I did some enlargement and pixel enhancement and it seems I was wrong, this is not a friction based setup !!!
In my opinion after figuring out the idea behind this, I retract what I said previously about not being viable for higher powered setups - with proper components, it could very well do the trick - in fact it gave me another idea which I hadn't yet thought of (more later..)
So instead of a roller on the chainring guard, the chainring is actually exposed... the thingy which looks like a roller is not, it is (I can't be sure of material but it is comprised of composite and somthing else, likely aluminum) a gear / sprocket?
Basically it's about 3/32nds (or chain link width) and it is in essense (it's hard to count) a 9t inverted and widened sprocket. Based on the coloring of the surface I would actually go so far as to suggest their assembly method is the inverse of epoxying magnets into an outrunner - more specifically it appears to be a hollow tube (to be mounted to output shaft of an internal reduction unit perhaps, more likely at the power level they are using its a single stage reduction) which has teeth machined, cut or otherwise formed from ?delrin - (I assume to prevent chainring damage and reduce noise of engagement) and then glued into slots or position on the aluminum tube to form splines... there may be retaining rings but I can't make those out.
So basically it's a low noise, low friction, long life 9t gear for driving a normal 3/32 bicycle style sprocket.
Assuming a chainring (I'm in the 20" world for this idea) of 58-60t which is the largest I have been able to locate for BCD 5bolt style (if you know of larger please let me know, in process of sourcing best possible gearing for maximum speed on a 20" with a custom 3,4,5 or maybe 6 speed cassette built up specifically for use with eBiking).. That gives you a reduction of 5.27:1 - 6.667:1 right at the crank and reduces weight of adding additional metal sprockets, belt pulleys, etc.
I figure it also means a single chainring which freewheels independent of it's pedals would do the trick nicely... this way at above the maximum gearing speed at 80RPM cadence of 25mph you can hold your pedal feet still and the motor can continue to drive - ie, pedals disconnected from driveline.
Torque would be the only issue I can think of for a HIGH POWER setup but then that brings me to my next idea... Why do we use chains and sprockets and belts for this purpose... why not a pair of gears... drive gear could be small (depending on the strength and material - steel much less prone to torque damage than others at weight disadvantage) say 8-9-11t and then a second chainring bolted on is a 3/32" thick sprocket of say 60t or better (smaller diameter due to pitch and engagement) located on the inner side of the pedal chainring)... Now you have possibly even higher ratios (I need to check into this) for instance I know a #219 would let me run 11t to 76t and the 76t would still be smaller in dimension than the 60t chainring - what if we can find appropriate gears capable of handling the torque loads - it still eliminates the chain addition and in most likely cases the weight of the 2 gears would be less (at 3/32 - 1/8") than the weight of equivilent bike or #219 chain.
The issue remains - even on a 10S pack with 100A peaks the torque an Astro 3210 10t would produce at the crank would be 277.880858 ft lbs after reduction to provide for maximum crank RPM of 60 RPM @ LVC (20mph).
Granted the the legal power mode operation with a current limit of 25A (750w @ 30v) the output torque would be 69.49 ft lb of torque and I don't really know too much about torque generated by a human rider but I will assume that we have less HP (hence the est of 100-200w for most riders, 250 for lance armstrong (not me) and if you assume a bicyle indended for a rider weight of 225lbs max lbs and has 2 power strokes accounting for (guesstimate) approx 80% of the possible duty cycle so 225 * .80 = 180 ft lbs torque expected / designed for.
Please if anyone understands how to compute these torque distributions and capabilities better, I am dying to understand more - I assume from TDC to end of stroke 10% is wasted on each side as stroke transfers from one foot to the other - hence the 180ft lb torque continuous rating I assume.
If that were the case - then the most you would want to drive the crank with in terms of torque would be about 65A @ 10S reduction level and 80RPM max crank (more reduction would increase the torque so voltage or current increase would exceed the value too far - even here were talking about 180ft lb or so continuous - actually I suppose that's perfect and will match human torque?
In either case... Though my initial observation of this was wrong, friction could be the best possible manor to setup a lower powered to legal powered eBike... even using cheap motors such as the tower pro 5330 9/10t or many others with a kv between 180 and 235 or even better with an Astro (94% efficient at legal 750w power levels)...
A bit of slippage could be good - spring tension engage/disengage?? (Steal other friction methods here from evTodd, etc)
Chainguard material - my folder has cheap plastic chainring guard (might be fine with a rubber coated drive spindle) - I am thinking version 1.0 aluminum (because I can finally make them here at my home) replacement (it is the kind that wrappers the chainring and is just a tad larger diameter than a 58t chainring.
I don't know the exact diameter but I do know that with a generic friction roller (alumimum tube with shrinkwrap or delrin tube epoxy bonded and then mounted to motor output shaft with set screws the reduction possible right there is about 6:1
This design eliminates the complexities of the cyclone style kit which requires the use of a large chain idler and a very non-effcient chainline path (too many bends to engage the motor in the driveline.
-- with regards to Miles build;
It took me quite some time to read all of miles folder build posts and cross thread info and even longer studying the pics of the actual bike (and I still don't get the little tiny mounts to the frame rails?) but the beauty of Mile's setup is the synergy between e and bike when he wants it... I think 8 useable gearing ratios for the pedal side and 3 for the motor is much better than 8 for the pedal side an 0 for the motor!!! Remember going up a hill - your motor wants to spin as fast as the voltage it's getting would permit but it can't, that's inefficiency... also consider a 20" bike - though you may have 30-50ft lbs of torque available if your single speed drive motor to rear - you may have the abiliity to shift pedal side for more efficient (or surviveable) required force at lower speed but unless you can do that for your motor... going up huge hills where you could be pushing 138.94 ft lbs through a reduction of 1.36:1 which would increase the final reduction from the 1:1 and give you more torque.
I am inspired by miles work (and that darn bike - hey bud, want to sell it when you upgrade? Dibs?) but what I am more trying to achieive is a simple method to drive the crank directly (yes IPS is required unless cadence is kept 60-80 RPM which most people can handle - I do) both efficiently and with as little required weight and visible "e" bike stuff.
Thanks for the feed back everyone... sorry to be so long winded but though i can't say I like the bike (the brakes are cool) I found it too inspirational and just had to figure out how it worked for legal power levels and what / if we could modify it for higher power useage without breakage.
-Mike
PS:
I've seen I think some DH bikes with gears in behind the pedals which then feed a chainring - if anyone knows, I am wondering 1.) what kind of ratio or virtual chainring can you get with something like that? 2.) Does anyone know where I can find gearbox stuff like that? 3.) The problem is with a 20" (god forbid 16") tire on a folder (or other smaller commuting bike) - you can dump tons of money and time engineering solutions to suspension issues, noises, balancing, proper fit, etc - you can even go so far (as I know it's the limit really) as to implement the 60t chainring / 11t high gear for 20mph at approx 62 RPM cadence - but I've made my folder exquisite in terms of alignment, balance, tire, suspension upgrades, joint tightening and finally getting it to the point where it feels better to me than my 26" - the issue is I can't pedal along more than 20mph for any length of time... I can do 25mph or 80 rpm cadence but only for a short while so I am hoping to be able to find a pedal system which would give me a 2:1 increase taking my input RPM and providing 2X output via a chainring and then onto the normal system?
Thanks in advance - know some is off topic
-Mike
