The Drivetrain

The Load

Generally the plan is to remove both engine and gearbox, and to use a motor through a reduction unit to drive each wheel. The reduction unit could be a chain, but will probably be a toothed belt arrangement.

DC Motors

Generally DC motors are series wound motors with brushes: the magnetic fields are proportional to current, so the torque is proportional to current; and the back EMF voltage is proportional to commutator speed, and hence to RPM.

Regenerative braking on these motors is normally quite easy, but comes in the form of a current proportional to braking torque with a voltage proportional to roadspeed. The circuitry to recover this energy is likely to be similar to the circuitry that connects motors to batteries - it should be possible to reverse the controller to get regenerative braking.

Lynch motor

The lightest motor that seems to do the job is the Lynch LEM-2x2-127. These deliver a maximum torque of 82Nm at 300A: the torque is quite linear with current. The speed is linear with voltage, up to a maximum of 3600rpm under load at 120v. No-load maximum is 4000rpm. They weigh 22kg each.

They tell me that these motors can be overdriven to 400A for a few seconds, or fairly continously if they are fan cooled. At 400A they should deliver a torque of about 100Nm. That converts to a tractive force of about 2000N for the two motors. At 120v they free-run at 4000rpm, but under maximum load this drops to 3600rpm.

At 10kW, the motor is about 91% efficient.

Sadly these motors were quoted to me at about £1900 a go. Which is a shame, as they are great motors.

There is also a 60V version - the LEM-2x2-126. Same price, double the current and half the voltage. That could be useful for building an electric ground-rocket, as it means the battery count can be reduced.

AVT motor

The AVT Supermotor looks like a rewind of one of the smaller Lynch motors (my guess is the LMC-200D-127) to allow it to be used for an EV. The weight is the same, the picture is very similar, but the price is much better.

Since it says 6500rpm at 120v, 5.75:1 gives 80mph at top RPM. If it is an overdriven LMC-200D-127, then the maximum torque is going to be about 50N at 400A, which will give about 1900N of tractive force for 2 motors. That's 5% less than the Lynch motor, but the motor is much cheaper at £1000 to £1300, depending on model.

It looks like it'll be about 90% efficient at 10kW.

For constructing ground rockets, there is no reason not to put two AVT motors on one toothed belt: a belt running over three pulleys is no problem. The result would be 100Nm, 6500rpm, and a peak power of 40kW.

Advanced DC motor

The alternative is the 203-06-4001 motor from Advanced DC. This is much heavier, at 48kg a go. The maximum torque is about 70Nm at 350A, and the speed is greater than 7000rpm no-load at 120v. Data for these motors is available from this catalogue.

A 5:1 reduction gives about 300Nm @ 300A, and the reference cruise point becomes 16Nm @ 6250rpm. This gives a figure of about 125A @ 105v per motor, which will voltage-convert to 219A @ 120v for both motors.

These motors are about 10% less efficient at maximum cruise speed, which will significantly impact battery life. But they're less than $1200 a piece.

AC Motors

Siemens range

Siemens motors are available from Metric Mind. The ACW-80-4 looks like a good motor, although it'll need a reduction gear. The 1PV5133WS18 looks good for no reduction gear, although the way it'd be overdriven it'd be an utter ground-rocket with a speed of well over 100mph!

No prices, though: although there are weights. The ACW-80-4 weighs 22kg each, the 1PV5133WS18 weighs 68kg each.

Homebrew Motor

The people over at the OtherPower website suggested I make my own. My first response was don't be silly but on thinking more, I'm not so sure it is silly. It's become quite a complex design, so it's on a separate page.

Conclusions

As by now you might expect, here is a comparison table for the motors. The gear ratios are selected for a top speed between 75mph and 80mph, which is sufficient for where I live, and the speed and traction figures are based on these gear ratios and on wheels of 330mm (13") diameter:-

Motor Rated Power @ RPM @ Voltage Stall Torque Efficiency @10kW Weight per motor Gear ratio Speed Traction Price
Lynch LEM-2X2-127 22kW 3600 120v 100Nm 90% 22kg 3.5:1 77mph 1050N £1900
AVT Supermotor 20kW 6500 120v 50Nm 90% 11kg 6:1 84mph 900N £900-£1300
Siemens ACW-80-4 21kW
peak 38kW
10000 200v 20Nm
peak 60Nm
88% 22kg 10:1 76mph 600N
peak 1800N
???
Siemens 1PV5133WS18 30kW
peak 65kW
3500 215v 85Nm
peak 175Nm
88% 68kg 3.5:1 76mph 892N
peak 1837N
???
Homebrew motor 10kW
peak 53kW
1000 120v 500Nm ?? 25kg? none 76mph 1500N £200?

All things considered, I'll probably go for the AVT motors. They're light and efficient, which is a winner.

The Siemens motors are a bit heavy, and well overspecified, but there would be something amusing about the 80kW output, which will give something like 150mph. But it's probably a bit over the top - and the batteries I'm thinking of are likely to only deliver 80kW for about 8 minutes. But they'd be fun minutes.

The homebrew motor is an intriguing idea. Probably not a wise idea, but intriguing nonetheless.


This page is part of an Open Source Electric Car Project, and is written and maintained by Simon. At this stage these pages are constantly under revision. Thoughts and comments are welcome.