Recently I got hold of a new e-bike drive system to test out on my cargo and kid carrying Surly Big Dummy.
The motivation is that for myself and many out there using cargo/sports utes, we sometimes have big loads strapped to our bikes, and in a place like Chapel Hill, big hills to climb with them.
That taxes the standard electric bike hub motor system. Some can handle it, but constantly pushing their limits may ultimately lead to failure. ( the same can be said for one’s legs – which is why I use a an electric assist on my cargo bike).
One solution to this problem has been the Stokemonkey. Instead of a hub motor, it uses the bike’s existing drivetrain – and gears. So, when you’re climbing a hill with it and you shift into a lower gear to give your legs a break, you’re giving the motor a break too. This increases overall system efficiency, and motor/battery system longevity.
But there have been two limitations to the Stokemonkey: limited supply (it is produced in small batches by our supplier in Portland, Or), and it only fits on Xtracycle-style cargo bikes.
A few brave designers have tried to crack this same nut with a system that doesn’t require an Xtracycle style frame.
The first was the Cyclone. I don’t have any experience with that system, but have heard certain things that have put me off from trying it – mainly that the installation is very involved.
Now comes the Electric Mountain Drive from the folks at Ecospeed (also from Oregon!).
It is another electric assist system that uses the bike’s own drivetrain, benefiting from the gearing on the bike to reduce motor strain and increase climbing ability.
I’ve been using it for about two weeks now, so this review is only preliminary.
Here are some benefits of the system:
- Because it uses the bike’s drivetrain, it can handle steep hills without strain (if I shift into the right gear)
- It mounted to the frame in a relatively straightforward manner
- It uses a standard electric bike brushless motor controller, so when the first one died (a note on that later), I was able to swap in an Infineon controller we had in the shop
- Using only a 36 Volt battery with a controller consuming 20 amps, the bike can achieve powered speeds of up to 25mph+ (depending on headwind and hills). Most of the hub motors I’ve tested – even the high speed ones – can’t do this on only 36V 20A system. For me those would top out around 22mph on the flats, pulling maximum amps.
- Its installation wasn’t too difficult, and the instructions were very detailed.
For certain kinds of applications such as steep hills to climb on a cargo bike without a spot to put a Stokemonkey, this appears to be THE solution.
But it does have a few drawbacks to be aware of:
- It is somewhat noisy. It is not louder than the cars on the road – but not a lot quieter, either. I like to operate in “stealth” mode on my local bike path so as to not get any of the other users upset that I’m using electric assist. It is hard to do with the EMD, unless I just entirely leave the electric off. That’s fine… except for that I’m usually in a hurry (note: I never, ever use the electric assist to exceed 20 mph on the bike path, and I always slow down for other users – doing otherwise would not only be rude, but would likely land me in trouble). Also, the way it mounts on the bike makes it more obvious that the bike has some kind of motor attached.
- I found the overall system efficiency to be disappointing – which means that I can’t travel as far on a single battery charge. When I used the eZee hub motor, I typically got 18 watt hours per mile or better (at 36V). That meant I could do a 20 mile roundtrip with my 10 amp hour battery. With the EMD system, I’m getting at best 24 watt hours per mile, reducing the range to around 15 miles. I think there are three factors causing this: a) It uses a chain/gear system with a oneway clutch that may loose energy; b) Some energy may be lost in my Nuvinci continuous variable transmission; c) it is easy to go too fast with the system, which always sucks down juice very fast (any speed over 20mph on an e-bike is usually quite inefficient). I’ve tried to keep the speed low, and still had poor efficiency. At some point, I’ll try it out on a bike with a regular rear transmission using cassette and derailleur, to see whether that makes any difference.
- The first controller fried within only 1/2 hour of operation. It turns out that the motor and controller are made by BMC. BMC makes decent motors… but their controllers have a not so good reputation for reliability (we won’t sell them anymore after a failure rate of over 50%). We replaced it with an Infineon, which has worked well so far (an is in general a very reliable controller). To their credit, Ecospeed did send us a new controller right away, and it is a different design. But it is still made by BMC. I think I’ll keep the Infineon for now.
- It requires a bike with a circular downtube – the tube from the handlebars down to the pedals (many bikes these days have ovalized downtubes). And, once installed, it does protrude down a bit.
Another attribute I noted that is neither plus nor minus is that to optimally use this motor, I had to get in the habit of shifting the bike appropriately. This requires letting off the throttle a bit, doing a rapid shift, then getting back on the throttle. At first it was a bit clunky for me – but just like learning to drive with a clutch and gearshift, once I picked it up, it worked well. I have come to enjoy the challenge of shifting properly through an acceleration cycle to get up to speed.
Bottom line: The EMD will be a perfect solution for people who have big/long hills to climb, and provides a worthwhile alternative to the Stokemonkey, especially if the latter isn’t available or if it won’t fit on your bike.
My assessment is that hub motors will be better for the person who has moderate hills, long distances, or is concerned about noise. Since I fall in several of the latter categories, I’m likely to return back to a hub motor system at some point.