Home made pedelec/pedal torque sensor

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Pedelecer
Oct 24, 2009
176
0
Shanghai
Daniel I'm a Brit now living in Shanghai, China and I'm now looking at all apsects of ebikes for future projects. I'm constantly researching what's available and getting together various parts for testing. You're welcome to drop me a PM and we could have a chat :)
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1
Daniel I'm a Brit now living in Shanghai, China and I'm now looking at all apsects of ebikes for future projects. I'm constantly researching what's available and getting together various parts for testing. You're welcome to drop me a PM and we could have a chat :)
Hello !

My understanding is that crankset / chainring force sensors lack the progressive range of a throttle control. Both systems work using Hall-effect sensors (and feed an electric signal representing the 0% to 100% range), although of course torque information is gathered from subtle flex variations / elastic deformations detected through dual rare magnet rings and sensor arrays (whereas a throttle device is a single Hall sensor).

As a result, the initial power uptake can be quite jerky, with some kind of on/off behavior as opposed to a gradual progression. I suspect that controller programming has a lot to do with the overall riding experience, especially when correlating data with the cadence sensor (which should remove the dangerous "put foot on the pedal => motor start" pattern !).

However I do not possess such crankset sensor, so this is all very theoretical in my mind. I'd like to get my hands on a recent unit to measure output currents. Maybe controller fine-tuning is all it needs, the hardware could be fine...

The TMM4 rear-dropout system looks well-engineered, but it requires intrusive and irreversible frame modifications. Thus why I am interested in more flexible off-the-shelf solutions (if any ?).

Cheers, Dan
 

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Pedelecer
Oct 24, 2009
176
0
Shanghai
I'll try to find out some more about the torque sensor and maybe try to get hold of 1, but unfortunately I am rather snowed under at the moment. Ananda offer a PAS display that mounts onto the bars and allows adjustment to the PAS assist level. I'll have to do some testing to determine what's going on with the signals to determine the type of signals used and how they are altered to adjust the assistance level. With a seperate PAS controller and the torque sensor as previously shown it may be possible to fine tune the way the power is dialed into the controller, to avoid the snatchy start up that is typical of PAS that I have used.

I used to fit strain gauges onto ships propellor shafts and helped to develop the product that measured the vessels torque and power, but it's gonna take some serious miniaturisation to apply anything like that sysyem to a bikes crank :rolleyes: but I'm sure there is available technology out there that can do just that. It's just a matter of ensuring it's both reliable and reasonably priced.

Personally I don't think the standard PAS speed sensor is so bad but could be improved by having some adjustable parameters, plus make use of more available data and have a more sophisticated algorithms using these additional signals.
 

Straylight

Esteemed Pedelecer
Jan 31, 2009
650
2
Maybe all it needs is software set power ramp,as opposed to letting the input directly control the output. Speaking purely theoreticaly of course, with little knowlede of how complicated this would make the controller :D .
 

emissions-free

Pedelecer
Oct 24, 2009
176
0
Shanghai
Once I've got some time I'm gonna get a scope into some controllers and try to figure out what's going on. I can't see why it's not possible to have the power ramp up more smoothly. I'm sure that with a PAS speed sensor, maybe a couple of other sensors and a small circuit that interfaces to the main controller, it should be possible. Of course it's much easier to talk about it than do it :confused: so we'll have to see....
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1
Update: Frank ordered several different units from a (neighbouring) Chinese supplier, to test the latest products. Apparently the manufacturer has stopped supplying the 5-step "speed" handlebar controller, in favor of a simpler 3-step one. Good to know that Frank is already looking into it :)

Cheers, Dan
 
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emissions-free

Pedelecer
Oct 24, 2009
176
0
Shanghai
Frank's got some pretty good products there. Why doesn't the UK have anything like that? Maybe it will soon :)

I think it's quite good the way he just sells the motors, controllers etc as individual items rather than just sell a kit. Also nice that you can buy a battery from him without having to prove that you also bought a kit previously.... It must be so terrible that someone actually goes out an buys a kit from China and then expects someone to just sell them a battery for £300without proof of a previous purchase...... :)

His prices are reasonable, but not cheap. Good luck to him, it's the way forward IMO :)

Daniel, my refernce to making a controller which could use the PAS sensor to control the power more smoothly was referring to making a new product, not just buying a completed product from a manufacturer and exporting it. That takes time and a considerable amount of work. I don't mind the work, but finding the time is a problem. I've got a sample PAS display which allows 5 levels of PAS assist. I'll have a play with it soon and let you know how it performs.
 

Haku

Esteemed Pedelecer
Jun 20, 2007
339
4
Gloucestershire
I'm not entirely impressed with the UM torque sensor, I mostly rely on my (derestricted) throttle to get smoother speeds and full power when I want it.
For example if I want a leisurely ride along the flat it's difficult with just the torque sensor to go slowly smoothly (ie below the 15mph motor cut-off), putting it in 6th gear and pedalling slowly the motor will cut in and out as my speed decreases and subsequent pressure on the pedals triggers the torque sensor. In a much lower gear the torque sensor wants to kick in much more because it's easier to put more pressure on the pedals.

