Was watching a downloaded old Sci-Fi movie on my laptop last night ("Alternative 3" if anyone is interested) and had a sudden brain storm light bulb moment and dropped it down to half screen size and opened up my CAD in the other half of the screen and quickly threw together some quick 2D sketches culminating in this:
For a while now I've had the idea that one could achieve variable drive ratios on a friction drive set-up by using a cone shaped driver of some sort but have had trouble actually getting a system to work effectively and smoothly. The "holy grail" of course would be fully automatic smooth and continuous CVT type operation but until now have been unable to figure out a way to accomplish it.
Those are three top, straight down, views of the same system in various positions. The green is the bike's tire (scaled to be a 2" wide smooth tread street tire), the red is the electric motor (scaled to be a 6374 149kV Turnigy), and the blue is the cone shaped driver sleeve around the motor that has a slight curve to it. The white is the tire contacting swing arm mounted behind the seat-post (similar to the "Commuter Booster" set-up) only the motor isn't mounted solidly to the end of the swing arm but rather is mounted in a yoke that twists to one side more and more as heavier and heavier loads are applied under the the pressure of a heavy compression spring (not shown).
Top position = Running on the flat at speed under only normal aerodynamic and rolling resistance lighter loads.
Middle Position = Start up a small hill or run into a head wind and as the load increases the motor torques down and pulls the swing arm further into the tire and the spring loaded yoke pivots under the pressure such that the tire contacts the driving roller further down its cone shaped curve and thus the total gearing ratio is reduced due to the smaller effective diameter of the driver. Thus keeping the motor from overloading and burning up and giving a better gearing ratio for climbing the hill or bucking the head wind.
Bottom Position = When fully loaded down the swing arm is pulled into the tire far enough to fully pivot the yoke back against its spring as far as it goes reducing the drivers effective driving diameter down to its minimum value providing maximum gearing reduction for maximum load conditions.
In my 2D quick CAD sketch up I assumed the set-up would provide over-drive gearing (minimum driver diameter = motor bell diameter, maximum driver diameter > motor bell diameter) but the same system could work with a shaft mounted curved cone shaped driver that provided under-drive gearing so long as the minimum diameter didn't get so small it would spin out and rip a hole in the tire (don't ask how I know that can happen, just trust me that it can with the tip of a cone that is too small at the tip).
Anyway, posting this for feed-back, thoughts, input on the idea from others who have messed around with RC out-runner powered friction drives as well, fire away:
For a while now I've had the idea that one could achieve variable drive ratios on a friction drive set-up by using a cone shaped driver of some sort but have had trouble actually getting a system to work effectively and smoothly. The "holy grail" of course would be fully automatic smooth and continuous CVT type operation but until now have been unable to figure out a way to accomplish it.
Those are three top, straight down, views of the same system in various positions. The green is the bike's tire (scaled to be a 2" wide smooth tread street tire), the red is the electric motor (scaled to be a 6374 149kV Turnigy), and the blue is the cone shaped driver sleeve around the motor that has a slight curve to it. The white is the tire contacting swing arm mounted behind the seat-post (similar to the "Commuter Booster" set-up) only the motor isn't mounted solidly to the end of the swing arm but rather is mounted in a yoke that twists to one side more and more as heavier and heavier loads are applied under the the pressure of a heavy compression spring (not shown).
Top position = Running on the flat at speed under only normal aerodynamic and rolling resistance lighter loads.
Middle Position = Start up a small hill or run into a head wind and as the load increases the motor torques down and pulls the swing arm further into the tire and the spring loaded yoke pivots under the pressure such that the tire contacts the driving roller further down its cone shaped curve and thus the total gearing ratio is reduced due to the smaller effective diameter of the driver. Thus keeping the motor from overloading and burning up and giving a better gearing ratio for climbing the hill or bucking the head wind.
Bottom Position = When fully loaded down the swing arm is pulled into the tire far enough to fully pivot the yoke back against its spring as far as it goes reducing the drivers effective driving diameter down to its minimum value providing maximum gearing reduction for maximum load conditions.
In my 2D quick CAD sketch up I assumed the set-up would provide over-drive gearing (minimum driver diameter = motor bell diameter, maximum driver diameter > motor bell diameter) but the same system could work with a shaft mounted curved cone shaped driver that provided under-drive gearing so long as the minimum diameter didn't get so small it would spin out and rip a hole in the tire (don't ask how I know that can happen, just trust me that it can with the tip of a cone that is too small at the tip).
Anyway, posting this for feed-back, thoughts, input on the idea from others who have messed around with RC out-runner powered friction drives as well, fire away:
