[dtbaker]

sounds like you've got a handle on it.... just be sure that you are sure you want to drive that 25 yr old car for another 10 when you're done. the rx-7 could be a ton of fun electric, but obviously won't have airbags et all, and probably in need of paint and interior....

 

[dougingraham]

sounds like you've got a handle on it.... just be sure that you are sure you want to drive that 25 yr old car for another 10 when you're done. the rx-7 could be a ton of fun electric, but obviously won't have airbags et all, and probably in need of paint and interior....

I've owned three RX-7's, the first was a 1982 which I got in 1985. The second was a 1987 which I bought new and traded the 82 in on. The third was this 1985 which I am converting now. In every way measurable the 1987 was a better car but I prefered the first generation car for the looks and the way it handled.

I am not even close to done with this conversion and I am already thinking about how I would do the next one differently.

As near as I can tell the car started life in Minnesota and then went to Las Vegas where it spent much of its life. The couple that owned it moved to Rapid City and were having their second and they just weren't driving it anymore. It had almost always been garaged and had been repainted in the late 90's. I have always garaged it since I bought it. There are only a couple of door dings and a little ding in the hood. The greatest cosmetic issue is a minor dent in the moon roof and roof behind it where my girlfriend closed the garage door on me when I was backing out. The interior is in great shape. There is very minor wear on the leather seat on the drivers side. If you looked at my photo journal I have a picture of one of the only rust spots I have found. And I understand why those rusted out. It was a stupid manufacturing mistake. I am guessing that I will get another 10 years out of the car if I keep an eye out for rust. If this one gets too bad I can just pull out the electric gear and buy a donor that is in better shape. Be a piece of cake to do a second time! The donor car only cost me $1500 and I drove it for almost 5 years.

 

[dougingraham]

I guess it is past time for an update. I got the car on the road on September 22 about 4:30 in the afternoon. Drove a total of 21.6 miles on that saturday afternoon. I put the car on the trailer the next day and went to EVCCon. I've been using it as my daily driver since I got back from EVCCon on Oct 2. There is still a lot to do but I had been putting off a lot of real life stuff over the last year that needed to be addressed. I will probably get back to work on the car in the next couple of weeks. Big stuff that still needs to be done.

Front battery box with an additional 19 cells.
DC-DC converter (depends on the front battery box).
Ceramic Heater (depends on the front battery box).
Vacuum pump for brakes (depends on DC-DC).
Mount the charger.
Instrumentation.

I am using the EMW10k charger off of a 110vac outlet in the garage. I've got it set to use about 11amps. My typical charge is taking about 5 hours so at the moment there is no need at all to put in a 30A 240VAC service in the garage. There are no public charging facilities in town yet so no need for J1772 at this time. I will probably do it even at just 110VAC in the garage for the convenience of the connector.

The car needs a little more instrumentation but as I was thinking about a year ago the only two things you have to have are the speedo and the odometer and thats all I have working right now. I am going to hook up the tach to the Soliton and hook the coolant temp to the motor thermistor. I dont see any need at all for a pack volt meter. It just isn't needed to drive the car. The charger tells me what it is when charging. The soliton will stop me if I get too low. I have wanted a battery ammeter from time to time to let me know if it would be more efficient to be in a different gear. I could put a shunt in the line and attach a volt meter to that for a week or so or once I get the tach hooked up I think I could direct the Soliton to output bat amps to the tach. I only need it for a couple of weeks and then I would know. I have so much more range than I need if I charge it every day it just isn't an issue even with only 33 cells out of the 52 installed.

I now have 303 electric miles on the car in 24 days which works out to an average of 12.6 miles per day. I have the charger plugged into a Killawatt meter and since I have still not settled down and started driving in a reasonable manner I am only getting 315 wh per mile. If measured at the battery this would be about 15% better due to charger efficiency or about 268 wh per mile. The car weighs 2300 lbs with me in it so the rule of thumb indicates I should be seeing 230 wh per mile. I think if I wasn't doing jack rabbit takeoffs and generally driving it like a sports car I could probably get it down somewhat. This is just a fun car to drive and I am looking forward to the bump in performance from adding the rest of the batteries.

The EV grin is real and alive in western South Dakota.

