Saturday, May 31, 2008

Ordering a Motor Adapter

After some significant debate at the Civic-EV Google Group on whether to use a clutched or clutch-less system, I'm going to pursue using a clutched system for the initial revision of this kit.

Here are some points I considered:

Clutched system for Civic:
  • feels more like the original manual transmission, allows people unfamiliar with EVs to drive it more easily; downshifting much easier
  • Allows troubleshooting of the drivetrain by allowing an intermediate disconnect point during operation
  • Adds a safety feature if the controller shorts and over-revs the motor
  • inertia from heavy flywheel slows acceleration
  • clutch slave cylinder interferes with placement of front golf cart batteries but not Deka 9A31s

Clutch-less system for Civic:
  • much less mass to spin up during acceleration
  • shifting is a bit slower as the driver uses the synchromesh to spin the motor down and up
  • shifting can only happen while the accelerator is not pressed
  • clutch slave cylinder doesn't interfere with 8V golf-cart batteries
  • this system still uses the springed center of the clutch disk to remove stresses on the drivetrain from bumps
With the clutch-less system, I would have had to order the shaft adapter from EV-America and then machined the outline for my own transmission adapter. With a clutched system, I just order the shaft and transmission adapter from Electro Auto and everything is just done. While the design of the shaft and transmission adapter is not open-source, there are many other parts (like the DC motor) that aren't open-source as well. Perhaps in the future, I can make an open-source adapter design, but I've found that the money saved in machining one's own adapter is small compared with the hassle of getting a local machine shop to do the job right.

For those of you wishing to make your own Civic-EV, Electro Automotive will ask you for the bolt pattern on your flywheel since they've had problems with Civic adapters in the past. Here's a picture of the bolt pattern I scratched from a purchased Civic flywheel. The resolution is 300x300 dots-per-inch. If you print this out using MS-Paint with the proper 300x300 scaling, make sure it exactly matches the bolt pattern on your flywheel before ordering the adapter from ElectroAutomotive.

Remember the transmission I pulled out of the Civic at the wrecking yard? I cleaned it up so I could get some measurements on it for the clutch-less system. I can verify the ElectroAuto adapter on this, but I won't need to measure it anymore since I'm not considering the EV-America clutch-less system for now.

Also make sure your transmission is the S20 transmission for the proper adapter plate. Here is a picture of my transmission label:

Next up: thinking about batteries and the controller system...

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