Human Electric Trike Thesis

Design of an electrically assisted human powered trike

Archive for the ‘Design’ Category

Completed design

Posted by Bob Dold on Thursday, October 5, 2006 11:35 PM

Below are images of the final design and a link to an eDrawing of the design:

Link to eDrawing: zeept.htm (may require eDrawings download)

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Swing Arm Stress Analysis – Updated

Posted by Bob Dold on Monday, October 2, 2006 10:57 PM

After checking my intitial analysis I found some errors that caused the arm to see 4X the loadin it should have, here are the corrected results:

 

I analyzed the swing arm with a 3G vertical load, 2G aft load, and 1G lateral load, with G being equal to 140# which is the loaded weight on the rear wheel. I used a mixed shell and solid mesh in CosmosWorks 2006 as shown below:

 Von-Mises stress plot and displacement are shown below:

 

Max stress at this extreme condition is 17ksi, which is well below the 42ksi ultimate and 35ksi yield for 6061-T6 aluminum tube (Mil Hndbk 5)

Displacement is accptable at about an 1/8 of an inch at the dropouts.

 

– Updated 10-8-06

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Fabrication Status

Posted by Bob Dold on Saturday, September 30, 2006 3:36 PM

Fabrication of components is progressing ahead of schedule, the spreadsheet below shows the status of the parts that have been completed and those that are left to build:

On Friday I went into the shop and cut most of the tubing to length for the frame rails and rear swing arm. I also did the the bonding of the lower a-arm assemblies using the Loctite 680 as the adhesive. Bond prep consisted of  cleaning with Scotchbrite and then wiping with Acetone and then applying the green adhesive. The 680 took about 15 minutes to set and seemed to completely cure in about 24 hours. The pictures below show the lower a-arm and the sides of the swingarms bonded together:

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Gearing calculations

Posted by Bob Dold on Monday, September 25, 2006 11:50 PM

A spreadsheet was constructed to calculate the optimum gearing for the trike, by using a 14 tooth sprocket on the scooter gearbox and a 34 tooth cog on a mid drive, the motor can be geared down enough to allow the motor to make it up a 10% grade.

The picture below illustrates the chain drive layout:

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Suspension motion analysis

Posted by Bob Dold on Monday, September 25, 2006 10:20 PM

Created a motion model using CosmosMotion software to predict loading on shocks throught the suspension travel. The plot below shows the loading on the front shock vs. the shock travel, the nominal shock position is at .5 inches.

The plot below is the loading on the rear shock from the swingarm:

In both cases the load increases near the end of the travel due to the mechanical advantage of the linkage. The applied wheel load is 1G in the vertical direction.

Link to rear suspention AVI: rear_arm.avi (9Mb)

Link to front suspension AVI: front_susp.avi (8Mb)

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Received Stealth 1000 scooter

Posted by Bob Dold on Thursday, September 21, 2006 10:28 PM

I received the Schwinn Stealth 100 scooter today and assembled it and then took apart the rear wheel drivetrain to measure the motor/gearbox. I was able to remove the wheel ad motor assembly after removing 12 screws and then tapped the wheel off the gearbox shaft. the wheel was keyed to the 12 mm shaft with a 4mm key. After removing the motor guard/mount I weighed the assembly and took of the gearbox cover to inspect the gears. The gearbox uses a 10 tooth pinion, 58 tooth idler gear , and 68 tooth drive gear for an overall reduction of 6.8:1. The gears are packed with grease as shown in the picture below:

Several other Stealth 1000 owners posted  that they replaced the grease with oil to get a quieter geartrain, although I didn’t think it made much noise on my first test drives. The next picture shows the gearbox with the guard/mount removed, this assy weighs about 9 lbs.

After measuring the gearbox I created a SolidWorks model of it and started trying to fit it into the rear frame:

After evaluating various methods for getting the gearbox power to the rear wheel I settled on driving a 5 speed cassette mounted from the swingarm with a 14 tooth freewheel on the gearbox output shaft. With this driving the 38 tooth cog on the freewheel I will be able to gear down the motor enough to drive the 7 speed rear cassette at the same speed as the rider’s cadence.

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Suspension Design

Posted by Bob Dold on Sunday, September 17, 2006 9:22 PM

 

The front suspension was designed using a layout skeych in SolidWorks to size the a-arms and locate each of the pivot points. The layout (shown below) was designed to minimize the wheel angle change (camber) and to try to keep the roll center locations close to ground level.

The image shown below shows the completed model developed from the sketch layout above:

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Swingarm Analysis

Posted by Bob Dold on Thursday, August 31, 2006 11:36 PM

Ran the first stress analysis on rear swingarm – used a 3G vertical load as the loading, and used symmetry to model only half of the swingarm. Results look okay, nect step will be to analyze full swingarm with side and fore/aft loads as well.

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First machined parts completed

Posted by Bob Dold on Wednesday, August 30, 2006 11:13 PM

Met with Pete this morning who had completed the spindles, a-arm brackets, and bellcranks. Parts look great, he is starting in next batch of drawings for frame and swingarm components.

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8/25 Update

Posted by Bob Dold on Friday, August 25, 2006 7:30 PM

Spent the last month redesigning the frame and swingarm to use round tubing. After completing the initial design using rectangular aluminum tubing I felt the design would require too many small components to build. The round tubing also allows a better glue bond as the clearance between mating parts is more easily controlled than it would be in a rectangular design. The following pictures illustrate the final design – analysis of the main components is the next step.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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