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Jim Martin

How far is too far to lean?

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41 minutes ago, erk1024 said:

At some point, the electrical system of the wheel cannot provide any more current, and you'll overlean because of speed. The wheel does NOT "cut out", it just can't provide any more current (which translates to torque) to the wheel, and you pivot forward. The amount of current available also goes down as the battery gets low on power. The wheels will beep and tiltback trying to warn the rider (unless you disable all that).

I'll be doing more research but something you said is very interesting. I never actually received beep or tiltback and I don't even know how I could disable it. (just checked and the app won't even open the speed settings... uh oh...)

When I had my fall, I can't remember exactly what it felt like but I do remember earlier on, I had something similar happen but never fell. I leaned really far forward because I was trying to accelerate as fast as I could and the autobalance just stopped. Somehow I managed to keep myself on the wheel (legs violently shaking forward and backwards trying to balance) until the wheel gave a beep and autoleveled again. It was so scary because I had no gear on but definitely made me trust the wheel less because I had no idea what had just happened. 
I want to say this is what happened when I fell but it's all blurry and can't say for sure. 

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2 hours ago, erk1024 said:

Image result for electric motor torque curve

Looks like this motor has "artificial" electronic limitations due to the controller. On the left the current is limited (possibly because to protect wires against overheating or due to battery current limitation). This may indeed also be the case for the EUC motor setup, so we wouldn't get the maximally possible motor torque at low speed. To the right the power is (artificially) limited, which is rather unlikely to be the case for EUC motor setups (the limit in the figure is 140kW, compared this to the under 2kW for an EUC motor). The physical (electric) limitations of electric motors in comparison are described here.

 

Edited by Mono

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18 hours ago, Mono said:

Looks like this motor has "artificial" electronic limitations due to the controller.

Those are awesome graphs you posted! (finally had a moment to look at them)  :)

I think when people talk about electric motors having a flat torque curve, they are assuming the motor is under load. In other words, if I had an electric motor turning a propeller on a drone, the torque of the motor would be the same even though it's spinning faster. Of course spinning faster requires more power, and the prop is putting out more thrust, so that makes sense. On an eWheel at a given speed, like 20mph, if you're going up hill that's more power, downhill, less power (or regenerative braking etc.), so no direct relationship between RPM and current.

The question is, how do we explain this to somebody who wants to know about overleans without burying them in data? 

Maybe something like this?

  1. When you lean forward, the wheel has to speed up (accelerate) get get back under you to "correct" the lean.
  2. Acceleration requires torque from the motor.
  3. More rider weight requires more torque to accelerate
  4. There is an upper limit to how much torque the motor can provide. If you exceed that, you fall forward.

Torque gets used for things other than balancing:

  • Speed uses torque because of wind resistance and rolling resistance, the more speed, the more torque is used.
  • Going up hill requires more torque to lift the weight of the wheel and rider
  • Accelerating uses torque to increase the speed 
  • If the battery is low, less current means less torque from the motor

The faster you go, the less torque you have until you get to an unsafe level remaining. One way to know if you're approaching the limits of the wheel is to watch the amount of current the wheel is using. 

Something like that?

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Here is a newbie question, so is it warning beeps, (ignore), tiltback happens (ignore)=faceplant cutout? I have read quite a few people say they "ride through tiltback".

Also what is a good amp alarm level for 16s?

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55 minutes ago, Sertified said:

Here is a newbie question, so is it warning beeps, (ignore), tiltback happens (ignore)=faceplant cutout? I have read quite a few people say they "ride through tiltback".

Also what is a good amp alarm level for 16s?

Maximum available torque reduces with speed.

So if one accelerates hard, one hits the wheels limit way before any tiltback or beep and overleans.

If one accelerates very carefully one can "ride the tiltback" while the wheel beeps like crazy (...as long as one hits no pothole/bump/incline...)

... So no answer to your question is available. Depends on your driving behaviour/anticipation/foresight/actual safety margin (depending on the wheel/speed and burden)/willingnes to take not (foreseen) risks...

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Thanks man, I get it now. How about setting an alarm level in wheellog for Amps? I'm 195 lbs on the 16S

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1 hour ago, Sertified said:

Also what is a good amp alarm level for 16s?

Imo not - depending on charge on could hit before max tiltback speed (35km/h) the overlean limit somewhere between 15 to above 30A.

Setting an alarm to 15A is very boring, setting it to 3x A gives just an usefull alarm at full battery.

So imho the best is to get experienced with your wheel and do just low accelerations at high speeds. Do the "show off"/fun accelerations just at low speeds.

Then the 35 km/h tiltback/beep will keep you save.

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3 minutes ago, Sertified said:

Thanks man, I get it now. How about setting an alarm level in wheellog for Amps? I'm 195 lbs on the 16S

Current alarms, as written above imho makes no real sense with an KS16S. 

They are for GW wheels to prevent blown mosfets/molten wires.

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2 minutes ago, Sertified said:

Thanks man, I get it now. How about setting an alarm level in wheellog for Amps? I'm 195 lbs on the 16S

That's a good question. I've seen readings of 32 amps when I accelerate hard on the 18XL. Using Darkness Bot. I'm 265 lbs. Not sure that helps at all.

