Re: New Idea for EV Bike

[John Bryan <jbryan@micron.net>]

Tim Voght wrote:

> Hey, that sounds a lot like those self-propelled lawn-mowers where drive
> sprockets engage into the back wheels which have treads cut kind of like
> sprockets themselves...
>
> Is that the *basic* idea?

        I haven't looked closely at those mowers, but imagine that it is
probably the same exact concept. A key detail is that a hardstop would
prevent the roller from bottoming into the tire. This would maintain a small
amount of backlash.

Peter VanDerWal wrote:

> I would think that the tire tread would wear out very fast.   <snip>
> Also friction will be very high, making your efficiency even worse than
> normal (for a roller drive).

        I've also given excessive treadwear some thought and agree that it
may be a problem. However, I feel that if properly designed and used,
treadwear would be minimal. Several considerations:

        1. The features on the roller would be a bit smaller than the
matching features on the tire to eliminate friction from pinching. This could
be achieved by using a fairly thick layer of mold release, if the part was
molded, or designing in some slack if it were machined.

        2. The motor/roller assy. would hit a hard stop just short of full
engagement with the tire to maintain some backlash at all times and never
develop any tension beside what is induced by actual power transfer.

        3. If the tire had a symmetrical tread design, it could be turned
around when the sides of the knobs/ridges began to show wear.

        4. The roller would be a bit less concave than the tire is convex, to
push mud and sand out the sides.

        If wear caused by sudden engagement of the system was noticeable,
that condition could be minimized by anticipating the use of power or regen
and locking the roller in ahead of time (while stopped). I would bet that
sudden engagement wouldn't be a problem though. The roller would strike the
tire and slip to the next alignment position, fall in, and away you go. This
would all happen in a millisecond and cause as much wear as hitting a rock or
a stick. The standard ZAP arrangement constantly adjusts tension according to
power transfer, which is a brilliant design. However, when doing powerful
regen on steep hills some roller tension is required to prevent slippage. The
biggest loss becomes when the tire gets compressed to get past the roller.
With the cogged roller, there would be no such drag and all energy would go
into actual regen.
        I hope to eventually find time to actually try this idea and find out
just how well it works. Just as the Continental 'Goliath' is =the= tire to
use with a ZAP friction roller (as discovered by Gail Lucas), I'm going to 
start scoping out which tires (tyres) may lend themselves nicely to use with 
a custom cogged roller.

John Bryan