thought I'd post some pics and info for those who might be interested.After sitting on almost every ready-made electric folding bike on the market over a period of 6 months, I decided I didn't like any of them - basically all of the frames too small and forcing the upright riding posture.
There was one possible - the Tern vectron, but it was £3000. so I set out to build my own.
I selected the dahon vigor for various reasons
- riding posture is quite aggressive for a folder, wheelbase is quite long, its stable at speed
- dahon T-post can take alternative stems (more on this later)
- quite light (12kg) in basic form, and cheap to buy.
whilst buying it, I had the bike shop up the spec on a number of items
- tyres to schwalbe big apple. stock tyres pretty basic, I wanted bulletproof and some "cushioning".
- brakes to magura HS33 hydraulics. Stock brakes were rubbish.
- ergon GP grips and bar ends
- rack for bag and battery carrying.
that all pushed the cost to £1000, but with cycle to work tax-free, that was only £600 of real money.
After I got it, I swapped the stock dahon stem for a "Tern Andros 85mm" which is the mark1 version of their andros stem (The newer one is 65mm), this was one of the most expensive bits as they are rare as hens teeth, 80 quid from germany. However after this adaptation, I now have a virtual top tube (seat post to bars if you will) the same as my road bike, so I can fully stretch out. the ergon bar ends give me even more and I can get quite close to a time trail bar riding position.
so now to the motor. Having read lots, and read more, and measured some, the rear hub on this bike is around only 125mm. All rear hubs seem to want 135mm and I didn't fancy frame stretching. The front hub is tiny (about 75mm) there was only one motor I could find that might work - Crystalite SAW - but it's direct drive and pretty heavy and expensive. I also didn't fancy a large chunk of angular momentum on the front wheel affecting my handling. I also spent a lot of time using the power calculators on ebikes.ca and I realised I would probably not get on with a hub, wanting something that would push consistently in a speed range from 5mph to 25mph. And finally, I figured I might want to convert from derailleur to hub gearing at some point. so crank it had to be.
I settled on the Tongsheng TSDZ2, the clincher being the torque sensor (having ridden a borrowed bafang bbs01 for several months). ordered from PSWPower, came very quickly.
Fitting was fairly straightforward - my bike spannering doesn't usually go beyond tyres/tubes/lights and drive train cleaning, but once I'd worked out how to use the crank puller it was fine! The most awkward part was that the central spindle of the TSDZ2 didn't quite fit through the bottom bracket bore of the bike. After various suggestions from this forum I dremeled a very thin layer of the inside of the bike's bore where it was touching, and got the motor in. I bought the BCD adapter spider with the motor, and fitted the original dahon chainring (53T) straight on, discarding the tongsheng one.
I ordered the version with throttle because I thought I might need it, I was looking into getting the optional magura brake levers that have integrated kill switch, but I really didn't need it, took it off after 2 rides so left the brake levers as they were. It was useful for the early stages of stand testing though, to power the motor up without cranks fitted. I chucked the tongsheng brake levers in the bin....horrible things.
The wiring all fitted nicely into the frame triangle just above the bottom bracket.
I knew I would not be able to fit the frame anti-rotation bracket to the motor due to needing to hang it round the front rather than underneath. however, a piece of foam stops vibration against the frame and the motor doesn't move with some loctite on the bolts and lock-ring.
The cockpit was hobson's choice - I opted for the larger VLCD display as I knew the grip one would interfere with my ergons. This was impossible to mount on the bar due to my stem configuration , so its on the vertical T post with a right angled velcro handlebar torch holder plus a length of tube from another bar space expander providing a mounting point. If Tongsheng did a tiny unit that was just a speedo display, or even a boxed control hub with no display, I'd get that - the small bar mount power up/down/on switch gives everything needed.
Battery, I bought a 10ah "pandapak" for £175, intending it to fit in the slot in the rack. however, it was just a whisker too big, so it lived in a rucksack strapped to the top for a while. Its cells have now been rehomed curtesy of jimmy at insat into a dahon rack bag that is designed to fits the slot exactly. If I had to do it again, I'd go straight to jimmy and get a custom made pack of much lower capacity, I've found its really a very economical motor.
I bought the PSW fork-mount front and rack-mount rear lights as I fancied trying integrated lighting. this works really well - just a button press on the control panel turns them on. however the front light is a bit feeble, I will upgrade it to a 6v german B&M at some point. the rear is nice and bright, with a decent reflector. I also pack a bunch of other LED battery lights front,rear and side on the bike as well as I am a bit of a lighting fiend..
In riding I've been very happy with it, for 4 months over the worst of the uk winter (ok I stopped when it was actually ice on the ground). The fold is only minimally impinged (the control panel stops the handlebar from going quite as tight against the bike as without it). Weight is 17kg without battery - part of the weight gain from stock is me upping the tyres, brakes. Weight with battery is 20kg, still very carryable, two handed when folded or one handed unfolded with the seat nose on the shoulder. for me at least.
I take it on/off trains to london most days, yes its not as small or light as a brompton but its a damn sight nicer ride for the long part at my home-station end.
Total spend, just over half the cost of a purpose made 20" high end e-folder such as the Vektron.
Its saving me around £10/day on diesel , parking and public transport so will pay for itself in a year.
torque sensing ride is very intuitive and can be tuned depending on power level selected. Geometry of the bike for the rider posture is road-bike-like, handling round corners also, no wobbles, over or understeer.
In turbo in top gear I can cruise at 22mph on a flat cycle path in an semi-aero with a non-sweat level of rider wattage. around town and junctions, eco mode just gives you a nice nimble fast accelerating bike (again without sweat). magura hydraulic rim brakes feel just as good as the hayes hydro discs on my MTB - I have no qualms about stop in any situation.
improvements I'd make:
chainline is quite bad in low gear. 1 and 2 of the 9 are unusable due to the chain angle, it drops every time. photo taken shows gear 3(14T) which is the lowest usable, fortunately with a motor 53T/14T on 20" wheels is low enough for most situations. A chain guide might help, but realistically I am thinking change to rear hub gearing in the future when these wear out.
longer cranks (tongsheng are 170) and maybe try to save a few mm of width with different shape if poss
smaller display/controller easier to mount not on bars
I'm in Central london often, if anyone wants a test ride feel free to ping me.
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