battery temp is apparently bad for balance.

[StridAst]

So today I took my gotway 14 for a ride on a hiking / mountain biking trail. The trail was a blast, I climbed up about 300 vertical feet according to GPS over a distance of about 1.7km. Then I came back down most of the way, then I went back up. Early on the second trip down, it started to lose horizontal alignment. It started beeping and the wheel kind of rocked forward and back. I checked temp on the gotway app, it listed 70 degrees C. After a couple min of letting it cool, and messing around with resetting horizontal alignment, the temp had cooled to below 65 and I was able to get it to work again.

Overall, I had a blast. According to the gotway app speed I was going downhill at 20-22kph. So realisticly 18-20 or so. But coming down the hills was a lot like skiing . Realy glad I didn't have to carry my wheel back. Next time I am checking temp and trying to keep it below 65 or even better keep it below 60.

Edit. The loss of horizontal alignment expressed itself as the wheel going soft. I leaned back to slow and had to lean back more and more until my heels started scraping gravel. Not a catastrophic loss of balance

[MvM]

Thanks for the post.

I am not sure why this would happen. However, AFAIK, the hotter the battery gets, the less power it delivers because of internal resistance.

Just like a Tesla car will only be fast the first couple of times and then slow down to protect the battery.

I am not sure EU's in general have the same kind of protection mechanism build in.

[hobby16]

So today I took my gotway 14 for a ride on a hiking / mountain biking trail. The trail was a blast, I climbed up about 300 vertical feet according to GPS over a distance of about 1.7km. Then I came back down most of the way, then I went back up. Early on the second trip down, it started to lose horizontal alignment. It started beeping and the wheel kind of rocked forward and back.

It must be more about regenerative braking than board's temperatures.

Going down compels the wheel to brake, (1) by sending back the motor's voltage to the battery AND (2) by shorting the motor's voltage.

(1)  has some limits, especially if the battery is full and if the emf is high with steep hills

(2) will heat the power mosfets, so the shaking to protect them from burning

 

I have the same behavior on a X3 clone : wheel shaking when going downhill with a full battery.

If you go up immediately again and there is no more shaking, it's a braking problem and not a temperature or horizontal alignment problem.

[Gimlet]

As the app measures board temperatures I would think it would take a long time to register any increase in battery temperatures.

I have read that you have to be very careful about excessive temperature build up in the motor itself as at relatively low temperatures the rare earth magnets on the rim become demagnetised permanently. But as far as I know that is not monitored.

[StridAst]

As the app measures board temperatures I would think it would take a long time to register any increase in battery temperatures.

I have read that you have to be very careful about excessive temperature build up in the motor itself as at relatively low temperatures the rare earth magnets on the rim become demagnetised permanently. But as far as I know that is not monitored.

good to know.  Also very good to know that the temp the app measures is the board temp not the battery temp.  

 

 

It must be more about regenerative braking than board's temperatures.

Going down compels the wheel to brake, (1) by sending back the motor's voltage to the battery AND (2) by shorting the motor's voltage.

(1)  has some limits, especially if the battery is full and if the emf is high with steep hills

(2) will heat the power mosfets, so the shaking to protect them from burning

 

I have the same behavior on a X3 clone : wheel shaking when going downhill with a full battery.

If you go up immediately again and there is no more shaking, it's a braking problem and not a temperature or horizontal alignment problem.

 

Well, the battery here was definitely not full when going down that second time considering I had already driven up the hills first.  I was at 60% power when I ran into the problem.  and it's not that the motor was shaking, more that it was just going soft, I could ride down 50 feet or so along the trail before my heels were scraping the ground and I had to stop. 

[hobby16]

Well, the battery here was definitely not full when going down that second time considering I had already driven up the hills first.  I was at 60% power when I ran into the problem.  and it's not that the motor was shaking, more that it was just going soft, I could ride down 50 feet or so along the trail before my heels were scraping the ground and I had to stop. 

Shaking is the alert mode adopted on Airwheels and Solowheel but maybe (my speculation) on Gotway, the alert is different.

 

You are correct that there is no battery overcharge, but the problem remains, since a temperature of 70°C can not affect any electronic circuit of the board, certainly not the gyroscope IC (the MPU6050, the gyroscope IC used on monowheels are is specified for the -40°C to 85°C range).

 

Look this way : the wheel MUST brake with its motor. The braking energy goes partly into the battery by regenerative braking but if the brake force is not enough to slow you down on a steep hill, the mosfets are shorted to have more braking (this is decided at every commutation cycle every milliseconds or tenth of ms). This generates heat that must go somewhere. And if the heat buildup is too much, the wheel must alert you by one way or another and I suppose that's what you had.

Monowheels have an inherent problem with heavy and prolonged breaking, and there is no way to circumvent it. None, accept avoid going downhill for too long.

[Gimlet]

I'm afraid that living near the top of a very large hill as I do gives me no choice but to make a long decent to get anywhere.

My son and I have found that the IPS132'S cope fairly well with this as long as you keep the speed/momentum down. Some of the steeper bits near the bottom we we slalom to reduce the slope.

This is one of the reasons that I now look for wheels with bigger batteries as it seems obvious to me that they will have a greater capacity to absorb the charge produced even if recently fully charged.

[hobby16]

I'm afraid that living near the top of a very large hill as I do gives me no choice but to make a long decent to get anywhere.

 

Solowheels are much more picky about regenerative braking overcharge, with alert triggering more often and much sooner, probably because, as usual, they are  more security & reliability oriented than others. So beware, even if some wheels seem to "cope fairly well" with long descents, it doesn't mean they really do cope well, it's just that they let temperature raise more before warning you ! Heat is heat is here, no wheel is immune to the laws of physics. Or maybe (my speculation) that IPS, with a more open housing, can dissipate heat more easily.

 

On most boards I see, there is no discrete temperature sensor, so the CPU must  get temperature from the integrated sensor in the gyroscope IC.

That IC is rather far from the power stage where all heat is generated during braking. If it senses 70°C, it must be hellishly hot at the mosfets, and that's BAD for reliability.

 

Bigger or with lower internal resistance batteries can only help. But to what extent, that remains to be investigated.

BTW, concerning the motor's temperature itself, I never witness any heating (you can touch and feel it after a ride) so I would not worry much about magnets' demagnetisation.

[Gimlet]

Heat is heat is here, no wheel is immune to the laws of physics. Or maybe (my speculation) that IPS, with a more open housing, can dissipate heat more easily.

Bigger or with lower internal resistance batteries can only help. But to what extent, that remains to be investigated.

It's the one small failing on the IPS132 that it does seem to protect the electronics very efficiently. At least that is what I assume is happening when I am going down a steep hill and try to brake too hard, also when the hill isn't very smooth and you hit a dip or ripple. The wheel just seems to go into freewheel and run off ahead leaving you either running g after it or sitting on the tarmac. It has a 260Wh battery so reasonably sized but nowhere near the size of the Gotways on which I always choose the largest available battery.