Electric Assist - Challenge Focus Sport - "el Focus"

Normal Electric Assist bikes is limited to 25km/h as the motor normally is a hub motor. That is around my normal average on the Focus, so I chose to let the motor work on the transmission instead to get assist in any gear. The motor has a specified speed at 160 rpm at 36V, so I just need to gear it so my cadence is about 80 rpm.

The Hardware is a 250W (400W peak) Schachner motor hub and control unit I found on German eBay - there is a motion detector on the crank, so I only get assist when I'm pedalling. The battery pack is made of thirty 1,2V 10Ah NiMh cells from Newtecs, which fits in two 75*300mm tubes. I have mounted the battery pack on the back of the seat - all the extra weight is close to the body that way, and shouldn't give me any problems.

I needed to make some changes to the hub because it drives the chain, not the rim - the sprocket is threaded, and will unscrew itself if it isn't locked in some way. I have made four 12mm holes in the hub body, and made adaptors to fit in the gap between the sprocket and the hub body, and extends into the 12mm holes. The adaptors is internally threaded, and when the sprocket is screwed on, I mount four 8mm bolts through holes in the sprocket, into the adaptors. The bolts is visible on the close-up.

Links :

Pedelecs forum
Stokemonkey
Schachner
Ebikes

I got myself a HP Velotechnik front fairing to protect my feet and lower legs from the rain and cold wind. Maybe it even makes it a bit faster - it feels nice behind the screen anyway. It is starting to look like the Behemoth :-)

The chain line also got a makeover, I really hope the chain snapping days are over - it is rather annoying to snap the chain when I try to get away from the Lance wannabes at the signal.

All the greasy parts got a slight makeover (wheel truing, brake service and so on).

It runs fantastic - easy to control with the extended wheelbase and OSS. The chain doesn't make any unwanted noise regardless of force applied, so I just might have solved the problem. I still need to find the computer harness in the messy pile in the garage before I judge the speed.

I think I fixed the hub, so I can test the Speedtronic again. lower gears didn't work due to bad assembly.

Besides that I replaced the gearing from 42/19 to 38/18. The smaller chain wheel gives me assist to a higher cadence - much needed when the battery is low and the voltage drops. Today I rode the 37,5km to work in 1h17mins ~29kph average - nice!

The battery was OK after a 8h charge - then the chain broke - or rather a SRAM quick link - in the storming subzero temperature. The chain guides had suffered, so anything above 4 amps to the engine made bad noises. To top up the problems the left crank arm mounting hole went from square to mostly round.

At night I went to Leitra for a warm garage, and replaced another half broken chain link - this time an ordinary one along with the remaining 3 quick links. Fixed the chain guides and replaced the crank arm, and rode home with 7 amps on the motor with the 13m/s wind in my back - nice :-)

I fixed the throttle, added the chain tensioner, tightened the headset, patched the rear wheel - sigh (note to self : buy a Schwalbe Marathon Plus for the rear wheel as well) and tightened the regulator mount.

This morning the trip was without any problems. Great! I think I made the 37km trip in 1h22m - that is close to my normal speed on the Optima Baron (see pic). Not too bad - 27km/h avg. With some fine tuning of the bike and myself it should be possible to do consistent 1h15m times. The battery seemed to be a bit tired at the end - or maybe I'm getting spoiled.

Today I did the 37 km to work, dropped the chain 4 times and broke the throttle when I dropped the bike. It is still usable with caution, but I have to dream up a bullet proof solution. A thumb control could be the answer.

The battery did fine in the cold (1-2° C) after a night in the garage - and I'm charging it in the office's bike shed as I'm writing. And I'm not as exhausted as I usually am after a 37km morning ride. I'm running out of gears - at ~34km/h in 7th the motor don't help anymore. I'll try with a 18tooth rear sprocket (10% increase). I think I can keep an average speed of 28km/h - maybe a bit more with the right gearing.

• the chain dropped off from the little sprocket in front of the motor 3 or 4 times, so something must be done. At gear changes the chain from the crank to the motor gets a huge slack, as I have to let off of the throttle. The chain tensioner at the rear wheel is not strong enough to keep the chain tension high enough.
• some funny occasional "chunk-sounds" came from the motor, chain or rear hub at the end of the trip - maybe because I forgot to mount the axle securing bracket. It seemed to sit solid enough, though. It could also be from the rear Sachs P7 hub - the gear shifter didn't have the best day of its life. The twist handle came apart, but could be used with caution. I'm curious how the gear hub will handle the extra load from the motor, but the constant torque shouldn't be too bad. Mashing up a hill without assist must be much worse.

The good news :

• the bike does not feel any heavier to ride than before, the weigh centred around my body is a huge factor I think.
• the motor isn't too strong - it just act as a friendly helper. The speed on the flats was improved significantly I think - I had no speedo on the bike :-). My effort could be kept reasonably constant both up the sealandish morainegaps and on the flats. The "power through the gears"-solution is definitely perfect for my use.
• the battery held up fine for the 20km trip with almost constant use - I let off a bit when the red LED (10A) came on, mostly just 1 or 2 of the 3 green LEDs was on on the flats (meaning 2, 4, 7 Amps). Pretty much the pattern I'm going to use on my commute.
• the crank/motor gear ratio seems alright, but the rear hub could do with a smaller cog. I was in 6th or 7th gear most of the trip.

I still need to close up the battery pack and make a solid and easy to use mount for it on the bike, securing the chain line, apply some paint and change the headset. But Monday I'll ride it the 20 km from the workshop to my house - looking forward to that :-)

The 250w isn't as strong as I imagined, but I think it is just perfect for my use. Not too many hills - long flat stretches on bike lanes and 2*37km. I wonder if there's enough battery for both ways. Time will tell.