it handle less dangerously as well.
If you keep it generally modest and smooth on the throttle it behaves well enough though, and the torquey acceleration is pretty fun, definitely no worse than the old setup, with the suspected increased efficiency as well it’s a pretty good first impression.
I’m still not a real fan of the hub motor- there’s just something wrong seeming to me about putting a heavy motor in the wheel hub, particularly on a suspended bike- but I’ll ride this for a little while as I consider where to go next- I don’t expect it to convince me to invest more in hub motors, but it has already made me reconsider whether the poly-V drive is the best option for efficiency and flexibility.