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Christoph Zens

We need better technical specs before purchase

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esaj    5,292
2 hours ago, Christoph Zens said:

I feel that torque over speed is the most important information missing as of today. In a wheel designed for 30kph operating speed, the motor could either barely make the 30kph and be almost out of torque (which would be very dangerous and should not be the case with any current wheel, just an example), or it could have beed designed to go 70kph or more, meaning that it still has ample torque available at 30kph. The drop in torque would be much more flat and less noticable, adding a lot to safety for 'fast' riders. Electrical motor power alone is a hint, but does not tell the whole story.

From what I've gathered, it's even more complex for electric motors. By altering the windings (amount of wire turns in the coils) of the motor, you can "adjust" the Kv-/Kt -ratio (rpm per volt and torque,  https://en.wikipedia.org/wiki/Motor_constants#Motor_velocity_constant.2C_back_EMF_constant ); higher Kv , ie. higher max speed for given voltage drops the torque and vice versa (see the equations, Kt = 60 / (2 * PI * Kv) ).

So the example of wheel that could go "only" up to 30km/h (for the maximum voltage) would have much more torque (before it runs out of speed, not torque at the highest voltage) than one with similar motor power but speed up to 70km/h. If both motors were compared at, say, 25km/h (because the other one's capable of 30km/h max only), the "slower" motor would have higher power output and more torque at the same speed (basically, the slower one would reach the peak power output at slower speed). Could be wrong though, that's just how I've understood it.

Edited by esaj
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Christoph Zens    284
8 minutes ago, esaj said:

From what I've gathered, it's even more complex for electric motors. By altering the windings (amount of wire turns in the coils) of the motor, you can "adjust" the Kv-/Kt -ratio (rpms per volt and torque,  https://en.wikipedia.org/wiki/Motor_constants#Motor_velocity_constant.2C_back_EMF_constant ); higher Kv , ie. higher max speed for given voltage drops the torque and vice versa (see the equations, Kt = 60 / (2 * PI * Kv) ).

So the example of wheel that could go "only" up to 30km/h (for the maximum voltage) would have much more torque (before it runs out of speed, not torque at the highest voltage) than one with similar motor power but speed up to 70km/h. If both motors were compared at, say, 25km/h (because the other one's capable of 30km/h max only), the "slower" motor would have higher power output and more torque at the same speed (basically, the slower one would reach the peak power output at slower speed). Could be wrong though, that's just how I've understood it.

Yes, since power is basically torque times RPM, there can be different motor configurations, all rated for the same power output, but with different RPM/torque ratio. That's what I meant by "motor power alone doesn't tell the whole story". From the power rating, the end user can not deduce what the motor configuration is and how much torque it would deliver at a certain speed. My example about using different motors in wheels rated for the same top speed did not assume same motor power.

When I decide on a car or bike (riding heavy motorcycles for around 25 years now), I always look at the torque characteristics of the motor for an educated guess about how the vehicle will perform. I would love to see such a graph for EUCs one day. Maybe legislation in Europe, which is in general pretty over-regulated in every aspect, will demand such measurements in some sort of official approval, to make sure the EUC is safe (as safe as it can be riding on one wheel) in the sense of providing enough torque to stabilize the unit in all common situations. Pot holes will always cause crashes...

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Rehab1    5,983
4 hours ago, Christoph Zens said:

I would like to make a case for better technical specs provided by the manufacturer in their data sheets. 

 

Best of luck! If GW happens to contact you please ask them what are the specs for their hall sensors!:) I have been contacting them for the last 2 weeks and have yet to obtain any data.

I believe many of the specific specs you would like to see are proprietary and releasing them to the public would provide the competition with an edge.  :ph34r: Just my opinion.

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Mono    1,287

@Christoph Zens, good points, in particular torque vs speed would be really, really nice to have. My guess though is that quite a few manufacturers don't even have these data themselves. BTW, at 20% actual (not the number shown in the app) battery capacity I assume many wheels don't even turn on anymore, let alone move with more than 5km/h.