I got to have a look inside one of the UM VPAC's when I had my one replaced (the sensor still worked but the chainring guard was smashed), it uses a similar system to an old mouse that uses a ball against a rotary encoder, when you press down hard on the pedals the inner ring moves independant to the main chainring and this causes gaps to appear in which the infra-red sensors get triggered.
It's quite weird first getting used to the torque sensor because of the initial give it has before it gets to the stopping point and then the power is transferred directly to the chainring. Check out The Gadget Show clip on UM's site see what I mean - Urban Mover - the future is now (I got to ride that actual bike :) )

Really they could do with some way of measuring not only how much force is put into pedalling but that you're actually pedalling and how fast, to then throw the numbers into some magic calculator to get a smooth ride at any speed up to 15mph and not have the bike always try to get to 15mph when you're pedalling.
They do have a new thing on their new controllers that allows you to set how much assistance in percentage (25%,50%,100% I think) you get when pedalling which might give you a smoother ride, a longer one for sure.
 
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Haku

Esteemed Pedelecer
Jun 20, 2007
339
4
Gloucestershire
I used to fit strain gauges onto ships propellor shafts and helped to develop the product that measured the vessels torque and power, but it's gonna take some serious miniaturisation to apply anything like that sysyem to a bikes crank :rolleyes: but I'm sure there is available technology out there that can do just that. It's just a matter of ensuring it's both reliable and reasonably priced.
There's a US tv show called Prototype This, they did some pretty amazing builds on the show often using technology most people wouldn't have heard of, one thing that caught my eye was how they turned a solid steel vertical mounted bar into a joystick control for a caterpiller tracked vehicle that can go up stairs to aid firemen, a normal joystick would be too fragile/sensitive for the job so they put a strain gauge on a solid bar to work as a joystick.

If you do a google image search for 'strain gauge' there's lots of miniature ones out there, including stick-on ones. Though how you get power & signal to/from a sensor on the cranks is beyond me ;)


I'm in the process of replacing the innards of a cheap R/C car with better electronics, I found that a lot of the off-the-shelf electronic speed controllers have slow acceleration and even slower reverse acceleration, mainly so you don't rip the nylon gears to shreds, but as this car is so low powered I needed something I could have full control over - so I built & programmed my own electronic speed controller using an H-bridge and a microcontroller, it's quite satisfying knowing you can tweak the acceleration control to exactly how you want it and not how a manufacturer thinks you want it to behave. It would be nice to be able to program the controller on an ebike so the acceleration & power assistance is just how you want it.
 
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emissions-free

Pedelecer
Oct 24, 2009
176
0
Shanghai
Haku, I like your thinking :)

I'll report back on the 5 stage PAS controller that I've got here to let you know my thoughts. I mean we're only talking about a 250W motor, it shouldn't be that difficult to feed that monster power in gently....

I've got a very powerful motor that I use sometimes and the PAS sensor on that is pretty useless. Basically I put the bike in top gear and the PAS sensor will just make the motor run full power and I can't keep up with pedals, in top gear, bye bye A2B and it cost a hell of a lot less to build too :) But it's no beauty, see attached :eek: If you could adjust the cadence that the PAS delivers full power that would be really useful. I mean some people like to pedal faster or slower than others. I mean, 1 size fits all, probably doesn't fit most....

Shouldn't have the same issues with a baby motor though :) I personally just select a much higher gear than I would ordinarily to keep the cadence low and then the PAS just gives a little assistance.
 

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daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1
The Urban Mover crankset / chainring torque sensor can be purchased from the UK:

Urbanmover VPAC Controller

(50 GBP though ! :eek: )
 
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emissions-free

Pedelecer
Oct 24, 2009
176
0
Shanghai
I doubt that a torque sensor would be compatible with a standard controller using a hall effect, speed sensor. So you'd need to figure in the controller too. Don't like the fact you have to swap crank, it looks a bit naff if you ask me... I don't know, 50 quid doesn't sound so bad.

If you can find out any technical information on how the torque sensor functions, please share. Be interested to find out more.
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1

flecc

Member
Oct 25, 2006
52,760
30,348
Torque sensors built into the motor were quite popular with Chinese designs at one time Dan, but unreliability and repair difficulty seemed to be the cause of their near demise.
.
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1
Thanks Flecc. That was just curiosity on my part by the way, not really wanting to use these. Cheers, Dan
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1
Frank posted a photo on the German Pedelec forum of the inners of a typical crank/chain-ring torque sensor:



You can clearly see the circular dual array of rare magnets, and it's easy to imagine the corresponding hall sensors inside the black plastic housing. The "clever" electronics are mostly inside the provided controller, which is bad news as it means that one would not be able to use this kind of sensor directly with a standard controller.

Reminder of how this normally looks like:



And another photo from a modder in the USA:





I like the "Chinese-English" technical description of the device (kind of makes sense, ... but not quite):

"
During riding the toothed wheel twisting moment sensor measures the pedal twisting moment and transmits the measured signals to the intelligent controller to synchronously modulate the speed and power output of the motor according to the pulse duration so that pedaling torque will be in proportion to the motor twisting moment and the torque will be doubled.
"
 
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Scatty

Pedelecer
Jan 15, 2009
160
1
i have tried these at poweredbicycles in the east midlands only a short run but hoping when the weather gets warmer ill be able to get down & have a longer go 1st impression's amazing! :D
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1
i have tried these at poweredbicycles in the east midlands only a short run but hoping when the weather gets warmer ill be able to get down & have a longer go 1st impression's amazing! :D
Looking forward to hearing your thoughts and comments :)

Cheers, Dan
 

Scatty

Pedelecer
Jan 15, 2009
160
1
Will do Dan apparently he has 5 or 6 different models with these systems on & personaly i can't wait to try these 2010 models.
 

daniel.weck

Esteemed Pedelecer
Aug 8, 2009
1,224
1