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Thread: A new type of controller technology?

              
   
   
  1. #1
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    A new type of controller technology?

    Now I will admit to not knowing much about motor controllers. I think they are what change the channels on my TV set. But the August (is it August already) issue of Motorcyclist magazine, in their Up To Speed section, on page 16, has an article titled "Smoother Than I.C.E., "How Electric Power Can Make You Faster". In this article it describes the advantages of an electric motor's torque spread when riding on a race track and then goes on to describe a new sophisticated controller technology developed by BRD that delivers torque in a pattern similar to a gas motor but more smoothly without the "between gear gaps".

    The article states that: The motor and controller technology used by BRD, for example, stays in the "constant power" zone for much longer, revving to 14,000 rpm and using an internal gear reduction to mimic conventional sprocket sizes, delivering more torque earlier in the rev range without sacrificing top speed. This delivers torque in a manner very similar to a gas motor but more smoothly - ......

    All very confusing to me. What about you?

    In the same issue of Motorcyclist, on page 20, is an article about the "One-Wheeled Wonder", the Ryno Monocycle (sounds kind of familiar to me), followed by a sidebar describing the McLean Monocycle, the BPG Uno, the Honda U3X and the Yike Bike (yikes!).
    Richard - Current bikes: 2018 16.6 kWh Zero S, 2016 BMW R1200RS, 2011 Royal Enfield 500, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior.

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    Electric Warrior CaptainKlapton's Avatar
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    Almost sounds to me like they are engaging the constant power region before the actual base speed... That would let the torque taper off like an ICE while increasing the range of the constant power region. I guess the gear reduction would boost the torque a bit while the torque is tapering off as the revs climb. Weird. I could be totally wrong though

    Full article here
    edit:
    Electric-Motors-101-v3-3.jpg
    This image seems to support that. Using greater reduction to boost torque while increasing revs and letting motor torque drop sooner. I would think the controller would need greater "leverage" on the voltage boost in order to get the extra revs though.
    Last edited by CaptainKlapton; 20 June 2014 at 0854.
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    Seņor Member podolefsky's Avatar
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    You can make any of those torque vs RPM graphs by winding the motor differently and changing the current and voltage. The slope of the line after base speed just depends on the torque constant, in ft-lb per amp. Theirs is just lower than other motors that have a very steep slope, so the kink is at lower RPM, and the curve extends out further. The location of that kink just depends on the controller current limit.

    Hard to say without more information, but don't think there's anything magical about it. They just tuned the motor, controller, and gearing to match a geared ICE torque curve.
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    Electric Warrior CaptainKlapton's Avatar
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    That would be a simpler explanation podolefsky. I was assuming that it was the same motor with fancy programming, but changing the wind is easier. Hopefully they tell us more soon.
    "Never let schooling interfere with your education."
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    Senior Member jonescg's Avatar
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    Well Voltron Evo is an interesting example of reaching base speed.

    We originally put a 17:42 reduction on the final drive. Assuming the motor could be spun to 5000 rpm this would give a theoretical top speed of 224 km/h. We got to 150 km/h and hit a wall, because the field weakening wasn't engaged; base speed was about 3600 rpm. It was the fastest 0-150 you'd ever experienced though

    Since then, we have changed the ratio to 17:38, giving a theoretical top speed of 248 km/h at 5000 rpm, or 170 at base speed. We're adding about 100 amps of field weakening, which means we start to lose torque at base speed, but gain rpm, meaning the outright power is pretty flat at this stage.

    We really need to get some onboard footage...

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    Seņor Member podolefsky's Avatar
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    Jones, I figure you know this - just for other peoples' benefit. Base speed and max no-load speed are only slightly related to top speed. Base speed is, by definition, the point where you have max voltage and max amps that the controller can provide. What ultimately determines your top speed is when motor power is just enough to overcome drag forces on the bike. If a motor is rated 5000 RPM no-load it is just that - at no load. At 150 km/h the load is huge, so your max RPM is much lower. You have to draw the power vs speed curve and see where the motor power and drag power lines intersect.

    You probably hit a wall because you reached the point where motor power = drag power. If you geared it just right, that might happen to be at base speed (which is, generally speaking, where you get max power). What can often happen is that if a bike is geared low, it will get above base speed before those two power curves intersect, so you're not at the max power point. If you gear higher, it brings you down near base speed where you have more power, which gives you a higher top speed. If you were to keep gearing higher, you would go below base and start losing power again.

    Part of why I think the BRD thing is a little misleading is that there is a difference between being in the "weak field" region vs "field weakening". Every motor has a weak field region - it is just anything above base speed. You don't have to use "field weakening" to get there, you just stay full throttle and the motor accelerates through those higher RPMs. There's nothing that stops the motor from spinning above base speed. The motor still produces torque at base speed, so it accelerates. As RPM goes up, BEMF goes up, which reduces current and hence torque. The torque plot of the BRD is exactly that - it is simply what happens when you apply full voltage to a PM motor.

    "Field weakening", as I usually think of it, is an active technique where you do something additionally to weaken the field. The most straight forward case is shunting current away from the field coils of a series motor. That weakens the field more, reduces the effect of BEMF and lets you get to higher RPM. It actually lets you get MORE torque above base speed, not less (because with less BEMF, you can draw more current, giving you more torque). That has to be the case, because field weakening makes the motor accelerate.

    Here's a video of doing true "field weakening" with a series motor. When I put the wire on, it is shunting current away from the field coils, weakening the field. The motor can already get well above base speed, this just lets you get a bit more torque than you would without field weakening.

    Last edited by podolefsky; 22 June 2014 at 2011.
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    Senior Member jonescg's Avatar
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    Actually no, we hit a wall because the motor wasn't tuned properly. If field weakening in a PM motor means you add current before the synchronous point to defeat back EMF, we were trying to add it after, so we literally hit a wall. No overspeed or tapering, just bam, top speed. Danny had to hold on when it happened.

    Once we tuned the motor properly, it steamed up to 3600 rpm and then it followed an asymptote to ~240 km/h. I understand the Evo motor is good for 5000 rpm while offering about 250 Nm.

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    Seņor Member podolefsky's Avatar
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    Ah, got it. I was thrown off because you said field weakening "wasn't engaged". I did the math, figured out you hit the wall around base speed and thought you meant the motor wasn't getting past that because there was no field weakening, which didn't make sense.

    Have to pardon me going off - for some reason I've got a bug up my butt about the way BRD describes their "advanced drive tech'. Maybe there's something to it, just to me it looks like a bunch of arbitrary torque curves where, of course, theirs looks the best. Maybe if I think about it more I'll understand why it's something special...
    - Noah Podolefsky -
    The GSX-E

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