Regen question

tbar23

Member
I have noticed that I have a very difficult time exceeding ~30 - 32 mph on my ST2S. I understand that assist will go away around 28 - 30 mph, but I can easily surpass 35 mph and push up into the upper 30s (and sometimes 40s if the grade is long enough) on steep downhill sections on my non-e road bikes. Note - in the Boston area, there are very few long steep downhill sections, so I would prefer not to turn this thread into the “I can hit 50+ mph on my local mountain” thread. ;)
I appreciate that my Stromer aerodynamics are lousy, but the additional weight should help going down.
Does the regen occur even if the brake levers are not being squeezed? Can this be adjusted with the brake sensitivity setting?
 

Johnny

Well-Known Member
There is a permanent regen mode, but you have to activate it, it does not turn on by itself.

I can hit the speeds(though I prefer not to, I don't feel safe) you have mentioned on descents of %5-10 grades. What is the grade of the downhill?
 

Timpo

Well-Known Member
I have noticed that I have a very difficult time exceeding ~30 - 32 mph on my ST2S. I understand that assist will go away around 28 - 30 mph, but I can easily surpass 35 mph and push up into the upper 30s (and sometimes 40s if the grade is long enough) on steep downhill sections on my non-e road bikes. Note - in the Boston area, there are very few long steep downhill sections, so I would prefer not to turn this thread into the “I can hit 50+ mph on my local mountain” thread. ;)
I appreciate that my Stromer aerodynamics are lousy, but the additional weight should help going down.
Does the regen occur even if the brake levers are not being squeezed? Can this be adjusted with the brake sensitivity setting?
Somebody correct me if I'm wrong, but I remember reading this somewhere and I'm like 95% sure, but not 100% sure.

Stromer has direct drive motor. Which means, the motor (stator) is directly attached to the hub.
If you turn the power off, the motor will act like a brake. This is why Stromer can have lock mode for theft prevention when power is off, because the magnets in the motor can act as a lock.

Okay so, if you are pedaling, the Stromer will accelerate.
What if you stop pedaling? Will the motor stop? Will the controller stop providing electricity?
No, the Stromer will still provide juice to simulate the normal bicycle feel of coasting.
What if you stop pedaling on normal bicycle on flat road? It won't stop right? It will slowly decelerate.
But Stromer can't do that, because of directly attached motor (direct drive)... therefore, it will still keep giving juice to simulate the stop pedaling (but coasting) effect.

Think about motorcycle.

If you stop giving gas, and if you grab the clutch, the motorcycle won't all the sudden decelerate.
However, Stromer does not have a clutch. It needs to keep giving fuel and be programmed to slowly let go of the fuel to simulate the clutch off (coasting) effect.

Now, here's your question.. you're having hard time reaching your normal top speed on downhill.
The motor can't propel over the max rpm by itself.
So if max rpm reach at 30mph (for example), then anything above 30mph is pushed by gravitational force by going downhill AND you pedaling.
At this point, your motor is only acting as a brake.

If your motorcycle's redline is 13,000rpm, and if you're in the first gear... can you go above 30mph (for example)?
(I just made a hypothetical example of a motorbike reaching 13,000rpm redline at 30mph)
Well maybe, if you use the gravitational force AND if you add a pedal on your motorcycle and push through the 13,000rpm redline to make it 14,000rpm.
But the motor is not helping you accelerate, it's only working as a friction generator at this point.

Again, somebody correct me if I'm wrong.
But I believe Stromer does not have a clutch (or anything to detach motor and hub when motor is not powered).
 

Johnny

Well-Known Member
Somebody correct me if I'm wrong, but I remember reading this somewhere and I'm like 95% sure, but not 100% sure.

Stromer has direct drive motor. Which means, the motor (stator) is directly attached to the hub.
If you turn the power off, the motor will act like a brake. This is why Stromer can have lock mode for theft prevention when power is off, because the magnets in the motor can act as a lock.
...

Again, somebody correct me if I'm wrong.
But I believe Stromer does not have a clutch (or anything to detach motor and hub when motor is not powered).

Ok if you are interested, there are some great threads on endless sphere such as this one:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=7891. You should be able to find technical answers to your question.

I will try to put it in layman's terms as much as possible.

I wouldn't start with an internal combustion engine analogy. Although regen braking has similarities with engine braking still it is not identical. The brake in this case is an electrical one not a mechanical one.

First of all, yes direct drive motors don't have a clutch, so they always have to turn. It causes a little bit of drag but it is not that significant.

Second, when you don't supply current, leave the circuit open, these motors will not brake. If that was the case you wouldn't be able to ride the bike when the battery was taken off. If I am not mistaken, the anti theft lock on Stromer is most likely an eddy current brake.

But these two are very unlikely to be the cause of OP's problem.

The concept in ebikes that is similar to engine braking is regenerative braking. When the motor is supporting the rider the current flows from the battery to the motor and to the ground of the battery.
When the motor is spinning a back EMF is generated. If this back EMF is greater than the input voltage of the motor than a current in the opposite direction will begin to flow, hence the motor turns into a generator and begins to charge the battery. This conversion of kinetic energy to electrical energy is effectively braking.

Now, it is possible when going downhill, the speed gets high enough that the back EMF actually exceeds the maximum system voltage that can be supplied by the battery and if the controller keeps the circuit closed then it will naturally go into this regen braking mode. However this will happen only if the controller keeps the circuit closed. I don't know if this is the case with Stromer.

And even if this is the case, I'd say it should still be at least 35-40mph until you hit this barrier. Ravi did a long climb and descent and in his descent he hit 35+mph speeds when going downhill with this ST2 if memory serves me right.


@tbar23 If I were you I would try two things. First try to see if you are actually regenerating. Second, if you can, take the battery off and ride downhill to see if you are still hitting the barrier.


Best of luck
 

bluecat

Well-Known Member
Does the regen occur even if the brake levers are not being squeezed? Can this be adjusted with the brake sensitivity setting?
The real regenerative braking works only, if the battery is not fully charged and has over 0ºC inner temperature. There are two ways to use is: left or right brake lever (with different regen strength!) or the driving mode, where the regen strength is set in different steps. There is als a maximum current whicht the battery can accept.

If you enter a steep downhill and let the Stromer speed up, then the motor brake will not brake down to zero. If you start with the motor brake from beginning, you'll be able to control the speed all the time.

What you not can do is racing downhill. As mentioned above, the motor has his native speed and will not go above it. The motor of Stromer is robust enough to deal with this on Alpine pass roads. But if you do it on the long downhill at Pikes Peak, you might damage the motor. But in fact, you have to climb the Pikes Peak first, which might be the more demanding part.
 

tbar23

Member
Thanks for the detailed feedback all.
I have been meaning to try a few hills without the battery and see what it is like. I know that there is a short steep hill up to my house, and I have tried to climb that hill without assist, and I’ve quit each time :(
@Johnny - how would you go about determining if I am actually regenerating? I know the setting is turned on, and I can definitely feel it when approaching a downhill stop sign while lightly pulling both brake levers.