# Motor ideas for <300kg car



## jk1981 (Nov 12, 2010)

Thinking about building an ultralight electric car, the aim being something cheap to build that I can ultimately commute in (20mi round trip, flat). Keeping it small and very light I'll only need 2-3kWH of battery, 5-6kw for uphill cruise at 40mph. 15kW upper limit to register it as a quad (not essential but I don't need more power). I'd like to run two motors and ideally fixed reduction ratio/direct drive, it potentially saves a lot of driveline weight. A pair of direct drive motors would need to produce ~90Nm each and spin to 700rpm.

What I'm struggling with is a source of suitable motor or motors I can modify available in the UK or EU. My thoughts so far but I'm looking for more ideas/links:

Chinese E-bike hubs: Broadly the right size and weight, direct drive, expensive as a pair especially if bought from EU stock.

RC outrunner: Cheap and broadly the right power range if spun fast. Low on torque, needs multi-stage reduction and sensor mods. Probably needs forced cooling.

Starter motors: Right sort of size. Poor efficiency, poor brushes

DC pump motors: Too heavy generally, I really need <10kg/unit. Open to similar suggestions since DC is simplest and cheapest to control.

Wheelchair motors: Probably a bit weak but numbers and details are hard to come by on the internet.

Small ACIMs, modified V/Hz inverter: Needs high battery voltage or extra boost stage. Not sure what sort of size or gearing would be required, nor of the limitations. Basically I'm unfamiliar with these. Cheap ish.

Large car alternators: Dirt cheap. modern units boast reasonable 70+% efficiency which may be improved with careful cooling mods, rugged, 150-200A units are in the right size range. Needs a field control module (I'm an electronic engineer).

Roll my own hub motors to suit: Cast powdered iron core hub motor. Lower cost than commercial units but more work and more risk that my models are wrong. Tempting to give this a go at this relatively small scale to see how it works out.

Other: I'm all for ideas and not dead against spinning a diff with a suitable motor. Also would consider 4WD especially if DC. Ideally I want motors-gearing or motor-gearing-diff-shafts <25Kg


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## Yabert (Feb 7, 2010)

I think you will have hard time to find your direct drive motors.

If you want to build a lightweight diff, I suggest you to modify a regular diff from a small car like the pictures below. After you add chain or belt to the motor.
As motor, Motenergy ME, lynch pancake PM motor or maybe golden motor.
Don't be shy to use a motor with decent power despite if it cause an overweight of few Kg. An overweight motor is better than a burn motor by an overload


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## Karter2 (Nov 17, 2011)

You could consider repurposing a complete golf cart electric drive line.
They are very durable and have been used for much higher power vehicles.
There is a lot of support and mods available.
It would save a lot of engineering problems.and you could run to whatever power level you want.


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## jk1981 (Nov 12, 2010)

Cheers guys. I should have added I've built a couple of motorcycle powered cars before now, a 400kg Seven type with a fairly conventional front engine, rear drive layout plus a transfer box for reverse and the other a transverse front-front layout using a chain driven diff of the type mentioned. In general, car parts, even well chosen and stripped back are too heavy for a small cyclecar if I'm to get anywhere near my empty weight target. I suspect a golf cart axle would be likewise at presumably 50+kg if I could even find one, they're not common in the UK.

http://www.evdrives.com/product_p/mot-me0708.htm these look the right sort of size but at that price it'd be one driving a modified 125 bike gearbox and the smallest diff I could find. Anyone know if the 4.8/15kW numbers are realistic and will they stand higher voltages? Edit: Actually having just run the numbers through my spreadsheet if these will stand 300A for 1min then one motor would just about suffice with a single stage reduction onto a diff. I suspect in reality it'd be thoroughly saturated at 300A and kT well below my estimate derived from Kv=70. Anyone know of measured performance curves for these?

With that geared driveline though a big alternator may suffice and they're nearly free if a little bit harder to control and lower efficiency as is using a gearbox & diff for a vehicle that will be mostly cruising steady state.


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## Yabert (Feb 7, 2010)

If you want decent performance, why take a chance to burn a small motor when you can have way more power with a motor only 5 Kg heavier: http://www.evdrives.com/product_p/mot-me1003.htm

Some inspiration: 
http://www.diyelectriccar.com/forums/showthread.php/street-legal-vw-sandrail-dune-buggy-125425.html
http://www.diyelectriccar.com/forums/showthread.php/dc-powered-mini-buggy-165001.html
http://www.diyelectriccar.com/forum...-electric-trike-lithium-questions-167810.html


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## agniusm (Apr 30, 2012)

There is a guy in UK who sells used lmc 200-127 dc motors. They are 7+ kw each nominal and around 10kg. Hes on ebay. I can dig him up if you want. I also know someone who has some navitas tmp400 controllers. Motors are 150gbp each and controllers around 80gbp. All located in uk.
You can do electric differential but you will need 250usd programminf cable for navitas
Around 700 quid total for 14kw nominal and 34 peak.


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## jk1981 (Nov 12, 2010)

If you could find a link they sound very interesting, thanks for the tip.


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## jk1981 (Nov 12, 2010)

I've emailed the guy on Ebay selling the DC LEM-200s, two of those would be perfect if he really does have a stock he's trying to shift. We'll see, so far silence.

In the mean time I've stumbled upon a nice free industrial ACIM salvaged from a compressor, the external dimensions of the can minus heatsink fins and fan are about 14cm dia, 18cm long (5.5" x 7"), it's 18kg (40lbs). Nameplate says:
U 100-110V 50Hz (Odd as I'm sure this was running from 220V 50Hz)
I 16A
n 1400 /min
P 1.1kW

Can anyone suggest some reading to help me guestimate out how much excess power this might realistically convert and how I might estimate (or calculate) the torque and speed this is capable of? After all... free is the best price and it's physically the right sort of size 

Edit: as this was single phase with a big run capacitor (lost I think) I guess options are pretty limited. Might put it back in the scrap bin.


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## agniusm (Apr 30, 2012)

Have youchexked your PM? Ihave sent you hes phone number.


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