Torque sensor for 3-gear Shimano hollow tech

[schwibsi]

Hello everyone,

I built my first custom bike last year, after 15 years of not riding a bike at all, and something's still not right about it.

It's a 28" Trekking bike
with a NuVinci 360 (17 teeth) in the back
3x Shimano Deore XT crank wheel 26-32-48 teeth (so I get over 660% shifting range with the whole range usable)
Magura HS-11 front and back
LED lamp head with 3x Seouls P7 LEDs (a bit brighter than the light of an old car)
I also added a Thudbuster suspended seat post,
The aged Brooks saddle, that I just love
matching brown leather grips
Mirobar X1 barends (with integrated periscope-like mirrors)

I should maybe add, that I'm 175 pounds now. A year ago I was about 220.
I used to work out a lot, when I was younger, but got hardly any exercise. I'm untrained, when it comes to cycling.
On a 10 mile straight, on my bike I will deliver a sustained speed of 17-18 mph.
I would like to get an electric motor for the front wheel (so I can keep the NuVinci) that will raise my sustained top speed to 30mph. I'll get scared going faster than that. (Don't get me wrong. I have no problem with doing 175mph in an Audi A8L or 190mph in 911 turbo) but somehow doing much more than 30mph on a bike is outside of my comfort zone.
Also, here in the Bavarian forest we do have real hills that aren't just gently sloped. So to go up to my parents' house, I ride the bike up 2 thirds of the hill and then I usually opt for pushing as my thighs start burning. It would be kinda nice being able to go up those hills, too. By the way, I would love to have a range of 60-65 miles even after one year of using the battery.

So here come the issues.
I really would like to keep the 3-gear crank wheel, but a torque sensor is a must, as I want the bike to support me -50% (as in recharging) 0%, 50%, 100%, 200% of how hard I pedal.
Is there any way to keep the 3-gears or at least 2 and at the same time installing a torque sensor.

I would be very glad for any suggestions or other input you may have. Any tips or criticism are welcome.
If the whole thing is a stupid idea, or impossible, please just let me know.
I haven't really looked into motors, controllers and battery yet, as the torque or power sensor determines a lot for me and the other details come later.

Thank you all a lot for reading and for your suggestions.
I greatly appreciate it.

Regards,
Andreas

 

[d8veh]

The only torque sensors that I know are from Thun, but I don't know where to get them from or how much they cost. If you find out, please let us know.
http://www.thun.de/de/produkte/

You can buy cranks with a built-in torque sensor, but they are single chain-wheels. They also come matched to a 250w controller, which will give a max speed of about 15 - 18 mph.
http://www.bmsbattery.com/ebike-parts/306-ebike-torque-sensor.html

30mph from a front wheel drive is not going to be easy, and would be dangerous because if your wiring or drop-outs failed, you'd go straight over the handlebars. A 350w motor is about as high as you should go on the front, which will only give about 20 - 22 mph.

A mid- drive system might be possible depending on how much you want to pay. The cheaper ones don't have good reputations for reliability, but this one looks better:
http://www.ego-kits.com/

Another solution would be to sell your bike and buy a Haibike or similar bike with Bosch motor. They make one that does 40kph but it won't give the range you want unless you carry a couple of spare batteries.
http://www.haibike.de/

You should have a look on the Pedelecs.de forum where there's a lot of info on these bikes and other solutions to what you want.

 

[schwibsi]

Hello d8veh, I take it you're German from somewhere around here, too.

buying a different bike is not an option for me. I love mine too much. I've worked, sweated and bled too much for this one. It'll stay with me until the day I die and pass it on to my son

Also, mid-engine is nice in Italian sports cars, I wouldn't want to punish my NuVinci with it. They company was quite adamant about the number of teeth to be used in the gears, so torque seems to be a major concern for them. Tripling the torque by adding a motor can't be high on there wish lists for things I should to to their hub.

Look, what I found:
http://www.ebay.de/itm/E-Bike-Umruestsatz-250W-36V-11Ah-Thun-X-Cell-RT-Torque-Sensor-digital-/170775250885

It turns out, you can buy the sensor without a whole bike.
Now, I'll just have to find out, if the sensor can be installed with the 3-gear crank and what controllers it would be compatible with...
All other problems should be solvable through research.

