Human Electric Trike Thesis

Design of an electrically assisted human powered trike

Archive for the ‘Updates’ Category

1-05 Update

Posted by Bob Dold on Friday, January 5, 2007 2:40 PM

Haven’t posted much in the last month because I was busy writing my final report and preparing my presentation. Needless to say I am a little burnt out after completing all of it and am taking a break until spring on the project. The presentation and report went very well and I received an A on my thesis which completed my Masters in Mechanical Engineering.

There are a couple of minor issues I need to address such as the lack of a freewheel on the pedals and some chain drive issues but otherwise the trike performed very well once I got the 8 speed hub installed. I have several events in the spring I need to show the trike at so I will need to get the fixes completed by then.

zeept1.JPG

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Added new 8 speed hub

Posted by Bob Dold on Tuesday, December 5, 2006 12:24 AM

Finally received the Sturmey Archer 8 speed rear wheel today after lacing it up and having it tensioned and trued up. This should fix the problems with the chain coming off due to the rear derailleur. The hub has a gear ratio of 1:1 to 3.05:1, with the standard 25 toothe sprocket it has a 1st gear speed of 11MPH and 8th gear speed of 30 MPH. I hope to find a bigger rear sprocket to lower the speeds a little to get more torque available for the hills.

Plot shown below is the results of the test performed yesterday before the 8 speed hub was added, and the trike was fixed at one speed. The gearing allowed 8 MPH up a 10% grade at 1000 watts.

I have some problems with the omega voltage logger as it is only reading in .05 volt increments, resulting in current readings in 5 amp steps. The stated resolution is supposed to be .01 volts which would give 1 amp steps if working correctly.

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Assembly nears completion

Posted by Bob Dold on Sunday, November 12, 2006 8:27 PM

Spent yesterday doing final assembly of the trike it is now just about ready to test under electric power. I bent up new handlebars out of .875 diameter 6061 tube using a conduit bender, these put the controls within easy reach while sitting in the seat. The left handlebar has the motor throttle from the X1000 scooter and the left brake handle, the right bar has the deraillleur twist grip shifter and the right brake handle. Both handlebars have rear view mirrors on top to aid in rear visibility as it is very difficult to see behind while reclined in the seat.

I also installed the three Odyssey batteries to make up the 36 Volt battery pack, the batteries were wired in series by connecting the positive and negative leads of the batteries using copper strips. The controller power was then taken from the first battery’s negative terminal and the third battery’s positive terminal. The batteries were secured bay riveting aluminum angle the the battery support tray to keep the batteries from sliding fore and aft. The frame rails restrain the batteries from moving side to side.

I also put new front tires on the wheels and put new brake and derailleur cables in order to prepare for the first test ride. The first test ride was under pedal power only since I am waiting on the freewheel adaptor for the motor to be completed – this part which should have been simple has been one of the most difficult to fabricate – it took three machinists and four different lathes to get the LH metric thread correct to fit up with the LH freewheel. Problems uncovered during this first ride include the following:

1. Can’t shift more than two or three gears on the rear cogs due to the sharp chain angle from the mid drive cogs to the rear wheel – two possible solutions, either shift the larger sprockets to the right and give up a few gears to allow a reduced chain angle or switch out the rear cogs and derailler for an internally geared hub. I will shift the cogs for now to allow testing to continue and order an 8 speed hub which will eliminate the problem.

2. The chain running from the mid drive up to the pedals rubs on the underside of the frame, to fix this I will use the idler pulley from my Sun tadpole to run space the chain out from the frame. I will have to make up a bracket to attach the idler to the rear swingarm.

3. When the trike rolls backwards the chain backdrives causing problems with the chain jamming and coming off the sprockets. I am not sure why this is happening, the rear freewheel pawls should disengage when rolling backwards but for some reason they are not – hopefully changing to a internally geared hub will fix this.

4. Trike leans severely when cornering, I need to check if this is due to springs that are too soft on the front, or incorrect suspension geometry.

Remaining items to be completed are down to the motor adaptor and the idler bracket, both should be completed tomorrow by Pete in the shop.

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11/10 Update

Posted by Bob Dold on Friday, November 10, 2006 8:26 PM

Fabrication is nearly complete, actually was able to ride the trike for the first time the other day using pedal power, still need to work out some chain routing issues, but for the most part it worked well. Based on my very short test ride a few things became apparent – #1, I am very happy with the suspension, it really smooths out the bumps and makes it more comfortable to ride. #2, the steering realy scrubs when pushed into a tight turn so I need to double check the geometry to check if the Ackerman compensation is correct. #3, running the motor unloaded produces a lot of noise, hopefully this will dissipate a little when it is hooked up to the drivetrain.

I tried instaling the handlebars from my Sun tadpole, but they are too short as seen in the pictures, I ordered some 7/8 aluminum tubing and hope to bend up some longer ones using an electrical conduit bender.

The drawings I got my disk brake mount locations from was incorrect so I had to space the mounts out about a 1/4 inch using a stack of washers as shown:

 

As with any prototype there are a number of things that have popped up that I would change if I had to do it over again, but that is all part of the learning process. Here are a few of them:

Adhesive bonding of aluminum tubes work well in some cases and not so well in others. The tubes I bought were not very round, so even though the blocks they go into were made very accurately, the tubes themselves were not round, causing uneven gaps which the Loctite adhesive did not like. On the block that holds the boom tube to the fram this was especially apparent and I had to reglue twice. It still is not a good joint and I had to rivet it to back up the glue bond. To fix this I would make the block longer to add more glue surface area, force the tube round using a mandrel, and add some sort of backup fastening system.

If this trike were to be manufactured, it would have to go to a welded contruction, the bonded construction requires too many machined components and requires precise tubing for the bonded joints. The welded construction would also produce a lighter weight frame by eliminating most of the blocks.

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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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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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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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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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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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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.

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