Motors: High Speed, Low Torque, or Low Speed, High Torque?

Yes, we’re going back to the question of drive motors.

For most EV conversions, it seems, the trend is to go with high-voltage battery packs, spinning the motor at high (5-7000 RPM), and running that high-speed, low torque drive through the standard transmission and differential (To get a geared-down wheel speed of 2000RPM). This seems to be because the only way to control motor throughput is to control the voltage, with higher voltages making faster cars. It’s my understanding that a motor will take as much current as it “wants”, which makes low-speed, high torque motors very difficult to get (at least, off-the-shelf).

Personally, I believe that simplifying the drivetrain as much as possible is definately the best way to go. My real preference would be for a pair (or two pair) of wheelmotors. This isn’t feasable (As explained in a previous post), unfortunately. So my next choice would be to mount a pair of motors inbound, driving the wheels from their driveshafts (So, replacing the differential with a pair of motors, running in parallel). This is a problem, however, as driving these motors at the typical EV’ers voltage would give a ridiculous top speed (with 15” rims and fairly standard tires, with a motor speed of 5000RPM, you’d get a top speed of 1032KPH(!!!)) with little torque.

Now, I could be wrong with all my assumptions here (Which is probably quite likely). It could be that if you run a motor with such high torque loads on it, it takes all the current it needs to drive the wheels. It does mean that I need a very high current controller (5,000 amp? Higher?) which doesn’t exist yet, and I’d need very high-draw capable batteries (Or several paralleled strings of batteries).

How would other people deal with this problem, apart from using the transmission and differential and including all the weight, friction and power loss included therein? Should I just bite the bullet and leave the tranny in, rather than having to worry about all this high-current nonsense?

Thoughts, comments, and more are always welcome!

Hybrids, in series

It’s been a little while since I’ve posted anything here, but there is good reason – I’ve been haunting the forums of DIYElectricCar.com. I do still have some thoughts to share here (And which may be posted on their forums also).

“Series” Hybrids. These differ from “Parallel” hybrids like the Prius in that you have a generator hooked to the batteries, which is then hooked to the drive wheels, rather than (as the Prius has) both motors (ICE and electric) hooked to the wheels with some kind of fancy balancing transmission system.

Sounds easy, right? Grab an electric-start genny, throw it in the trunk of the car, make a quick-and-dirty bridge rectifier, and when the batteries get low just fire up the genny to recharge them as you go. Unfortunately, it’s not quite that easy (When is it ever that easy?). You have to get the voltage requirements and power load worked out properly too. For instance, the above won’t work if you’re not running a 120v battery pack. Your rectifier will give you a 120v (or 240v) feed, which will be too high/too low for your batteries and damage them, or not help in any meaningful way.

Of course, the other potential problem is that to recharge a cell you have to supply it more power than it runs at. So, to recharge a 12v lead-acid cell, you have to pump in 13.8v (Or there abouts). If you’re supplying higher voltages to your batteries, your drive motor is more likely to run directly from your generator, as there is more power available from there, and the batteries won’t see (much) charge. Some might consider this not an issue. If the motor needs the power, it would be draining it from the batteries anyway, and during the “lean” load periods the batteries will still be getting their charge.

A solution would be to run two battery packs in parallel, and when the time comes to start the charging system, switch one of the packs from “Run” to “Charge”, reducing the batteries driving the motor to one pack (And so halving the runtime) and charging the other, and switching between the two as needed. So, for instance, when the pair of packs reach 75% DoD, disconnect one pack and start charging. When the remaining pack reaches 70% (The danger zone for most battery packs), or the charging pack reaches 100%, switch packs so the freshly-charged pack drives the motor while the depleted pack now gets charged from the genny. The issue here would then be balancing the packs so they can be used in parallel once again. Of course, you could always just hook up the packs in parallel again and let them balance each other out, but that’s something that’s not so good for the batteries.

Any thoughts? Suggestions? Comments?

Keeping the metals happy

Here in Canada, we have a major problem with making and using BEVs. The ambient (before windchill) temperatures here can range from –45c in winter to +48c in summer. That is a huge range to cover, and most technology is only meant for temperatures down to –25c.

