Suspension and Drivetrain

We cut out a large steel frame for the table top.  This will be a weight bearing aspect of the frame, so we used our beefy stuff.  We welded up a nice rectangle a few inches smaller than what our table will be and put it on top of our wooden jigs.  We just needed to attach tubes from the lower frame to hold it up.  But, rather than going with 4 straight tubes, we decided to utilize our cheapo tube roller from Harbor Freight to put some beautiful curves in the steel.  This gives us a few perks: it increases the room for our knees under the table, the curved lines hide flaws in our precision alignment, and it just looks fantastic!

Next we welded in some brackets for our riding lawnmower transmission and differential.  A few notes about this thing…  It was hooked up to internal combustion engine, meaning that it’s expecting an input in the range of 500-1000 RPM at least.  We surely can’t pedal that fast.  The gears inside of it step down the RPMs quite dramatically.  Low gear is 1:64 and high gear is 1:16.  To get a decent speed we had to step up the gear ratios of the rest of our drivetrain.  From pedal crank to cassette, from cassette to driveshaft, from output shaft to wheels, all are stepping up the speed.  I plugged all of the numbers into a spreadsheet and arrived at some decent numbers for us to use.  If each person is pedaling at 60 RPM the bike should be moving at ~2 mph in low gear and ~8 mph in high gear.  That seems about the right speed for a banquet table.

The differential built into the transmission (is it called a transaxle?) allows for the rear wheels to turn at different rates.  This will allow us to turn much more easily than if we had a solid axle.  We’ve also got a built in reverse, so we’ll be able to comfortably parallel park.

Next we had to start installing the suspension so we could actually have this thing sit on it’s own 4 wheels.  I appropriated a trailer spring built to hold up a 2000lb trailer.  This is only one of the pair of springs, so it’ll hold the 1000 lbs we’ll put on top of it.  The ends of the leaf spring will pull down on the wheels, all of the weight will be transferred through the spring.  Hopefully this will result in a comfortable and smooth ride for the passengers and their delicate meals.  The wheels will be pivoting on the axles of the transaxle so the chain connecting them will never lose tension.

We once again decided to utilize our tube roller to get some great looking curves.  We had to have clearance for our rear pilot’s pedals, of course.  We’ll finish it by attaching some more curved tubes that come down from higher up.  This will result in a strong geometry and almost a roll cage around our rear pilot.  He’ll have to do some climbing to get into the bike, but he should be the most limber and alert rider on the table anyway.

We’ve got a lot more work to do, but we’re definitely making progress.  We’ve got 5 weekends before the Pasadena Doo Dah Parade, so we need to hustle!