Compact Tandem v2.6

[fitek]

I've shown off the previous version of this bike at a couple of shows (Maker Faire and Google I/O Conference) and.

It has three problems that bug me:
1) with a passenger on the back, there is a wobble in the steering at low speed, probably because the passenger's CG is at or behind the rear axle (my hypothesis)
2) the front boom is too high and its not comfortable to kick my leg over
3) the Kollmorgen chain drive gets loose over time and the chain gets slack, noisy, then falls off. I have to carry tools for whenever this happens.


So... to address each issue:
1) remove the original rear stays and replace with ones extended by 10 inches, these will also be parallel to each other in the plane of the frame for easier mounting of the Kollmorgen
2) cut off the boom and relocate it several inches downwards, possibly put a bend in the middle to give me clearance for mounting
3) for now I'm replacing the motor with a Bafang, later on I will have a new motor mounting plate and hardware made from aluminum

Also I wanted to make the bike look more stylish. I had lost interest in a Schwinn rebuild project so I decided to steal parts from the 60s Schwinn.

Attached is the before picture.

 

[fitek]

I was trying to get the bike ready by the Palo Alto EV Rally this past Saturday, but due to work commitments I didn't even get a chance to get started until Friday night, and I was really tired.

I didn't have time to do things terribly well, so I just ran over to Home Depot about 8:30 and grabbed some 3/4" and 1/2" EMT tubing. I cut the 3/4" EMT to 22" length for the chain stays (original was 14") and bend it in a EMT bender. I cut slots in the ends of the pipes and brazed on some horizontal drop outs I made from thick steel plate.

Maybe due to the late hour, maybe due to my rush, I was a bit sloppy with the mitering of the tubes and took off too much material on the left hand chain stay.

I just slapped a lot of filler on to make it stay.

The 1/2" EMT for the seat stays I eyeballed and bent. My chop saw couldn't cut the 60 degree or so angle into the wheel end of the seat stay so I had to use a reciprocating saw. Worked out better than the chain stays.

Without a proper jig welding this up was a PITA, I used some clamps and scrap tubing.

Saturday morning I went out to the garage about 7am and man it was scorching hot already. I had to convert my battery pack to 72v configuration to use with my one unused ecrazyman controller. I heard it was wise to use a metal gear, so I'd have to open up the motor and swap in a metal gear.

Well by the time I had the motor open and in the vise it was 9am, 1 hour to the show, I was sweating like crazy and could not get the damn clip holding the gear in place out. I had to get my significant other to hold one part of the C clip with a chisel while I poked away at the other end with needle nose pliers. It finally came off after half an hour and I swapped in the other gear.

10am rolled around and I was ready to crash so I totally bailed on the show.

I thought it was nice that the bafang and ecrazyman wiring is color coded the same, but actually hooking it up via colors didn't work. I swapped the phase wires randomly till I found a combo that worked.

Then I went for a test drive.

Wow, the bike is much faster than at 36v. It is a bit noisier than the Kollmorgen (when the chain was setup right). I'll take it though!

On Sunday I threw on the white wall tires and fenders from the Schwinn.

Trying to think of other ways to get the 50s-60s vibe. I looked through photos of 57 Chevys and other stuff and it seems like way more chrome and a set of wings are the way to go. Also thinking of asking my friend with a CNC to machine some new plastic cargo boxes with writing in a font like Sandoval cut into them.

Woot