Let me add a few important measurements:

  • available negative torque vs speed, i.e., the graph of maximal brake power depending on speed
  • inner and outer pedal ground clearance
  • pedal dimensions, which are rarely available from the data sheets but IHMO quite important 

I would also be interested at which voltage the wheel shuts down completely and how many Wh are left in the battery then.

Edited by Mono
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esaj    5,292
35 minutes ago, EU GUY said:

Would it be possible to test the euc's power at different speeds with a dyno?

Some people in Russia (I think) already did that, the pictures of the charts are floating around somewhere in the forums...

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meepmeepmayer    2,406
7 minutes ago, esaj said:

Some people in Russia (I think) already did that, the pictures of the charts are floating around somewhere in the forums...

I can't re-find it, but this is a fantastic power test of a few wheels on some Russian site (Google translate makes it very readable). Everyone interested in the topic should have a look at their findings. I'm sure someone knows the link.

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Kingtide    3
44 minutes ago, meepmeepmayer said:

I can't re-find it, but this is a fantastic power test of a few wheels on some Russian site (Google translate makes it very readable). Everyone interested in the topic should have a look at their findings. I'm sure someone knows the link.

Here you can find the Russian site with the dyno test:

http://airwheel.ru/test-monokoles-na-dinostende/

Use google translator to get at least an idea of what they are saying. 

 

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Christoph Zens    284
22 hours ago, Mono said:

@Christoph Zens, good points, in particular torque vs speed would be really, really nice to have. My guess though is that quite a few manufacturers don't even have these data themselves. BTW, at 20% actual (not the number shown in the app) battery capacity I assume many wheels don't even turn on anymore, let alone move with more than 5km/h.

Let me add a few important measurements:

  • available negative torque vs speed, i.e., the graph of maximal brake power depending on speed
  • inner and outer pedal ground clearance
  • pedal dimensions, which are rarely available from the data sheets but IHMO quite important 

I would also be interested at which voltage the wheel shuts down completely and how many Wh are left in the battery then.

Oh yes, pedal dimensions! I don't know why this is missing most of the time. Maybe for Asia, pedals are by far large enough and no one really cares, but for Europeans, they can feel pretty short at times. Ground clearance is related to maximum lean angle, but I agree it should be specified since it's a different kind of property. It would not tell you how much you can lean into a turn, because maximum lean will also depend on pedal width, but it tells you how big a stone or other obstacle can be, before it will hit the pedal (going in a straight line past the obstacle, like in a near hit of something laying on the ground).

I added your points to the list in the OP, thanks.

Edited by Christoph Zens
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steve454    2,228
On 4/13/2017 at 6:06 AM, esaj said:

At least on the phone-industry, it seems pretty common practice that the day your product is released, the competition is already taking it apart to see how it's made... :P

Reverse engineering is great, it spreads knowledge to people who can possibly improve on it.  Might not be ethical, though.:confused1:  I think that happened to Nokia phones.  I had one or two a long time ago and really liked them, but I think they were bought by some other company.  Liked the name too.  It just looks good for some reason.  Nokia.

Edited by steve454
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On 4/13/2017 at 3:55 AM, Rehab1 said:

Best of luck! If GW happens to contact you please ask them what are the specs for their hall sensors!:) I have been contacting them for the last 2 weeks and have yet to obtain any data.

I believe many of the specific specs you would like to see are proprietary and releasing them to the public would provide the competition with an edge.  :ph34r: Just my opinion.

Gotway might not even know what specific hall sensors are used in their wheels as they are supplied wheels on order from another company.  They probably just had the motor sent to MicroWorks to program its specifics into a custom controller board for them, and Gotway does the main assembly.  MicroWorks might know the specifications, but I don't see them frequent the forums any more.  You could try contacting some of those guys in the MicroWorks threads.  @Lz Lee @Rein-tech

Edited by Hunka Hunka Burning Love
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