Human Electric Trike Thesis

Design of an electrically assisted human powered trike

Archive for October, 2006

10/29 Fabrication update

Posted by Bob Dold on Monday, October 30, 2006 12:03 AM

Spent most of the past few days assembling the components to build up the trike. Most of it has gone smoothly, I did have a problem getting the motor into the already assembled swingarm so I had to partially disassemble it and cut a the shaft bracket to get it to fit. I also had to drill out the rivets holding the shock mount to the swingarm in order to rotate it to clear the motor while it was slipped in place – this means the motor cannot be removed without drilling out the mount rivets. Suspension seems to work fine with weight placed on it, loaded batteries and sat in the seat and suspension drops about an inch which is what I had designed.

With seat and boom attached:

Front suspension:

Motor and batteries:

Awaiting steering rods to be fabricated and another order of McMaster hardware in order to finish assembly, hopefully will have it ready to ride within a week.

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CFD Velocity plots

Posted by Bob Dold on Monday, October 23, 2006 11:32 PM

Plot of velocity profiles at several different locations:

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Fabrication pictures

Posted by Bob Dold on Sunday, October 22, 2006 11:10 PM

Spent about 20 hours this week assembling the frame, the process consists mostly of loctiting a joint, letting it set overnight and then moving on to the next joint. The assembly has to be put together in a certain sequence or the parts will not go together. To start I put together the rear of the frame as shown below, using the waterjet cur seat tube support to space everything correctly.

    

After the rear section was put together I assembled the front bulkhead. I cut 3/8 tube spacers to space the plates apart about 1.285 to allow clearance for the front suspension rocker arms to swing freely.

At this point I connected the front and rear sections using the longitudal frame rails which had their suspension mounting blocks already bonded on:

The completed frame assembly is shown below, at this point the mounting holes for the suspension rod ends need to be drilled and tapped to accept the control arms. So far I had only one bonded joint fail – this happened when I had to use a mallet to pound the lower frame rail into place through the tight fitting bulkhead – loosening the rear block where the swingarm will mount. I removed the block and rebonded a new one – I think the large impact loads from the hammer caused the joint to fail, in actual use none of the joints should see axial impact loads of the magnitude the failed joint saw.

Frame assembly ready for tapped holes and suspension mounting:

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Installed drain brain

Posted by Bob Dold on Sunday, October 15, 2006 9:10 PM

Received the Drain Brain on Thursday and spent today installing it on the X1000 scooter. Installation requires splicing the shunt between the batteries and controller and hooking up a wheel sensor. The picture below shows the unit installed on the handlebars:

 

The drain brain displayes the speed, watts, battery voltage, and distance traveled. It also stores the maximum current drawn and maximum wattage. After using it for a couple charge cycles it can calculate the miles left on a charge. After a brief test, it confirmed the maximum current was limited to about 30 amps, this occured when accelerating up a slight grade.

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10-15 Dry fit

Posted by Bob Dold on Sunday, October 15, 2006 9:03 PM

  Took some of the bonded parts I put together yesterday and did a dry fit with the parts I have completed. The batteries are sitting in their position between the frame rails.The shock is shown in it’s installed postion connected to the bellcrank.

 

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10-13 Received parts

Posted by Bob Dold on Friday, October 13, 2006 8:57 PM

 Received all waterjet parts from BigBlueSaw yesterday and picked up majority of machined parts from Pete at the WNEC shop. The picture below shows most of these parts laid out:

 

The plan is to bond together what I can over the weekend to be ready for the unfinished parts when they are completed.

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Fabrication progress

Posted by Bob Dold on Friday, October 13, 2006 9:19 AM

Stopped in to see Pete this morning to check on progress, he has completed the majority of the parts, the chart below shwos the parts left to complete:

Remaining parts should be complete in the next two weeks.

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CFD Analysis

Posted by Bob Dold on Monday, October 9, 2006 8:50 PM

To get an idea of the aero drag on the trike with a rider I built a FloWorks model of it to study the drag loads and flowline around the trike. My first model is a crude model withhalf of the trike and rider modeled to take advantage of symmetry to allow the model to run faster. The picture below shows the simplified trike model used in the analysis.

For this analysis I used an external air flow speed of 25 MPH, ground effects and spinning effects of the wheels and pedals were ignored. From this run, the solution converged after 44 iterations at about 2.4# for half the trike, or 4.8# total. The plot below shows the pressure on the rider and trike at 25 MPH:

 

To compute the Cd of the rider and trike, the drag is divided by 1/2 the density times the frontal area times the velocity squared.

Cd = Drag / (.5 * density * A * V^2)

Published values for the Cd of a traditional bike and rider vary from .70 to 1.1, a fully enclosed trike with an aero shell similar to the GoOne would be around .150. A recumbent trike should be somewhere inbetween these values, probably on the order of .50 to .70. From the model the frontal area is 5.58ft^2, filling in the rest of the equation yields a Cd value of .53 – right about where it should be. To study further reducing the drag, a fairing may be added to the simulation to see how much it helps reduce the trike’s drag.

 

Flow trajectories at trike centerline:

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Front Suspension Analysis

Posted by Bob Dold on Friday, October 6, 2006 7:05 PM

Today I used CosmosWorks to check the front suspension design, I used the same loading as on the rear swing arm; 3G up, 2G aft, and a 1G lateral load. G is equal to the loading on each front wheel, which comes to 125#. A solid tetrahedral mesh was used on the a-arms, spindle and pushrod with a total node count of 79,560 and 43,415 elements. The stress plot below shows fairly low stresses except for the lower rod end which is around 50ksi. The rod ends are steel so this is an acceptable stress for them.

 

The displacement plot below shows a deflection at the spindle of about .040in, which is acceptable. However, it also shows a large deflection of the pushrod of up to .080″ which indicates it may have buckling problems.

To check the buckling I modeled the push rod by itself and applied the axial load it is seeing of 530# at the 3G, 2G, 1G case. The results of this analysis show a buckling factor of below 1 (.53), indicating there is a problem. I plan on rerunning the analysis using a steel pushrod to see if can withstand the load without bucking, my other alternative is to go with a larger diameter aluminum pushrod.

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10/6 Update

Posted by Bob Dold on Friday, October 6, 2006 5:55 PM

Received Garmin Edge 305 yesterday, charged it up and used it in my car on my trip to work this morning. The speed seemed to be accurate to my car’s speedometer within a MPH, I logged the entire ride and was able to plot out the time vs. speed, grade, and elevation. The default sample rate was about once every 3 or 4 seconds, it can be set to sample every second which I will set it for when doing the test runs. See below:

The steepest grade on my way to work was about 15%, right at the start of the ride. I also found a program (G7ToWin) that lets me export the raw data to Excel so I can combine it with the Omega voltage logger data when I receive it.

The 305 also let you export your path to a Google map, as seen below:

Also went ahead and ordered 3 Odyssey PC925 motorcycle batteries from BatteryWeb for $98.88 each, these will be wired together in series to form a 36V, 27 amp-hour pack weighing 78 pounds.

Big Blue Saw emailed me and said they would be delivering the waterjet parts next week, so I should be able to start assembly next weekend.

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