Getting the power to the road

Having thoroughly discussed wheelmotors on here, I think it’s time to change subject completely and talk about wheelmotors.

Yes, you did read that right, and no I haven’t lost it.

Several home-built EVs, especially ones done for-cheap (For instance, Forkenswift), they’re done with DC motors taken from old forklift trucks. Usually the “drive” motor is used, and all is well. But flicking through the Princess Auto catalog a little while ago (What else do you do at 2:30am when you can’t sleep?), I came across a few interesting things, not least were some small, but reasonably spec’d Hydraulic motors. (I can’t link to them, their website is stupid – If products have the same name, you can only see one of them!) A little more digging, and I find a set of things called “Inline Axial-Piston” motors, which have great characteristics (Torque up to 83 ft-lbs (each!), top speeds of 3-4000 RPM). So my thinking is that, perhaps, one could take the “Pump” motor from a forklift, hook up some high-pressure hoses, and have the basis for a very space-efficient vehicle. With no need for drive shafts at all, it gives all kinds of space for batteries, and if you were custom-designing your vehicle, you could have a flat floor with the batteries inside (Using thin cells like LiFePO4 laid on their sides, for example), a small “Engine” compartment with the motor, controller and hydraulic splitter, and just some high-pressure hoses going from there to the wheels. Driving the motors in series/parallel would give reliable performance with behaviour like a limited-slip differential, and the difference in displacement between the pump and motors will act as the gearbox. And the units themselves are reasonably small and light, which completely throws away the whole “messes up the handling” problem.

But I’m no hydraulics expert (Heck, I wouldn’t know where to begin, to be honest), so ideally what I’d really like is for some hydraulics guru to take a look at this and tell me if I’m nuts for considering it. I know hydraulic drive is used in some low-speed vehicles (dump trucks, forklifts, that kind of thing). So why not high(er)-speed situations like this? We don’t need all 3000 RPM (heck, with 15” wheels and average tyres, you reach 120KPH (75MPH) at 1185RPM! 1500RPM would suit perfectly (give a little leeway for the racers out there :) )), but we do need the torque and power. Ideally, this system should also drive backwards. Not only for reversing the vehicle, but to be able to drive the motor ‘round, giving the option of regenerative braking too.

So, someone who has an idea what to do with these pipes and things, drop me a line and let me know if this’ll work or not.

Wheelmotors (yet again) and the Eliica

Yes, I’m going to talk about wheelmotors again. Mainly because I recently saw a video on the Japanese Eliica project. This uses 8 (yes, 8) custom designed and custom manufactured wheelmotors. Which, again, are not available for purchase anywhere. And this was debuted way back in 2004. Over 5 years ago. According to Wikipedia (Not the most reliable source, but it’ll do for this case), there are only 2 in existence, and while they’re fast (370 kph, or 230mph for you old-world proponents), and have a decent range (200km/120miles for the “Speed” version, 320km/200miles for the “Street” version), no-one is anywhere near touching them, or the technology they’re made from.

Just what is happening with the motor industry? It’s obvious the technology exists out there – all my previous posts here show it’s around. All we need is someone to take these disparate parts, put them together into one working shell, and float it on the market. Tesla is leading the way, but we need more. And while Obama’s plan in the US to incentivise EV production may also help the home converter, there’s still a lot of hurdles needed to jump before any kind of EVs really make it into the mainstream. And when the media stops with the whole “Look at this insane person – he took a working car and turned it into a high-speed golf cart” angle, and move closer to “covers all local commuting, costs $0.10 to ‘fill’, built by a novice for less than $5,000, will last for 10 years”, they might start getting the public more interested, and less amused.

On the subject of frozen metals

I have been reliably informed that LiFePO4 batteries will actually warm themselves in use (The internal resistance generates a little heat). This means, with a well-insulated battery box (and plenty of fresh-air cooling for during the summer), using and charging the batteries will keep them nicely within their operating temperature.

Of course, another idea would be to funnel “exhaust” air from the cabin through the battery box on it’s way out of the vehicle, too. As LiFePO4 are sealed, there’s no need to worry about gassing (As you need to with PbA). And at –40, you can bet the cabin heater will be running!

So then all you have to worry about is when the vehicle is sitting idle and not charging, say at a place of work with no available outlets. Then you really do have a problem, and it might be an idea to fit some kind of “command start” system for remote warming, or a temperature monitoring device, to ensure the cells don’t get too cold. And I believe it would be quite simple to repurpose a system for ICE cars (yes, they have them – keep your car nice and warm while you pop into the shops, it just idles the gas engine while it waits. Talk about inefficient!) to do a similar task for a battery box.

