Electric MV Motor Question

[mhenstell]

Hi all,

I'm building a small, hybrid MV. The car is built from scratch, about 7 feet long, and will weigh about 500 lbs including frame, batteries, generator, and body. I expect to be able to carry one driver and up to three passengers (so figure an additional 600-800 lbs, or about 1100-1300 lbs total weight).

The motor I'm considering buying for this is a Motenergy ME0909 (http://www.robotmarketplace.com/product ... E0909.html) which is a PMDC motor rated for about 4 continuous horsepower. As far as I can tell, this is roughly in the golf-cart range. It would be great to hear from people with more experience in electric motors, just to confirm that this motor is powerful enough to haul my car around at full capacity for a week without burning itself out. I plan to run it at 36 or 48 volts, geared down, with a controller controller capable of outputting 100 amps continuous.

Also, I see many people mentioning hybrid cars in this forum. If anyone has any recommendations for specific battery chargers I can look at for continuously charging my battery bank off a 2000 watt generator, that would be swell.

Thanks all.

[trilobyte]

If you're doing a continuous charge off of a gas powered generator, you would be wasting both money and energy. If it's going to be under continuous gas power, then just build something that uses that, and skip the expense, weight, and carbon footprint of all the extra parts you're buying) of an electric motor and battery cell system. Because of conversion losses, going from gas combustion to batteries to then power the electric motor, you'd be a lot less energy efficient than if you were just gas combustion to begin with.

[mhenstell]

Although it's tangential to the original question, the batteries are there for smoothing the load. Generators can't provide the sort of instantaneous power output that electric motors need, and running the generator at full-out 2000watts when nothing is drawing power is much more wasteful than having small batteries on board. The batteries don't need to be large enough to power the car for any significant period of time, just enough to act as capacitors for smoothing out the power draw from the motor. Also, heavy-duty battery chargers are common and easily obtained, 48v 100amp power supplies not so much.

[Dr Helix]

I'm with Trilo on this. Ditch the electrics. Almost all the people who do electrical MV's say the same thing; underpowered. You're ALREADY running a gas gennie just to keep topping the batteries. The gas power is on the demand and only used when the vehicle is running. I tried all electric my first year. Complete waste of time. All i was doing was keeping the batteries charged. You certainly are more than welcome to go that way (radical self reliance!), and you sound like you have WAY more experience in electrics than I do. All I can speak from is my own experience. Good luck and see you there!

[Canoe]

https://endless-sphere.com/forums/index.php

[Captain Goddammit]

If you waste your time and money on the hybrid electric setup, and you also design in a nice sturdy cleat on the front, I'll be happy to give you a tow back to camp when your electric junk gets messed up by the playa dust.

[Elliot]

In other news.... How did you arrive at 500 pounds? I once built a two-seat pedal car -- and discovered it weighed almost 1,000.

[mhenstell]

Yes, I know you all have hard-ons for gas engines. I've read every thread you've commented in, Captain Goddammit. Trust me, I didn't embark on this project yesterday. A combustion engine isn't feasible for this project because of several constraints. Glad it works for you, though.

Canoe - Thank you, I found this forum before and totally forgot about it. I will ask over there.

Elliot - Back of the napkin math. The metal frame is complete, and I can still lift it, which puts it at around 150 lbs. Drivetrain and electrics adds another 200 or so. The plywood body and sound system account for the remainder. I do add 20-50% for real calculations, but if I knew how to translate from motor torque output I wouldn't be asking here

[Captain Goddammit]

Yes, I know you all have hard-ons for gas engines....... Glad it works for you, though.

That's all us people who have been running stuff on the playa are trying to tell you.
However, huge credit to you for scratch building!!

[Captain Goddammit]

Seriously, we gave you a little shit about using electric drive with good intentions because we've seen it being troublesome on the playa, but I do really respect and admire anyone that scratch builds an MV instead of decorating a truck to look like a cardboard box or whatever.

[BBadger]

I don't think you'll burn out the motor. It can handle 300 amps for short durations, and your power system won't even approach that.

Maybe check out this thread on powering a charger that powers your vehicle. Then you can size your battery bank and voltages according to what is reasonable for a charger.

