samsavvas said:
Hi Matt and Friends,
I have had some off/list correspondence with Matt regarding use of his V4 drive with a small Astro motor on my old Greenspeed GTR. My intention is only to:
- add some assist, particularly when keeping up with traffic
- provide some extra 'oomph' on hills.
I am not particularly interested in speed per se and would be quite happy with a max (no pedaling) of 32km/h (20mp/h). I don't plan on not pedaling and indeed, would fit a CA/cadence-sensing BB if it works with the Astro set up. I am very attracted to the V4's compact size and relative simplicity. However I'm still at a 'thinking about it' stage, mainly I guess because I haven't had an opportunity to see it or try it out and nearly all of the discussion I've found seems to focus on it's 'speedier' characteristics rather than it's capacity to assist in every-day cycling situations, lower speed 'pedal assist' hill climbing and negotiating traffic.
I'd be very interested in reading comments from users regarding 'real world' experiences in such situations. I'd also appreciate it if someone could point me to a discussion of efficiency issues vis a vis hub motors and a drive like Matt's.
thanks, Savvas (Adelaide).
I might be closer to your situation than most others although I am using a thumb throttle rather than a torque or speed sensor on the cranks. I do have a relatively tame setup - mainly by virtue of selecting a motor with a lower Kv. My goal was after a less "frantic" setup with lower RPM and quieter operation in lieu of maximum power. The quieter operation comes mainly from lower belt and chain speeds.
I also always pedal. I am also powering a trike - in my case an ICE QNT which was previously assisted by an eZee hub motor.
Powering with one of these 32XX series Astro motors is significantly different from using a hub motor. These motors act much more like 'ideal' DC PM electric motors in that they slow down much less and deliver more power under load (with a corresponding increase in current). Combined with a sensorless hobby controller that is designed more for high loads only at high RPM it is indeed less conducive to a 'light assist' application than a hub motor.
But...
Efficiency of the motor is far superior. I can't do anything that gets the little Astro motor hot in my relatively tame setup, yet it has way more hill-climbing power. Generally gearing these setups for only 32km/h will provide oodles of hill climbing torque. I'm probably near only 10% inefficient with the motor climbing a 10% grade. With a hub motor, it could be 3 to 10X more inefficient, the latter occurring under a complete stall condition. So despite going much faster overall - especially up hills, I don't use any more energy from the battery on my standard routes.
Flexibility of gearing is another advantage. Prefer more speed or more hill climbing torque? Just change the ratios.
There are pros and cons for sure as indicated above.
I might suggest a 10-turn 3210 with a drive ratio of 14:1 to 16:1 if you have a 20" rear wheel. This will get you very close to where you want to be speedwise whilst maintaining a relatively calm and quiet system.
I ride with someone who is planning to outfit his trike with a similar setup to mine. Matt - do you have V4 Drive parts in stock? Expect a call or email from Bill about this soon.
