The frame design was driven by my desire to avoid welding. It would also have to accomplish three things: replace the stressed members that were removed from the frame, serve as a mounting plate for the motor, and provide a means of securely mounting the battery stacks.
First, I inserted a piece of cardboard in the frame in the location where the left metal plate would go.
I marked the locations of the attachment points: three at the lower aft end, one mid-way up, and one on the front downtube. I also drew a horizontal line on the cardboard for reference.
After removing the cardboard, I drew a vertical line on the cardboard to create a reference system for measurements. Then I measured the locations of all the attachment points vertically and horizontally. I drew in the frame, using dimensions that would fit the battery stacks. I plotted the location of the center of the motor shaft by referencing the photo I had taken earlier, but I raised the shaft about 3/8 inch to ensure the motor body would fit. Witness marks from the chain on the top of the swingarm pivot told me that raising the shaft might be a good idea anyway. Using the motor dimensions from the manufacturer’s drawing, I drew in the motor body circumference.
I confirmed that the motor body would not interfere with the existing frame, then drew in the motor bolt hole locations and an inner and outer ring to define the motor mount.
The cardboard with the frame drawing looked like this:
I transferred the drawing into a program called Inkscape, a freeware vector graphics program. The program loaded easily and a 20-minute tutorial video was enough to get me started.
After I finished the left plate, I modified it to make the right plate. The right plate was simpler because it did not include the motor mount, but it had to clear the motor body by a fraction of an inch. The motor only required four bolts on one plate to mount securely, so no bracing was required on the right side.
The completed frame design looked like this:
To ensure the shelf bolt holes would end up in the right place, I set aside the frame design until I designed, ordered, and bent the tabs on the battery shelves. This allowed me to measure the actual displacement of the shelf attachment holes after bending, in order to get the precise location for the shelf bolt holes in the frame plates.
I designed the battery shelves by measuring the battery modules and the holes in the corners. The shelves would sandwich the battery stacks with bolts through the corners of the modules to keep them from shifting around.
The completed shelf design looked like this:
Notice that I added a spare battery shelf with tabs in both directions, so I could practice bending on it before I bent the actual shelf tabs. Also, since I happened to need a few more 1/8 inch-thick items, I added to the order four spacers that I needed to take up space in the lower frame, and two battery module spacers to match the Leaf OEM battery spacers (I needed one more pair). I also added eight small pieces that I would bolt together as a bend radius guide.
I ordered the shelves and accessories in 5052 aluminum 1/8 inch sheet. 5052 series is strong but bendable. I was concerned about breaking the tabs, so I designed in enough bend radius for the thickness and type of metal. There are plenty of online sources with minimum radius guidance for cold bending.
I uploaded the design to Big Blue Saw, which has a great website for providing instant cost estimates for many types of materials.
They also have a plug-in for Inkscape that exports a file they can use for waterjet cutting. Their website describes everything you need to know about designing and uploading a good file, and it fully describes the limitations of waterjet cutting. I purchased the parts, specifying the direction of the ‘grain’ of the aluminum to ensure my tabs would be bent across the grain.
The result was exactly what I was looking for. Here are the shelves as well as the other 1/8 inch pieces:
Before bending the tabs, I bolted together the pieces to make the bend radius guide. The bend radius guide is designed with corners of 2, 4, 6, and 8 mm radius. I designed the tabs for a 6 mm bend radius since the minimum recommended for 1/8 inch 5052 aluminum is around 5 mm.
I clamped the shelves in a vise with the bend radius guide at the right place to create the bend in the tabs.
I bent the tabs by tapping a wooden stick with a hammer until the tab was bent 90 degrees.
The relief cutout of the tab and the bend radius guide helped to ensure the bend occurred in the right place. Note that the bend is perpendicular to the grain of the metal (you can barely see it in the picture). This makes it less likely to break.
Using nuts and washers as spacers, I extended the width of the bend radius guide before bending the fourth (uppermost) shelf, because it had larger tabs.
Bending the tabs on the upper shelf was also very easy.
After the shelf tabs were bent, I measured the distance of the tab bolt holes on the three lower shelves, and used this measurement to ensure the bolt holes would be cut in the right place in the frame plates. Then I ordered the frame plates in 3/8 inch 6061 aluminum plate, which has excellent strength.
Finally, I ordered two pieces of rectangular 6061 aluminum tube. The tubes would be sandwiched between the frame plates to add strength and remove flex. The lower piece was 2×3 inches, 1/4 inch thick, and 18 inches long. The upper piece was 1.5×3 inches, 3/16 inches thick, and 12 inches long. Both pieces were cut to size with an angle grinder, and the holes were drilled using the frame plates as templates.
A drill press would have been nice for this job, but I only had hand tools, so I did the best I could.
At that point, there was nothing left to do but to put the motorcycle together. That’s when the project really got fun!
Next: Assemble the Frame