Thursday, May 22, 2014

Battery box for second bike

The second bike is a longtail and although the frame is being stretched, several compromises were still necessary for fitting the battery inside the frame.  The goal was to place the battery low and in the center of the bike for better handling.

(Click on images to enlarge)
Preliminary measurements showed the battery was too wide to fit on the chain stays and needed to be above the chain.  However it looked like the rear rack could fit above it, and be used to hold the top of the box in place.

I was open to making the box out of sheet metal, fiberglass, thin plywood, or heat molding sheets of plastic, but since the battery was wide, I decided to use sheet metal.  The first design had sloped front and rear sides to match the seat tube and rear fender angles, but this interfered with the front derailleur, and because the side wall when laid out flat would have had a Z shape requiring more seams or material, it was simplified to plain vertical sides.  I also wanted to avoid any sharp square corners but did not wish to get into two axis compound curved panels, so I chose a simple vertically rounded front, and tapered the tail after the battery down to the width of the fender.  This gave the box a tear drop shape, which probably does not do much for aerodynamics because it is in a turbulent air flow area, but looks reasonably decent.

Going roughly left to right:
-Metal scrap bucket and magnet for cleaning area (people and animals walk barefoot here), snips, files, hammers
-Sheet metal from local hardware store.  The black paint on the stovepipe is a plus- besides preventing rusting it is good for writing on, and if you are careful will work as a primer too.  Stovepipe can be a bit thin for structural purposes, (this was 24 gauge, 0.022"), but if you use corners, folds, and curves in your design to stiffen panels it can be made to work.
-Cereal box template, top and bottom plates with bent lips on corners, and side wall with front curve started
-You will also note special tools #Maytag washer agitator counterweight, #Volvo transmission U joint flange, #Wide flange I beam chunk from construction job I was on, #Satellite dish (old style) azimuth mounting pole, #Digital Equipment Corp dot matrix printer bars (these things are solid!), that have taken years of experience to collect....  These are used mostly as mandrels, sometimes as long straight edges.

The basic box is styled after a NEMA 3R box, with an rolled flange around the top that overlaps the sides to keep water out, and a removable side cover that slips up underneath the top.  If water comes in the front edge I'll put a stick on gasket on the cover.  The bottom plate is 1/16 inch smaller than the top, (it will nest inside the top), to allow the sides to fit without distortion.

This is a trial assembly after the pieces were bent.  I rolled the edges of the opening to strengthen them and prevent sharp edges.  The bottom and side rolls are 5/16", but the top is 9/16" for a better lap over the side cover.

I do all my grinding and welding outdoors in the driveway for fire and fumes reasons.  If you get into doing this, don't mess around with the safety aspect.  It's possible to weld something like painted or plated metal (or we wouldn't have galvanized farm gates or road sign posts) and survive short term, but these coatings are neurotoxins and eventually you will wish your body worked a bit better.  It's better to prep and do the job correctly, and the welds will come out stronger too.  Basic safety equipment I use is glasses, ear muffs and gloves for grinding, and a face shield for welding.  A couple of things specific to this work is long sleeves and pants (both for sparks from grinding and the UV rays from welding), and work gloves for when you are handling sheet metal are a good idea.  I sliced the tip of one finger off on a sharp edge years ago. The simple enclosure of 4' x 8' sheets cut in half that I use is a great shield for containing grinding spray, preventing other people or animals from viewing the welding arc or torch (it can cause eye damage similar to looking at the sun), and blocking wind for either welding or painting, but still allows good ventilation and lighting.

The enclosure is held together by one hook and eye screw in each of the upper corners.

Since my gas torch would have severely warped the sheet metal, I used MIG welding, (I don't have a TIG setup).  If I was going to do a lot of boxes, I'd probably get a spot welder.  This photo is the bottom edge outside corner, you can see that I ran for only an inch at a time before rotating around the box to another section to let the metal cool down for minimizing warping.  When ground down this weld gave a nice smooth corner with no sharp sheet metal edge.

All the welding was done using solar power only.

After the box was finished I added sheet metal interior partitions for the battery, and module mounts with either studs or nuts welded in.  Because the space was tight, I dressed the welds and primed as I went along.  All of the edges are deburred, and most of them also have a rolled lip to prevent any possibility of an electrical wire getting cut. The battery partition lips were rolled around a wire to increase their stiffness.

The key switch hole (upper right in the previous picture) needed a flared lip on the curved front to hold the switch in place.  A 14 mm socket and 3/4" brass close nipple with a bolt up the center were a good press and die set with a minimal bearing surface width, so that it fit into the curved wall fairly well.

Normally I would not have painted the box at this stage because it will be scratched while the frame is being built around it, but I wanted to bring it to the Upper Valley Electric Vehicle Forum.  You can see the finished lip for the key hole in this picture.

Modules mounted inside the box:
-Upper left is the motor controller
-Lower left is the data logger
-Center is the battery (it will have 1/8" foam padding around it)
-Upper right is the key switch
-Middle right is the solar controller
-Lower right will be the DC to DC converter (in the wiring harness) for lighting 

The cover is not made yet, the frame is next as I want to be sure the pieces are fitting somewhat close to plans, and order new parts or change plans if necessary.  For example I wanted to check the leg to battery box clearance before going any further- I knew from building bicycle blenders this could be a problem.

My elementary school Principal Judy Callens and Town Manager Bob Stacey making smoothies during a national healthy eating week.  Originally I built these bike blenders for Transition Town Hartland, but they have proven to be incredibly popular and I've brought them around the Upper Valley for 10 to 12 other events each year for the last 5 years.  Kristin Gage of the Vermont Farm to School program has just done an amazing thing and convinced the Randolph tech school to build 4 more, which are now being used in 3 school systems as part of an approved agricultural curriculum.

The second bike blender has a rear platform cut from plywood, and I had to deeply scallop the front edges to prevent them from hitting the rider's thighs.  Before going further on the longtail frame, I wanted to be sure the battery box didn't have this problem.

I cut the rear triangle off the donor bike and made a wood stand to hold the pieces in the correct locations.  After clamping it together I got on and pedaled- there was 3-4 inches of clearance to thighs, and 1.5-2 inches of clearance to heels, which is good to go.

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