When Dennis called me he asked if I could make him a custom Anura with a bottom gear of 9 Gear Inches and no derailleur. Always up for the challenge, I said "you betcha!" We eliminated the derailleur by mounting a Shimano Alfine as the mid-drive. We got the gear range by using a Schlumpf High Speed Drive (27T).
Mounting the Alfine as a mid-drive presented a few issues because it had to be placed above the rear differential. We wanted our mount to be able to slide on the main frame tube so the chain tension could be easily adjusted. With the transmission hanging at an ange over the differential we needed a torque arm to prevent the mount from flexing. The result was a rock solid mount.
Main Drive Chain
To make it easiest to mount the primary drive chain, we used the disc brake mounts on both the Alfine and the differential to mount our sprockets.
Shimano Alfine Transmission
The heart of our new drivetrain is the Alfine transmission. Our new favorite! This transmission gives us eight super smooth gears. The Alfine is Shimano's most efficient hub transmission.
We pair the Alfine with the Nexus Revo Shifter. It's a grip shifter that is very easy to turn with a good solid click for each gear.
Schlumpf High Speed Drive
To get the gearing we needed we went with the Schlumpf High Speed Drive. In low gear it gives us a 27T chainring. In overdrive it gives you the equivalent of a 68T chainring. Combined with the Alfine in the rear it gives us a total gear range of 9-69 gear inches.
A modified chainline was needed to get the power from the Schlumpf to the Alfine. We moved the power idler to the rear seat bolt position. For the return side we are using an idler built into our mid-drive mount and some modified chaintube routing.
The color just seemed right for the Greenspeed Anura. Anura is a species of frog which makes it even more appropriate.
One of the key features of the Anura is its geared differential. This works just like the differential in your car. It allows both wheels to be driven even when you take turns.
The Anura fender system is slick. The fender stay clamps on to the rear axle frame and then the fender slides on the top. The fender is secured with a clamp.
With the seat off, you can get a clear shot of the chainline.
You can see the return idler mounted to the mount. This idler acts as the primary chain guide for the drive sprocket. Mounting the idler here also increases the wrap on the sprocket to lessen the need for high chain tension.
Not the best shot for what I wanted to show, but with no derailleur hanging below the trike we now have lots of clearance.