Cyclone Cadence - gear up human speed?

[oldskoolhead]

how about a crank bearing cup with a fixie screw on cog and locking ring perhaps welded into place too to prevent it unscrewing...........perhaps a crank bearing ring could be placed in there as well

 

[boostjuice]

There can be up to a couple of hundred Nm of torque through it, so if welded that should work reliably. I wouldn't personally trust just a lockring.

It is a good thought to also place the outer dual-freewheel-structure support bearing in the same BB cup, but the reality is I don't think you'll find a bearing that has the dimensions needed. Most -if not all- in-shell (non-external) bottom bracket bearings are 'special size' (non-bearing-industry standard) and have a 16mm ID/ 31mm OD, yet the BB spindle will usually be ~5/8" (15.875mm) right up until the factory ground (~15.99mm) bearing locaters for the spindle support bearings located further inward. This presents a problem (too loose a fit for the 16mm bearing ID over the spindle if fitted along the outer portion of the spindle, exactly the problem with the GNG kit's loose fitting spindle support bearing)..... hence the reason why I used a 15mm ID 6002 bearing (fitted over turned-down outer spindle portion) and the 32mm OD fitted into the turned-out FW removal tool collar. I couldn't find a less-than-or-equal-to 5/8" ID cartridge bearing with a OD smaller than this.....

 

[boostjuice]

My custom one-off dual freewheel crank kit is now for sale over here >> http://endless-sphere.com/forums/viewtopic.php?f=9&t=52522

 

[Fredorbea]

Hey Boostjuice I know this is an old thread but I was wondering why you chose the 219 sprocket that you did.
It was a composite kevlar rather than aluminium, was this to make it quieter or lighter? Did it wear ok?

Cheers Al

 

[ARod1993]

I was thinking of something more like a transformer that can step-up or step-down AC voltages with minimal losses. the only trouble with using one of these is that you need to change the number of turns of wire on the coils to change the output voltage, or maybe have a switch to flick between a set of small transformers with different windings. It wouldn't be too hard to retrofit one of these to the output of your controller if you really did want to change the voltage.

You can't do that, but you can do something roughly analogous for a simple trapezoidal three-phase controller. Instead of trying to retrofit transformers to the output of each of the three phases, what you do is put a buck converter between the battery and the controller inputs. Below is a simplified model of a three-phase brushless motor controller; the brain takes in throttle and e-brake signals,then converts those into six overlapping on-off sequences that it sends to the gate drivers; the gate drivers in turn pulse the MOSFETs on and off, controlling the voltage at the center nodes of each half-bridge. Here's the schematic:

Basically, that circuit converts the DC voltage coming off the battery (shown there as V1, sitting at 36V nominal) into a set of three trapezoidal waveforms (one for each phase wire) offset from each other by 120 electrical degrees:

There are a couple of different means of controlling the voltage seen by the motor; the easiest is to simply PWM the high-side MOSFETs at a switching frequency (usually several kHz) far higher than the frequency of the trapezoidal waveforms, and I'm pretty sure that's what Kelly does. The other option, which I think has been done successfully in some commercial controllers, is to slap a controllable buck converter between the battery and the motor controller; that would let you adjust controller voltage on the fly, and (if your controller has current limiting) then you should be able to use the lower voltage without frying anything due to increased current.

I'm not sure whether you'd want to try to retrofit a commercial DC-DC converter onto a motor controller (since as far as I can tell most of the cheap eBay ones are only good for a few tens of watts), but if you're designing your own controller you could just integrate an extra few half-bridges (with supporting passive components) onto the input stage and use some sort of twist pot or rotary-switched resistor array to set the duty cycle (and thus the output voltage). If you're not doing that but you really want that kind of functionality, get a cheap brushed DC controller, tie the throttle to a twist pot or a rotary-switched resistor array, and put that between the battery and the brushless controller.

 

[boostjuice]

Hey Boostjuice I know this is an old thread but I was wondering why you chose the 219 sprocket that you did.
It was a composite kevlar rather than aluminium, was this to make it quieter or lighter? Did it wear ok?

Cheers Al

Yes, quieter (less 'clackity' as the steel chain rollers slide onto the composite teeth), although the planetary gearbox was so noisy I really don't think it matters when used with a Cyclone type motor.
The composite sprockets also do supposedly have increased wear resistance over Aluminium sprockets, although I didn't run the system long enough before decomissioning it to be able to comment on this in practice. Weight-wise, not enough difference between aluminium & composite for it to be a significant reason to choose one over the other IMHO.