Electric Fixed Gear

[Clarkey]

Hello All,

I like riding fixed gear bikes (one gear, no freewheel), though I am not some kind of purist "fixie nutter". It occurred to me that a lightweight electric boost system would be the just the ticket for getting away from traffic lights and helping out on steeper hills. The assistance would let me run a higher gear than otherwise for easy cruising and faster descending.

I would be after a range of 15-20 miles, contributing a fair amount of effort.
The Cytronex system looks like it might be just the job - I understand that they might be offering a kit soon? Of course, no pedelec sensor would be strictly necessary - the pedals must be turning if the bike is moving anyway.

Feel free to think I am mad but I would really welcome your suggestions.

Chris

 

[frank9755]

You could add a kit to a fixed wheel bike in the same way as any other. I suspect few have done it, but whatever you like, I guess. If you shut the motor off suddenly it might feel a bit heavy on your legs, but there's no reason why it can't be done.

 

[Clarkey]

Thanks for the reply. Yes, a front hub motor kit would certainly be one way. Which is the lightest "well thought of" kit of this type though?

I suppose another option would be a cyclone kit (if they are still available?) - there would probably be no need for the clumsy freewheeling chainwheel either. To be honest, motor drag on the 'overrun' would probably be beneficial to avoid speed building up too much on descents (my little legs can only go so fast!). I guess the drag could be neutralised with a whiff of throttle in normal riding or doesn't it work like that?

 

[flecc]

The nano motor in the Cytronex is unique in having virtually zero drag, so it wouldn't help to keep speed down. It is the lightest and smallest of the adequately powered hub motors though. Even the majority of internally geared hub motors which have some drag will still allow speed to run away downhill, depending on the steepness, anything up to 40/45 mph depending on wind resistance. Opening the throttle a bit wouldn't help with most designs, so there would be some dependence on braking to keep cadence within sane boundaries.

Otherwise there's nothing wrong with having a fixed gear bike with motor assist for hills and headwinds, and the Cytronex-Trek is the most like a normal bike in that respect.
.

 

[Clarkey]

Yes, I think the Cytronex is probably worth a good look - I work quite close to Winchester so might pop in for a go. I like the idea of the simple controls and the water bottle battery. I will give up on the motor drag idea - after all, I have my legs and two brakes to slow down with, the poor old motor can just concentrate on making me go!

I currently ride with a 65" gear on the road, I guess I would try about 73-75" with a motor to help out - no point going mad, I only want to cruise at 15mph with a relatively easy cadence and maintain it up most hills by adding bit of grunt at the pedals.

Thanks for the quality input. Does anyone have an idea what price a Cytronex kit might come in at?

 

[Tiberius]

Hi Chris,

Welcome to the forum.

I've not ridden a fixie, well not for more than 40 years, so I may have this wrong. I don't see how you get round the fact that the motor will drive the pedals, one way or another. With a low power motor and if you are always careful its not necessarily a problem, but one day it could catch you out on starting off.

You say a pedal turning sensor isn't needed - I'm not so sure. Yes, there is the fact that it could never turn off once it was triggered, but it would act to prevent the motor starting until you did. But it would trigger if you just pushed the bike forward before you put your feet on the pedals.

What I think you really want is a pedal, or crank, torque sensor. These are built into the Panasonic system and there have been a few posts on here about being able to source them separately. With a pedal torque sensor the motor could be set up to only run when you actually applied (forward) force to the pedals.

Nick

 

[Patrick]

You say a pedal turning sensor isn't needed - I'm not so sure. Yes, there is the fact that it could never turn off once it was triggered, but it would act to prevent the motor starting until you did. But it would trigger if you just pushed the bike forward before you put your feet on the pedals.

Ouch! According to A-to-B's review* of the Cytronex it doesn't have much in the way of safety features, you press the button there's a brief delay and then the front wheel starts turning until either brake is pulled (activating the brake sensors).

So if you accidentally pressed the button before you were ready you could end up with a bruised shin. On the other hand I think you would quickly learn not to make that mistake, and I haven't seen anyone complaining about runaway Cytronexs so I'm guessing that in practice the break sensors are enough to keep things under control.

[*If you get a digital subscription to A-to-B from A to B magazine, folding bikes, electric bicycles, trailers, sister publication to Miniature Railway magazine you can download the review in the Sept 2008 issue as well other back issues.]

 

[andyh2]

I think it's a grand idea. What would be perfect is a light weight free running hub motor with regen facility. That way the regen braking effect could help keep cadence down on downhills without needing the brakes.

I think the Trek bikes have vertical dropouts making them difficult to 'fix' unless you go for ENO eccentric hub, eccentric BB or 'magic gear' solutions, but Mark from Cytronex has mentioned on here that he'll have a kit available 'soon' and that'll likely be just the ticket.

