RC motors, efficiencies, gearboxes and more?

[liveforphysics]

Every technology has its applications.

Luke is correct in general. However, some applications require much less weight than a large hub motor. Also, rotating, unsprung mass is an absolute no no for handling.

Fire ultra light weight with high peak power, small high RPM motors with additional reduction seem best with current technology. For simplicity and ultimate direct drive, powering the wheel directly had is advantages.

Arguing this is like arguing the merits of a trim hammer versus a sledge hammer. They are each ideal for their intended purpose.

Matt

It has the potential to be both lighter, more efficient, more powerful, more torquey, and cheaper.

It only isn't today because designs embracing the potential of electric drive aren't even close to mature yet.

 

[recumpence]

Unsprung rotating mass is still an issue.

Matt

 

[liveforphysics]

Unsprung rotating mass is still an issue.

Matt

A single power transfer stage like a belt or something likely will make sense for at least a few years still until the right topology exists to put the motor into the rim while adding negligible additional weight.

Right now, using a very today-feasible technology like Mile's ultra-light hubmotor magnetic design, a very high power motor could be added to a wheel for less than the mass of a motorcycle tire. Once the structure of the rim starts serving the second function of also being the motors rotor (maybe induction?), things will start getting very light weight.

Essentially, the greater the surface you can get your motor to occupy, the higher the power per unit of weight the vehicle will be capable of once optimized. If you take the magnetics for your electricity to torque conversion machine and wad them all into a little compact ball, this is kinda the worst case for continuous power (which is always a thermal limitation). If you take the same mass of magnetics as the small motor has, but spread them out on a working radius the size of the rim, you improve the continuous performance by perhaps an order of magnitude.

Think of taking the same ~2lbs of iron and copper in a compact RC motor, and distribute that same mass of iron and copper around the diameter of a rim. The slot for each tooth is maybe 2-3mm deep or whatever, it's going to have maybe 500 teeth or whatever, the magnets (or go short-flux-path switched reluctance) are maybe 0.2mm thick, perhaps in a halbach array or whatever. You end up not weighing any more, but making the torque through applying a force on a long moment arm this way, and the parts that get hot have a whole order of magnitude improved surface for thermal dissipation.

I realize that there is nothing like it for sale today. This is because EV drivetrains are still very much evolving in a mindset tainted by previous limitations of ICE engines that needed to be tiny and high RPM to have decent power density. Electric doesn't suffer any such limitation to be light and powerful, one may simply push the limits of the geometry and manufacturing processes until you arrive at the electricity to torque converter one finds best suited towards turning a wheel.

It is the inevitable path forward, because all other paths are performance/efficiency compromises. May take 5-10 years or something before we see anything like it available off-the-shelf though.

 

[macribs]

Unsprung rotating mass is still an issue.

Matt

A single power transfer stage like a belt or something likely will make sense for at least a few years still until the right topology exists to put the motor into the rim while adding negligible additional weight.

Right now, using a very today-feasible technology like Mile's ultra-light hubmotor magnetic design, a very high power motor could be added to a wheel for less than the mass of a motorcycle tire. Once the structure of the rim starts serving the second function of also being the motors rotor (maybe induction?), things will start getting very light weight.

Essentially, the greater the surface you can get your motor to occupy, the higher the power per unit of weight the vehicle will be capable of once optimized. If you take the magnetics for your electricity to torque conversion machine and wad them all into a little compact ball, this is kinda the worst case for continuous power (which is always a thermal limitation). If you take the same mass of magnetics as the small motor has, but spread them out on a working radius the size of the rim, you improve the continuous performance by perhaps an order of magnitude.

Think of taking the same ~2lbs of iron and copper in a compact RC motor, and distribute that same mass of iron and copper around the diameter of a rim. The slot for each tooth is maybe 2-3mm deep or whatever, it's going to have maybe 500 teeth or whatever, the magnets (or go short-flux-path switched reluctance) are maybe 0.2mm thick, perhaps in a halbach array or whatever. You end up not weighing any more, but making the torque through applying a force on a long moment arm this way, and the parts that get hot have a whole order of magnitude improved surface for thermal dissipation.

