In wheel hub electric motors??

Controllers will always have a nominal efficiency at some point of their power curve.
I'm thinking for example, if we were talking about Brushed DC, then beyond a certain speed (when trying to reach top speed). It might be better to just eliminate the controller and have a direct connection to the batteries (assuming the setup is well balanced and the motor won't burn out).
By doing this you can eliminate any losses in the controller.
if the speed becomes too great you just power off from the pedal and roll until you need to boost again. (could be annoying if your not just holding top speed). Then perhaps there is reason to switch in a different type of controller solely for top speeds. By designing one that is more efficient at those high rpm high current demands there may be a little leeway as far as tweaking for speed or economy gained.
If we are talking in wheel motors then that is potentially 4 controllers worth of lost economy when operating outside of the nominal range for efficiency.
I'm getting carried away. I really don't know enough about efficiency of brushless motors and their controllers. I'm guessing a computer can control a variable frequency type drive and tune for efficiency continually. Although everything does have a nominal range at the end of the day depending on what it was designed for.
I doubt that there exists much of a solution for brushless apart from changing the timing perhaps.
It would be interesting to see the difference in top speeds with and without the controller in a brushed setup.
I remember my 1st RC car's speed controller. It was manual and controlled by a servo. at full speed it was just a straight connection to the battery, otherwise it had to pass through a high power resistor or two.
As far as the controller limiting rpm or speed, that may be the case but there is often a way around that by re-programming, over-volting or modification.
Once you have unlocked the full potential of the system, you would just need to be aware of your motors limitations in the respective wiring configurations.
You would need a watt meter or perhaps even an ammeter for each mode and just treat it like a rev counter. Don't red line for too long! Or just ask the controller to do this for you.
Perhaps have one controller for Delta and one for Wye. Each one setup differently to work best at those speeds. The switching relay could switch controllers at the same time as switching the wiring configuration.

Well Weather or not 4 controllers have more or less loss than one 4x their size is hard to say. But i guess my point was that there is always some loss in a speed controller and that they are probably made to be more efficient at nominal speeds (depending on the application).
I really think there could be a significant amount of power saved by eliminating the controller at top speeds which could work with a brushed motor especially if you were maxed out on a freeway for example.
I was just wondering if there might be a way to do something similar with three phase in order to get the best efficiency possible at top speeds. Since you need some sort of controller for three phase the only other option i could think of is to have multiple controllers that are designed to give better efficiency at different speeds. So for town driving the car would switch to the controller that was made to be most efficient at lower rpm. And when of the freeway the controller best suited to high speeds would kick in and the other/s would switch out and turn off.
The difference might not be much but who knows it might be as much as a 5% increase in range or it could potentially decrease the battery size by 5% which could result in a saving of weight (depending on the weight of the extra/modified controller).

Great point but perhaps 1% is not being generous enough
If i told you that there were two battery types available for your project and that one of them had 1% or 2% more stored energy available then you might decide to buy the better battery no?

If enough other tweaks could be made in other areas then might it be possible to see an even higher overall gain in efficiency?
If in the future electric cars start to cover longer distances as standard then this concept might prove worth while.

Cars could be covering many more motorway miles and thus the advantage may be realised more than 20% of the overall driving time, which is the ratio that you had suggested that we might be benefiting from if high speed economies were achieved if we changed the controller at different rpm (or by redesigning the controller to have a wider efficiency characteristics whilst still providing adequate output power across the rev range).

Also since motorway driving is done at higher speeds this also means that it is most likely going to be the time we see the highest current draw from the batteries. Which means that just a few percentage gained in efficiency will go a longer way at 300A per say when compared to the saving of a few percent at 80A for example whilst poodling around town or when driving at medium speeds around the suburbs.
If battery exchange / charging stations or perhaps even super fast charging stations are to be implemented in the future then perhaps these small gains will not be worth it, perhaps such technology would only be implemented in the higher end cars.
But at least for anyone out there who might be running brushed DC motors, it might be worth considering.
I doubt even the best controllers are actually more than 90% efficient in real life conditions. So imagine gaining 10% efficiency when running at full speed.
A pain in the ass when the only speed control becomes pedal on pedal off but perhaps there is still something to be gained here for someone reading this.

well you can start with this very thread
http://www.diyelectriccar.com/forums/showthread.php/wheel-hub-electric-motorsii-184393.html

and expand your search to the entire site with some googlefu
https://www.google.com/search?q=hub...m/forums&oq=hub+motor+site:diyelectriccar.com

But basically:

lots of unsprung weight, poor handling.

low torque (lack of gearing, otherwise 350nm isn't too shabby), might get stuck on a hill etc.

low power, comparatively. If you geared these down so you could climb a hill, you would have a top speed of like 10mph.

electrical bits splashing in puddles.

bouncing your motors off of curbs and ruts.

more rotating mass, more energy consumption.

less room for things like brakes.

motor cables flexing and work hardening, and generally being more exposed.