Oh, about the speed, don't get me wrong. I don't want the bike to do 30mph on it's own while I'm sitting there enjoying the beautiful countryside flying by me.
The 30mph should be reachable in situations where, without support, I'd be doing 20mph on my own. So, the 20-22mph you speak of, well, I will reach those on my own without the motor. I'm aware of the fact that above 15mph, drag due to wind is, what we're working against, so I'm hoping the motor will deliver the additional 10mph at that speed.

I'm not too worried about the 500W motor in the front, as the maximum setting I want to give it is 200% added support. So for every Watt I put in the back, it should add 2 on the front wheel.
My guess is that this will be a lot different from a bike that is purely front-wheel driven. as the power distribution is always max two thirds front, one third rear.

 

[d8veh]

Most controllers work as speed controllers, so they give a lot of power to reach the speed you've chosen with the throttle or whatever. They don't give power in proportion to pedal effort. I would guess that that Thun torque sensor is matched to its own controller, so might have that possibility. If the sensor gives out the normal 0-5v range, it could work with a normal controller, but the motion wouldn't be smooth or efficient. It would be like opening and closing the throttle with each pedal stroke. You'll have to think about the motor too. That 250w motor in the kit will only go to about 18mph. The torque sensor and controller might not be able to handle a bigger motor. If you stick with a 250w motor, you'll need a 24v one for a 20" wheel (about 400rpm) and run it at 36v.

Personally, I think that you've set too many constraints. I'd build a new bike with a Bafang BPM motor with normal throttle and pedal sensor. It would be easier, cost less, and do everything that you want. You'd need a code 11 or lower and at least 44v to reach 30mph. When you have an electric bike, you don't need all that fancy gearing. The only thing I look for is good air suspension front and back, then you don't need any special saddle. To get the range you want, you'll be looking at a battery with at least 20aH which will be relatively big and heavy. You'll also need to think about where to put it - too high and it'll spoil the handling of your bike.

 

[MadRhino]

http://factory.dhgate.com/electric-bicycle/pedelec-power-system-p40930384.html

 

[schwibsi]

@ MadRhino: I've looked at the chinese torque sensors, but afaik they don't support multi-gear cranks, which I definitely need. (the 360% gear range of the NuVinci is not enough for a slow pedlar like me while at the same time having to climb the mountains we have here.

@ d8veh: The sensor delivers a signal between 0 V and 5 V, with 2.5 V being 0 Nm, 5 V being the maximum forward torque and 0 the maximum backwards torque. So the signal would have to be converted, but that is just an issue of electronics, definitely solvable (not by me alone, but we'll find someone, I'm quite confident of that)

The wheels are 28", with my assistance, the bike and I should surpass the 18mph easily.

I understand, where you're coming from, and for most people that would be sound advice, but I'm still a young "pimp my ride" ride kinda guy (without the hiphop and the bling) and I want to keep my bike, just make it a little better. Buying another one, maybe even off the rack would be like giving up on a child that doesn't learn a new trick instantly. Even if they can't do it right away, you keep loving them and trying your best to teach them, whatever you can.

Maybe 30mph are a little other the top, but a sustained 35-40kph (22-25mph) shouldn't be technologically impossible, as I am doing the 18mph on my own without any assistance and I don't want it to do those speeds without my pedaling anyways.
Also, the hills I climb with the bike aren't more than maybe 300m long and if I really exhaust myself I can still sustain 5mph. I imagine the motor has about twice as much power as me, so keeping speed over 10mph should not be that big of an issue either.

 

[kfong]

I think the Thun would be a great addition if it could be easily purchased separately. I would be interested in getting one.

 

[schwibsi]

After reading up some more, I am more and more leaning towards installing a Bosch middle engine system.

They already have a nice torque-, power and speed sensor and control installed and they still seem to play nice with the NuVinci 360 and I am hoping I can at least keep 2 gears on my crank wheel.
I'll have to look into the cost of doing that and what that would mean for my crank wheel.

If anyone has some cheap sources for the parts needed, I'd be happy to hear about them.
Thanks a lot.

 

[MadRhino]

@ MadRhino: I've looked at the chinese torque sensors, but afaik they don't support multi-gear cranks.

