anarce wrote:motomech, I enjoy your posts so I opened this thread for the first time. I'm a noob and haven't read much about 2WD bikes yet, but I had a thought (dangerous!) after reading through this. I wonder what would the performance be like if you went back to a 26" tire on the front? How would the power balance be with both motors running at the same time? The rear motor would give you more torque off the line and push you up to speed, and then maybe the front would pull you up to a higher speed and help fight the wind resistance as you go faster. I've seen other bikes on here where people use a smaller tire in back, but I'm curious how that would work with 2WD and how it would affect the efficiency.
Yes, If I was doing it over, I probably would have gone with a 26"-frt./24"-rear, although I think the fast wind in the 26" wheel would be too tall, even with some help from the rear.
When I selected the original components, I had 2 things in mind. Using 2 of the same, simplest kits out there. And changing from 26" wheels to 24" wheels.
The wheel change was prompted by the height of the MTB, it's a 20.5 inch frame and with 5" of rear wheel travel, the seat is way up there[I'm 5'11", but with a short 29" inseam]. It also has a very high top rail, so that even off the seat, I can't really flat-foot it. But what I found, to my suprise, is that it's too low with the 24" wheels, I can't pedal though a corner without the pedals hitting the pavement. part of that problem is due to the soft rear suspension. It's an air shock and as they are want to do, it looses a bit of pressure over time and after a week or so it's back down to 95 psi form where I set it at 125 psi. I have this little hand pump, but it's lame. I recently aquired one of these and now it's easy to keep the shock where I want it;
So to recap, I didn't really like the throttle feel of two identical Q100 kits hooked together by a "one wire" throttle. I don't think I imagined it either as it was the first thing I noticed when I first rode it..
The easiest way I can think of to describe what was going on is to use an analogy comparing an electric motor system to a sound system. We all know the sound reproducing systems do not have a perfectly linear freq. response[not that our ears would like that anyhow]and due to introduced artifacts, there are peaks and valleys and usually,, they are considered distortion. Usually[but not always], the less expensive the system, the more distortion. In this case, one low-powered system doesn't produce anything unfavorable to be noticable, by running the two Q100 systems in sync., the result was to amplify any "distortion" that resulted from the interaction of the motors and controllers.
I don't want to make a big deal out of this. as anything to get the two systems out of lock-step would probably make the issue disappear. It could be running a "fast wind" and a slow wind" motors together would do it, or mixing wheel sizes, or isolating the throttle by using two or simply running one throttle signal though the Cycle Analyst.
But I've moved on and probably won't take the time to re-install the 24" Q100 frt wheel to try out any of these "solutions.
I went back to the MXUS 26" frt. because that is what I had on hand. And while the lowly BMS Battery 15A controller worked fine with the MXUS, I went with the hard-hitting Lyen Mini-Monster because the power is addicting
But in making these changes, I completely changed the goal of this build from trying to make one Ebike "pedal assist" set-up better, to making two Ebikes[maybe even three, depending on how one looks at it].
So this is what I have now;
System #1[rear only]-Docile pedal assist that only "sees" an Amax of 17 Amps and is capable of returning W/hr numbers in the low 20's[looking to improve that as I get in better shape].
System #2[combined system #1 and #2] A peppy system that on 14S see peak Amps of 50 and total Wattage peaks close tio 2K/W. With a top speed of over 30 mph, it's getting close to being capable of dealing with traffic, something I rarely do. Having a relatively powerful frt. motor on the frt. for street riding is actually fun once you get accustomed to it. An example; This morning, I had to blend into traffic for a few blocks, so I came around a slow corner doing maybe, 10 mph, and punched both throttles and the frt. tire started spinning for a couple of revolutions, cool. This is heady stuff for a guy who has been using a single mini on 48V/17A for the last couple of yearo
But it comes at a price. Much of this is abusing my small Zippy 15C packs and consumption climbs up into the high 30's W/hr.s.
So like most everyone else here before me, I've ordered more Lipo[Turnigy 20C this time, to be built into larger packs].
Also comes the concern about how long the MXUS would tolerate this behaviour if if became the regular way I ride.
But far and away, the best use is to steel myself with some disclipline, and stay on the rear motor only and only use the frt. when needed. One area, maybe not needed, but enjoyed, is using the frt. to reduce "rowing though the gears". On the rear system alone, I find that I need to use at least 5 or 6 gears to maintain momentum. With a little judicious use of the frt. three gears will do nicely.
So that about sums up where I'm at now with this set-up.
Things that I still need to do include;
Getting that 48T chain ring hanging on the wall mounted.
Consolidating my Lipo all to 12S[I have various sm. packs at 12S, 13S and 14S, I just had to try every possibility out. Should have taken Dogman's advice and started and stayed with 12S