Monday, February 23, 2009

Brief Hiatus

I'll be taking a brief hiatus from the Electrojeep over the next 3-4 weeks - I'm building a 5/8 scale model Benz Patent Motorwagen and putting an electric motor in it for a local theater group. You can follow my progress at the voltwagen blog.

See you back here in a month or so!

Monday, February 16, 2009

Declaring Victory and Moving On

I finally got some time and good weather today to finish up the motor install. Although I had some back-and-forth with helpful blog readers, I decided to stick with my current plan for now. I'll re-examine the motor mounting this summer to see whether anything is being stressed by this design.

Here is the motor from the top. The side bolts have blue thread-lock applied, and are torqued to 80 foot-pounds. In addition, there are washers exactly filling the space between the forks and the cradle to reduce the torsion about the motor mount bushings:

After placing the front rack and batteries, I jumped up and down on the front bumper a couple of times to settle the springs, then took this picture. There are now roughly 4 inches of clearance between the motor and the front differential:

As I said at the beginning, this is not probably the very best motor mount - a torsion bar of some sort between the two forks would be very helpful, as would additional bolts between the forks and the cradle, but it will be adequate for now. I'll consider a rebuild this summer.

Sunday, February 8, 2009

Pumpkin Interference, V

Man, this motor mounting project has turned into a pain... This week, I finished the motor mount I had designed last week. I cut it, welded it, bolted it, painted it, and installed it on the motor. When I went to install the motor, the trouble started... but let's step back in time first. Here are the original parts, all primed pretty:

The bolts are torqued down to 25 foot-pounds per typical specs on Grade 8 hardened steel bolts. The primer is just rattle-can metal primer. The welds are there to keep everything aligned more than for structural purposes - the bolts themselves are plenty strong to hold everything together. The two longer parts I call the "cradle" since it cradles the motor feet. The two shorter parts are called the "forks" for obvious reasons (they go around the motor mounting bushing).

I finished painting the parts (rattle-can black) and mounted the cradle on the motor. The 3/8" bolts holding the cradle on were torqued to 45 foot-pounds, along with some blue threadlocker. Those guys won't come off unless I want them to. The forks are temporarily mounted for photogenic purposes. The handy thing about the cradle is that it provides a good place to loop chain or cable around for lifting with a hoist:

And here is where the trouble began. I'm not sure how, but I measured the distance between the two motor mount bushings incorrectly. I measured it at 19" - but it is really closer to 18.5". This means it is impossible to mount both forks at the same time. In this picture, you can see that I have mounted the passenger's side fork, but that the whole motor is pushed over toward the driver's side about one quarter to one half an inch:

Because of this skew, I could not install the driver's side fork. So, I put a temporary bolt on the driver's side just to support the motor while I went back to the drawing board (this is obviously only a temporary measure):

The good news is that there is sufficient clearance between the highest point on the motor mounting system and the bottom of the front battery rack (so at least I measured *something* correctly):

After much thinking, I came up with a new design. The issues were:

  • The current design is too wide
  • But I can not make the fork tines shorter while still using box tube because the main 1/2" bolt head will interfere with the motor mount bushing retainer
  • Additionally, the box tubing on the fork "tines" was too thick to easily get a nut onto the bolt that goes through the bushing
  • And, I'm not happy using threaded rod - I'd rather use a grade 8 hardened steel bolt thru the motor mount bushings, and those typically only come in 6" or less lengths (unless you special-order them).
I finally realized that I could do three main modifications to the fork design:
  • Replace the long box tubing with an angle iron
  • Shorten the tines by 3/4"
  • Cut the tines in half at the motor bushing bolt end to make more clearance for bolt heads etc.
So, I did it. Here is a rendering of what the completed motor mount will look like with the modified forks:

Here is an exploded view of both the driver's side cradle as well as the new driver's side fork:

And, I built and painted the new forks. Installation will have to happen some time this week or next weekend. I'm out of daylight...

You may find a PDF of the blueprints for the driver's side motor mount (both the cradle and the fork) here. Note that the passenger's side is a mirror image of the driver's side.

All this for a stupid front differential... if only I could have found a two-wheel-driver front axle and transmission...