Nik, I appreciate the expertise and input you are providing.
Is the point you are trying to make that electric motorcycles don't need transmissions? Or that multiple motors is a better transmission solution for an electric bike than a transmission?
I'd love to understand, because from a physics standpoint, saying an EBike does not need a transmission just defies physics and common sense. I'm not arguing to argue, I'm arguing to learn...
I notice the KTM FreeRide is 30HP, but limited to 45 MPH top speed. That seems like a damming indictment of a transmissionless electric motor right there, but maybe KTM neutered it for other reasons.
It would be fun Glitch. I'm pretty tempted. If I thought I could build something like the Brammo Engage for $6k, I'd start next weekend. The part that scares me is riding an R&D project for a few years... I'd love to do it, but my "life stage" right now pretty much precludes it. I have a limited amount of time while my kids are kids, and I am not going to miss it.
Is the point you are trying to make that electric motorcycles don't need transmissions? Or that multiple motors is a better transmission solution for an electric bike than a transmission?
The latter, sort of. More that electric propulsion systems are different, and there are different ways of solving the problem that is accomplished by a transmission in an ICE vehicle.
Multiple motors is one. Multiple sets of windings in one motor casing is something I'd like to see. Connect the motors or sets of windings so they can be switched from series to parallel and end up with a motor system with multiple torque/rpm ranges, just like with a transmission. Water cooling and a controller with enough headroom to feed the motor would also go a long way.
I have a limited amount of time while my kids are kids, and I am not going to miss it. And a fine family you have! Me, on the other hand am finding myself a smaller and smaller part of my boys life. Not by choice mind you, it's just one's on his own already, one is trying to get out on his own, and my youngest is about to graduate high school and is visited all the recruiters in the area, enough for them to all know us. I've thought of doing it myself, but Ann and I are saving every penny to buy a farm and become as self sustaining as possible. If you'd like just send me the six grand and I'll do it at your direction, I'll even call it the Kilgallon Kilowatt In all reality though, I'll just read and dream about it learning a thing or two alog the way. I've done a lot of research on wind turbines, and this kind of fits in a bit here and there. There are some turbines that are geared to get the most out of the wind. The trouble with wind is that the higher gear you use the more wind you'd better have. A transmission on a turbine would be awesome, as weight isn't a factor, it'd only need a couple speeds I reckon. I digress. This is the kind of thread I love to read and it makes me think, which is a good thing, since I've been told that sometimes I act like I don't know how
how is it that the mag lev electric trains manage to scoot so damn fast ?
is any of that forced closed loop magnetic repulsion tech applicable here ?
I have the notion that two counter rotating motors in different fields of polarity, reciprocating off of each other would do something -.... I just can't imagine what.
(this is why I sucked at science, never could do the math )
on a side note, if y'all haven't guessed, my technical / mechanical skills are on par with Wyl E Coyote.
Excellent! With regards to that first article, he has the right pieces of the puzzle, but he assembled them wrong.
He actually nails the reason why a transmission is less helpful to an electric motor than it would be to an ICE, he just didn't realize it.
quote:
Most motors can put out a lot more maximum horsepower than they can sustain continuously.
That's it, right there.
For a normal electric motor application, you would most benefit from a transmission when you are accelerating. You know, drop a gear and haul ass. Once at cruising speed, you can "shift into overdrive", which is effectively bypassing the transmission on an ICE as well.
But think about it... how long do you need to accelerate? If you can do 0 to 60 in 15 seconds, then you only need to do it for 15 seconds. So you can use the ability to do a short term "overload" of your motor as a substitute for a transmission.
You could benefit from a transmission even more, but in this case, the "problem" you are solving is "how do I get extra power for acceleration". The answer could be a transmission (which would give more RWHP by allowing the motor to run at its most efficient RPM).
But the answer could also be "overload the motors windings with extra current which is safe for short periods of time".
And the answer could also be "add another motor winding". All three could be valid approaches, and you would have to grind through the math for the bike, it's target costs, and it's riding profile to make the right call.
That is also where the new Brammo motor could be a real ground breaker. It is liquid cooled. My guess is that the thing putting the time limit on "overloading" the motor is thermal... too much current causes too much heat, and you have to cut it off to save the motor after you have heated things up too much.
So what if liquid cooling changes the "burst" power rating of the motor? So with liquid cooling, what used to be burst is now the steady state power rating? Great, as in you can get more power out of a smaller motor. But you just lost your "boost" margin. You can't overpower it anymore.
Now, suddenly, the transmission becomes a lot more important. The transmission becomes the RWHP power booster.
how is it that the mag lev electric trains manage to scoot so damn fast
Fair question. To Nik's point, the maglev trains are so fast because they have many motors.
