Mr Motor, meet Mr Transmission

I have been out of town for the last couple of weeks, so I was excited to work on the car all weekend. The shaft locks arrived while I was gone, so I set to work attaching the motor to the transmission. I had one small setback. The motor is a metric 112M size, which means that it is 112 mm from the base to the center of the shaft. It also should mean that it has a 28mm diameter shaft. For some reason, though, this one had an 1 1/8" shaft. This was a problem because the shaft lock I bought is 28mm. No worries, though. 28mm is smaller than 1 1/8", so I just turned the shaft down on the lathe.
This was good, as it gave me an excuse to take the motor apart.

Next, I test fit everything, and ran the motor for the first time attached to the transmission


Everything ran smoothly, so time to start putting it all in the car!

Shaft locking

Since I finished pulling the engine, I have been working to source parts to couple the electric motor output shaft to the transmission input shaft. Instead of using a splined or keyed shaft, I will be using keyless shaft locks from Lovejoy, combined with a hub I will machine myself. The keyless shaft locks work by drawing two concentric wedge profile rings together with jack screws. As the rings come closer, they wedge against the outside of the shaft and the inside of the hub, to form a very tight fit. I will post some pictures of this once the parts arrive.

Engine pull day two

Here is the sequel to last week's movie, where the engine finally comes out. It took a bit of work to get the tail of the transmission over and out, but there were no mishaps.

Engine pull day one

Today I started pulling the engine. I nearly finished, but the hoist I scrounged up was not strong enough to lift the engine and transmission. I am doing the work at TechShop, down the street from my house. It's nice to have a place with enough space to work and all the tools I need. The big engine hoist they have there needed some repairs, so I will finish the job later this week. Meanwhile, check out the time-lapse video from today:

Thoughts about energy

Since I've been thinking about building an electric car, I've gotten a lot of questions about them. I'm far from being an expert on the subject, but I have picked up a few answers as well. I think the most frequent question is something like "Can you put some solar panels on the roof and make it run that way?" The answer is yes, but the car would be slow even by classic British standards. For comparison, an average-sized solar panel makes about as much power on a bright day as a healthy adult in a hurry on a bicycle. You could maybe fit three of these panels on a car without looking ridiculous or getting in trouble with the law. That doesn't mean it is a stupid idea. Solar car races (I guess "rayces" if you're into that sort of thing) are pretty cool. And then there's this guy if you prefer the Mad Max look. The best thing is to have a solar powered carport to park your car under while you're at work, or just a roof full of panels at home. Even if you get all your electricity from the power company, though, electric cars are an improvement over the gas variety from an environmental view. The movie "Who killed the electric car?" presents arguments from this side quite well.

Engine sold

I listed the gas engine on Ebay last week, and there was a fair amount of interest. Some in the motor itself, but also quite a bit in the idea of an electric conversion. I'm glad I started this journal, so I could point to it as a place to begin learning about electric cars. The auction ended last night, at a little over two hundred dollars. I'm mostly happy to have the engine out of the way so I can begin the conversion, but I don't hate two hundred dollars. That's almost two batteries!

Bench test

I tested the motor + drive system last night, and overall it was a success. I ran the motor up to 7500 rpm with no problems. The cooling fan sounds like a jet taking off at that speed, though. It's nice to have a lot of cooling air, though. Unloaded, the motor consumes about 750 watts at top speed, which seems reasonable. I can run the motor down to about 30 rpm, where it uses about 50 watts. It would have been nice to get an idea of torque output, but I don't have an easy way of loading the motor.

The motor controller has two modes: V/f and sensorless vector. At its simplest, V/f mode makes the voltage to the motor linear with frequency, so for example, to run the motor at 30 rpm, the drive would supply 10 Volts at 1 Hz, and at 7500 rpm it would supply 230 Volts at 250 Hz. This is fine for constant load applications, but if the load increases too much, the motor can stall. In sensorless vector mode, the drive uses a mathematical model of the motor to calculate the torque applied at any time. It can then change the voltage and frequency to match a requested torque or speed. This is much better for an electric car, because motorists are used to an accelerator pedal that requests more torque from the motor. Because the motor's rated capacity is much smaller than the drive's (5 HP vs 30 HP) the drive was unable to model the motor, so sensorless vector mode is not working. I will see if I can input parameters specific to the motor and get it working. Otherwise, I will probably need a bigger motor eventually. In the meantime, I can set the acceleration and deceleration times for the drive to be long enough so that everything works. This just means that the drive will take the car's inertia into account a little better, and won't ask the motor to turn at 7000 rpm when the car's speed is telling the motor it must turn at 500 rpm.

Now to get rid of that pesky gas engine so I can start putting things in the car...