Drive System

I took my foot shells and a few other parts off to the powdercoater so I thought it would be fun to work on the drive system while I wait.  This shows the parts I needed to build one foot's drive system.  I am using the Senna frame design but modified it slightly.  The side frames have larger (1 1/8") bearing holes as I am using ball bearings instead of bushings.  I also made the motor mount brackets 2 3/4" wide instead of 3" so they are reversible and fit easier in the foot.  The #35 gears and chain came from surpluscenter.com

This top view shows the 1/2" keyed shaft going through the frame/bearings.  The spacers are AN 960-816 aircraft washers.  Shown on the left is 1 AN 960-816L washer (which is the thin version) to keep the gear from hitting the bearing housing.  On the right I used 3 AN960-816 washers to keep the chain from hitting the bearing housing.

Here is the motor mount bracket mounted with 2 bolts just to get everything fitted up.  I used AN4-6A bolts with a AN960-416L (thin) washer on the outside and a AN960-416 washer and AN365-428 locknut on the inside.  This way everything fits fine and no bolts need to be cut.  The aircraft hardware is far superior to anything else you can use, comes in many more sizes and is dirt cheap compared to the hardware store stuff.  I buy it online from Aircraft Spruce & Specialty.

This shows the gears and shafts all mounted up.  I used a flanged bronze bushing in the center idler gear.  I looked into ball bearings but I felt the small size would not hold up to the loads, plus getting them to stay in the gear was a problem.  I used 2 AN960-816 and 1 AN960-816L washer under this gear for a spacer.  The idler shaft is a 1" piece cut off the motor shaft.

Top view of the frame showing all the gears, collars and spacer washers.

#35 chain fitted to the gears.  I never fitted chain before and finally found a chain breaker at Harbor Freight that worked well.  Also I wound up using 4 of the offset chain links instead of the standard type to get the chain the correct length.

Finished drive systems.  I ran them for a bit with a 12v battery and they work just great - I am really pleased.  Super thanks to Mike Senna for a great design.  I can hardly wait to get my feet back to try this out.

This is a bottom view of the finished frame.  To mount it to my metal foot I will use AN4-6A bolts with an AN960-416L under the bold head (ouside the foot) and a large AN970-4 washer inside the foot shell.  The AN970-4 washer really distributes the load and should keep the frame very solid.  This bolt setup has a tensile strengh of 125,000 psi so two on each frame will be plenty!!  When I wrote this the bolts cost only 14 cents each.  Also the fine thread bolts just never loosen up under use - important in the drive system.