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19 minutes ago, Sertified said:

How about setting an alarm level in wheellog for Amps?

 

14 minutes ago, Chriull said:

Current alarms, as written above imho makes no real sense with an KS16S. 

They are for GW wheels to prevent blown mosfets/molten wires.

Current alarms, as the famous 90A alarm used by @Marty Backe with GW wheels saves him from cutouts (blown mosfets/molten wires) at "low" speed, high burden situations like his hill climbing tests. They will not prevent any high speed overlean! These happen at much lower currents and are very depending on charge %==battery voltage.

Edit: his "low" speeds are not to be recommended for us KS16S riders, as he has the new much more powerfull wheels!

 

Edited by Chriull

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The 18XL will alarm ”Overpower” and initiates a tilt-back if the current power demand gets close to the max available power. But the 16S doesn’t have that warning, so it can be overleaned at any speed without a warning.

Also worth noting that Gotway wheels don’t measure the amps drawn from the battery like other manufacturers do, so the values are not at all comparable. I seem to recall reading that GW reads the amps from the motor phase output(s?) instead.

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7 hours ago, Sertified said:

Thanks man, I get it now. How about setting an alarm level in wheellog for Amps? I'm 195 lbs on the 16S

I didn't even know you could set an alarm in wheellog

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52 minutes ago, Giffy said:

 

I didn't even know you could set an alarm in wheellog

Swipe from the left to access the configuration screens where you can set 3 different speed, temperature, and amperes alarms. You can enable vibration and/or sound alarms.

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17 hours ago, erk1024 said:

4. There is an upper limit to how much torque the motor can provide. If you exceed that, you fall forward.

And 5. This upper limit is not constant but reduces with increasing speed (more or less linearly towards zero). The maximal motor torque does not remain the same when the motor is spinning faster.

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17 hours ago, erk1024 said:
  1. There is an upper limit to how much torque the motor can provide. If you exceed that, you fall forward.

 

 

4 minutes ago, Mono said:

And 5. This upper limit is not constant but reduces with increasing speed (more or less linearly towards zero). The maximal motor torque does not remain the same when the motor is spinning faster.

And 6. This limit decreases with battery voltage. With fully charged batteries (84V) compared to empty batteries (20*3,3V=66V) one has a 84/66 * 100 % higher limit.

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2 hours ago, Mono said:

And 5. This upper limit is not constant but reduces with increasing speed (more or less linearly towards zero). The maximal motor torque does not remain the same when the motor is spinning faster.

Interesting to hear that it's more or less linear. Out of interest, is there a 'maximum torque' rpm for our euc motors? Or is it simply max torque at min rpm, reducing linearly to max rpm?

I like this stuff, it helps me understand why euc motors can often spin quicker (quite a bit more it seems) than the max speed they are designed to be ridden at. I was amazed how much extra speed you can get from a hacked Z10 (61kmh?!) but now it makes more sense - that 'buffer' between 45kmh and 61kmh is there to keep a certain amount of torque in reserve at the factory 45kmh speed limit I guess.

It does make me realise that riding one at 60kmh must be insanely risky :o

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10 minutes ago, Planemo said:

Interesting to hear that it's more or less linear. Out of interest, is there a 'maximum torque' rpm for our euc motors? Or is it simply max torque at min rpm, reducing linearly to max rpm?

Yes, maximum torque rpm is at standstill (stall torque).

Some/most/all wheels have some current limiting implemented, as at standstill this maximum torque implies a huge current destroying the mosfets and wirings. So at high accelerations from standstill some riders reported stuttering noise.

Just GW was reported to have no limiting at all in firmware - maybe their new motor drive algorithm takes care of this? Or it's just some misunderstanding.

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Let me plug the e-bike motor simulator page^1 here again which gives (almost) right out of the box this picture plotting torque, power, efficiency, and load vs speed at 100% throttle:

1453036095_ScreenShot2019-09-19at16_17_15.thumb.png.658f7672ed34be281d5d65be66de4d21.pngHere is my question though: the torque (in blue) is constant for low speed (which I understand comes from a simple current limiter) and goes linearly down for high speed (as to be expected from the basic motor model). In between however it has some sort of 1/velocity characteristics. Where does this come from?

The same at 2% grade:
201245372_ScreenShot2019-09-19at16_23_06.png.60396f7a9c577daf2be107556a0a0b62.png

Because the load is different, the crossing point of load and power changes with different grade. All motor output measures, including the change point to linear torque characteristic, however remain the same.

EDIT: I found an answer here: the controller limits the power/current on the battery side. I still don't fully see why a limit doesn't lead to a flat graph.

^1 https://www.ebikes.ca/tools/simulator.html

 

Edited by Mono

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1 hour ago, Mono said:

In between however it has some sort of 1/velocity characteristics. Where does this come from?

Could be the "

The actual model in SimulatorV2 is substantially more complicated, taking into account the commutations that happen on a regular basis as a function of the speed and number of poles of the hub motor, and determining the resulting current waveforms that are produced when this is applied to the inductive motor windings.

torque_equation.gif" he mentions at the end of the page.
There is a term depending on the square of the angular speed.
 

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2 minutes ago, Chriull said:

There is a term depending on the square of the angular speed.

looks like this should make the graph concave rather than convex.

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