It's officially underway... 1986 Mazda RX7 EV project!
 

As of today, my EV project is officially underway. I purchased a 1986 Mazda RX7 with a bad motor in it. More details and pictures to come. I'm hoping to turn this thread into the next Forkenswift style documentary of the process.

For those thirsty for pictures, here are some before and after pictures of my motor after a rebuild:
Before:
https://twigmouse.ipupdater.com/miscp...p?a=dl&ID=2699
After:
https://twigmouse.ipupdater.com/miscp...p?a=dl&ID=2702

Is it just me, or is that one big motor?

12" dia by 13" long. Dual output shafts. It's a Baker forklift drive motor. Brushes have been advanced 10 degrees. According to my dial indicating torque wrench, it produces 25 ft lbs of torque at 12v, 0rpm. Don't have an ammeter (yet) to measure current though. Either way, it should be MORE than capable of propelling my RX7 with 120-140v worth of NiCad cells behind it. I hope having a bigger motor doesn't effect economy the same way having a bigger gas engine does.

Quick reference:
Goals for my EV:
30+ Mile range minimum (70 or more hopefully)
65+MPH continuous speed
On-board 110v charger.
Minimum cost.

It may, but it won't have the same magnitude. There may be a ~10-20% difference between efficiency, motor size, and average power needed, but it's not like gasoline engines where efficiency can drop by a factor of 2-6 depending on gearing and displacement. I'm curious, if you're trying to minimize costs, why did you go with NiCad batteries?

Ya, that's a biggie... Super cool! I hope it all goes great for you!

Sweet project! I hope you keep us updated step by step!

I'm getting the NiCad cells for free from the airline I work at. They are "unservicable" cells, which means that they're no longer fit for use on aircraft, but so far all (11) of them seem to be just fine for my purposes.

https://twigmouse.ipupdater.com/miscp...p?a=dl&ID=2701

Each cell is 1.4v and 40AH. It will take me quite a while, but I'm planning on collecting about 100 of them. Of course, I don't plan on stopping when I get to 100. Gotta have spares and room for upgrades of course ;-)

Also, a picture of the car, just to keep things moving:

https://twigmouse.ipupdater.com/miscp...p?a=dl&ID=2704

Free batteries, nice! What's the cd on that car?

Holy! 1.4V each! That's a lot of wiring batman!!

Pretty cool project there! With my new business of working on golf carts this summer, I think I might have to score a motor and controller and related parts for a future EV project of my own.

Neat-o. Was the motor free too? Where'd you get it? Who did the rebuild & what was done?

Looking forward to watching the progress.

No idea on the Cd of this car. It's pretty sleek though ;-)

Nope, got the motor for $200 (I'll post a table with my costs so far and a running total as I spend more on it). Got it from a forklift wrecker. I rebuilt it myself with new bearings and a 10 degree brush advancement. The comm and brushes are still fine, so I didn't touch those. Media blasted and repainted the case with polyurethane enamel (light gray).

Sweet deal all around! Always loved that body style of the RX7,EV power makes it better still. Definitely keep updates coming .

You scored free SAFT NiCDs? :eek:
I H8 you so much right now.... :D :thumbup:

FYI, cartest lists the CD as .31 for a 1986 rx7, it didn't have a frontal area figure.

Is that good? What is cartest? Any use for an EV?

Mayfield has the same .31 figure w/ a reference area of 1.784 square meters.

Very resourceful.

Our forklift guy said: "$500 for the motor (if we remove it for you) or $500 for the whole forklift, your choice."

I'm glad we took the whole thing, seeing as the traction motor ended up being too fat (girth wise) to use with our transaxle. You won't have that issue with RWD though.

Do you have the bumper for the car?

Say... what do the specs say on your motor tag?

At first glance, it appears to be very similar to the torque monster we have. (Had - it's sold, but the guy hasn't come to get it yet.)

https://images6.theimagehosting.com/1...riveway.th.jpg

The main difference appears to be the big internal fan on our drive end, so it's a bit longer overall @ 15.5 inches (not counting shaft). You might have to set up forced air cooling (depending on what kind of range/amps you're going to be dealing with.

Did you get a coupler with it? Are you going to mod something to work with the square shaft, or get a round shaft pressed in?

