How do these Bottom Bracket Sensors Work?

Electrically assisted bikes, trikes, etc.
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DaveP
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How do these Bottom Bracket Sensors Work?

Postby DaveP » 19 Sep 2020, 10:00pm

I'm pretty unfit at the moment and I'm finding that worrying about not getting back up the hill on my way home is actually putting me off setting out, so I'm contemplating adding some assistance to a bike - probably the Brompton because it's the only one I can reliably bestride just now.

I'm trying to understand the nature of the control systems.The versions I have seen so far... well I can see that they would be able to measure your pedalling cadence but I can't see how they could possibly detect your effort. How does the black box - sorry - bag :D decide whether your feet are slowing down because you are struggling with a hill or because you are taking it easy on a level road. Needless to say, a wrong call would be a pain.

All I'm after is some help with the steeper hills. In my innocence I have wondered if I might actually be better off with some sort of simple hand switch or throttle - just a little push when I'm knackered... but I have heard somewhere that there might be legal issues with this approach.
Any thoughts about this aspect of electrical assistance would be very much appreciated - I'll think about the hardware later!
Trying to retain enough fitness to grow old disgracefully... That hasn't changed!

Jdsk
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Re: How do these Bottom Bracket Sensors Work?

Postby Jdsk » 19 Sep 2020, 10:05pm


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DaveP
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Re: How do these Bottom Bracket Sensors Work?

Postby DaveP » 19 Sep 2020, 10:10pm

That was quick!
Thank you very much - just off to do some reading...

Edited to add: Those links take you to a commercial site that is really generous with tecchnical information and guidance. If they had a UK branch the chequebook would be opening... As it is, I've come away with some useful questions for whoever I decide to favour with my custom. Thanks again!
Last edited by DaveP on 19 Sep 2020, 11:07pm, edited 1 time in total.
Trying to retain enough fitness to grow old disgracefully... That hasn't changed!

Jdsk
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Re: How do these Bottom Bracket Sensors Work?

Postby Jdsk » 19 Sep 2020, 10:26pm

: - )

If you find a good picture of how strain gauges in the bottom bracket work please post it...

Jonathan

stodd
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Re: How do these Bottom Bracket Sensors Work?

Postby stodd » 27 Sep 2020, 10:20am

Almost all cadence sensor systems don't even use the cadence, just whether or not you are pedalling.

Cadence sensors are more common with hub systems and torque sensors with crank systems; but there are many exceptions.

Torque sensors give a more 'natural' feel, like riding a bike but with extra strong legs. You always need to put in some effort with these; typically on highest setting it multiplies your effort by 300% to 400%; so you still need to do at least 1/4 or 1/5 the work. With cadence sensors you can just keep the pedals turning but not provide any effort and the motor will do its job. For people with some health issues this can mean cadence is better; less likely to be caught out on a steep hill near the end of a long ride where you are just too tired to put in any effort.

Torque sensors are better at hill starts (especially over junctions) as they provide power almost immediately; cadence sensors tend to need around 1/2 pedal turn before they kick in.

Most cadence sensors have settings that control how much current the motor can use which gives pretty smooth control. Some cheaper ones have speed control settings; I've never ridden one but they are said to be much more awkward to control nicely which makes sense.

hemo
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Re: How do these Bottom Bracket Sensors Work?

Postby hemo » 27 Sep 2020, 11:04am

Bikes with so called cadence PAS ( a simple 3 wire hall sensor and a magnetic disc) one can simply ghost pedal. this allows the user with poor stamina or energy levels to still ride. The best option is a system that has a controller that uses current control and five levels of assistance to choose from the power range. The KT (Kuenteng) ones are hard to beat, from PAS 1 to PAS 5 one gets power assistance of 13%, 20%, 33%, 50% & 100% respectively.

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DaveP
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Re: How do these Bottom Bracket Sensors Work?

Postby DaveP » 28 Sep 2020, 10:59pm

The phrase that I particularly liked was that "Cadence PAS allows you to decouple your effort from the power required".
Yes, I know, slippery slope... but I think that is probably what I actually need. I have two issues - a loss of strength and fitness over the last two or three years largely resulting from arthritic hips, the worst of which is no longer with me. Unfortunately I have other dodgy joints so I probably need to avoid sytems that require you to push hard in order to get help. I need to spin spin and nothing but spin!.
I could turn lazy, but I'm hoping the desire to get back onto a traditional bike one day will keep me on the straight and narrow :D

I'm currently wondering if I could both practically and legally add a switch to the system so that I could preset the level of assistance (low!)and then just turn the power on / off when required, with the + button safely out of reach! Not quite the same as a throttle, as far as I can tell.
Trying to retain enough fitness to grow old disgracefully... That hasn't changed!

Bonzo Banana
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Re: How do these Bottom Bracket Sensors Work?

