Motor Current Limiting: More Power and Less Heat!!!

[safe]

If you know the limitations of your motor, you can prevent it from getting too hot in the first place by controlling the throttle and avoiding the inefficient operating zone.

There are a lot of things that the "perfect throttle user" can do. But in a sense what a controller is supposed to do is to act out what would be the ideal throttle usage. The only control mechanism is the duty cycle... so it just seems to me that if it can be proven (which it can) that the peak power of a motor is found at a relatively high rpm and that high rpm represents the maximum heat production that the motor can safely allow (sort of like the "rated load" however pushing the limit a little closer to the real edge rather than the safer edge of heat that they publish) then if you can downshift your way or upshift your way into that perfect rpm all the time then you can't improve on that. All the potentially harmful (from a heat perspective) torque that you might have at your disposal is only going to count as a negative in comparison to proper gear usage.

As a guy with a geared electric bike I simply laugh sometimes at the very idea of riding around on a fixed geared bike. (it seems that so much of the psychology is bound to the fixed gear mindset) Once you have a geared bike you will never look back to a fixed gear in the same way. I just don't spend more than a few seconds in each gear (except on long uphills of course) as I accelerate and decelerate around town. To the geared bike user heat is a matter of gearing and NOT throttle control.

When you want to cool your motor you downshift.

When you want to heat your motor (for no good reason) you upshift so that the gear is too high.

When you want the maximum power for the minimum heat you get the gear selection just right. 8)

The "ideal" controller needs to help the user know when to select the right gear. That's the only thing that is really important if you think deeply about it... if you are in the right gear then the controller really needs to be nothing but an "on" switch... just let the battery flow to the motor because everything is going great in that situation.

Fechter, you ought to have a geared bike of your own as well as your fixed motor machine. It will open up a whole new world to you on the pragmatic usage of such a thing. Until you make a habit of it you just won't have the "feel" of it in the back of your mind. People who own multiple speed electric bikes can imagine what a fixed gear would be like, but the reverse is not true.

 

[xyster]

Fechter, you ought to have a geared bike of your own as well as your fixed motor machine. It will open up a whole new world to you on the pragmatic usage of such a thing. Until you make a habit of it you just won't have the "feel" of it in the back of your mind. People who own multiple speed electric bikes can imagine what a fixed gear would be like, but the reverse is not true.

Yah Fechter, since you've never driven a stick shift, played with gear ratios, performed a thought experiment, or ridden one of those new-fangled bicycles that use more than one gear, you obviously have no idea what you're talking about! :lol:

 

[safe]

Yah Fechter, since you've never driven a stick shift, played with gear ratios, performed a thought experiment, or ridden one of those new-fangled bicycles that use more than one gear, you obviously have no idea what you're talking about! :lol:

If you get used to a "habit" that involves using a fixed gear electric vehicle you will tend to start to think only in terms of a fixed gear. Any serious discussion about heat (remember that was the topic we were focusing on) has to take into account the effect of gear ratios.

There seems to be a sort of "self deception" going on when it comes to the electric motor. I think by now we've all looked at the electric motor powerbands enough to realize that things are not really all that much different than on a gasoline powered motor. A gas powered motor will overheat if you bog it down... so will an electric motor. A gas powered motor produces it's best efficiency at it's highest rpms... so does the electric motor. So as I see it there's this sort of "magical thinking" that people are telling themselves that makes them think that the electric motor is in some ways "new" compared to the gas motor and you can in a sense "reinvent the wheel" better than the old ways.

The electric motor is just like the gas motor... they are essentially the same in practice...

(despite the desire to feel like one is participating in something "new" it's really the same old story being repeated)

That's been my observation in all of this... the old wisdom of the racing world is still valid and needs to be applied in the electric world. Power, heat, gearing, these things are timeless and the sooner the electric world embraces history the sooner we "get back" to where we started... Right now the hub motor is essentially the same idea that Porsche had in the early 1900's before he switched to gasoline engines.