[EspressoDude]

what are plans for wheels and tires? bigger and wider lowers rolling resistance/sinking in the dust. try pulling your rolling chassis through a hayfield or soft sand. now try it with two engine blocks sitting on it. probably hundreds of pounds pull. figure that force at the radius of your tires and that gives torque needed. 200 pounds of pull on the chassis, 30 inch tires: 200 * (30/2) = 3000 inch pounds or 250 ft-lbs of torque required.

from FM 20-22 Vehicle Recovery Operations force required to move a vehicle (drawbar pull)
smooth road: vehicle wt/25
grass: vehicle wt/7
gravel: vehicle wt/5
soft sand: vehicle wt/4
mud: vehicle wt is minimum

using 1200# estimated weight and soft sand you will need 300# force at the tire tread: 30" tire ~ 375 ft lbs of torque

[mhenstell]

Seriously, we gave you a little shit about using electric drive with good intentions because we've seen it being troublesome on the playa, but I do really respect and admire anyone that scratch builds an MV instead of decorating a truck to look like a cardboard box or whatever.

Well I was going to stick some cardboard on a truck, but when all you have is 150 sq ft on the 4th floor in downtown Brooklyn, you're limited to what you can fit in a freight elevator.

Maybe check out this thread on powering a charger that powers your vehicle.

Thanks, I skimmed that thread before but I'll look through it again, that looks helpful.

what are plans for wheels and tires?

The two rear wheels are 18" x 6". Thanks for the calculations and example, that's helpful. I'll try and plug my own numbers into that and see what I come up with.

[Token]

The Dude is wise. Listen to the man.

I think his calculations are a "bit" off and you don't need a 300 #ft tug out there or half the cars would never make it off the highway.

But, he is right in the fact that aside from the weight of the vehicle, you omitted all the important stuff used to determine what kind of motor you need.

1. Tire - Tell what your vision is on tires. Wide and flat is good, Look for Elliot's pedal powered monsters for examples. Ultimately you need to know diameter and rolling resistance, or just fudge it and go wide for good measure.

2. Got some kind of axle? Is there a differential?

3. You want direct drive or is there some kind of gearbox? Remember that all the motors you are looking at typically go into vehicles that will drive quite a bit faster than 5Mph required on the playa.

4. Never ever use brushed motors like the one you linked for the playa. Brushes = Dead Motor in days. PMDC is the worst choice. I understand the appeal; simple PWM controller, cheaper overall, available, efficient. You need sealed brushless design. Right now the sweet spot in brushless motors price wise is sealed hub motors, which leads me to the next point ...

5. Two motors is always better than one, at 50% more cost (Controllers). This way you have a backup plan to limp home at 1/2 power. I bet you two 1.5KW 10" hub motors with a belt drive 10:1 to a half-shaft on each rear wheel will outperform a single 4KW unit running a gearbox, differential combo, plus give you redundancy and ability to switch to single tire drive for light loads.

6. Read the power curves. Look at the RPM you need at the motor shaft to support your desired speed and load. See where you stand. If you try to run a motor designed to spin 5K RPM max efficiency and never go past 1K RPM, you don't got the right motor or correct gearing.

Understand the specs of these types of motors.

RPM per Volt
Inch-pound of torque per Amp

Your goal is to run high voltage and low current to get the best range. You need some amount of torque even when cruising (your lowest steady-state load, as compared to taking off from a standstill) and the solution is gearing the thing right.

And finally, massive props for building from scratch. That is what it is all about!

[mhenstell]

Thanks, makes sense.

1. Tire - Tell what your vision is on tires.

Wide and flat. Two tires, 20" x 8" wide (I was wrong above). They're very close together in the rear, so it will do a little bit of skid steering but I think for all intents and purposes it's a trike with a very wide rear tire.

2. Got some kind of axle? Is there a differential?

Live axle connecting the rear wheels with a drive sprocket and disc brake. No differential.

3. You want direct drive or is there some kind of gearbox?

I was planning to use a one- or two-stage jackshaft system with sprockets to gear the motor down from 3000-4000 RPM to about 170 RPM, which would put me at 10 MPH (limited to 5 on playa of course).

4. Never ever use brushed motors like the one you linked for the playa.

Point taken. This was my biggest concern. Even if it does work, I'm guessing the motor would be more or less trashed pretty quick.

5. Two motors is always better than one, at 50% more cost (Controllers). This way you have a backup plan to limp home at 1/2 power.

I had thought of this, although I guess I was banking on a brand-new PMDC lasting at least a week. I'll look at sealed hub motors. I guess my concern is driving one live axle from two separate motors, which will probably have minor variances in speed. Is this a terrible idea in practice? I could add a differential but that's a bit more of a pain.

Hopefully that all makes sense. Thanks for the input guys.