So, it seems, for Canadian conditions, LiFePO4 cells are the best bet. For now, anyway.

EV Speeds Calculator

Here is a nice little EV speed calculator…

Tyre Type Wheel Rim Diameter (mm) Tyre Depth (%) Tyre Width (mm) Total Diameter (mm) Wheel Circumference (mm)

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Motor Max RPM Gear Ratio Differential Ratio Final Drive Speed

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Top Speed (kph) Top Speed (mph)

Tyre Types should be entered using their standard notation (For example: “P175/35 R14”), or you can enter the numbers manually. Gear and Differential ratios are entered in standard x:y ratio format.

If you have any problems with it, drop me a line in the comments, and let me know what browser you’re using.

Motors: DC? PM? AC? SepEx?

Yup, I’m back, and thinking about motors again. “Didn’t we already cover this?” I hear you asking (Where is that shrink?). Well, some of this, but Motors are a big subject, and as they are the only moving part in an EV (if you’re direct-driving, anyway) they’re kinda important.

So, what are our options?

• DC Permanent Magnet
• DC Series Wound
• DC SepEx (Separately Excited)
• AC Printed Armature
• AC

Great. That tells you not a lot at all, doesn’t it? Let’s try a little more description of each.

DC Permanent Magnet

In this motor, you have a wire-wound iron core with a series of permanent magnets attached to the outer rim, or a “Squirrel Cage” rim, with a core of permanent magnets. When you power the coils with a DC current in the right order, which is handled with brushes in the first case, and switches in the second, it creates a magnetic field that pulls the core around. The more power you apply, the more torque you get, and (potentially) the faster you can go. However, as you increase speed, the magnets begin to induce power back into the coils. This power (Called Back EMF, or Electro-Motive Force) must be overcome if you want to increase speed further, and there comes a point where the Back EMF is the same as the power coming from the battery pack, at which point further acceleration is impossible. It is theoretically possible to harness the Back EMF to slow the vehicle and supply power to the batteries (Called Regen, short for Regenerative Braking), but very few controllers do so, owing to the complexity required.

DC Series Wound

This is like the Permanent Magnet motor above, but rather than having the permanent magnets, their job is done with a second set of coils, which are connected in series with the first set. This makes for a more powerful, but potentially less efficient motor. Also, as the coils are all connected, Regen is not possible with this motor, as if the coils are energised, they will be trying to drive the motor.

DC SepEx

Here, the inner core and outer core can be powered separately. This means that if you want to slow down, you can apply a small current to the inner core, which will induce a current in the outer rim. That current can be drained to create drag on the core, and to create Regen. It also means at higher speeds, you can lessen the inner core power, which reduces Back EMF and allows more acceleration, at the cost of decreasing the available torque.

AC Permanent Magnet

This is very much like a DC Permanent Magnet motor, but rather than just having two points of contact for + and – terminals, these motors have connections for each set of coils. This means when you apply an AC current to them, not only do you attract the magnets toward your coil, but when the polarity switches you push them away again. If you time the waveform of the power to the rotation of the core, you get a very fast, and very powerful, motor system. As the power is flowing in both directions through the coils, it also means that back EMF is neutralised (Indeed, the back EMF is used, rather than having to be fought). An AC motor is also the only other kind that can be easily used for Regen.

AC Printed Armature

This is like the AC Permanent Magnet motor, but the coils are stamped out of flat sheets, and applied to a disc, rather than being wound wire on a stator. These are typically made small, and used in servo motors, though some companies have been trialling making these for vehicle-sized applications. Difficulties with making strong discs to mount the coils to, along with a seeming lack of interest from the industry, is making these almost impossible to find, and definitely impossible for an individual to buy.

In order of preference, These should be arranged:

1. AC Printed Armature
2. AC Permanent Magnet
3. DC SepEx
4. DC Permanent Magnet / DC Series Wound

But availability and controller complexity has made real-world implementations read more like this:

1. DC Permanent Magnet
2. DC Series Wound
3. DC SepEx
4. AC Permanent Magnet

And for most car-sized EVs, it’s PM motors only. SepEx are only available in sizes up to around motorcycle size, and there doesn’t seem to be any AC PM controller out there.

Oh, and all these (that are available) require some kind of transmission, as they don’t have the grunt to start a vehicle from 0km/h without some kind of torque multiplication (a gearbox).

If money was no object, I’d buy 4 AC Printed Armature motors (Custom made), a Citroen C6 “Glider” (That is, car without engine, transmission, differential, fuel tank etc), a massive load of Li-Poly batteries (200-500Ah minimum), plus a BMS to manage them all, and stack of meaty ultracapacitors to help with acceleration and regen braking. Which would be just about everything needed. Still, we can dream, right?

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.