This one single ring seem to have the standard 5 bolt chainring pattern, so it is only a matter of adding 2 chainrings of your choice to make it meet your requirements.

A Bosch mid drive would be better of course, but at a much higher price too.

 

[schwibsi]

I've been told by a few retailers now that the Bosch drive will only be sold in exchange for the old one and that you need a special frame for it, so it will not fit in a regular 28" frame.

I also found out that torque and power sensors for bikes do exist, SRAM, Garmin and Polar for example make them. But they're all more expensive than what I'd be willing to pay for a set of bikes for the family incl. the motor, the controller and the sensor.

I've found a few other mid engine solutions that may incorporate a a torque sensor, but it really looks like I'm going to be stuck with a cheap Chinese torque sensor, if no one has a solution, how to get the Thun sensor installed in a crank wheel....

 

[schwibsi]

I'm getting closer to a solution.

To start off, I will probably first convert another Trekking bike
using a
Magic Pie III with 7 sprockets in the back
the new Cycle Analyst
a Thun X-Cell RT with sensors for cadence and torque
and a 48V 10Ah battery
a thumb throttle to assist while pushing the bike and to assist at low speeds.

Thun can obviously be combined with a square crank

For my bike, I will probably use a

- mid motor eg. from GNG Electric installed between saddle tube and down tube
- Thun X-Cell RT Sensor
- 3-gear crank with freewheel
- New version cycle analyst to control motor power
- Battery installed between top tube and saddle tube

What do you guys think

 

[crossbreak]

I got his one from bms battery, sadly the display is broken, so nothing works at all. I hope I get support from bms-battery to fix this. I will report on how it might work. I already enlarged my bottom bracket to a 135mm one for my tongxin midrive, now with the torque seonsor it will become very tight. Three chain rings are not impossible to build in, the bracket axle just have to be even wider, and you would get big problems with chain alignment. I guess this would look very funny.

Thats what I got from bms-bat:

If we look closer at the Thun X-Cell RT Sensor, we see that it can only measure the torque of the left pedal. That's very sad, but that cannot be changed

Not easy at all this topic... i hope to get this bms-bat sensor to work with an infineon controller.

 

[schwibsi]

Sorry to hear that it didn't make the trip alright. I hope they'll replace the part soon and help you figure out how to maybe work it until then.
I'm currently doing a lot research for the project in different areas.

The guys from sickbikeparts seem to have a freewheel with a double bearing, which is supposed to handle the side loads pretty well. So, check on that.
I'll push research on the rest of the crank back, until I have a solution for the motor/gearbox.

I would like to use the sensor from greentrans rather than the Thun, but it seems like they only want to sell complete kits, which is quite a pity, as their sensor seems to be double sided.

About the motor, I'm probably the last one on this forum to figure this out, but I'll post it anyways.
Cadences while pedaling on the crank are going to be somewhere around 60-80 rpm. With a 3:1 gear down that leaves us with some 180-250 rpm on the sprocket, which we want delivered at peak efficiency.
The issue with most electric motors is that their kv is much too high for our purposes. Even just at 24V we would not a kv of 10rpm/V, when 100 is about as low as I've seen so far.
So, either I find a motor that has a decent efficiency at those low rpms, or I find a gearbox that will not be to heavy, bulky and inefficient to geardown 10:1 or 20:1, depending on what motor is used.
I'm also afraid that high revving motors and gearboxes will be a lot noisier than one that is slow revving on it's own.

I'll look into this some more, I really hope, I'll find a light RC motor that will meet the requirements. The videos of the turbocharged sounding bikes that I've seen on youtube is nothing I could use to get around town and to go shopping. I really wouldn't want the attention of everyone around expecting my bike to burst into flames at any second or to witness, how I miraculously disappear in a flash of lightening warping back in time to the 50s.

In any case, I haven't given up yet

 

[crossbreak]

you should read my tongxin middrive project:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=34146&p=542312#p542312

It is as silent as it can get. I use a 32:13teeth reduction and have a second bearing (polyamid) between shaft and the 32T sprocket.

The tongxin still holds up @15amp and 10s lipo. I did about 450km yet with my new chain drive (2nd try).

 

[Miles]

Ref: http://www.endless-sphere.com/forums/viewtopic.php?p=496618#p496618 [and following pages]