 

[flecc]

It should be remembered that the Cytronex usage instructions are to pedal away without power up to approximately 5 mph before pressing a power button. That's therefore a safety factor with using a fixed gear, since you would not be pressing a power button at a standstill, that only done when the bike is already loaded and not able to give too much of a surprise.

Re: the Panasonic system mentioned above. That cannot be used as a fixie since it's a three freewheel system, one on the rear wheel which could be fixed, but one on the motor drive sprocket and one on the chainwheel which cannot be changed.
.

 

[Clarkey]

I think it's a grand idea. What would be perfect is a light weight free running hub motor with regen facility. That way the regen braking effect could help keep cadence down on downhills without needing the brakes.

I think the Trek bikes have vertical dropouts making them difficult to 'fix' unless you go for ENO eccentric hub, eccentric BB or 'magic gear' solutions, but Mark from Cytronex has mentioned on here that he'll have a kit available 'soon' and that'll likely be just the ticket.

That is exactly what I wanted to achieve, you just put it rather more elegantly than I did. I did think of a Bionx kit to get the regen facility but getting a fixed sprocket mounted properly on the thread for a freewheel cluster would not be easy and availability does not seem great. Also I don't really like the chunkiness of the Bionx motor but that is just vanity on my part!

I think I will make an enquiry re. the availability of the Cytronex kit. There will certainly be a need to exercise some care with the power but fixies tend to demand a cautious approach anyway. To be honest though, I find it scarier riding bikes with a freewheel now - there is that frisson of terror when I slow my legs down but the bike just goes on at undiminished speed! I feel much less in control.

 

[frank9755]

To add a couple more points:

I agree that the Tongxin motor would give you the most satisfactory result for this, being lighter than others on the market and with increasing reliability. In case you're not aware, there are other suppliers apart from Cytronex; I can recommend JohnP on this forum - although I don't know what he has available at the moment.

I see that you want it for steep hills and starts, get a low speed / high torque motor. The Cytronex uses a 175 rpm motor in a 700c. Tongxin does a 160rpm which would meet your requirements better (at the expense of cruising speed on the flat / moderate uphills).

Good luck

Frank

 

[Clarkey]

That is a good idea about selecting a motor with more torque - if i convert my fixed mountain bike I will go for that.

My maddest scheme though is to add the assistance to a Bike Friday "One Way Tikit" (16" wheels!) for what I hope will be a sweat free bike-train-bike commute. I gather that the Tongxin motors may be somewhat better suited to small wheel applications anyway.

 

[frank9755]

I gather that the Tongxin motors may be somewhat better suited to small wheel applications anyway.

Not so; it's just a question of choosing the right motor speed for your application. For a 16" wheel you'll want a 260rpm to avoid it spinning!

Cytronex owners rave about their bikes, a Torq owner on this site actually replaced his motor with a Tongxin, and my own bike goes very well - all with Tongxins in 700c wheels.

 

[Clarkey]

Not so; it's just a question of choosing the right motor speed for your application. For a 16" wheel you'll want a 260rpm to avoid it spinning!

Cytronex owners rave about their bikes, a Torq owner on this site actually replaced his motor with a Tongxin, and my own bike goes very well - all with Tongxins in 700c wheels.

Glad to hear that the Tongxin motors seem to be performing well, I could never really get an idea of the true extent of the problems by perusing the various threads. They look so nice too.

I have just noticed today that Sturmey Archer are finally getting their 3 speed fixed hub to market - my dream, power assisted super fixie is getting closer and closer!

 

[frank9755]

The main problem with earlier Tongxins was that the controllers had some under-specced components, so kept blowing. This was more likely to happen with more demanding applications, and bigger wheels - other things being equal - means higher gearing for a given motor and hence a more demanding application. So there were fewer reported failures with small wheels, but some people had no problems with large wheels.
The later generation of controllers seem to be far more reliable, and I'm not aware of any recent failures being reported.

 

[rog_london]

Glad to hear that the Tongxin motors seem to be performing well, I could never really get an idea of the true extent of the problems by perusing the various threads. They look so nice too.

I have just noticed today that Sturmey Archer are finally getting their 3 speed fixed hub to market - my dream, power assisted super fixie is getting closer and closer!

Ah, well, you must be one of the younger fellas.....

Back in my boyhood fixed-wheel 3-speed Sturmey Archers were not uncommon. They didn't make them that way though - you had to get them modified (usually by SA or someone with the necessary tools and rebuilding skills) to have a fixed wheel. I've ridden them myself though never owned one.

Just goes to show that there isn't much about which wasn't available long ago! Truly a case of 're-inventing the wheel'.

Rog.

 

[Clarkey]

Ah, well, you must be one of the younger fellas.....

Back in my boyhood fixed-wheel 3-speed Sturmey Archers were not uncommon. They didn't make them that way though - you had to get them modified (usually by SA or someone with the necessary tools and rebuilding skills) to have a fixed wheel. I've ridden them myself though never owned one.

