Thursday, October 29, 2009

Fun with Paper & Glue - Upper Tray Begins

(Editorial note: this entry is for the absolute beginner and my documentation.  Experienced EV builders can skip this one)

In working with the sheet metal pieces, I've developed a system of modeling and checking fit without having to cut metal.  It's pretty common in the EV world to do Cardboard Mockups, but here's my take on it for sheet metal.
Model the sheet metal part

Print a full scale version of the flattened 3D model. In this view the flattened model has the bend lines and some additional construction lines to indicate where the curved surfaces will start, since I'm creating sharp creases, rather than gradual bends like the the actual part.

 Use spray adhesive to adhere the Print to some Posterboard and and trim the outer shape.  It's important to let the glue dry overnight while laying flat. When dry, use a straightedge to make straight creases along the fold lines.

Using the Posterboard model, I can get a feel for how things look and fit.  Obviously, it's a lot easier to make adjustments in paper.  This is the 4th verision of this particular paper part, and I'm finally ready to cut the real thing in 3/16 Aluminum sheet (5052 alloy).

Sunday, October 18, 2009

Mounting the Shield

Finally got around to mounting the Shield.  I had planned to use the original motor mounts and have the bolts thread from the outside to the threaded bosses on the interior of the frame.  Problem is that the threads are lined up horizontally, and the surface I'm fastening is about 12 degrees offset.

I had to make a decisions to backtrack on the purely "bolt in" philosophy, but I figure anyone converting thier bike should have a drill and a grinder. I ground the motor mount bosses down close to the frame, but not too close as to remove all the welded material.  Then I clamped the shield into place and drilled holes slightly bigger than the existing threads (5/16"). The holes are perpendicular to the frame surface, positioned so the drill reamed out the threads at the new angle.

I then clamped the Tray to the Shield, drilled four holes, and threw in some 1/4" grade 8 bolts.  Eventually, I will probably use some stainless button head screws but, for now I like the looks of the gold colored grade 8 hardware.

Wednesday, October 7, 2009

Lower Battery Shield

My earlier misfortune with the plasma cutter turns out to be a blessing in disguise.  I had second thoughs about having relief holes on the frontward facing piece of the battery tray, because I would like it to protect the batteries from road debris and water.  This functionality prompted me dub the piece: "Shield".  I decided that using 1/8" sheet instead of 3/16" was accepble for the Shield, beacuse it's not really expsosed to direct flexing loads like the Tray. Even the 3/16" might have been overkill on the Tray, it's overly stout.

The  end result looks pretty decent, and even though it's 1/8" thick, seems plenty strong.  In hind sight, I would have liked the mating tabs between the Shield and the Tray to overlap a little bit more, but it's certainly functional.

I had intended to bend the top tab over at 45ยบ, but I kind of like how it fits between the old oil-cooler mounts. The two piece design of the lower battery support system allows me to remove the Shield in order to load the batteries or perform maintenaince.  Now to drill some holes to mount it to the frame and the tray.