Coolant can (and frequently does) freeze in the lines unless treated with special anti-freeze for low temperatures. Diesel fuel gels (and can freeze solid in extreme cases), again unless treated. Standard lead-acid batteries will freeze also.

So, how do the regular Auto makers handle this?

Most (if not all) cars in Canada have a “Block heater”. This is a 110v electric heater that keeps the engine block and lines at or above 0c, and runs from a standard household power plug. Houses and apartment parking always has a block heater outlet, as do many stores parking lots, for their staff. This is great for us EVers, as it means we can get a nice charge during the day, while parked, from somewhere other than our own house! But we still have the freezing problem.

For “water-cooled” motors and electronics, the water can be replaced with a 50:50 mix of Ethylene Glycol, which doesn’t freeze until –40c. For most purposes, this is adequate. For lead-acid batteries, however, the same won’t work. Most cars with lead-acid batteries use a “Wrap” to warm the batteries, powered in a similar way to the Block Heater, but with additional coils from the battery itself. Other battery technologies are more resilient to extremes of temperature, for example LiFePO₄ batteries don’t freeze ‘til –40c, and NiMh perform similarly. Unfortunately, both are more expensive than PbA (Lead-Acid), but they also have greater energy density. However, while newer battery technologies don’t freeze so readily, they do still decrease in current availability as they get colder.

I guess the only real option is a thermostatically controlled heat wrap for your batteries, no matter their technology. It’s a shame that such a measure will reduce (potentially drastically) the range of the vehicle in winter months, which is arguably when you need the range most. I guess I’ll have to look into a GenSet, then. Or having the batteries in the passenger compartment, which would be heated (Or cooled in summer) for both passenger and power circuitry comfort.

Thoughts? Comments? Am I completely wrong about how batteries handle the cold (Probably)? Is the heat more of a problem? Let me know!

Re-Inventing the Wheel

Yes, that simple strip of folded and inflated rubber isn’t good enough for some people, including Michelin. So let’s have a look at the contenders.

DISCLAIMER: I’m not an engineer, or a physicist, nor do I have a doctorate in anything at all. I’m just an observer, and this is what I’m observing.

Michelin’s Tweel

This tyre removes the inflated bit, and replaces it with a mesh of strips of some kind. Obviously, they’re not revealing too much at this time, but this does have promise. I do see some problems, however.

• The “Contact patch” is very large, and very flat. This could lead to friction (“Rolling resistance”) issues.
• Just how this will handle turns is not shown. Seeing how solid it appears to be, in a lateral sense, this tyre may have issues turning, especially at low speeds.
• With all those “Spokes” straight like that, does anyone else see a potential problem with torque ripping this thing to shreds? I wouldn’t want to try a high-speed peelout with this.

Birtek’s Energy Return Wheel

This tyre also removes the inflated bit, but replaces it with hard metal bolts and a strip of “Stuff”, probably rubber or some kind of High-Density plastic foam. Problems?

• Incredibly hard ride. These are solid tyres, in all but name, with little to no deformation or give. I hope you like your spine shattered.
• No mention whatsoever on how this thing handles bumps and ruts in the road. With no cushioning in there, there could be shattered rims happening every time you hit a crease in the tarmac.

Peter Becker’s Super Tweel

Here we have a lawsuit of a name, waiting to happen. Let’s have a look at the problems, and bust some of his claims.

• He claims his tyre doesn’t deform like the Tweel, that it doesn’t go flat at the bottom. Yet when he shows his test on how his “Super Tweel” handles bumps in the road, the bottom is deformed just like the Tweel. Coincidence? No, it just shows his wheel concept is the same as the Tweel – Under load the contact patch deforms. This is not a bad thing, all tyres do it (Except perhaps the Energy Return Wheel, which may have grip problems due to the lack of contact with the road).
• Again, as with the Tweel we have the potential torque problem. This could be more of a problem due to the decrease in spoke density, though it could also be mitigated by the angle of the spokes (At least in his drawing – the model has straight spokes, just like the Tweel).
• Here, because of the crossing of the spokes (in cross-section), we have an issue with the tyre curling around the rim when a sideways load is applied. This design seems very prone to this, and is shown very well when he holds the “Super Tweel” next to his test stick and pushes down – The inner rim can be seen to twist quite alarmingly.