We need to go "Back to the Future".

The land speed record for an electric vehicle was set with a motor that has a transmission that had something like six gears. If the hub motor was such the "miracle cure all" that people imagine it to be then it would have been used for setting the speed record. (which is something like 300 mph)

 

[xyster]

I think by now we've all looked at the electric motor powerbands enough to realize that things are not really all that much different than on a gasoline powered motor.

They are very different beasts. In most electric motors, torque is highest at 0 RPMs. In gas motors, torque is pitiful until the engine revs up, usually peaking above 1000 rpms. For this reason, properly-sized electric motors need no gears. The Tesla sports car uses two forward gears and one reverse. The killacycle manages a 1 second 0-60mph time with direct drive (no transmission).
http://www.dragtimes.com/Dragster-Motorcycle-Timeslip-7621.html

http://en.wikipedia.org/wiki/Power_band

 

[safe]

The Tesla sports car uses two forward gears and one reverse. The killacycle manages a 1 second 0-60mph time with direct drive (no transmission).

Let's see...

Tesla... that's a $100,000 sports car that needs a drivers license and a whole load of other stuff to operate legally.

Killacycle... that's a motorcycle that if it's even street legal would require a license, etc...

For anything legal in the electric bicycle area for the forseeable future the American limit on power is 750 watts or just a little more. Let's say you are able to trick it out to a couple horsepower while still dodging the law. In such a situation where we know that given about a 2 to 1 performance advantage (for any given motor, gears roughly double the performance) with gears it makes sense to "push to the limit" to see what gear ratios can achieve. If the law caps the motor at 750 watts (which we know it will be otherwise your company can get sued because such a bike is considered "toxic waste") then you have nowhere to turn but to extract the last ounce of performance out of the limited motor resource. The natural evolutionary sequence becomes:

1. Forced Air Cooling.
2. Overvolting.
3. Overamping.
4. MCL. (to keep the heat down)
5. Gears to make full use of it all.

And heck... if you can get 750 watts (times 2) out of a 5 lb (or less) motor then it's all the better... :wink:

It's like we are forced to pass through a hole of a certain size that the government will allow. Once through the hole (a legally 750 watt rated motor) you can expand that on the other side to trick it out.

I just don't see any other way...

No matter where you "start" with a motor, adding gears always makes that motor "2x" what it starts out to be.

And your chart doesn't help your case very much... the peaky engine has 50 more horsepower... so in a race situation with a good driver that keeps the motor in the peak power all the time it will out perform the other less powerful motor that has better starting torque.

Peak power is everything up until you start having to deal with too much wheelspin, then you start to work backwards and try for more low end. Until wheelspin is a serious concern peak power is everything.

 

[dirty_d]

the tesla has an induction motor not a DC motor with an incution motor you can change the amount of slip between the rotor and stator by changing the frequency so you can change the amount of torque at any speed you're not stuck with a static speed/torque curve so you can do all kinds of funky electrical stuff to have the same effect as changing gears on a DC motor.

the killacycle is made to move 1/4 mile as fast as possible, not to reach the highest speed possible while minding motor efficiency, killacycle is all about power and keeping the maximum possible torque at the rear wheel to maximize acceleration.

 

[safe]

the tesla has an induction motor not a DC motor with an induction motor you can change the amount of slip between the rotor and stator by changing the frequency so you can change the amount of torque at any speed you're not stuck with a static speed/torque curve so you can do all kinds of funky electrical stuff to have the same effect as changing gears on a DC motor.

I'd really like to see the actual powerband of something like an induction motor. If it's possible to radically overcome the inherent limitations of the regular motor then it might be something to seriously look into.

Can you imagine a 750 watt motor that used the induction technology so that it produced nearly the same perfect 750 watts and high efficiency at all rpms? That would be the ideal motor to place into a street legal american machine...