Birdy Pedelec Design: Request for ideas

[essexman]

Hi,

I was looking at the extra energy tests and saw the Birdy bionix again. I note its gets a good review and in concept is not too disimilar to the nano brompton (a true star apparently). The obvious flaw in the birdy design is that some fool put the battery on top of the handlebars. Why not the front rack? Beyond me.., thats where i'd put it. It got me thinking, my birdy is still a great bike, but it would be nice if it had hill climb assist, and maybe a boost on the flat. Maybe i could fit retro fit a motor to give me that.

Anyway what i'd want is a light motor and battery. I dont need long range say 15 miles tops. I'd like it to give me some assist on hills and some push on the flat at speeds of 12+mph. So a compromise hub motor probably ideal. Suggestions anyone?

• System?
• Front or rear wheel mounted?
• Small battery ideas?

I have the 24 speed birdy, so i guess i can lose some gears.

PS I'm no mechanic, but i have a plethora of cambridge bike shops that could do a wheel rebuild for me.

 

[jac]

why not try cytronix to see if they will sell you water bottle battery as that might fit somewhere

jim

 

[flecc]

The Tongxin Nano motor immediately springs to mind as it's very light and economical.

However, on the Birdy there's question marks:

How will those cantilever front forks behave with the motor weight and drive in there.

Will the fork opening be wide enough.

The rear Nano motor option is available, but that would mean an extensive loss of gears. If the fork opening could be made wide enough, at least 135mm to 140mm, a Nano with a seven speed freewheel would fit, and that could have a 291% range with sprockets of 11 to 32 teeth, but no 9 tooth option for a really high gear.
.

 

[essexman]

thanks Flecc. I'll get me tape measure out.

As to those cantilever forks.... well what can you do. The birdy is a superb folding bike (superior to the brommie in all the ways that counted to me) with a great big dumb set of forks. I'm sure there must be a way of supressing them, but i havent quite worked it out.

 

[flecc]

They are funny old things those forks, some love them, some absolutely detest them. In this instance I'm worried about how they might behave when a motor starts pulling forward in the forks. It might be ok, or the forks may extend and lift the handlebars each time you accelerate.
.