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What determines maximum speed on a downhill slope?

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The app for my wheel (E+) shows the energy flow.  A negative amperage value is regenerative braking and a positive amp value is the normal use of energy on flat terrain. 

I've noticed that when riding down hill I can usually find a "perfect" speed which results in close to zero energy usage according to the app.  I was wondering if this means whether there is a higher top speed when going down hill, since very little energy might need to be used in that specific situation. 

Braking from those high speeds would still be a problem, as it could easily cause an overcurrent condition.  Does anybody know how wheels handle this?

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Posted (edited)

I would imagine that the fastest speed on a downhill slope would be about as fast as you can hang on? Now stopping from a downhill may be dependent on power and current. I wonder if a wheel would tiltback once you reached 31mph+ but werent applying any power? I may be nuts, but I'm not sure I want to test this one.... Hey gotway guys.... How fast CAN you go downhill on a monster while actively trying to NOT slow down? Any takers? The test is only valid if you conduct it until you fall off... Don't be a pussy! If a wheels response to overspeed is simply cutting power, wouldnt you continue to gain speed IF you could stay atop it? Great question Musk!

Edited by ShanesPlanet

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41 minutes ago, ShanesPlanet said:

I would imagine that the fastest speed on a downhill slope would be about as fast as you can hang on? Now stopping from a downhill may be dependent on power and current. I wonder if a wheel would tiltback once you reached 31mph+ but werent applying any power? I may be nuts, but I'm not sure I want to test this one.... Hey gotway guys.... How fast CAN you go downhill on a monster while actively trying to NOT slow down? Any takers? The test is only valid if you conduct it until you fall off... Don't be a pussy! If a wheels response to overspeed is simply cutting power, wouldnt you continue to gain speed IF you could stay atop it? Great question Musk!

The speed at which the wheel is drawing almost no power going down a shallow hill is, in my opinion, surprisingly low. It's somewhere between 18 to 25 mph, far far lower than the same hill on a bicycle. So while a bicycle will easily hit 30 mph, on the same slope the wheel won't go past 25.

The upright stance of a wheel is extremely inefficient versus the sitting position of a bicycle, so essentially the wind resistance balances out gravity.

Now once that slope gets past 6 degrees, all bets are off. The wheel goes as fast as you dare, which is to say you will crash regardless of your skill, motor size, and battery level.

 

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All wheels except GotWay (and now Veteran) have their top speed limited by software. The energy consumption makes zero difference for them, it’s only the speed that triggers the top speed tilt-back. Only if the battery is low enough for the wheel to limit the top speed further, riding downhill might allow the battery to recover or regenerate, which may push the top speed back up a bit. But never beyond the hard top speed limit of the wheel.

 On a GW with the tilt-back removed, you can ride until the wheel has no more power to keep you upright. Riding slightly downhill means the power requirement is very low, so you can get closer to the free air speed. But never above, since the controller has zero control over a motor beyond that speed, so it would be like riding with the wheel turned off.

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19 minutes ago, mrelwood said:

All wheels except GotWay (and now Veteran) have their top speed limited by software. The energy consumption makes zero difference for them, it’s only the speed that triggers the top speed tilt-back. Only if the battery is low enough for the wheel to limit the top speed further, riding downhill might allow the battery to recover or regenerate, which may push the top speed back up a bit. But never beyond the hard top speed limit of the wheel.

 On a GW with the tilt-back removed, you can ride until the wheel has no more power to keep you upright. Riding slightly downhill means the power requirement is very low, so you can get closer to the free air speed. But never above, since the controller has zero control over a motor beyond that speed, so it would be like riding with the wheel turned off.

But if you COULD manage to stay upright and the hill WAS steep enough, can we assume that you would reach speeds like that of a road luge racer? If top speed shut off is simply the removal off power delivery, what if the hill IS your power delivery? WOuldnt it take the wheel applying negative force to stop you from free wheeling to your demise?

