Human Electric Trike Thesis

Design of an electrically assisted human powered trike

7-25 Update

Posted by Bob Dold on Tuesday, July 25, 2006 3:11 PM

Accomplished alot in the past week, have gone through and pretty much redesigned the entire frame to make it easier to produce.

New Design

The front shocks have been moved aft a few inches so they can have a clevis mount tied to the bottom rail rather than an overhanging bolt mount.

Shock Mounts 

 The rear suspension has been redesigned to move the motor above the swingarm. The wheelbase was slightly shortened to allow for a more compact packaging of the components. The motor mount and geartrain were redesigned to better integrate them into the rear swingarm.

 Swingarm

Front disk brake mounts were designed for the front spindles along with the mounting points for the steering arms. The design of the mounts allows the same parts to be used for the right or left spindles to decrease the part count. The front a-arms were redesigned so the blocks that tie the arms and roda ends together are undirectional, again reducing the part count.

spindle

 The steering design has been started, a design spreadsheet from Peter Eland, http://www.eland.org.uk/steering.html, for three wheeled vehicles was used to design the links so the correct steering geometry is obtained. Without the correct geometry the tires will scrub while turning, increasing rolling resistance, and increasing tire wear. The correct geometry is known as Ackermann steering geometry which basically insures the inside wheel turns at a greater angle than the outer wheel since it is at a smaller radius. The schematic below shows this:

Ackermann steering diagram

The independent front suspension makes design of the rods a little tough since the rod pivots have to be located so they are along the pivot axis of the suspension travel to elminate bump steer. If they were not, every time you hit a bump the tie rods would pull the trike to one side or another. Another design consideration is trying to improve on the ratio between handlebar movement and wheel movement. My current trike is very twitchy since a small movement of the bars causes a realtively large movement of the wheels. By increasing the ratio I hope to reduce the twitchiness at higher speeds. I will be using two tiller type bars that pviot fore and aft connected to a pivot plate to actuate the steering arms, by varying the pivot radius of the connecting rod joint outward,  I should be able to increase the ratio of the steering.

The last remaining design issues will be the boom connecting the pedals to the frame and the seat mount. I would like to make the boom so it can be pivoted up and out of the way to allow for easier storage and transportation. I am also toying with the idea of a carbon fiber seat base that doubles as a battery cover.

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