"Tim Wescott" wrote in message
news
I use "thingie" in the title to not give anyone a false impression of
what I do or don't know.

I'm working with a client who's using one of these in his specialized
bike:

https://www.amazon.com/dp/B01KYKEP2Y...xx_P1400_1000?
tag=dradisplay-20&ascsubtag=c73ee0e485a804ac76001596b2b029f4_S

He's currently using the 250W version, but we're having problems of
insufficient torque -- this is partially due to re-purposing a board, and
we're on top of that part, but I'm thinking ahead (well, borrowing
trouble, in proper engineering fashion). So we thought -- hey! We'll
use the 350W version (that's the one in the link).

The problem is that the 350W version actually has a lower current-to-
torque constant -- it gets its higher power through pulling more current
for the torque, and delivering more speed.

So -- any thoughts on an easy way to gear the thing down? I just
recommended to the customer that they put two chain rings on the crank,
so that they can drive the pedals at one speed and the bike at another.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
================================================== =======

Well, to lower the gearing you either need a smaller drive gear and 9 teeth
is the smallest common one I found ( I found one 8 tooth gear but I would be
afraid the diameter is getting too small for durability), or a bigger driven
gear and you say that is fixed so external changes are out. How about going
inside the gearbox on the motor? In the amazon listing there is a sticker
on the motor for www.unitemotor.com, and while I don't read Chinese if you
go there and then click on the button halfway down the right side you get to
another site which appears to be a distributor. Open up the box you have
now just so you know what your are dealing with, then contact them to see if
you can get different gear ratios. You can use translate.google.com to get
the gist of the site, and hopefully someone there speaks english. If you
are going to need these in quantity anyway, maybe you can just order a batch
with a custom gear ratio.

--
Regards,
Carl Ijames