Postby Bonzo Banana » 29 Sep 2020, 9:46am

DaveP wrote:The phrase that I particularly liked was that "Cadence PAS allows you to decouple your effort from the power required".
Yes, I know, slippery slope... but I think that is probably what I actually need. I have two issues - a loss of strength and fitness over the last two or three years largely resulting from arthritic hips, the worst of which is no longer with me. Unfortunately I have other dodgy joints so I probably need to avoid sytems that require you to push hard in order to get help. I need to spin spin and nothing but spin!.
I could turn lazy, but I'm hoping the desire to get back onto a traditional bike one day will keep me on the straight and narrow :D

I'm currently wondering if I could both practically and legally add a switch to the system so that I could preset the level of assistance (low!)and then just turn the power on / off when required, with the + button safely out of reach! Not quite the same as a throttle, as far as I can tell.


It's perfectly legal to have a throttle on a bike you buy today. The issue is in the past the bike's motor was operated purely by the throttle but now you have to pedal to enable motor power but that power can have multiple settings or be variable like a throttle or it can be linked completely to rider effort as per mid-drive motors or torque sensing bottom brackets. A throttle is still a great option if you want to control the power level as you approach hills, overtake etc. Sounds like a throttle is ideal for you.

hemo
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Re: How do these Bottom Bracket Sensors Work?

Postby hemo » 29 Sep 2020, 10:50pm

A Bonzo say's if the bike has a throttle post 2016 it must only work after one has started pedalling. stand alone aren't legal.
All ebikes that utilise a pedal sensor on the BB will be a simple cadence/rotation sensor.
Most of the Halfords Carrera bikes are torque sensored so be careful and ask when you buy.
The controller programming responds to how quickly the magnets on the magnet disc pass the sensor head by way of a signal.

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DaveP
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Re: How do these Bottom Bracket Sensors Work?

Postby DaveP » 30 Sep 2020, 12:49am

That's the legalities sorted then - Thanks!
The more I read, the more I'm sure that a conventional cadence controlled system will suffice. The only thing is I really don't want continuous assistance. It would be very welcome when needed, but at other times I don't want any at all - I'd rather receive the full exercise benefit of the stretches that I can handle :D
Could the bike be set up to work like that or would I neeed to use a "kill switch"?
I probably need to take this up with the lucky supplier, who at this point in time seems likely to be Woosh!
Trying to retain enough fitness to grow old disgracefully... That hasn't changed!

hemo
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Re: How do these Bottom Bracket Sensors Work?

Postby hemo » 2 Oct 2020, 4:49pm

Good hub motor kits or ebikes that use a simple PAS rotation sensor will have a zero setting as well as other assist levels so simply set to zero assist and work those pedals. Because of the extra weight of the hub pedalling sometimes gives the illusion of riding thru treacle or resistance, one gets used to the extra weight. Geared hubs have an internal clutch that disengages when no power is selected whereas the DD (direct drive) heavier hubs don't even Geoff capes would struggle to pedal one of them with no power.

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DaveP
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Re: How do these Bottom Bracket Sensors Work?

Postby DaveP » 2 Oct 2020, 7:43pm

hemo wrote:Good hub motor kits or ebikes that use a simple PAS rotation sensor will have a zero setting as well as other assist levels ...

Thanks, I can work with that. I hadn't managed to pick that up from anything I've read so far.

hemo wrote:(direct drive) heavier hubs...even Geoff capes would struggle to pedal one of them with no power.

As bad as that? I can understand why they don't put that in the publicity!
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Bonzo Banana
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Re: How do these Bottom Bracket Sensors Work?

Postby Bonzo Banana » 8 Oct 2020, 9:01am

hemo wrote:Good hub motor kits or ebikes that use a simple PAS rotation sensor will have a zero setting as well as other assist levels so simply set to zero assist and work those pedals. Because of the extra weight of the hub pedalling sometimes gives the illusion of riding thru treacle or resistance, one gets used to the extra weight. Geared hubs have an internal clutch that disengages when no power is selected whereas the DD (direct drive) heavier hubs don't even Geoff capes would struggle to pedal one of them with no power.


I think direct drive hubs when unpowered require about 10-30W to create a no resistance feel depending on size of hub so you can certainly ride them easily unpowered with reduced efficiency where as if regen is enabled even going downhill you may have to peddle to keep speed up such is the resistance. So a direct drive hub normally has 2 levels of resistance depending on if regen is enabled. The geoff capes quote sounds like regen is enabled rather than a shortfall of power of 10-30W. Direct drive hubs can work out quite well as you use assistance for the hills, switch off to ride on the flats and peddle while going downhill with regen on to create a very long range ebike that gets charged while going downhill and doesn't use the battery on the flats. It means a fairly consistent level of input from the rider for maximum weight loss and health benefits as well as hugely expanding the range of a bike. A crude estimate is a bike that has a range of 20 miles purely with assistance could provide a range of 80-100 miles.