It's officially underway... 1986 Mazda RX7 EV project! - Page 4 - Fuelly Forums

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Old 08-30-2007, 12:13 PM   #31
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Yeah, yeah, but what's the squirrel on the stick for?
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Old 08-30-2007, 01:48 PM   #32
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PS if you want to save money, you don't necessarily have to buy a shunt. AFTER I bought our shunt & ammeter (600A, which it turns out is too high a rating for our needs), I read you can make your own. It's just a calibrated conductor, with a known voltage drop across its length.
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Old 08-30-2007, 04:09 PM   #33
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PS if you want to save money, you don't necessarily have to buy a shunt. AFTER I bought our shunt & ammeter (600A, which it turns out is too high a rating for our needs), I read you can make your own. It's just a calibrated conductor, with a known voltage drop across its length.
I spent a good amount of time searching for information on making my own shunt. I ended up buying a 1200A 50mV shunt, which I am sure is WAY too high, but you never know with Ni-Cad batteries. I'd rather build things to too high a capacity than start burning stuff up. I'll be using a home-made serial interface 6-channel multimeter plugged into a spare laptop and running custom Visual Basic software for my gauges, so I'll be able to calibrate it to whatever the full-scale reading actually ends up being. I do only have 1.2mV resolution on the meter though. If I end up running 40amps or so for most around-town driving, I'll be reading only 1.6mV, which will be pretty much the bottom of my scale. For acceleration though, it should be a bit better.

Perhaps I can use the shunt I bought to calibrate some other conductor. Then again, one of the guys at work says he's got an old airplane shunt or two for me if I want them. I'm guessing they're around 200-500A.

My project is going over-budget very quickly with "R&D" spending, but I won't be including that in the cost 'to build the car'. When I get everything dialed in and know it works, I'll put it up open-source style for the rest of us wanting to make an electric car for a reasonable amount of money (sub $2000, including car, not including batteries).
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Old 09-08-2007, 01:31 AM   #34
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A milestone...

Got the motor mated to the transmission last night. Ended up going clutchless afterall, just for simplicity's sake. I guess I'll regret it when the synchros give out. that's okay, Swapping a clutch onto it won't be too difficult, just short on cash right now.

I ended up taking the original clutch disk apart and having the hub machined to mate with the coupler I got with the motor.


Mated it all up with a custom 3/8" steel motor adapter.

Had to cut the pilot for the transmission off unfortunately, was able to put it all together with just 0.3" worth of spacers.

Here's a link to a video of it running on YouTube. Perhaps I'll hook up my poor-man's motor control to it soon. Don't want to burn out any more IGBT's though.

Next step, build motor mount.

Still collecting batteries. Might have to end up just buying some. My guess is that the car will be ready to go before I get enough batteries to power it. Nobody says I can't collect NiCad's while driving around on lead-acids.

Making quick progress, that's for sure.
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Old 09-08-2007, 10:46 AM   #35
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Awesome, awesome. I love the video - reminds me of how fun it was going past that milestone.

Hope your momentum lasts longer than ours. It sure seems like things are happening fast when you're doing "big" stuff like ripping out ICE parts and mounting EV parts. But man, there are a lot of details that seem to slow things down once the big things are in place.

Either that or I'm lazy & slow.
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Old 09-08-2007, 10:48 AM   #36
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PS - I see you nabbed a front bumper too. Good stuff.
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Old 09-22-2007, 06:16 PM   #37
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First controlled run of motor...

Finally got the PWM and IGBT driver portion of my home-made motor control figured out. Hooked it up (minus the snubber/freewheel diodes) and performed my first speed-controlled run of the motor. The lack of the diodes caused a nasty arching sound, although no visible sparks could be seen anywhere. At higher speed settings, it quiets down. The controller works very nicely although it's still on the breadboard. Going to draw up the final schematic for my records before transferring it to proto-board until I can afford to have some PCBs made up. Here's a YouTube link to the video.

Anybody got any idea how to measure the RPM of the electric motor? The tach works on voltage pulses, so it should be easy to do with a hall sensor or something. My worry is that the massive rotating magnetic field from the motor would interfere with any magnetic-type pickup I'd use. Perhaps optical?
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Old 09-23-2007, 06:29 PM   #38
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What will be the specs of the custom controller?

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Anybody got any idea how to measure the RPM of the electric motor? .... Perhaps optical?
How about http://www.instructables.com/id/Ardu...al-Tachometer/ ?
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Old 09-24-2007, 08:04 AM   #39
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What will be the specs of the custom controller?
I'm using two 600a IGBT's in parallell for a total capacity of 1200 amps. WAY more than I need. The IGBT's can handle up to 1200v, also way more than I need. I'm using a fairly modular electronic design so I can control any number of IGBT's by simply daisy-chaining them.

As for the PWM driver, 16khz 0-100% duty-cycle. Monitoring will be through a 6-channel AD-converter hooked up to a "carputer" with my own software for displaying amperage, voltage, heat-sink temp, amp-hour counter, state of charge, and anything else I can think of. The stock tachometer will be used for RPM.
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Old 11-30-2007, 04:19 PM   #40
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The CD of the 2nd gen Rx7 ranges from .31 on the GLX & turbo while the Sport is a .29. I have a Sport w/ a turbo convertion.

How are you planning to heat the interior of the car? Have you thought about a small gas generator to recharge the onboard batteries during travel? There is definatly alot of space in these cars for batteries or anything else for that matter.

I used to have a few documents with the frontal area of the 2nd gen Rx7. I'll dig around to see if I still have it.
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