King Song official claim: No shut-offs at high speed like Gotway

[KaleOsaurusRex]

Hey everybody!

So, I'm not sure if this issue has been discussed yet, but if you read around a bit you might already know that Gotway unicycles are awesome, except that they have a reputation for consistently turning off unexpectedly at high speeds.

Many people know that King Song unicycles are most similar to Gotway, and that they appear to be higher quality in certain ways.

I just talked to Tina at King Song, and she says that the main board is different on King song unis, and she says that the high-speed shut off will not occur.

Does anyone here know what exactly it is that causes high-speed shut off in Gotway unicycles? Is there any way we can confirm King Song's claim, besides human testing?

@hobby16

@esaj

@Jason McNeil

[Jason McNeil]

@John Eucist reports that GW will [finally] be releasing models with pedal-tilt-back to prevent riders from falling of the speed cliff. As I understand it, all hub-motor have a max RPM go beyond this & there's insufficient torque to support the pedals.

[KaleOsaurusRex]

Ah, so it's the natural limitation of the device. King Song uses tilt-back to protect the rider from riding in a manner that triggers the stall, which is reaching/sustaining a speed above the tolerance of the motor. Gotway units on the market now were designed in a way that allows the rider to push the limits, giving the rider the added responsibility of knowing what those limits are.

I think I understand?

[Jason McNeil]

Exactly, that's spot on.

[Daan]

Ah, so it's the natural limitation of the device. King Song uses tilt-back to protect the rider from riding in a manner that triggers the stall, which is reaching/sustaining a speed above the tolerance of the motor. Gotway units on the market now were designed in a way that allows the rider to push the limits, giving the rider the added responsibility of knowing what those limits are.

I have been thinking about this -- what does it mean for a wheel to be "safe"? (and I think we, as a community, need to get more clear about this to manufacturers).

- clearly, any wheel will fail to balance at some point if you 'overlean' or do a incline that is too steep, etc.

- similarly, any wheel will 'cut-off' the batteries when being exposed to extreme conditions at some point: like overheating, short-circuits, physical damage to the batteries, etc. This is done by the basic BMS system, basically to prevent fires and explosions  But all of this is ok -- they are basically results of some outside influence beyond the rider riding the wheel.

So, for me, safety for a EUC means:

1. The wheel warns the user when it is being pushed to its limits (with a  good safety margin): i.e. pedal tilt or beeps at a certain speed, and a warning  when reaching low battery levels.

2. The wheel should *never* cut-off the batteries due to just riding: i.e. on severe overlean, a bump at high-speed, etc, (i.e. big power draw) the board should regulate the batteries such that the BMS never cuts off the batteries. It should always try to keep balancing and/or slow down the wheel. Protect the rider first!! then the batteries.

With regard to the Gotway, it is unsafe since it does not satisfy (2): it will cut-off if going too fast (because the BMS is triggered).

With regard to the King Song, I think the manufacturer clearly states that it will do (1), ie. give a warning. But whether it satisfies (2) is unclear I think? 

[KaleOsaurusRex]

Well put, @Daan , we need to operationally define "safety." Here's an explanation of the 2 main kinds of shut-off, as best as I can understand it, and perhaps someone can add to this or help me clarify:

1. BMS shutdown

Most popular low-priced generic style brands, and many other popular brands of the last generation, are made with an electric bicycle style battery management system (BMS). This part can try to protect the battery and shut down instead of protecting the rider, even in the best conditions.

Brands known to be affected by a bad BMS include Airwheel, Firewheel, TG, Rockwheel, many other brand names, and most generic imported models. Even Ninebot has a battery management system with unknown variations. These can be modified, but the safety of the modification is controversial.

2. Main board shutdown

As the battery gets lower, the voltage decreases. With lower voltage, a higher current is needed to produce the same power to the motor as with higher voltage. This causes heat, and if it gets too hot, the unicycle will shut down. This problem is solved in units with safe low-battery behavior; one example is Ninebot, which speed limits riding starting around 40% charge.

High speed can also cause main board shutdown. Most brands tilt back and beep to tell you to stop going faster, and some talk to you. Some unicycles will just go faster and faster until they turn off because the motor can't take it anymore. Gotway and Rockwheel are examples that will experience a speed-cliff type mainboard shutdown.

King Song avoids main board shutdown by implementing a high-speed tiltback, but according to @hobby16 it also includes an aluminum heat sink in a high airflow location to lower main board temperature (link here to hobby16 King Song disassembly page)

I also agree that I am not yet entirely sure King Song is clear for BMS safety (in @Daan's post above - #2 BMS). Any opinions @Jason McNeil ? I have browsed the forums in search of a detailed ( @esaj @hobby16 hahaha) reasoning about why King Song's BMS is safer, but perhaps I missed it. Does King Song lack the telltale BMS design, visible in pictures? (link above with main board pictues) Maybe we need to look at the battery too, as I guess this is where the BMS is usually located?

[esaj]

Try to find someone crazy enough to try it (ie. send a free sample to @@vee73  ), then we'd know for sure. Hobby16 has stated on a couple of occasions that there should never be the need to turn off the motor from an electronics point of view, or at least that's what I've understood, the components should be able to take it.

[Mono]

Try to find someone crazy enough to try it (ie. send a free sample to @@vee73  ), then we'd know for sure. Hobby16 has stated on a couple of occasions that there should never be the need to turn off the motor from an electronics point of view, 

in other words, limiting the current should always do, and setting the current current limit  to zero should never be necessary (unless the batteries are empty). Sounds logical.

[MetricUSA]

I like the eco (efficiency) curve, so what is the actual rated operating point (speed) of vehicle...

[Jason McNeil]

Oops, didn't see that tag. One of the topics that doesn't get discussed with the BMS shutdown/shunting is how much current, is the shut-off threshold for a particular eWheel. I agree in principle with Hobby that it's invariably better to degrade the batteries by over-exertion than to cut off power, but the underlying fact is, with or without shunting, a single Wheel that's supporting your most valuable asset (you) really ought to have at least 28 cells (Ninebot) for that reserve power reservoir—unless their LiFePo4's—16 cells just doesn't cut it.  

I'm reliably informed that the KS BMS does not regulate current to the CB. But with all 64cell eWheels, because of the parallelization of current, any manufacturer with a morsel of sense will at least use the same load/cell BMS cut-off value as the cheap & nasties, which gives you 4x the power to play with.