Thorn Me’n’U2 Electric Conversion

The bike is fantastic, however pulling a total of about 180kg up long hills leaves me worn out. It is ok until I hit bottom gear but at that point there is nowhere else to go other than leg power. We’ve always got up the hills – and I am definitely fitter and stronger than I was – but with my partner having an electric bike she has been suggesting routes that I don’t want to do due to the number of hills. I’d like to be able to ride further without worrying about the hills. I’m also curious about the kits and how they would work in practice.

So I did my research and bought a BPM kit from Woosh. Woosh have a great reputation and Andy’s patient answering of my innumerable queries has been outstanding. The BPM motor has a good reputation for lugging heavy bikes up steep hills where other motors simply melt – very important given that I’m expecting this motor to cope with pulling anything up to 250kg up 17% (1:6) hills. It is a front wheel motor; as mentioned before the rear wheel of the bike doesn’t have much weight on it and I get wheelspin on slippery surfaces with pedal power.

The kit arrived promptly and quality was good.

Opening the box
Bits in the box – not a good photo!

I’d already established that there would be a number of challenges to fitting the kit.

Battery

To keep everything at the front of the frame, to aid balance and keep short cable runs, I wanted to fit the battery under the pilot’s position. It will just fit.

Just possible to fit the battery at the front, and even get the battery in and out

However the bottle cage mounts don’t line up, nor is there enough space to drill for the rivnuts that Woosh supply. I therefore made some aluminium brackets to clamp the battery to the frame. This also helps support the battery mount which is a bit flimsy.

Custom battery mounts

It all seems to fit ok.

Pedal sensor

The kit was supplied with a couple of pedal sensors. However these require that a wider bottom bracket is fitted to make room.

I didn’t want to do this for a few reasons:

  • I think they need to be the same width down the length of the bike to keep the timing chains aligned;
  • I didn’t want to buy more bottom brackets – they are £25 each;
  • I didn’t want the kids feet to be spaced any wider apart.

As a triplet this bike is fitted with a standard front RHS crank arm with drilling for a small inner ring. So the plan is to use these threaded holes to mount a custom magnet disk to the crank arm. Then I can make a custom aluminium bracket to mount the sensor to the frame. This will also look a lot neater than the clip-on sensors.

Front drop-outs

The front drop-outs will have to be filed out to 10mm. This is slightly worrying as the forks are beautifully minimal, although extremely strong. I will be fitting torque arms to the drop-outs to take the torque and there are plenty of braze-ons to transfer the torque to. I may use part of the supplied torque arms or I might make totally custom arms.

Cable lengths

Fitting everything – battery and motor – at the front of the bike means that cable lengths can stay at stock length. I require one cable extension for the speed sensor as it is designed to reach the back wheel (on a single seat bike) but I want it to reach the front wheel. I might shorten some cables but I’ll get it all working reliably first.

Conclusion

Lots still to do – probably tackle the pedal sensor next – but so far so good.

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