Torque sensing build for Tern folder

John Galvin

Pedelecer
May 14, 2014
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Hi

I want to build an ebike using a Tern Link P9 2014. This has a 20" 9 speed derailleur setup. I want to keep the weight as light as possible, so a mid-drive kit isn't the way to go. Besides, I won't be tackling huge hills.

Because the forks are aluminium, I want to mount the motor in the rear hub. I'll use a pair of torque arms to be safe.

I know that 250w is the EU limit, but I'd possibly go to 350w but no more as I don't want to go mad.

I'd really like a proper torque sensing controller. I tried a Peugeot AE 21 recently and it rode beautifully because of a properly sorted torque sensor. I'd like to recreate that experience as closely as possible.

I know the Bionx kit would give me everything I need but it's pretty expensive. At the other end of the scale, I came across this:

http://www.aliexpress.com/item/XMK-Electrical-Bike-System-Kit-Meter-Controller-Motor-Torque-sensor-Speed-Sensor/593238722.html?tracelog=back_to_detail_b

This appears to do everything I want but is it any good? It would also mean building a wheel around the motor - how much roughly would that add to the cost?

Is there some other kit I should be looking at or am I mad to be trying for a torque sensored solution. Cadence sensored kits are much more readily available and I'm wondering how they ride. I've heard they're not great at hill starts for example.

Any ideas gratefully received.
 

trex

Esteemed Pedelecer
May 15, 2011
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this XMK motor



is the clone of the XOFO motor with built in torque sensor XFC
like in this Woosh Sport TS:

Weight wise, it's about 3kgs + 300g for the controller, you are not far from the 3.7kgs crank drive kit BBS01




XOFO will bring out shortly (end of this month) a crank drive version with built in torque sensor called the XOFO MMT - initially in 250W but later in 350W (36V 25A). Similar look, same weight, same wiring as the BBS01.
The crank drive kit is much easier to fit - no wiring mess, no wheel building. You can get up to 22-23mph with the BBS01, the XOFO XFC is wound for 230RPM, on 20" wheel, you only get 15mph at best.

 
Last edited:

John Galvin

Pedelecer
May 14, 2014
77
2
51
Just an addition

I've just come across a Torque simulation controller on BMS Battery. Any good?

I've also come across Cycle Analyst V3, which, with a torque sensor fitted to the crank, should also should do the job.

Hi

I want to build an ebike using a Tern Link P9 2014. This has a 20" 9 speed derailleur setup. I want to keep the weight as light as possible, so a mid-drive kit isn't the way to go. Besides, I won't be tackling huge hills.

Any ideas gratefully received.
 

John Galvin

Pedelecer
May 14, 2014
77
2
51
Final question for tonight.
I've put together a set of components from BMS Battery: A torque simulation sine wave controller, display, battery and 20" front hub.
I'm back to front drive as I can change the forks to steel for little more than the cost and weight of two torque arms.
I've asked BMS if the 20" wheel will fit the Tern i.e. 83mm hub.

My question is: Once I have all the bits, how do I connect them? Is a wiring loom available or do I have to crimp plugs onto my own wires. What's the best way to do this?

TIA
 
D

Deleted member 4366

Guest
Lots of questions. I'd forget theCycle Analyst route. That Thun Torque sensor is quite heavy, and the software to use it in the CA is not very sophisticated. In fact I'd forget the whole idea of a torque sensor as there's no real advantage.

The"torque simulation" controllers are lovely controllers, but I wouldn't switch on the torque simulation. I think that they work very well with speed control. Maybe torque simulation (current control) would be better for a crank-drive.

If I were you, I'd use a standard controller with speed control and an LCD with 5 levels of PAS plus a standard PAS crank-speed sensor.

For your Tern, I'd get the 328rpm Q100 ready-built into a rim. Add a DNP free-wheel; S06S controller with LCD, PAS and half-throttle on the left side (backwards), and a 12S lipo battery for the extra speed and power.

Have a look at this thread that might give you some ideas:

http://www.pedelecs.co.uk/forum/threads/electric2011-dahon-jetstream-p8.10584/page-4

missing photos here:
http://s451.photobucket.com/user/d8veh/library/Dahon?sort=3&page=1
 

John Galvin

Pedelecer
May 14, 2014
77
2
51
Well after reading the replies and doing a bit of reading, I'm going to forget about torque sensing and just build a simple PAS + throttle.
I've ordered a steel fork for the Tern so I can go front hub if I want.
What would people recommend, front or rear power? I got advice from a US supplier that a Dahon (similar folder to Tern) can have weight distribution problems with a rear hub.
My supplier has confirmed that my nine speed derailleur will fit on a powered rear but I'll get them to confirm again before I order a rear hub.
The front has its plus points too, with better weight distro and 2wd - probably a simpler install too.
So which would you choose? The bike is a Tern Link P9 folder with a nine speed derailleur and 20" wheels. It's on Evans Cycles if you want a look.

Final question - if I go front with steel forks, do I need 1, 2 or no torque arms?

TIA
 

trex

Esteemed Pedelecer
May 15, 2011
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if you go front hub drive without suspension, you're going to hurt your wrist.
 
D

Deleted member 4366

Guest
You'll have a lot of trouble with installing your gears on a bike like the Tern, so I'd go with a front motor. I don't know who told you about weight distribution problems with a rear motor, but mine worked perfectly, and Cwah used a big motor in his, so I'd say that's a load of ball-cocks.
 

John Galvin

Pedelecer
May 14, 2014
77
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51
With it being my first build, I'm not inclined to have to do anything too complex so I may go front to keep things simple.
Any thoughts on torque arms? I'll be keeping it to 250w.

You'll have a lot of trouble with installing your gears on a bike like the Tern, so I'd go with a front motor. I don't know who told you about weight distribution problems with a rear motor, but mine worked perfectly, and Cwah used a big motor in his, so I'd say that's a load of ball-cocks.
 
D

Deleted member 4366

Guest
Not necessary with steel forks and a 250W motor. Saneagle doesn't have them on his bike, which has enough torque to wheel-spin on tarmac.
 
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John Galvin

Pedelecer
May 14, 2014
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Thanks

Somehow felt I'd be OK once I'd switched to steel. I'd rather the fork bent rather than broke.


Not necessary with steel forks and a 250W motor. Saneagle doesn't have them on his bike, which has enough torque to wheel-spin on tarmac.
 

peerjay56

Esteemed Pedelecer
May 24, 2013
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Nr Ingleton, N. Yorkshire
I have a front wheel mounted motor in steel forks, without suspension, albeit on a 700c hybrid. My wrists do not hurt.:p
 
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trex

Esteemed Pedelecer
May 15, 2011
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I borrow a friend's e-bike this afternoon for a spin on the sea front in Southend. His has RST Gila fork, V-brake and rear hub. Mine has Rockshox Dart, Auriga Comp and crank drive. You know how it feels to downgrade. Now would I swap mine for a 350W motor mounted on a steel fork with only a 20" tyre for comfort?