Tuesday, June 2, 2009


It was quite a marathon push to get the car done in time for the play, so I did not blog (sorry). I'll post some more construction details later this month. But, for now - a video of the car in action:

And here is a photo from the same scene (actor's faces deliberately blurred out):

Sunday, March 8, 2009

Motor Controller Wiring Diagram

As part of this week's activities, I also drew a schematic of the controller wiring. The online manual includes a dual contactor reverse circuit. Since this car will never go in reverse (and since it has freewheel ratchets - it *can't* go in reverse) I don't need that part of the circuit. Also, this picture documents the attachments of the throttle I got:

Frame and Steering Knuckles

Welding is nearly complete. Here is the undercarriage - basically, the two live axles connected by slightly smaller tubes:

Note the forks on the front axle. These are left over from the Electrojeep project. I made two steering knuckles to fit inside the forks. They are made from 1 1/4" conduit (the main bearing), 1" conduit (the axle screw), and 1/2" conduit (the tie rod connection). I found that 1 3/8" bearings fit *exactly* into 1 1/4" conduit after a little bit of heat application - keeps them in there nice and tight. The wheel axle screws into a 10x1.0 nut welded inside a washer, which itself is welded to the knuckle. Not the prettiest welds (this thin-walled tubing is a pain) but strong:

And here is the frame for the top. On top of this will be placed wood boxes / flooring / etc.:

The undercarriage will be attached to the main frame through full elliptical leaf springs. These were made by Amish craftsmen using hand tools (really!):

Rear Dual Sprocket Differential

One of the two main problems that early automakers had to solve was the rear differential. The rear wheels spin at different speeds when turning - the outside wheel is traversing a larger circle than the inside wheel, so it has to spin faster. If you don't do this, the tire "scrubs" and the vehicle resists the turn. It's very hard to find pictures of how Benz solved the problem - but it looks like his belt-drive motor turned a drum that had an interior freewheel ratchet driving the wheels, so that they could spin at different rates. I adopted that idea to the technology I had at hand. I designed up a mechanism using two freewheel ratchets, one for each secondary axle, driven by sprockets on the tertiary axle, itself driven from the motor:

The ratios on the sprockets shown here are 15:80, or 1:5.333 - so when the motor is spinning at 1500 RPM, the secondary axles will be spinning at 280-ish RPM. The discs with all the holes are the brake discs - again, one for each axle, since they spin independently. The tricky part: how to make sure the torque is transmitted to the axle? Bicycles solve this problem, of course - so I drew it as a bicycle hub with brake mount on one side and freewheel thread on the other:

Unfortunately, I could find no such item handy (I'll keep looking). In the meantime, I did find two mountain bike front hubs (with disc brake mounting points) and a spare rear flip-flop freewheel hub:

The trick is getting it all together... I cut all the hubs in half using a pipe cutter on two of them (the third hub had walls 1/4" thick and I had to use the cutoff wheel):

After suitable cleaning, I expanded three of the spoke holes to 3/16", bolted the mismatched halves together with 8-32 machine screws, and applied liberal quantities of JB Weld to the mating points to hold it all together. The screws will stay to provide some additional mechanical strength:

Here is a mockup of the sprocket and brake disc on one of the hubs:

Still to do on this part of the project: weld a 1/2" threaded coupling to a washer, tap & die two set screw holes in it, and JB weld the whole thing to the hub.

Changing Gears

Since the car will be used in a production of "Wind in the Willows" it was decided that it should be a four-wheel vehicle rather than a three-wheel vehicle. In keeping with all the research I've done on Benz and his early motorcars, I decided to go with something that looks like the 1899 Benz Rennwagen:

"Rennwagen" means "Race Car" in German. In addition to four wheels, you'll note that there are boxes enclosing the motor and a front box enclosing unknown items. This actually saves time, since I won't have to make a detailed replica of the motor. Instead, the rear box will contain the electric motor guts and batteries. Here is a Sketchup that is getting close (it does not have fenders, and the front box still needs work):

Sunday, February 22, 2009

Wheels and Bent Tubes

I found some of the dimensions of the original Motorwagen on the web today. This table shows those dimensions, plus the 5/8 scale version of them (metric and US). The last column is how I adjusted them for easier building / measuring:

I found that the Sketchup model I found before was not drawn very well to scale. So, I started from scratch. Here is the current dimensions (you can find a PDF here):

I also added the wood slats. It's starting to look like the Motorwagen...

So, with design well underway, it's time to buy some parts. I got wheels at my local Recycled Cycles store - two 700C, one 20" BMX front wheel (the smallest they had):

The 700C wheel have "flip-flop" hubs. They have standard 1 3/8" x 24 TPI freewheel threads on both sides, but one side has a reverse thread for a lockring for a fixed speed gear. I threaded the axles through in such a way to leave a long stub for threading into the live axle. This is standard very fine pitch 10mm x 1.0 thread:

I also bought 1" EMT conduit to build the main frame. Using a conduit bender, I put the appropriate 30 degree bends into the tube:

Using setscrew-tightened conduit interconnects, I temporarily rigged it up to test fit a few things. This is *not* how the wheels will attach. And I will weld the frame permanently before I'm done. But it was fun to see it starting to look a little like the Motorwagen:

Next up - probably more modeling, plus the rear supports / rear axle.

Saturday, February 21, 2009

Side Track - Benz Patent Motorwagen

I've taken a break from the ElectroJeep to do a sprint project - a 5/8 scale Benz Patent Motorwagen powered by a 1 kilowatt electric motor. The Benz Patent Motorwagen was the first automobile designed from the ground-up as an automobile. Invented in 1886 by Karl Benz (of later Mercedes-Benz fame), it was a tricycle, with a 1-cylinder gas motor and wire spoke wheels:

Benz's original drawings can be found in his 1886 patent. Here is a side view:

And here is a bottom view:

Note that the one he actually built and put into (handmade!) production was slightly different, and that's the model I'm going to build (because there are so many more pictures of that model). There's even a Sketchup model of it. I snagged it and scaled it to the size it will be, with a human figure next to it for scale. I chose 5/8 scale because that's pretty close to the ratio of the original wheel size (1260 mm) to typical bicycle road wheels these days (700 mm):

I'm redrawing it to exact scale so I can get the right bits-n-pieces - here is how it's looking so far:

I've ordered the motor, controller, cables, etc. and the fully elliptical leaf springs for the rear axle. I'm now off to buy bicycle wheels (700C for the rear, 450C for the front). Deadline: three weeks and counting...