Bike keeps Lunging forward

[Stacky]

Hello all
I hope someone can help me. My wife has a Pendleton Somerby. A problem has arisen where when she starts to pedal the bike keeps lunging forward as if at top speed. This in my mind is not safe to ride until problem is sorted.
Thanks for reading .......... John

 

[cyclebuddy]

If you look in your Pendleton Manual, you'll see a graphic which explains how power is applied:

If the bike is in maximum assist, it will "lunge" as it applies maximum power as soon as the pedals are turned until it reaches 15.5mph, the legal limit.

You need to turn the assist level down to start; it applies limited current to a lower speed limit, then up the assist level once moving.

It's common with many of the cheaper cadence-based control systems fitted in cheaper bikes, of which the Pendleton is far from the worst.

 

[Bonzo Banana]

Does this happen on all three power settings? Have you tried cleaning around the cadence sensor and perhaps re-positioning it if its been knocked out of position?

Looks like it has a metal crank cover, its possible the metal of that crank cover is interfering with the crank sensor if the position has moved.

 

[Stacky]

If you look in your Pendleton Manual, you'll see a graphic which explains how power is applied:

If the bike is in maximum assist, it will "lunge" as it applies maximum power as soon as the pedals are turned until it reaches 15.5mph, the legal limit.

You need to turn the assist level down to start; it applies limited current to a lower speed limit, then up the assist level once moving.

It's common with many of the cheaper cadence-based control systems fitted in cheaper bikes, of which the Pendleton is far from the worst.

Many thanks mate. I`ll give that a try

 

[Stacky]

Does this happen on all three power settings? Have you tried cleaning around the cadence sensor and perhaps re-positioning it if its been knocked out of position?

Looks like it has a metal crank cover, its possible the metal of that crank cover is interfering with the crank sensor if the position has moved.

Thanks Bonzo BUT I have no idea what your Technical Terms mean e.g cadence sensor ? If you can explain I`ll look into. Cheers mate

 

[Stacky]

Many thanks mate. I`ll give that a try

Many thanks mate. I`ll give that a try

Hello again mate. I tried your fix but bike is on lowest speed setting when turned on. Still does the same thing. I`m lost now

 

[Stacky]

If you look in your Pendleton Manual, you'll see a graphic which explains how power is applied:

If the bike is in maximum assist, it will "lunge" as it applies maximum power as soon as the pedals are turned until it reaches 15.5mph, the legal limit.

You need to turn the assist level down to start; it applies limited current to a lower speed limit, then up the assist level once moving.

It's common with many of the cheaper cadence-based control systems fitted in cheaper bikes, of which the Pendleton is far from the worst.
[/QU

If you look in your Pendleton Manual, you'll see a graphic which explains how power is applied:

If the bike is in maximum assist, it will "lunge" as it applies maximum power as soon as the pedals are turned until it reaches 15.5mph, the legal limit.

You need to turn the assist level down to start; it applies limited current to a lower speed limit, then up the assist level once moving.

It's common with many of the cheaper cadence-based control systems fitted in cheaper bikes, of which the Pendleton is far from the worst.

Hello again mate. I tried your fix but bike is on lowest speed setting when turned on. Still does the same thing. I`m lost now

 

[cyclebuddy]

If you can change between the three different levels on the display, but can't tell any difference between low, mid, and high assist being applied (i.e. it's just full-whack all the time), IMHO it's probably the controller at fault.



There's a sensor on the crank by the pedal so that when you pedal it sends a signal to the controller to apply power - that's what Bonzo is referring to. Sometimes it can get knocked out of alignment, but if it were that the power would apply intermittently (i.e. sometimes you would get assist, sometimes not) which isn't what I think you've said.

If all you're getting is full power regardless of what you set at the display, I think you need to get Halfords to check/replace the display/controller.

 

[Benjahmin]

I'm not sure that's the right graph for this bike.
If the Pendleton is speed control, which it appears to be, then it will apply full power on whichever setting it is on.
So, on setting one, it will apply full power up to the set speed (lets say 8mph).
On setting two it will apply full power up to, say, 12mph.
On setting 3 it will apply full power up to, say 15mph.
This gives the 'lunge' feeling that some people find disconcerting, it's a kind of all or nothing thing.
I'm not sure there is actually anything wrong with your wife's bike, it's just the type of control system it has.
Good luck with getting any sense out of Halfords 'mechanics'. They don't have the best rep.
Control systems with current control offer a smoother application of power. I suspect the graph above applies to one of these systems.

