02. Design Decisions


A woodstrip sailing dinghy, similar to the canoes I used to build.

Some day in 1975?

The beginning: Years ago, maybe 30 years ago, I dreamt of making a fun 3-wheeler powered by a motorcycle that would get great gas mileage, making the body of the same lightweight construction of woodstrips and fiberglass that I use in my canoes. I imagined the front suspension to be a nice piece of Sitka Spruce, since that is a very tough, light, and springy wood. I had no idea how it would steer or brake.

If you are unfamiliar with 3-wheelers, take a look at this excellent discussion of one rear-wheel "cycle cars" with numerous photos and drawings. 



February 16, 2005

First scale layout sketch: I am hoping to have the chassis and drive train completed by the end of summer, and the body finished before the rains start next October. In my first layout, I put the driver and passenger slightly offset so they could be closer to the centerline without mashing elbows, and half of the batteries in the very front of the body to get 66 percent of the weight on the two front wheels. The other half is underneath the driver and passenger in order to keep the center of gravity low and forward.





At this point, I have bought plans for building the El Chopper ET electric motorcycle ($40), fromMegawatt Motorworks, and The New Electric Vehicles by Hackleman ($25) from Sierra Solar. In a burst of over-confidence, I also bought the rear end of a Kawasaki 650 ($75) from a motorcycle salvage yard... 


...and the front suspension of a '66 VW Beetle, rebuilt. This could be my first of many mistakes, because having invested $750 in the VW front end, I was pretty much married to it. It's not very salable because it's the ball-joint style. The VW front suspensions in demand for dune-buggies have a king-pin style.

March 2, 2005

Second layout: I didn't like the first sketch because it made the vehicle too tall, and I wanted something low and sporty, in spite of the risk of not being seen by aggressive drivers in their SUV's. I had a conversation with Mark Murphy of Blue Sky Design, who fortunately lives nearby and is the designer of the Gizmo Neighborhood Electric Vehicle, (NEV), as well as many other concept vehicles, such as the FireAero. The Gizmo has very similar weight and performancecharacteristics to what I am aiming for, and it is also a tall vehicle. Anyway, Mark pointed out the danger of having the batteries in front in a head-on collision, which might cover the passengers in battery acid. So I placed them behind, and tried again to get the weight forward by placing the front wheels further back. It looks very crowded!

I'm an artist, not an engineer. I wanted to obtain a set of proven, matched drive-train components that I could just "plug in" to my project without having to research and re-design from scratch. No such luck, as Hackleman warns in his book. Suppose we assumed a combined chassis/body/wheels & tires weight without batteries of 350 lbs., and a maximum payload of driver/passenger of 350 lbs., if you add 600 lbs. of battery, making a total of 1300 lbs., what could you expect for performance? Mark said, "the more batteries you have the more range you get, but the more weight you add, the less range your get.....This is a problem we had with the Gizmo..at some point it becomes self-defeating." 

March 15, 2005

Other ideas: I looked in books, I looked on the web and found shapes and styles that I liked, particularly the doorless, open T-top entry of Stephen Taylor's Doran:(plans, specifications)

Also see Marc Kohler's construction log, with photos.

...and the sleek, low-slung sporty look of Alex Smith's Vortex: (plans, specifications)













Dan Lenox also has a construction log, with photos.

I joined the Vortex 3-wheeler online discussion group, and finally build up enough courage to reveal my naivete by asking simple questions. I wandered around the twisted and torn steel bodies of cars in a junkyard with a tape measure, looking for a nice windshield, and think a Saab 900 wraparound would be nice. I also wondered how I would survive a crash. 

I am hoping to extrapolate the El Chopper 48-volt system to 8 batteries, two banks in parallel, and use the 15 HP (peak, at 325 amps) Etek motor. I like the idea of a wood-fiberglass monocoque body, but I question the need for the complex plywood chassis of the Vortex. I have the goal of a rounded, tear-drop shape like the Vortex, using a composite skin with only two pieces of plywood as full bulkheads at the two ends of the passenger compartment. This would leave the interior mostly hollow, like my canoes, and save alot of weight, I think. The bulkheads would be the mounting-plates for the suspension parts, which would be welded to matching steel plates. 

I know that building a prototype in this fashion makes it impossible to make chassis modifications after road-testing if unexpected problems show up, but I am willing to take that risk if I can get as much advice as possible ahead of time. The Tryanne (right) is an example of what can be done with another boat-building technique, cold-molded veneer. It is a 900-lb. three-wheeler that gets 70 mpg on a Citroen engine. Click on the photo for the full story. 

