Saturday, July 26, 2008

Motor Design Considerations

Not too much progress on the car, but I've been talking with the guys and gals at to get a few design questions answered. By the way, if you want to convert a car and have a question go check out that site. The people there are great.

I've got the old engine on 2 different classified sites trying to find a new owner but still no interest. I had decided on a 120V system but not on the motor.

My goals...
Right now my wife and I don't -need- a second car. I ride my bike to work and she rides the bus to school. Once she is done with school we'll have to have the two cars though. For now I'd like an easy cruiser (using Lead Acid). It should be highway capable, but it will rarely if ever see it (Phoenix is a perfect grid with plenty of auxiliary roads to take). Its acceleration should keep up with regular traffic without destroying the motor/batteries/controller, but I don't need to win any races. Range is just a bonus as I don't 'need' this car. The further the range the more I'll do with it but everything is pretty close. A reliable 20 miles is minimum, and 30 is more than enough. In 2 years when I'm back in Texas I'll spring for Lithium Phosphates that can go for 40+ miles range.

Over the past week I searched through a bunch of EV supplier sites to find the best motor for me (and of course I made a huge excel spreadsheet with all the stats).

Here's the top few...

ADC FB1-4001A, 9.1",, $1550, 143 lbs, Double Shaft
25.2 HP @ 120V Continuous
27.5 HP @ 120V 1 Hour
43 HP @ 120V 5 Minute
85 HP @ 120V Peak
40 mph range: 30.4 miles

ADC 203-06-4001A, 8",, $1350, 106 lbs, Double Shaft
21.7 HP @ 120V Continuous
24 HP @ 120V 1 Hour
37 HP @ 120V 5 Minute
83 HP @ 120V Peak
40 mph range: 24.1 miles

ADC L91-4003, 6.7",, $929, 85 lbs, Double Shaft / Reversible
16 HP @ 120V Continuous
17.9 HP @ 120V 1 Hour
31 HP @ 120V 5 Minute
72 HP @ 120V Peak
40 mph range: 23.8 miles

ADC X91-4003, 6.7",, $949, 87 lbs, Double Shaft
16/10 HP ??

D&D ES-31B, 6.7",, $1154 ( may have it at $1085 though), Single Shaft
18 HP @ 96V

Obviously you get what you pay for. Bigger and more expensive gives you more efficient longer range. The ADC FB1-4001 seems to be a standard among EV conversions, but my car is substantially smaller than many EV conversions. The ADC 203-06-4001A gives better power than the ADC L91-4003 but not much better range. After debating about it for several days (researched for months), I've decided to go for the ADC L91-4003. It's 40% lighter and 40% cheaper than the FB4001A. Excluding the pretty mountains in the distance, Phoenix is completely flat so engine power isn't critical now even with Lead Acids. Texas has more hills which will either need more power or less weight. Fortunately Lithiums are substantially lighter so I should be okay.

The guys recommended that I thoroughly clean out and paint the engine bay. 2 reasons: protect from rust and make it extra beautiful when people look under the hood. Apparently when you have an electric vehicle everyone wants to check out the motor. :-)

I was originally going to keep the clutch, but after seeing how complex it would be to make an adapter for it, we decided to scratch it. (We being my machinist friend Matt who is helping me out a ton.) The car should run fine clutchless. Electric motors have full torque at 0 rpm, and they have minimal mass when changing gears (it just takes a couple seconds longer). The synchros will help smooth the shift without needing a clutch. The guys at diyelectric also warned me that the transmission in these cars is very poor, and I may want an after market Japanese unit. Depending on the performance of the L91-4003, I may just do all my driving in 2nd gear. If that's the case I can replace the transmission with a single-speed gearbox and use the motor's reversible capability. I probably won't reach highway speeds with the single gear though.

It looks like I'll need 3 items manufactured for the motor. A coupler from the transmission's shaft to the motor's shaft, an adaptor plate to cover the bell housing / attach the motor to the tranny, and a rear mount. For the rear mount, we'll probably build a metal cradle between the old engine's attachment points that has a curve in the middle matching the new motor's shape. Then add a tight strap over the top of the motor connected to the cradle. The adaptor plate will handle the torque and the cradle will help support the back of the motor. Also the guys at diyelectric recommended we keep the rubber engine mounts to help absorb bumps. Matt was checking it out with me, and he thinks it'll be a breeze. Sweet.

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