The PlanetDrive is an in-water gear assembly which efficiently increases pedal power to a propeller. Think of it as the stern unit of an inboard/outboard motor, except the inboard portion is a foot pedaled crank.

It is an inexpensive way to greatly increase the rpm at the pedal power end to the prop end. It is intended for the DICY small bobtailed and the pedal boat manufacturing markets.

The gear assembly comes in increaser ratios of 1:7 and 1:49 (each with a

maximum torque of 157 lb-in), and 1:5 and 1:25 (each with a maximum torque of

200 in.-lbs.).  Optimum input (pedaling) rpm for the unit are from 50 to 100.

The PlanetDrive is a permanently sealed assembly 4 inches in diameter and 9 inches long, including the 12 mm diameter input and output shafts with simple cotter pin slots for prop and coupler attachment. It comes with an anodized aluminum clamp for attachment to your boat.

Once attached to your boat, you fasten your shaft to your pedal mechanism (MPB’s MitrpakDrive or a twisted belt or chain system), add your prop, and you are off and running.

History

There are two major issues in human powered pedal boat mechanisms. The first is to change the direction of the pedaling motion 90 degrees so that power can be transmitted to a shaft and prop, and the second is to increase the rotations made by the pedaling motion by the time power reaches the prop without much loss of energy efficiency so that the prop rotates many more times than the pedaling motion.

Note: This discussion relates to pedal systems that drive a prop, and not those which drive a paddle wheel (usually less efficient and required significantly more space) nor fin-type such as the Hobie MirageDrivetm (which does not allow for reverse).

The right angle transfer is usually solved by employing either a twisted chain or belt mechanism from the upper pedal crankshaft or, less commonly, a beveled spur gear box. Marco Polo Boats is currently developing two alternatives to these methods.

The second issue of increasing the rpm from the crank rotation to the propeller is most commonly solved by having a larger sprocket or sheave at the pedal crank, and a smaller sprocket or sheave at the lower crank which is at a 90 degree angle from the upper sprocket. The difficulty here is that as the ratios between the two sprockets increase, the harder it is to keep the chain or pulley in alignment and therefore kept on the sprockets or sheaves. Usually the ratio is no more than 1:2.

MPB’s PlanetDrive, through special gearing, places all of the the increaser activity in an assembly just in front of the propeller. Therefore, twisted chain or belt “front end” systems need only be 1:1 and much easier to construct and maintain. This front end is then attached via a shaft of whatever necessary length to the PlanetDrive, with the increaser ratios available in 1:5, 1:7, 1:25, and 1:49, with the single digit increasers having a 98% efficiency and the double digit increasers a 95% efficiency.

Drawings/Assembly

Below is a 2D sketch of the PlanetDrive.

To assemble, attach a prop appropriate to your boat to the 12 mm keyed output shaft of the PlanetDrive.

Next, use the included PlanetDrive clamp to attach to your boat. Finally, connect the PlanetDrive to your “front end” pedal mechanism via a shaft to your specifications. You will need shaft couplers to mate with the PlanetDrive 12 mm keyed input short shaft.

Specifications

The PlanetDrive comes in four versions. Each version is 4” in diameter (not including the clamp), and approximately 9 inches long (including the stub shafts).

Ratio     Max. Torque                Price

1:5        200 in.-lbs.                  $449

1:7        157 in.-lbs.                  $449

1:25      200 in.-lbs.                  $549

1:49      157 in.-lbs.                  $549