 

[Nealh]

I believe speed control is used and is common with the three PAS levels only & as Ben has said no matter which power level, one will get the harsh power acceleration. They shouldn't be termed as power levels but speed levels, we have seen and heard the same issue time over with these control type systems.

 

[sjpt]

I'm not sure that's the right graph for this bike.

As cyclebuddy said, the graph It is the one that comes from Pendleton Somerby manual.
(https://washford.a.bigcontent.io/v1/static/Somerby E Bodo Workshop Manual page 11.)
Maybe there have been different versions of the Somerby with different control systems? Or even by oversight the manual was always wrong?

The initial harsh power will depend on two things.
(1) Whether the controller is current controlled (as in the graph) or 'pure' speed controlled as described by Benjahmin and Nealh above.
(2) Whether there is some kind of ramp up of current as the motor engages, or whether it instantly goes to the max current from (1) as soon as pedal cadence is sensed.

If there is no ramp in (2) there will still be an initial kick regardless of (1), it's just that with the current controlled system the kick will be less in lower PAS levels,

 

[Bonzo Banana]

Interesting reading, I would of thought that type of bike was the type of relaxed bicycle where you would not want to have such a surge of power. It might make sense on a speed optimised road bike but surely not for that type of bike.

Sounds like a bike that really needs a throttle control. So once you start cycling you can apply power gently up to the chosen power level maximum.

Looking at the handlebar controller its just a simple 790 which I think typically work with KT controllers and assume this is dictating the 3 speeds to the main kt controller. I wonder if you can hack a throttle in there and possibly remove use of the 3 speed controller. The voilamart kits can use those 790 controllers I think and they are limited in the same way if they don't have a throttle.

I could be wrong but I suspect there is an unused throttle connection on the main controller board which I guess is incorporated into the battery?

Also could you replace the basic 790 with a LCD display which has more sophisticated functionality? Do the more sophisticated models with LCD displays actually control the motor more smoothly?

The basic violamart kits don't even have any speed settings just a throttle. Yet you can add a LCD display to add more functionality and speed settings etc.

 

[cyclebuddy]

I'm not sure that's the right graph for this bike.
If the Pendleton is speed control, which it appears to be, then it will apply full power on whichever setting it is on.

As sjpt spotted, the graph is the correct one from the Pendleton manual. Not all cheap e-bikes just use pure speed limiting: My own "cheapy" Fiido £800 folding e-bike (with unrestricted throttle) uses exactly the same current limiting/speed capping (It's why I didn't feel any need to change to a KT controller) - I'd say the power profile is identical to the Pendleton graph, although the controller is described as "Fiido's own system". On mine, there is no "ramping-up" other than the motor is only 35nm, so the weight on the bike determines how fast the motor can spin-up. A lightweight rider may well feel it's a bit too urgent even in low assist.

The Pendleton has been around for a good few years now; it may be the earlier ones were just speed limited? The OP hasn't told us how old his wifes' Pendleton is.

 

[sjpt]

The same manual for the Somerby report the motor as 32nm.

Going back to the original post I notice he says

Hello all
A problem has arisen where when she starts to pedal the bike keeps lunging forward as if at top speed.

So presumably the bike didn't have the issue originally, and we need to think of possible faults that could cause the problem, rather than possible limitations/issues with the Somerby system itself.

No mention of 'reset' in the manual. I wonder if its worth trying things like holding the power button for several seconds, or pressing and holding power and mode at the same time.

 

[cyclebuddy]

So presumably the bike didn't have the issue originally, and we need to think of possible faults that could cause the problem...

My own diagnosis remains the same: The controller is screwed.

It may be one-step up from a truly basic speed limited controller, but it isn't a KT with a user programming menu, or a Bosch or Bafang with apps you can twiddle and alter parameters. Even Halfords new Hyena system has a programming menu, but you can't actually change anything.