 

[MalcolmB]

Congratulations Doug, this has to be the shortest build log ever

I was checking out your photos earlier today, looks like you put a lot of thought and time into this. I especially like your lightweight (and non-conductive) battery boxes. Hope you get lots of fun out of driving her.

Malcolm

 

[dougingraham]

Congratulations Doug, this has to be the shortest build log ever

I was checking out your photos earlier today, looks like you put a lot of thought and time into this. I especially like your lightweight (and non-conductive) battery boxes. Hope you get lots of fun out of driving her.

Malcolm

Thanks! The build log is in my google doc and it extends out to some 50 or so pages. The battery boxes got a lot of attention at EVCcon. Several people thought I should do a video about how to make them and send it to Jack. The other piece of the build that got a lot of attention was the laminated motor mounts I made with Aircraft ply fiberglass and carbon fiber wet layups. They look good and after being trailered for 2200 miles and driven for 300 plus miles seem to be holding up fine.

I've owned four RX-7's (still have one with the wankel and the EV version) and they have always been one of my favorite cars. This EV doesn't quite drive as well as the ICE one yet but I am getting there. It certainly has more torque but with the low voltage (only 33 cells now) it runs out of torque too soon. Its a lot of fun! I read your Mini build thread and it looks like you are close. Good luck with that. Mini's are neat cars.

 

[dougingraham]

Well it has happened! One of the things I was worried about when I started building my EV has come to pass. I was giving a demo ride yesterday and as I have been doing for the last month I put the car in second with the clutch out at a standstill and then floor it. Amps go to 1000, 277ft lbs of torque hits the gearbox, the occupants are thrown back firmly into the seat and a second later we are doing 25. Only this time there was a loud thud from under the hood. We still got going 25mph but something didn't feel right. I popped the hood and looked around expecting to see torn carbon and fiberglass from damaged motor mounts but nothing looked wrong. I decided to drive the 4 miles home and did that without incident. I did notice that under light acceleration the shifter would move to the right a couple of inches. When I got home I jacked it up and inspected the transmission mount but I could find nothing wrong there. I opened the hood and again inspected everything and still I couldn't find anything. I grabbed the aux shaft on the warp 9 and gave it a pull and I was able to lift the motor off the drivers side motor mount. Yep, I broke the Mazda motor mount!

I was worried about the parts I had made, not the factory pieces. I figured the first thing to go would be the clutch. I won't know for certain until I get the broken mount out what exactly failed but I am guessing the 28 year old rubber isolation block tore under the load.

I am both elated and depressed by this. More elated than depressed. The depression comes from having to fix it although it will not be difficult. The elation comes from thinking about having so much power I was actually able to break something.

 

[dougingraham]

Mazda is a really the high speed car

I did a quick calculation last night.

WarP9 torque at 1000A = 277ft lbs (Taken from Jack Rickards Dyno tests.)

2nd gear Transmission reduction = 2.186

Differential ratio = 3.909

Final drive ratio in 2nd = 8.545

Rear tire radius (185/70 R13) = 11.6 in.

Torque on motor/transmission (propshaft torque) is 605 ft.lbs which is what broke the motor mount. Part of this goes to the transmission mount and part to the motor mount. The transmission mount is quite a lot softer so most of the force went to the motor mount.

Torque delivered to the wheels in 2nd gear is 2367 ft lbs.

Force delivered to road is 2449 ft lbs.

Each rear tire sees half of that or 1224 lbs and carries about 600 lbs of car.

The car weighs 2200 lbs and has a limited slip differential. This torque in 2nd gear is a lot and it surprises me I am not seeing wheel spin. I am also surprised the clutch isn't slipping. It is a stock disc with stock pressure plate with about 40k miles on it (mostly highway pre conversion.) I do see wheel slip in 1st gear but the 1st gear transmission ratio is 3.622 making the final reduction ratio = 14.16 so the potential force on the road is 4057 lbs. Nearly twice the weight of the car. In first the motor never would get loaded to 1000 amps because there isn't enough mass to accelerate. You see this on Jack Rickards dyno results with the Speedster.

In 2nd gear I believe I can give a Tesla a run for its money (at least up to about 30 mph or when something breaks).

Someone check my math and let me know if I messed up. The numbers seem right but then often things that seem right are not.