Braking hard on KS 18XL 2000W

[UniMe]

I'm very new to EUC's and my first wheel is a KS 18XL 2000w. I'm progressing fairly well and enjoying the process.

I have noticed that if I brake hard on the wheel is starts to make a faint sort of grinding noise. As I get better at riding I'll probably be able to exert a lot more force on the wheel when slowing down and I anticipate there is a limit to how hard I can brake before some sort of overvolt situation happens. The obvious concern is that the wheel may fail in a hard braking situation and send me headlong into what I was trying to avoid i.e. a big truck, bus or... mother with a stroller?

Don't get me wrong, I'm a cautious person and not prone to reckless riding. Stuff happens though and like with any mobility device (car, motorcycle, bike) I need to understand the limits of emergency braking.

I'm using EUC World and thinking perhaps there is a value I can monitor on the app that will teach me when I'm at the mechanical limit of braking on the wheel. It's abundantly clear already that I can't skid the tire under any circumstances. I'm also a heavier rider at 235lbs and I have fairly strong legs for my size i.e. I'm getting older but have spent my fair share of time in a squat rack. I have a Tacx neo 2t smart trainer with a 2200 watt resistance motor for my bike that begins to slip at 88 newton meters and can easily overpower it in the first 3-4 lower gears when hill climbing, I'm guessing the EUC will slip in a similar manner at some point...

Edited August 16, 2020 by UniMe

[Chriull]

10 hours ago, UniMe said:

I have noticed that if I brake hard on the wheel is starts to make a faint sort of grinding noise.

Could be just the control algorithm or overcurrent protection?

More possibilities could be loose axle/pedal hangers or motherboard. Or some cracks in the inner shell. All this could create a feedback loop while braking causing such a "resonance"/rattling sound.

The one case i heard of the crack in the shell was finaly diagnosed as this rattling/grinding noise while braking went away if one applied pressure on this one side of the shell. After inner shell replacement it was gone.

10 hours ago, UniMe said:

I'm using EUC World and thinking perhaps there is a value I can monitor on the app that will teach me when I'm at the mechanical limit of braking on the wheel.

Never really looked into the details of whats how limiting braking and if and how this is reported.

The generated power by braking P = Torque * speed = I_motor * U_motor.

As U_motor is kv * speed the maximum possible motor current is the limit of the braking torque. (The faster one drives, the higher the motor current/braking torque can become)

The first intuitive way to find such a limit would be to get the max braking current by calculating the short circuit current - I_motor_braking_max = U_motor/R_coil. But this case would imply zero battery current and i've never seen a KS log which shows zero current while braking - so this method is most probably not used and so leading to no insights.

Second way of braking could be by "applying the battery voltage in reverse to the motor" leading to I_motor_braking_max = (U_battery+U_motor)/R_coil. This would imply a (high) positive battery current reported. Is as good as not to be seen/found in logs so unlikely, too.

So leaves regenerative braking with negative battery current shown - the normal picture from the logs. Here the motor generated voltage is transformed up to a bit above battery voltage, and the motor current down to battery current with the same factor.

One could set up the formulas quite similar to the situation while driving (acceleration) as shown in https://forum.electricunicycle.org/topic/7549-current-demand-versus-battery-voltage/?do=findComment&comment=100560

and calculate the motor current and max motor current (proportional to braking torque) possible in different situations.

This numbers got for driving led to the understanding that the from KS wheels reported "inverter load" shows the wheels limit. (EUC World shows now "safety margin" which is 100% minus inverter load).

Could be that this value shows a valid percentage for braking, too? My first glimpse on these values for braking did not lead to positive confirmation of this. But i had no nice logs with strong braking manouvers at hand and really only a very brief glimpse at this. So this number could be an easy start to look on in detail for this with some good chance of success.

[UniMe]

Thanks @Chriull , I'll look into the safety margin on the EUC app to see if i can record some hard braking sessions.

Have you ever heard of a situation where an EUC rider has overpowered the motor during braking and caused it to slip, leading to an accident?

It's a strange experience when the motor in my bike trainer slips, it seems the technology is similar and if it is possible to cause this on an EUC it could really be a problem. That said, I expect if it did emerge early on there has been some sort of fix that sacrifices the motor rather than allowing the motor to slip during emergency braking...?

Has anyone been able to skid the tire of their EUC during hard braking going in a straight line? I've seen a video that recommends making a slight turn during hard braking to increase contact area and friction on the tire. In terms of skill I'm simply not there yet and turning while braking would probably cause me more problems than it would solve.

Edited August 16, 2020 by UniMe

[Chriull]

29 minutes ago, UniMe said:

Have you ever heard of a situation where an EUC rider has overpowered the motor during braking and caused it to slip, leading to an accident?

Just over wet manhole covers, but not leading to an accident!

Somehow i can't really remember accidents while braking reported here? Just "in the old times" when motherboards fried while braking.

29 minutes ago, UniMe said:

It's a strange experience when the motor in my bike trainer slips, it seems the technology is similar and if it is possible to cause this on an EUC it could really be a problem. That said, I expect if it did emerge early on there has been some sort of fix that sacrifices the motor rather than allowing the motor to slip during emergency braking...?

The motor imo can't easily be sacrificed - the electronics should give up before.

Comparing some artificial current limit vs. electronics frying the latter leads to an accident for sure. The limit should be "safer", but of course limits a bit braking possibilities. Which seem to be "very good" with nowadays wheels.

Afaik the firmware does not let the motor "slip", the limiting is more like "stuttering". So more like "high frequency micro slips".

I would not worry. Better you train with great safety gear emergency braking from low speeds on - to get a feeling what your wheel can provide!

29 minutes ago, UniMe said:

Has anyone been able to skid the tire of their EUC during hard braking going in a straight line?

In @Kuji Rolls   youtube video (?veteran with street tires?) it seems that the tires are at the limit while braking multiple times. They don't slip but the wheel seems to start "jumping". But this could maybe just have been road irregularities?

[UniMe]

super informative -- thanks!

[null]

Interesting theme, thanks for all the info. I’ll have to train braking a bit stronger, I didn’t yet due to worrying about the controller / batteries.