Effectively (if I am understanding the technology correctly, I've spent all of the last two minutes researching it) the maglev train has another motor (propulsion coil) embedded in the wall every few feet. Good for a train where it always goes the same place, as both the motors and the energy source don't have to move. Just the train moves.
Without a doubt heat is a big enemy to an electric motor. Even worse it creates more resistance in the coils creating yet more heat if you try to keep the power on. Same issues in all the wiring, battery, and controller. I wonder how much of the system actually gets liquid cooling on the Brammo. Of course you can also just specify equipment that will handle more current without burning itself up.
I see a problem with with only allowing full power for a limited time. I see lawsuits coming from not having the expected power available when you expect to be able to use it. I have a feeling that this is 1) why the claimed torque curve of the Zero is so flat at low RPMs, and 2) why the Zero lacks power off the line. I'm pretty sure the controller limits the amperage available to keep from burning things up. Electrics motors don't like full power at low RPMs very long. The simplest solution is to not give them full power at low RPMs... Ever. At higher RPMs the simply won't draw as many amps and will naturally stay cooler.
I think a transmission may get you to where you don't have to limit the amperage more quickly. There are obvious performance tradeoffs with weight and parasitic drag however. There's going to be another weird quirk however. We are used to IC engines that like to cruise at lower RPMs to achieve efficiency. This also helps them keep all the reciprocating parts from destroying themselves. An electric reaches maximum efficiency at high RPMs however. This creates a situation where shifting to higher gears fails to gain economy (one of the key goals with electrics right now).
Think about all of this as a package. Electrics have good torque at very low RPMs, as long as you don't over feed them and burn them up. This reduces the need for low gears. Electrics gain efficiency at high RPMs (and don't have reciprocating parts). This reduces the need for high gears. The target market for electrics are not those looking for long expressway rides, so the have little need to go past 60 MPH. So if you build it to top out at 60 you still have a fairly low gear to pull away from stop lights (probably already geared between 1st and 2nd on normal bikes), you get the benefit of low gears for taking off and the efficiency of high RPM at cruise. It's a different way of thinking than with gas. Also where a gas bike that tops out at 60, you would never want to run at that speed for extended periods. The electric is very happy doing so. It's for these reasons that a transmission isn't as useful on an electric. When you factor in the additional cost, weight, and parasitic drag, I just don't know that a transmission is a winner in the electric world.
I don't understand this idea of 2 stage windings. More winding will make a stronger magnetic field yielding more power. They also require more space, weight and electrical resistance, unless you reduce the gauge of the wire, then you reduce allowable amperage. More amperage will also yield more power, limited by your power supply. You basically want to design a motor with enough windings to generate a magnetic field that will get the job done without burning things up. You can always reduce power by reducing amps delivered. I don't see the need to complicate things with complicated wiring. While there's a real chance I'm very wrong about this, I just don't understand the need. Who's doing this stuff?
By more windings, I was referring to the discussion at one of the links above... the author was advocating adding a second motor (what I meant by more windings) instead of adding a tranmission. I don't know that I was completely convinced, but the argument is rational. The second motor didn't weigh much more than a tranny would, it spreads the load across two motors, and it allows you to get 2x the power out of the same voltage (at 2x the current of course).
A transmission might help with cooling in other ways as well. If you have a fan attached to your crank, then forced air cooling will be much more effective at higher RPM's for the same power output.
Power is "amount of work done". There are two ways it is manifest relevant to this discussion, a beautiful intersection of electronics and physics.
Electrically, Power (P) is Volts (V) times amps of current (A).
P = V * A.
Physically, Power (P) is Torque in foot pounds (T) times RPM (RPM) divided by a constant (5250).
P = (T * RPM) / 5250
So you can run a motor with the same voltage, but twice as much current, and double the power.
Likewise, you can have an internal combustion motor that runs at half the RPM, but twice the torque, and double the power.
Likewise, an electrical motor can run at twice the voltage, but the same current, and double the power.
And an ICE motor can run at twice the RPM, but the same torque, and double the power.
In the "two electrical motor" scenario, you have doubled the current, and doubled the power, without increasing the voltage (and without increasing the heat load in one motor).
In the "add a transmission to the electric motor) scenario, you are halving the torque, but doubling the RPM's, thus making exactly the same power, and drawing the same current at the same voltage (but now with a faster spinning crank, which means if you have a fan on it you are moving more air).
>>> how is it that the mag lev electric trains manage to scoot so damn fast ?
Low aerodynamic drag and no rolling friction either.
But top speed isn't the parameter dictating that a transmission is valuable for an e-bike. The issue of concern is acceleration from low speed, which even for a mag lev train can be pretty underwhelming.