Personally, to judge this more fairly, I would like to see two of these “Super Tweel” models made, with the angled spokes as shown in the drawings, and fitted to an axle of a small trailer/cart. That way they could be loaded with a known mass (appropriate to the scale of the wheels and cart), and the deformation of the “Super Tweel” could be seen accurately, as could the bump clearing performance.

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Well, those are my thoughts on this, anyways. Any comments? Leave them below.

Motors, Transmission, Wheelmotors Oh My!

In my mind, there seems to be 2 ways to convert an EV.

1. Take out the ICE, petrol tank, exhaust system, hook an electric motor up to the drive shaft on the (manual) transmission and stuff it with batteries
2. Take out the ICE, petrol tank, transmission, differential, drive shafts, brakes¹, petrol tank, and fit a wheelmotor to each wheel.

Option 1 is obviously simpler, but introduces plenty of losses with transmission and differential gearing.

Option 2 is more complex, but rids the car of a lot more weight, and gives no gearing loss, along with simple 4-wheel drive. However, it does change (increase) the “Unsprung weight” of the car (A bad thing). Oh, and (at the moment) there is the not-so-small issue that there are no wheelmotors available on the market at the moment.

There are a few companies advertising wheelmotors, and they all have glowing stories (and video, in some cases) of their wheelmotors in action. But none are available. Let’s list the ones I’ve found:

PML Flightlink’s Hi-Pa Drive.

I’ve been watching this one for a while. They used to have a lot of technical details on this system on their site, including nice PDFs. But now the company is in administration, and their Hi-Pa Drive link goes to a very pretty site that is sadly lacking in technical information. They also used to state that they were not going to sell to individuals. While that piece of text is gone from their site, important details are still missing, and it’s not looking good for prospective EV converters.

E-Traction’s TheWheel.

(You’ll have to find it on E-Traction’s frames-infested site. It’s under “The-Wheel direct drives” –> “SM450”)

This is apparently up and running on a few busses in the Netherlands, and while they have pictures up on their site for a car-sized unit (The SM450/1), it’s not actually been made in any working form yet. They, too, will not sell to individuals.

TM4’s “Electric Corner Module”

(I kid you not – It’s meant for using to supplement existing ICE drive systems, but can (as they admit) be used as a totally electric drivetrain.)

This Canadian company (Quebecois, of course) shows these wonderful systems. The key phrase here, however, is that “Our experienced design team will work closely with you to meet your specific needs for an AWD drivetrain, using electric wheel motors or any other configuration, whether centrally mounted or not.”

In other words, call us, Mr. motor industry executive, and we will quote you a nice, exorbitant price for a complete system, including assembly-line tooling and the like. Small-batch buyers (Like individuals and small businesses), you’re not welcome.

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And that’s it. There are no other makers of automobile-grade wheelmotors, anywhere. Why is this? Is it that these three companies, between them, hold the patents to effectively choke anyone else out of making wheelmotors? Is there no other use for a small, efficient, and agile motor like these? You would think, with EVs, PHEVs, Hydrogen Fuel Cell’d EVs and the like, there would be more demand for such a groundbreaking technology.

1. Yes, brakes. With wheelmotors, you can Regen down to 0MPH, and they have a small mechanical brake for parking.

Starting out, what a thing!

I’ve been following many EV converters (Jealously, I hasten to add) for some time now. I’ve been wanting to get my hands dirty and make my own EV for many a year now. Unfortunately, finances are never available for this, nor indeed is the technical know-how to actually do anything with these strange auto-mo-cars.

“So why is this here?” I hear (Well, I imagine I hear… I suppose I should really see a doctor about that, but that too is not in the budget) you cry. “Why the heck are you boring us with this inane drivel?”

Well, I’ve been sitting and looking and thinking for a long while now, and there are certain things I just have to get off my chest about this whole EV thing. Some questions I want to ask, and some opinions I want to express, along with some responses to YouTube videos that are greater than the 250 character (or whatever it is) limit will allow. So I thought to myself “Self” (Yes, really do need a doctor’s visit, and soon), “You have a blogger account, from way back when it was still run by Pyra, why not use it for something worthwhile?” So here I am.

I guess that’ll do for an introduction. We’ll see what happens from here on out.