Human Electric Trike Thesis

Design of an electrically assisted human powered trike

Archive for July, 2006

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.

Posted in Design, Updates | Leave a Comment »

7-18 Update

Posted by Bob Dold on Tuesday, July 18, 2006 3:06 PM

Was on vacation last week so not a lot was accomplished, after going through and pricing out some of the frame components I decided it needed to be redesigned for easier and less costly fabrication. My new concept is to use 3/4″ aluminum plate at the tube junctions that will be joined to the tubes by 1″ u channel, rivets and epoxy. Round tubes will connect the crossmembers at the front and rear to tie the frame sections together.

Posted in Design, Updates | Leave a Comment »

eMachineShop.com

Posted by Bob Dold on Tuesday, July 11, 2006 12:09 PM

Downloaded CAD software from eMachine Shop and drew up and quoted several of the machined parts. Rocker arms are about $90/ea for two or $50/ea for four. Will try to optimze design to reduce part count and use as many common components as possible. Software is very useful for instant quotes on simple 3 axis or waterjet parts – cannot import existing solid models into software so models need to reconstucted for quotes.

Posted in Components | 1 Comment »

eDrawing of current design

Posted by Bob Dold on Sunday, July 9, 2006 11:29 PM

Clicking on the attached link should bring up an eDrawing of the current design – unzip the file and run the executable to view the file: zeept_7_9

Posted in Design | Leave a Comment »

Rear Swing Arm and Front Suspension Design

Posted by Bob Dold on Sunday, July 9, 2006 11:24 PM

Went through and finalized the design of the front suspension rocker arms and their attachment to the frame. A 1/2″ machined aluminum plate will be used to tie the frame rails together and serve as a mounting point for the rocker arms and shock mount. A pivoting shock mount was designed to tie the the shock bottoms together through a central pivot point to act similar to a sway bar.

pic.jpg

Designed rear swing arm and gear train to provide 19:1 gear reduction for motor. Swing arm is constructed on 1.25 x 2.5 x .125 6061-T6 aluminum riveted and bonded to welded steel shock mounts.

pic2.jpg

pic3.jpg

Above picture shows the motor mounted to a bent 3/16 aluminum plate bracket that also supports the shaft for the sprockets used in the gear reduction. Motor is mounted below swing arm to keep CG of trike as low as possible.

Posted in Design | 1 Comment »

gizmag Article: World human powered speed record – 53.43 miles in an hour

Posted by Bob Dold on Friday, July 7, 2006 12:52 PM

gizmag Article: World human powered speed record – 53.43 miles in an hour

Posted in Uncategorized | Leave a Comment »

Schedule

Posted by Bob Dold on Tuesday, July 4, 2006 11:03 PM

Project schedule:

schedule.JPG

Posted in Updates | Leave a Comment »