Virtually nobody does it, and those that do don't share all the relevant details, success is measured by if it backs out of the garage with little to no assistance.

etc. etc.

they are fairly practical on a commuter bicycle fyi, and with various mods you can push them hard enough to actually be good. But those are simple no suspension and already lightweight machines.

My stupid idea is to take an already perfectly good gas guzzler and add a pair of hub motors to the rear wheels of a 4x4.

Why has no one created a design like this:
You pull off the rear brake discs and mount a bunch of permanent magnets in a ring bolted to the wheels.
Then mounting a ring of windings to the brake calliper mounts.

This adds a small amount of extra weight, over what you've already removed.

You still have your front brakes which should be strong enough to stop the vehicle anyway. Using the rears now as regen.

Giving your car ability to increase its acceleration by only applying current from the batteries under acceleration (<30mph depending on throttle position) and under extreme acceleration (throttle >50% open).
If throttle position 0% enable regen.

Should be generic enough to work on any car, for a number of rear wheel sizes. Creating ones to replace the rear discs.


Please poke holes in this idea.

DrEVILish said:

... You pull off the rear brake discs and mount a bunch of permanent magnets in a ring bolted to the wheels.
Then mounting a ring of windings to the brake calliper mounts.
...
Please poke holes in this idea.

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The general idea is a parallel hybrid, and that's sound... due to the benefits of regenerative braking and making power available for greater brief acceleration without a larger engine.

The electromagnetic reality is that with these in-wheel non-geared motors running at wheel speed, they will have very low braking torque (too low to be effective) and low driving power (too low to be very useful). There is a reason that every practical traction motor is geared to run at much higher speed than the vehicle's wheels (and so the torque delivered to the wheels is much higher than the motor output torque).

A practical issue of construction is sealing these large-diameter rotating assemblies. A gap large enough to tolerate road dirt would not be efficient.

But the problem which kills the idea is that the motor/generators would be insufficient as rear brakes, because they would be neither sufficiently reliable not be sufficiently effective to be the primary braking system. The assumption that front brakes by themselves are adequate is false.

This sort of scheme has been proposed as an add-on to the brakes, rather than replacing them. That still has most of the same problems, and is less desirable than a conventional parallel hybrid (with the motor/generator mounted between engine and transmission) because it would be more expensive, heavier, and less effective.

WolfTronix said:

The brake disk its self could be the rotor in an axial topology AC induction motor. No magnets needed.

You could still have your brake pads and caliper for hydraulic brakes.

Then the rest of the circle is taken up with the stator coils.

Click to expand...

I'm sure this has occurred to many of us while daydreaming about future possibilities, but I usually imagine the rotor as PM. Induction helps both cost and temperature tolerance (needed because of the friction brake), but adds a challenge for regenerative braking at very low speed (because there is no torque without slip).

The rotor ends up completely encircled, which is a serious cooling challenge, so it would need to be vented (which is normal for front brake rotors, but not rears on production cars), with airflow radially through the stator.

Windings would normally be a major issue for a rotor which needs to withstand being used as a friction surface for braking; however, the intention would presumably to use the normal squirrel-cage design (rather than the relatively rare wound induction rotor); due to the axial flux the conductors would run nearly radially and be shorted by rings at the rim and inside of the stator face area. To my surprise - although in hindsight it makes sense - these rotors do not have insulation between the conductors and the laminations, so the brake pads could actually slide across the conductors and wear down their surface. Still, I wonder about the compatibility of a mix of iron and whatever the conductor material might be (aluminum or copper).

It may even be practical to use a solid aluminum rotor, although this would presumably be less efficient than a design with conductors across iron laminations, and would be problematic as a brake rotor. Aluminum brake rotors do exist - they're even a regular production item from Wilwood - but they are not ideal (for multiple reasons); they require an anodized, ceramic, or plasma-coated surface, and I don't know how that would affect induction motor performance. Solid aluminum would be simple.


There are two major issues with the motor-instead-of-brake idea: the loss of the brake, and the effectiveness of the motor. WolfTronix's dual-purpose rotor idea addresses the first, but still leaves the second.

WolfTronix said:

If you could manage 5HP continuous per wheel, and perhaps 10-25HP peak, it could work as a bolt on hybrid conversion.

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Even if the brake issues are manageable, as a motor the interrupted stator is interesting. With a PM design I can see how this could work, but with induction it is not so clear. Even if three-quarters of a stator is three-quarters as effective as a full stator, this is still a motor running at wheel speed, and not an optimal one at that.

The combination implies (in practical terms) that the motor gap would be open, rather than enclosed.

It might be a "bolt on" conversion, but it would not be a simple one, because the vehicle will have a mounting bracket for a brake caliper... not for a stator assembly. Vehicles designed for drum brakes but available with disks would probably be easiest, because they would accommodate a stator mounting plate similar to a drum brake backing plate. It also looks like a workable stator would be bulky compared to a typical disk brake caliper, so fit may be a challenge.