I realize that there is nothing like it for sale today. This is because EV drivetrains are still very much evolving in a mindset tainted by previous limitations of ICE engines that needed to be tiny and high RPM to have decent power density. Electric doesn't suffer any such limitation to be light and powerful, one may simply push the limits of the geometry and manufacturing processes until you arrive at the electricity to torque converter one finds best suited towards turning a wheel.

It is the inevitable path forward, because all other paths are performance/efficiency compromises. May take 5-10 years or something before we see anything like it available off-the-shelf though.

Wow. I wonder why engineers have not already embraced that idea. When you lay it out on the table like this it does seems obvious, it makes all kind of sense and one can not help to think why have this not already been done? Are even engineers biased and narrow minded like the rest of us or are there hidden problems we don't see from where we stand?

Are you aware of anyone working towards this? You mentioned Miles. Is it a train of thoughts for Miles or is he actually making progress or doing real world tests? Imagine 40 Kw peak or more in the wheel without adding significant weight. And think of the efficiency, we could probably get even more from the batteries then today just by the added efficiency alone.

Maybe then we will see even 2WD that does work fully as intended without the drawbacks of today. We would see even faster acceleration, less chance of flipping over during flat out take offs and traction on 2 wheels when it matter the most. Would make for a great traction control/ESP base function in the controller. And surely that would find its way into other EV markets as well as e-bikes and motorcycles/scooters.

A real world example is Tesla and their drive unit problems. What if they had motors like this directly in-wheel? Would the copper/magnets needed to get enough power be too on par with the motors they use today or would it even be possible to use it for 19"/21" car wheels without drastically add unsprung weight. And could added weight be countered by using even more exclusive alloys or materials for the wheel? I know Brabus have an Electric Mercedes E class with 4 hub motors. But they have not done the research to make their own motors in any way like you sketched here. Rather they bought over the counter hubs with the penalty of more unsprung mass/weight where you in fact need to lighten things for better handling.

Is it really that long ahead you think, as 5-10 years? What would be the main problems to overcome you think? Imagine you start with a blank paper. Nothing needs to be as we know it today. Not the rims, spokes hubs, magnets or copper. Where would you start and what problems can be predicted?

 

[recumpence]

Unsprung rotating mass is still an issue.

Matt

A single power transfer stage like a belt or something likely will make sense for at least a few years still until the right topology exists to put the motor into the rim while adding negligible additional weight.

Right now, using a very today-feasible technology like Mile's ultra-light hubmotor magnetic design, a very high power motor could be added to a wheel for less than the mass of a motorcycle tire. Once the structure of the rim starts serving the second function of also being the motors rotor (maybe induction?), things will start getting very light weight.

Essentially, the greater the surface you can get your motor to occupy, the higher the power per unit of weight the vehicle will be capable of once optimized. If you take the magnetics for your electricity to torque conversion machine and wad them all into a little compact ball, this is kinda the worst case for continuous power (which is always a thermal limitation). If you take the same mass of magnetics as the small motor has, but spread them out on a working radius the size of the rim, you improve the continuous performance by perhaps an order of magnitude.

Think of taking the same ~2lbs of iron and copper in a compact RC motor, and distribute that same mass of iron and copper around the diameter of a rim. The slot for each tooth is maybe 2-3mm deep or whatever, it's going to have maybe 500 teeth or whatever, the magnets (or go short-flux-path switched reluctance) are maybe 0.2mm thick, perhaps in a halbach array or whatever. You end up not weighing any more, but making the torque through applying a force on a long moment arm this way, and the parts that get hot have a whole order of magnitude improved surface for thermal dissipation.

