The Patterson Transmission is a two speed internally geared crank. Unlike the Schlumpf Drive, it's shifted with a standard front derailleur shifter instead of pressing buttons with your heels, which is far easier in my opinion. The Patterson is also far less expensive than the Schlumpf and does not require modification to the frame. The Patterson is fitted with a 28 tooth chain ring, and can operate in either 1 or 1.6 to 1 ratio, giving the equivalent of a double crank with 28 and 45 tooth chain rings. I've been eying the Schlumpf Mountain Drive for a few years, but the price, method of shifting, and requirement to modify the frame has kept me away. Last January I purchased a Tour II 8 speed as a rolling frame set, and decided to experiment with the Patterson.
The Patterson is designed for upright bikes, but it can be fitted to a Tour II with a couple of accessories. Since it's designed for an upright bike, it's expected that the shift cable will come from above. However, on the Tour II the cable comes from below, so an accessory cable stop is required. Patterson sells a cable stop as an option that bolts to the back plate. Alternatively a third party cable stop clamped to the derailleur post could be used. The second issue is related to the torque arm, or torque limiter. The torque arm is suppose to sit firmly against the chain stay of an upright bike, and it keeps the Patterson back plate and mechanism from rotating under heavy load. On an upright bike the chain stay comes very close to the back plate of the crank, so a small torque arm is sufficient. However, on a Tour II the torque arm must engage the center of the boom, or the crank could become damaged. This requires a much larger torque arm with a longer reach.
In the picture below the part circled in red is the optional cable stop from Patterson. Take note of the black part bolted to the lower right area of the back plate. That's the stock torque arm. Now compare that to the underside of my Tour II and you will see a much larger torque arm that reaches to the middle of the boom. The torque arm is a custom part designed and manufactured by Utah Trikes. They sell two sizes, one for 1.5 inch tubes and the other for 1.75 inch tubes. The Tour II requires the larger of the two. Rover owners interested in the Patterson should be happy to know that the stock torque arm works just fine on the Rover. I installed a Patterson for a friend that purchased it new late last year, and the stock torque arm fully engaged the big square boom.
Details about the Patterson drive, installation instructions, and even an installation video can be found on the Patterson site at http://pattersonbike.com/
After watching the video it was a bit unclear to me which special bike tools would be needed to install the crank. I finally figured out that a Park Tool BBT-19 and a BBT-18 were the correct tools. If you are installing your own crank you will need appropriate tools to remove your old crank, standard tools as listed in the installation instructions and video, and the two Park tools I mentioned. I paid around $37 for the two Park tools, and I alredy had everything else. If you are not already armed with tools, then it might be cheaper to pay someone to install the crank for you.