[Elliot]

Roughly 900 pounds empty, propelled by bicycle pedals. The saving grace -- what gets this thing across Playa Dunes without hardly slowing... the tires; about 32" tall, 18" tread width.

[mhenstell]

That is awesome. Do you have selectable gears? Where do you get giant tires like that?

[dustyfux]

I run a 1K watt 48V hub motor. Batteries are 4 x 12V gel 50Ah. I use 4 smart chargers that I handpicked to work with the gel batteries. Typically, I see an 70% charge to full in 6 hours, and that translates to 18 -20 miles depending on speed and weight. Playa average is 650 pounds loaded at 3mph. I stop a lot, some say at every bar but that can be argued. Higher speed and/or weight will translate to a fraction of that range, one night while pulling about 900 pounds I probably cut my range in half. Charging is done by a Honda EU2000 and I would just tap in while it was running the camp.

One tip - put a kill switch in there somewhere. You think its unique enough that fucktards won't fuck with it, but fucktards fuck with everything. Its one thing to come back and find your rusted down fat tire has been liberated, but don't want to lose the thousands involved with an electric setup.

There was a couple out there last year who were running a setup similar to mine except on a recumbent trike with solar panels. They carried their whole camp and lived off the trike all week. I offered them to patch into the grid and have a long bar session, they took me up on the booze but were content with their solar.

[Token]

If you stick with a single motor, any 0907 (48V) or 4201 (72V) generic PMAC synchronous (not PMDC) will meet your original 4KW you linked.

[mhenstell]

dustyfux - thanks for the info, my car will definitely have a keyed kill switch.

If you stick with a single motor, any 0907 (48V) or 4201 (72V) generic PMAC synchronous (not PMDC) will meet your original 4KW you linked.

Oh cool, I didn't even realize they made PMAC motors in that same form factor. I'm guessing the dust isn't a big problem if you don't have brushes. It looks more difficult to find controllers for those but I'll take a look, thanks.

I'm also looking at hub motors, they seem tricky to find online (without shipping from china) although I might be able to find them locally. I'm not quite sure how I would rig it up though (a flat belt sounds iffy, maybe grafting a sprocket onto the side would work, but I would have to see one in person I guess.)

[Elliot]

On that red pedal car, I have used several different changeable gear arrangements over the years. I'm still trying to invent the ideal setup.

The tires are from dirt track race cars called Sprint Cars. They are best recognizable by the huge square wing on top, and they drive sideways around the corners. The tires are very thin and light.

[Canoe]

... I'm guessing the dust isn't a big problem if you don't have brushes. ...

Sounds plausible, but I don't know if that's been determined or not.
All the times I've ended up pushing someone back to their camp, it's been electric, batteries have charge, and they tell me that's what happens to electrics on the playa.
My cheap bolt-on-the-stays e-bike brushed motor works.

[Captain Goddammit]

Riding lawn mowers often have a nifty rear transaxle with a narrow track that has gears and is belt driven... of course I'd recommend using the engine too, but you could use your electric motor with one and have the ability to shift into low gear to get torque or just to run your motor at a good rpm while maintaining 5mph.
I lived in NY in the '70s... I suppose finding lawnmower pieces in Brooklyn might be a challenge but there's probably plenty over on Long Island.

[mhenstell]

If you stick with a single motor, any 0907 (48V) or 4201 (72V) generic PMAC synchronous (not PMDC) will meet your original 4KW you linked.

Token - out of curiosity, would you happen to have any experience with PMAC controllers? It seems like using regular BLDC controllers is a bad idea, and the only real PMAC controller I can find (Sevcon Gen4) sounds like a total clusterfuck.

[Token]

Yes. It is basically a 3-phase sync motor with Hall effect sensors. The thing Tesla (the inventor) crated a long time ago.

Controllers are pricey. Cost as much as the motor.


Sevcon and Kelly are the go-to guys for this.

It is a 3 phase power and 3 line Hall effect sensors with two of the Hall lines crossed out of phase 120 degree.

Go to Kelly as they also sell motors to go with their controllers.

Here is one of their kits for the 0907

http://kellycontroller.com/mars-0907-kit-p-677.html

[EspressoDude]

comment on earlier post: sample calculation was not intended to imply the playa is sand; or soft. most places would be considered 'hard surface' so drawbar pull to move the vehicle is closer to weight/25.

Brushes: have 'repaired' at least one vehicle alternator with a thump to the case. adjustable wrench, of course

[WileE13]

For an electric motor, you might want to look at forklift motors. Lot's of power for cheap. Better yet, get the whole forklift and use all the components.