I realize that there is nothing like it for sale today. This is because EV drivetrains are still very much evolving in a mindset tainted by previous limitations of ICE engines that needed to be tiny and high RPM to have decent power density. Electric doesn't suffer any such limitation to be light and powerful, one may simply push the limits of the geometry and manufacturing processes until you arrive at the electricity to torque converter one finds best suited towards turning a wheel.

It is the inevitable path forward, because all other paths are performance/efficiency compromises. May take 5-10 years or something before we see anything like it available off-the-shelf though.

The problem here is what is possible versus what is available.

If someone asks me if a steel saw is better than a carbide saw, I would not answer "You should buy a laser". First, that is not their question. Second, that is not something that is available to the mass market for their intended use.

I completely understand your point. A friend of mine was working on a rim motor that functioned like a linear motor (almost like a rail gun) that was round and became the rear rim. He did not have the resources to take that project any further. I am sure many people have considered this. But, since it is currently vaporware, there is no reason to promote this technology in a thread asking a simple question regarding the best direction to go for a build.

Please understand, I am not arguing your position. In fact, I agree wholeheartedly. I have a huge amount of respect for your contribution to the EV revolution and your presence here.

Many things are possible. But, only a limited number of products are available currently. We need to build with what is available today.

Matt

 

[liveforphysics]

The problem here is what is possible versus what is available.

If someone asks me if a steel saw is better than a carbide saw, I would not answer "You should buy a laser". First, that is not their question. Second, that is not something that is available to the mass market for their intended use.

I don't create or impose my own imagined restrictions upon what someone thinks may be mass market intended use of things. If I were the type to make choices for what was mass-market-intended-use case for things, I would have never bothered to make an ebike. Do you see using RC heli/plane motors to power bicycles as the mass-market intended usage of the product?

In the case of carbide saw or steel saw, I am suggesting the laser. I think that's a good example. If you wish to eventually see lasers in the world, step one is letting people have awareness it's also something that exists in the realm of the possible.

Many things are possible. But, only a limited number of products are available currently. We need to build with what is available today.

Matt

If everyone followed your advice my friend, we would never again see innovation or improvement. It is only through the act of creating and building what isn't available today that we grow the bleeding edge of ebike development. No amount of making endless copies of compromised designs results in the creation of an uncompromised design. Uncompromised designs will only occur after folks first gain awareness that uncompromised designs are an option.

It is this first critical awareness that I am bringing to the minds of those who are creating the future of ebike with each new project.

Ultra-light ultra-efficient direct drive hubs have so much to gain from your amazing machining and design and fabrication skills my friend. So many mechanical design challenges in packaging and adequately supporting the uber-thin magnetic stage, we could all use your awesome mind and tools towards creating the path of uncompromising efficiency and light-weight performance.

I'm not in any disagreement with you on what is currently possible to order parts for and assemble and ride. My objective is to spur the thoughts that provide awareness of an even brighter future of EV performance than we know today. One can't take the critical next step in EVolution until one has awareness of the direction to travel.

 

[panurge]

Compared to you 2 guys (Luke and Matt), I know nothing in these arguments, but I think that you are among the members on the forum that show everyday with your skills funds and time, what could be done "thinking outside the box" each one in a crucial field of application and research for the re-volt: the state of the art for small production runs using non mass stuff (Matt) and the material state of science-fiction for racing purposes and concepts on electric bikes (Luke). I completely Agree almost all of your statements and comments (both) so that, from my perspective, I know your words and concepts are not in contrast, but otherwise complementary....

Anyway, Luke, the MAGrim concept that all of us has figured out at least 1 time, is not yet at least prototyped by the germans of LightWeight with the "Velocitè"?

http://road.cc/content/news/128979-lightweight-show-e-bike-concept-eurobike Me and Justin, we have seen that proto at Eurobike....unfortunately it was not working there, But I know (from them but even from external channels) that it works.
What surprised me is that this e-bike (14.5kg) has more weight in electric stuff than in the donor bike itself...(less than 7Kg) What do you think about? it is ironless or what? they say even to me at the show, that could reach potentially 80kph...