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5 hours ago, ShanesPlanet said:

But if you COULD manage to stay upright and the hill WAS steep enough, can we assume that you would reach speeds like that of a road luge racer?

Most probably not, as the wheel cuts off once lift cut off speed is reached (it beeps and then it stops turning - never trierd if it brakes or just turns off "power"). Although lift cut off is reached while in a "driving situation" and going downhill is a "braking situation". So this theoreticly could be handled differently in firmware - but i would'nt try it voluntarely!

If the inverter/motor controller could be used while regenerative braking to act as a step down converter the wheel could still balance and bring one safely down the hill.

But i highly doubt this is implemented in firmware (if by the electronic circuitry possible at all), because there's one big caveat - once one reaches the end of the hill with a speed above no load speed no forward acceleration for balancing is possible anymore...

So back to the realistic scenarious:

Imo the limits are:

"Something below" lift cut off speed:

"Driving" Motor burden is (much) lower downhill - so the safety margin at higher speeds is bigger.

Even with reaching tiltback speed one could go on, if one is able to stand tiltback. As it is no limit but just (very) uncomfortable.

For balancing even riding down some motor torque is needed - so one still reaches the motor limit before lift cut off load and overleans...

Just if one has some downhill gradient and speed to be "safely" in the regenerative braking mide the wheel could balance one by solely modulating regenerative braking force.

One would not be limited by the normal max torque over speed limit (overlean limit) anymore.

But this is speculative/theoratical again, as not too much is known about the used firmware algirithm (by me at least)...

Battery voltage:

With regenerative breaking the battery voltage is dragged to higher voltages (negative sag) and the internal battery voltage rises by beeing charged. As a max battery voltage limit is enforced by the firmware afaik vy every wheel by beeos/tiltback and then cut off this limits downhill riding (quite abrupt), too

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Posted (edited)
9 hours ago, Chriull said:

One would not be limited by the normal max torque over speed limit (overlean limit) anymore.

There is another alternative. The BC Wheel or Impossible Wheel would essentially have you going downhill with a non-balancing wheel.

However, the difference in skill between a normal unicycle and a BC wheel is as great as between an electric unicycle and a normal unicycle. While I can ride a normal unicycle, the impossible wheel feels, well, impossible. It's unfathomably hard.

Edited by LanghamP

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On 6/29/2020 at 3:01 AM, musk said:

The app for my wheel (E+) shows the energy flow.  A negative amperage value is regenerative braking and a positive amp value is the normal use of energy on flat terrain. 

I've noticed that when riding down hill I can usually find a "perfect" speed which results in close to zero energy usage according to the app.  I was wondering if this means whether there is a higher top speed when going down hill, since very little energy might need to be used in that specific situation. 

Braking from those high speeds would still be a problem, as it could easily cause an overcurrent condition.  Does anybody know how wheels handle this?

Control? And able to stop in reasonable time/distance? Loose that and your.... f'd. :)

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On 6/29/2020 at 3:01 AM, musk said:

The app for my wheel (E+) shows the energy flow.  A negative amperage value is regenerative braking and a positive amp value is the normal use of energy on flat terrain. 

I've noticed that when riding down hill I can usually find a "perfect" speed which results in close to zero energy usage according to the app.  I was wondering if this means whether there is a higher top speed when going down hill, since very little energy might need to be used in that specific situation. 

Braking from those high speeds would still be a problem, as it could easily cause an overcurrent condition.  Does anybody know how wheels handle this?

The fall!!!!. Then you go from there 80-85%. Lessons learned. PROTECTED. ;)

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Posted (edited)

Maximum cutoff speed is not any faster than the lift test. That means that if you were perfectly skillful and the road was perfectly smooth you should be able to travel downhill at the lift test cutoff speed and the motor should be able to compensate for back lean in order to slow down, but (as usual) not have any available torque for forward lean.

In practice, while going uphill lowers your loaded cutoff speed, going downhill doesn't really increase it much at all compared to flat ground.

Edited by Dan Hillary

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