Sorry for all the questions. :o

No, no bumper for the car yet.

I've got the couplers (both sides) for the motor, but I'll likely end up machining the motor side one down to mount my flywheel to it.

The motor dataplate lists it as an A-9044-Y4, no specs on it though.

Nice score on those batteries :thumbup: . I had an 87' rx-7, it handled nice, I've always liked that body style. Good luck

I'm still on the fence about whether or not I'd retain the flywheel if I had to do this over again. I'm getting used to driving the car clutchless (including downshifting, which was a bit of a problem before I figured out the right technique).

I take it you saw the info I posted from EVDL motor guru Jim Husted, on forkenswift.com:

https://forkenswift.com/baker-12-in-motor.html

Yup. I actually met Jim last weekend. Talked with him quite a bit about my motor and EV motors in general. Very helpful guy indeed.

Was that at the NEDRA event? Did you buy a raffle ticket? :D

No, it was at the Saturday morning car show thing the morning after the first night's races. I didn't actually make it to any of the races :-(

FYI...

The admin of the listserv is trying out a web forum style "archive": https://www.evdl.org/archive/

You can reply to posts using your browser, but you have to be registered on the old-fashioned mailing list for them to go through. (You can then set your listserv prefs to "suspend" so you don't actually get all the email.)

Details: https://www.nabble.com/New-EVDL-Archi...html#a12099227

Got the gas engine out of the RX7 yesterday. Currently trying to figure out how to mate the pressure plate to the output shaft of my motor. I'm planning on using the coupler that came with it (square drive lovejoy coupler). The stock RX7 pressure plate doesn't have a flat mating face, it has a bore. Not to mention a massive integral counterweight. I figure my options are to either take the stock pressure plate to a machine shop and have them cut the hell out of it to make it flat on the back side, remove the counterweight, take some un-needed material off of it, and balance it to neutral. That sounds expensive.

I'm also playing with the idea of making my own pressure plate from a flat 3/8" piece of steel. Would already be flat on both sides, would be much lighter (even with some stiffeners welded onto the backside), and I could have that balanced when I'm done. Just curious if the kind of steel I'd get from a steel yard would hold up to the wear ant tear of being used as a friction surface for a clutch.

Oh well. I'll be removing (or attempting to remove) the stock pressure plate tonight and I'll see what my options are with a little more clarity.

On another note, work on my homebrew controller is coming along nicely. Waiting for some P-channel MOSFETs to arrive so that I can couple one with my existing N-channel MOSFET to build a push-pull amplifier for output to the IGBTs. It seems that the IGBT's 'latch' in either the on or off state. This means that the gate requires V+ to turn the C-E on, and a V-(but GND works) to turn it off. Luckily, the PWM output of the chip alternates between +5v and GND for it's cycle, so this should work well to drive the MOSFETs, which then drive the IGBTs. More experimentation to be done, but experiments with a small magnetic radioshack motor show promising results. Since the IGBT's high current/voltage portion is insulated from the gate, It shouldn't matter whether I'm running a CPU fan or my monster 12" motor to the PWM controller. If all goes well, I'll be into the controller for less than $75 in parts.

My total investment is quicky approaching $700 though, and I've still got a fair amount of additional spending to do (welding cable, copper bus-bar for batteries, 1000a shunt, misc parts for the RX7 to make it road-worthy), so I doubt I'll hit my sub $1000 goal. We'll see though.

home-made motor control...
 

Here's my PWM motor control as it looked on the breadboard:
https://twigmouse.ipupdater.com/miscp...p?a=dl&ID=2720

I've tested it on my 12" motor and it works, but unfortunately I burned out a couple of my IGBT's by using them without a snubber capacitor. It works fine with the little motor though. I've got some capacitors and a heatsink on the way, so another high-current test will take place at that point.

Yeah, yeah, but what's the squirrel on the stick for? :)

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).

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.
https://twigmouse.ipupdater.com/miscp...p?a=dl&ID=2743

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.

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. :)

PS - I see you nabbed a front bumper too. Good stuff.

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?

What will be the specs of the custom controller?

How about https://www.instructables.com/id/Ardu...al-Tachometer/ ?

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.

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.