Thursday, September 13, 2007

Two Week Commuting Report

Since I don't work Fridays, this is the end of my second week commuting to work fifteen miles each way. Two things have definitely made the car more fun to drive. 1. The batteries are broken in so I have more current to work with and more importantly 2. I've learned some of the tricks to driving the car.

The biggest trick involves starting from a dead stop. Apparently, the AC motor feels like it has more torque at non-zero RPMs (perhaps just a false perception). However, if I start from a stoplight in the same way as a gasoline vehicle (rev the engine and slowly let out the clutch), I can start much more quickly than if I just leave the clutch out and floor the accelerator from a stopped motor. The same thing helps when starting from stopped on a hill.

With the charger plugin at both work and home, the PakTrakr fuel gauge doesn't seem to drop below the 80% mark, so I think the batteries will last a little while. The DC-DC converter is still working fine, so the car is actually quite convenient to drive. I haven't touched my gasoline car in two weeks now.

Sooooo, with everything working reasonably well------ it's time to drop the motor/tranny again and revisit the flywheel vibrations again. (doh!) I called around to several Porsche repair shops and finally found Dan Hall's Auto Machine. Apparently Dan is the only guy in the Portland area that has a flywheel balancer with a small enough mandrill to fit the 914 flywheel hole (1/2 inch or so). While I hesitate to dismantle a working car, I'd really like to rev the motor safely up to 7000-8000 RPM to get more torque and run the car on the freeway in second gear (!).

I contacted Azure Dynamics and asked them how I could measure the RPM on the motor so I could drive the tachometer in the middle of the dash. They strongly recommended against tapping into the encoder signals since they had noise issues themselves with the encoder signals. With the motor out, I'm going to look into RPM kits for electric cars that use spinning magnets on the flywheel with a magnetic sensor to generate a signal. Stay tuned...


Ross Cunniff said...

Re: tach sensor - could you paint a white spot on your flywheel and then put an optical sensor + LED on one of the access ports in the transmission bell housing?

Roger Daisley said...

I have, but not yet installed, a nice unit the uses a magnetic detector (probably some kind of Hall device) that counts the starter ring teeth on the flywheel and then will convert to pseudo-ignition pulses that my original in-dash VW tach can use. It seems like a nice little device and not too expensive. It installs in the inspection/timing hole on the bell housing.

I think you cut off the starter ring, so it wouldn't work for you, however, since you are going to tear down the engine anyway, you might consider installing a new flywheel, with ring intact. (I really don't see much need for a lightened flywheel anyway, unless you intend to drag race the car, which seems to be a bit abusive for a daily-driver. Hey ... build up a drag car, just for the purpose.)


TimK said...

Thanks for the ideas. After searching around the internet, I think I'm going to try Ross's idea of the IR LED and optical sensor. Radio Shack sells an emitter/detector IR pair for cheap that I could probably put through a 741 op-amp and 555 one-shot timer to clean up the signal. First, I have to get the flywheel/clutch balanced. Cheers, Tim.