Cheers

 

[Punx0r]

It would be very, very cool if stator windings covering such a small part of the rotor (wheel) like in that prototype worked well. Then again, bicycles often have mud guards, so you could cover 1/4 to 1/2 of the wheel without affecting functionality. Obviously there'd be a large clearance around the tyre for mud, with just a tight clearance at the rim where the magnets are. We might also have to redesign the wheel to increase stiffness and reduce run-out.

 

[kenkad]

The Velocite is a great idea!

Carbon fiber rims are not all that expensive, are they? What if I hit a pot hole and some of the magnets disappear? Just order new ones from K&G Magnetics! But first, what if the wheel rim wobbles? No problem, just put rollers on it to keep it true. Aw shucks, more drag, does that mean lower efficiency? What else can go wrong? Try changing a flat. Even better, the coils should actually float using some type of vibrating coils that tracks wheel wobble. So much fun making technology.

Yes, I do have sheet metal parts cut by CNC laser machines. BUT, if I need machining accuracy, I still have to use a CNC mill. Everybody loves technology, until they have to either fix it themselves or pay big bucks to have it fixed. Then, I wish I was still driving my 1978 Sirocco instead of the over electrified new Miata. No chance of fixing that in spite of designing uC based electronics all the time. I guess I am just getting too old. Do not take this seriously!
kenkad

 

[DanGT86]

That is a cool idea. It has me really wondering about the forces at work on the wheel. In a normal motor there is a lot of rigidity so the fields driving the motor cause it to spin rather than just deforming. If you had a high powered wheel motor like that I wonder if the field would push/pull the wheel out of round rather than rotating it. I also don't understand motors well enough to know if they prefer to spin in a circle because of the way they are energized or if its just because they don't have much choice due to how strong the materials are. This forum always gives me something to wonder about.

 

[windtrader]

The bike using the rim as part of the electric drive seems promising, too bad it did not work. My knowledge of electrical and mechanical theory, principles, and design fits inside one grain of sand but it seems with current electronic and materials technologies, there should be working prototypes of whole wheel motors with the rim behaving like an outrunner and the inner space used to drive the outer shell (rim with tire). Is the primary issue weight or mass or efficiency, etc?

 

[halcyon_m]

That is a cool idea. It has me really wondering about the forces at work on the wheel. In a normal motor there is a lot of rigidity so the fields driving the motor cause it to spin rather than just deforming. If you had a high powered wheel motor like that I wonder if the field would push/pull the wheel out of round rather than rotating it. I also don't understand motors well enough to know if they prefer to spin in a circle because of the way they are energized or if its just because they don't have much choice due to how strong the materials are. This forum always gives me something to wonder about.

most motors will have significantly more force pulling the rotor to contact the stator, rather than move parallel to it. Typically that factor is 3:1 or 10:1, so the mechanics of constraining the rotor and stator become significant. There are tricks to balance forces, like maintaining equal gaps on each side of an axial flux machine, so the rotor doesn't get pulled in one direction or another too hard as the forces mostly balance (though the outer-most elements really want to collapse on the whole motor like a brake caliper). Another trick is to use an ironless stator (brushless) or rotor (dc brushed) which then allows the force on the wire to be completely orthogonal to the magnetic field, which is typically in the direction of rotation.

It's more a mechanical issue than anything. If mud, sand, or gravely bits get into an open-frame style motor like we are discussing here, it can cause a lot of damage and kill the motor quickly. Besides the topic of practical weather seals, as I brought up before, the key to maintaining mechanical clearance in a mechanically compliant (soft/squishy/bendy) system, is locally coupling forces. This means putting multiple small roller bearings around the outer rim to keep the rotor and stator from rubbing. This is kind of like a roller coaster car running along a track.

 

[jerrydubois3]

Are you guys still using batteries? I switched over to the "Flux Capacitor" years ago....of course I can only go 88 miles per hour

 

[recumpence]

My nuclear radio isotope flux reactor is in the prototype stage right now. :wink:

Matt