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New Specs
| Battery |
25.2 V
15 AH air cooled Lithium Ion w/ custom charger |
| Controller |
Built-in KollMorgan 24 V |
| Motor |
KollMorgan 300W, 24 V, Brushless
DC |
| Drivetrain |
Two speed manual transmission,
ratchet coupled at rear
wheel |
| Weight |
~55 lbs |
| Max speed |
26 MPH in 2nd gear |
| Range |
20 miles @ 20 MPH (mostly flat
ground,
no pedaling) |
Transmission and drivetrain development:
I was not fully satisfied with the initial drivetrain that I manufactued and installed on the bike. The EV Warrior motor is a poor man's choice for electric bike locomotion. It is very inefficient and being originally a fan motor does not have enough magnetics to take advantage of battery current loads exceeding 300 Watts. Running a belt further reduced efficiency and isn't really any quieter than a chain. In fact, the noise produced is very unbikelike and ironically stands out even more. Furthermore, I came to realize here and in other projects that there just is no substitute for mechanical advantage - that is, a mechanical multi-speed transmission. The obvious choice was running a 2nd derailleur on the other side of the wheel. But I was skeptical that I could make one work properly. There is very little room left on the other side of the wheel since it is specially offset for the sprockets on the right side. Derailleurs tend to be finicky and have to be shifted under power. Having to worry about the two derailleurs on the bike already is work enough. With the addition of maybe 1-2 lbs to the bike I could build a manual 2 speed transmission that would be as efficient as a derailleur, far more reliable, out of the way, and very easy to shift. I acquired a $200 KollMorgan brushless motor for very cheap on ebay. These are the same motors that are put into many of the e-bikes on the market including Currie. Though rated at 300 Watts I knew it could pull a lot harder and had superior magnetics to take advantage of higher power loads.
With the broad picture in hand I engineered a chain driven, dog engaged two speed transmission. The shifting is assisted with ball detents. The ratios differ by a factor of two. There is an initial chain reduction stage of about 2.23 leading into the gearbox and a final drive ratio of 3.21 from the gearbox to the rear wheel. After all the brainwork was done I got back to the familiar task of machining all the components. Of course, that actually takes even more brainpower, but it is lot less frustrating when at the end of the day you have something in your hands instead of a picture on the monitor.
 Transmission box side view in SolidWorks. |
 Top view with the two ratios visible, note the slider and fork. |
 Iso view. |
 New drive train assembly with the new motor and mountplates. |
 The complete ensemble of parts about to go on the bike. On the left are all the transmission components. |
 Close-up of the transmission case. |
 Close-up of the transmission sprockets, dogs and slider. |
 The shift fork. |
 The gearing stacked up in the case. |
 Sub-assembly coming together. |
The new drivetrain on the bike. It looks gorgeous, in my opinion. |
The shift lever and throttle on the handlebars. Simply push down to go into 1st gear and up to go into 2nd. |
 Custom charger feeding on the 12 V battery charger. It's time to head to the field! |
Being stupid at the shop. |
 Popping a long wheelie in the parking lot |
 Jon Birdwell giving it a go |
Testing
I have to say this is probably the first time in my life that something I've made surprised me and beat my expectations. Dramatically so. I couldn't believe the difference. The new motor, the elevated efficiency, the two speed ratios and the potent Lith-Ion pack all come together to make an incredible trail blazer. To put it into perspective - I tested it at the Tiger Mountain gravel roads. This is one of my favorite rides as you can get really reckless on the descent. But to get there you have to ascend up three miles of steep fire road. I was in shape when I did this ride without the assist last season and pushing myself at about 5 mph I was ready to pass out when I finished the last mile. Today I was completely out of shape (first ride starting the season) and I averaged 10-15 mph all the way uphill and barely broke a sweat. When I got back home I checked the charge on the pack and it was still HALF CHARGED. Oh, and I forgot to mention, the batteries are probably two years old and I've noticed a decline in capacity to about 80%. Still I could have turned around and gone for a second pass :) And it shifts like a dream. There is no hesitation, just snick-click and whiiiiirrrrrrrrrrr away. First gear is a stump puller - if there is enough traction it will pull up any hill. The torque in 2nd gear was enough to break traction and fishtail in the snow while doing 20 mph. I am amazed that it came together this well. I think this bike easily outcompetes any e-bikes on the market right now, considering the light weight. I think the only bikes that comes close are the sporty versions of the TidalForce bikes. But with a big NiMH battery in the front wheel and a big hub motor in the rear wheel those can't be as light or agile.
Credits
Again I'd like to thank the Birdwells (Mike and Jon), John Shwabacker, Tim Lang, and Bill Bailey for their help and advise.
Alex M
aka CopperSnot