Just goes to show that there isn't much about which wasn't available long ago! Truly a case of 're-inventing the wheel'.

Rog.

Actually a fixed three speed was available from the factory - the ASC. Since they stopped making them (in the '50's?) some people have converted Sturmey AW hubs but I think you only end up with two speeds and lots of backlash.

Since original ASC's now fetch astronomical prices, many people have been badgering Sturmey (now based in Taiwan, unfortunately for British manufacturing industry) to make a new one. Apparently, the new S3X is more robust than the ASC and has a wider gear range - the ASC was reputedly a bit fragile and had closely spaced gears for time trialling.

Actually, thinking about it, I would rather use the 3 speed on a non-electric fixie. After all, one of the points of the electric motor was to mitigate the lack of low gears anyway.

 

[rog_london]

Actually a fixed three speed was available from the factory - the ASC. Since they stopped making them (in the '50's?) some people have converted Sturmey AW hubs but I think you only end up with two speeds and lots of backlash.

Since original ASC's now fetch astronomical prices, many people have been badgering Sturmey (now based in Taiwan, unfortunately for British manufacturing industry) to make a new one. Apparently, the new S3X is more robust than the ASC and has a wider gear range - the ASC was reputedly a bit fragile and had closely spaced gears for time trialling.

Actually, thinking about it, I would rather use the 3 speed on a non-electric fixie. After all, one of the points of the electric motor was to mitigate the lack of low gears anyway.

That's interesting - the only ones I was ever aware of were the converted ones. I suppose those of my mates who were sufficiently into 'fixies with gears' took the cheaper way out and had the standard ones modded. I don't recall only having two gears though. We are talking about the late 50s early 60s, but I'd be the first to admit that my memory ain't that good.

Logically, removing the freewheel would appear to make the thing somewhat less complex on the surface of things, though thinking a bit more about what you said it does make me realize that it's not necessarily so, since the moving parts now have to deal with thrust in both directions rather than in just one, and if the linkages are internally 'angled' to make selection more positive, a reverse thrust might simply push out of a gear into false neutrals.

You'd almost certainly need straight-cut gears rather than the inherently stronger and quieter helicals you could probably use with a freewheel. If the ASCs were a bit fragile, straight-cut gears could well be the reason, and you'd need straight-sided dog clutches with some clearance to make your selection, which would certainly result in backlash. One-way drive (i.e. a freewheel) would almost certainly be much less of a design challenge.

Rog.

 

[Clarkey]

That's interesting - the only ones I was ever aware of were the converted ones. I suppose those of my mates who were sufficiently into 'fixies with gears' took the cheaper way out and had the standard ones modded. I don't recall only having two gears though. We are talking about the late 50s early 60s, but I'd be the first to admit that my memory ain't that good.

Logically, removing the freewheel would appear to make the thing somewhat less complex on the surface of things, though thinking a bit more about what you said it does make me realize that it's not necessarily so, since the moving parts now have to deal with thrust in both directions rather than in just one, and if the linkages are internally 'angled' to make selection more positive, a reverse thrust might simply push out of a gear into false neutrals.

You'd almost certainly need straight-cut gears rather than the inherently stronger and quieter helicals you could probably use with a freewheel. If the ASCs were a bit fragile, straight-cut gears could well be the reason, and you'd need straight-sided dog clutches with some clearance to make your selection, which would certainly result in backlash. One-way drive (i.e. a freewheel) would almost certainly be much less of a design challenge.

Rog.

It is certainly true that the loads on a fixed hub gear can be large and in both directions. There has been some discussion about the layout of the new hub - I think it may actually use two seperate planetary gear sets to cope with this rather than rely on pawls acting in both directions on one set, if this makes any sense - and it sound like you have a much better understanding of these things than me!

I seem to remember reading that the ASC had a false neutral between a couple of the ratios. Some keen riders used to exploit this 'freewheel' to speed down hills - rather precarious when it might to slip back into gear at any moment and instantaneously accelerate your legs up to 200rpm!

Anyway, I seem to be drifting off my own thread!

 

[rog_london]

I seem to remember reading that the ASC had a false neutral between a couple of the ratios. Some keen riders used to exploit this 'freewheel' to speed down hills - rather precarious when it might to slip back into gear at any moment and instantaneously accelerate your legs up to 200rpm!

Anyway, I seem to be drifting off my own thread!

I've always had this idea that really 'keen' cyclists were probably slightly bonkers by definition - though this 'opinion' may be born out of envy on my part. Using a false neutral at high speed would also stand a fair chance that you might end up with a hub full of metal filings by the time you reached the bottom of the hill if it did slip back into gear!

These threads do tend to get 'interestingly' technical. After all, there's only so far you can go with the basics of how far and how fast an e-bike can travel, etc. etc.

Rog.