Archive for April, 2007

Rained out

Sunday, April 22nd, 2007

There are several disadvantages to having an open-air workplace, but the worst is being at the mercy of the weather. We were already to accomplish big things today, but every hour or so a little sprinkle from the sky would send us scurrying to cover up tools and parts.

So we concentrated on solving a problem which had presented itself — the adaptor plate needed an edge to be milled, or reduced in thickness by about half, for a couple of inches where it would have gotten in the way of the axle. Milling machines are large, costly items, and I didn’t even want to think about what a machine shop minimum charge would be to remove 1 cubic inch of aluminum. So Nick and I ended up at Home Depot in the tool section, rationalizing dubiously that someone else in the world must have needed to mill aluminum inexpensively at home and had created some unique tool to help rescue others from their predicament.

Our search led us to a tool I’ve wanted to own for a long time — the Dremel Moto-tool. It’s a mini-drill that goes 35,000 rpm–kind of like a dentist’s drill for hobbyists–with hundreds of available attachments. One of those attachments is a carbide saw blade which, cutting from two directions, I am planning on using to cut away our extra metal. It just…might…work…


Sunday, April 15th, 2007

Over the past couple weeks I’ve been busy pursuing a detour into Lithium-Ion land, and specifically the company I mentioned earlier, Thunder-Sky. 45 of their skinny book-sized batteries would deliver the same voltage and amp/hours as a big lead-acid back, at about half the weight and 1/3 the size. Zero maintenance, and roughly twice the number of cycles. Though it would have required an expensive charger and BMS (battery management system), altogether costing nearly $10,000, from the perspective of buying a new car I decided this was an investment I could afford.

Anyway, like anything too good to be true, it was too good to be true–Lee Hart, one of the regular posters on the EV Discussion List and inventor of several ingenious battery management devices, emailed me this:

“I bought a set of Thundersky LP90 lithiums. They did not meet specs, the warranty was worthless, and performance was too poor to use in an EV. Beware!”

Though tried-and-true lithiums might have been worth it, this roll-of-the-dice was well over my risk/benefit threshhold. So it was back to Trojan T-1275s (I just saved myself $8,000 — why do I want to throw a party?) I’ve finally come up with a suitable arrangement: there will be 7 in a battery box in the back with an sturdy steel brace to stop almost 12,000 lbs of force in the event of a head-on collision (581 lbs x 20Gs), and the remaining three will end up under the hood…somewhere. In the future, when dependable Li-Ions become affordable, I can swap them out. And I will continue to enjoy Thunder-Sky’s website with the cheesy seagull animation…

Meanwhile, the adaptor plate, adaptor disk, clutch disk with coupler, and “alignment tool” arrived from EVAmerica. These pieces allow you bolt an industrial-strength motor onto the transmission where the engine used to be. But the metal plate arrives unadapted to your transmission, so you need to drill the corresponding mounting holes and cut it to shape. This has occupied the last three or four days, but despite the lack of a drill press the plate has turned out 100% spec–a relief. Next we hoist the new motor/transmission assembly into the car, bolt the transmission back in place, and try to come up with a mount design for the other end of the motor.