April 15, 2005

Through the online discussion groups, I am learning that a series-wound motor is more suited to my vehicle weight than the permanent-magnet Etek motor because it will have better acceleration. I sent out inquiries to EV parts suppliers online, and received more than I expected from EV America in New Hampshire. The guy who runs it is an engineer, Bob Batson. Not only did I get a complete catalog, I also received an article on safety, and what thrilled me the most was a computer analysis of my electrical system needs, complete with a parts list specifying everything (the "package!") that would give me the range and speed I wanted for the given weight of the vehicle.

April 20, 2005

I am working on what I hope to be my final drawing of the vehicle. Today I met with a welder, Pat Blair of Thompson Motorsports (owned by Lyndy Thompson, the daughter of famous race car driver Mickey Thompson) for discussion of the metal work that I need. He seems to be easy to work with, an excellent craftsman, and has built race cars and street rods, so he will be able to help with the design of a light, strong frame. I have let go of the wood/fiberglass monocoque body idea in favor of a safe, steel cage with a wood-strip shell hung on the outside.

April 27, 2005

Be still, my beating heart! I made another major commitment of funds to this vehicle this morning, forging ahead into only vaguely outlined waters, by ordering most of the electrical system parts from EVAmerica. I spent almost $1800 on motor, controller, switches, fuses, and meters. The batteries will be ordered later. The 72 volt system will drive the series-wound motor at 12 HP.

I went to a junk yard and measured the T-top of a Nissan 300ZX, hoping to adapt the entire windshield and roof to my project, but I decided it was too wide in the aft end, and I would have to take a different route. "Hang loose" is my motto these days, telling myself that the design will work itself out. After much internal discussion, I decided the seating would have to be thin and tilted back just a few more degrees in order to get me and the height of the vehicle lower. I think the seats will be a folded air-and-foam camping mattress ....with lap-shoulder belts!

May 5, 2005

I STILL do not have a final drawing for the body of this vehicle, and am exhausted from wandering through the junkyard with tape measure and clipboard. I am now brainstorming many possible ways to implement the weight distribution, door/entry, and open top for the least weight and cost. I am almost ready to buy a complete parts car, a non-running but intact vehicle, just to get all the little pieces I want. Junkyards ask alot for one piece at a time.

The first shipment of electrical system parts has arrived in good shape, and the prospect that lies ahead of me is both exciting and daunting. I feel like I just emerged from treeline and got my first look at how steep, really steep, is the slope above me. It looks like post-graduate Electrical Engineering 404 at this point, but it is interesting how a good night's sleep and an inspiring song about how Jamaica fielded a bobsled team in the Olympics, makes me ready to carry on.

May 8, 2005

I finally have a layout drawing of the vehicle. I find that my design solutions come to me at odd moments when I am not staring at the drawing, such as when I am riding my scooter to work. I had some black tea that was keeping me awake at night, so I decided to utilize my time by staying up until 3:30 AM to finish the drawing. I finally managed to get the center of gravity at 66 percent of the distance from the rear to the front. All six propulsion batteries are behind the front wheels with the controller and converter, fuses, etc. on a board above them. The auxiliary battery for the lights, horn, blowers, etc. will sit above the main propulsion batteries, and is placed on the right side to counterbalance the driver somewhat. I will have to make a quick-disconnect restraint for that aux battery so I can do maintenance on the batteries below. The exact shape of the front end is yet to be worked out in a 3-dimensional, carved foam model.

The removable door will be hinged off the windshield post (this was never implemented), have a plastic window, and open part of the roof, making it into a T-top in the summertime, as well as allowing easier entry and exit. I've decided to use the windshield of a Saab 900, which I will obtain complete with its steel frame. The overall height and width of the vehicle is just slightly bigger than a Miata, the length is the same. 



May 28, 2005

Now I am enrolled in Automotive Frame Engineering 101, having a couple of meetings each week with my welder, Pat Blair. I am spending late nights on the computer, using Photoshop Elements to make my drawings of the frame, which change after each meeting with Pat. I always bring my red "correction pen" to alter the drawings as we talk. This drawing, a snapshot of progress being made, will no doubt morph into something different next week. 

June 1, 2005

Today was "Jump on a Volkswagen Day!" I made measurements of how far the springs were compressed in a VW bug with comparable suspension to the one I am using when loaded with two adults in the two front seats, and two adults on the front bumper to simulate battery load. Pat and I have decided on the last of the important triangles in the design of the frame, and I have started building the battery box so that he can build the frame around it. It feelsgreat to be at the beginning of the actual fabrication phase! 

Frame Fabrication  


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