Sociable Tadpole for 2 (legal bicycle)

[jmygann]

Goal ....... sustain 2 people(sitting side by side) ... 35mph on the flat with 48 Volts - min pedaling .. I know the legal speed is 20mph and the legal assist is 1000 watts (or maybe 2000 watts for 2 ?)

Thinking ...... SRAM dual drive rear hub ... gives three motor gears ... with front derail er gives 9 pedaling gears ??

Main issue .... will I break the SRAM

OR

Can I have a controller restricting the torque/amps to keep it from breaking ??

How many electrical horsepower needed ?

Prefer to stay with 48 volts because of my solar system

KMX or Maybe this frame ...http://www.terratrike.com/rover.php

 

[amberwolf]

If you can use the SRAM not as a rear hub but as a jackshaft right off the motor, before the reduction (if you use a fast motor that needs one), then it will see less torque (but higher speed, possibly requiring more or different lubrication).

Additionally, if you place a coupler with shock-loading-absorber between the motor and SRAM, or SRAM and wheel, it'll take the hit isntead of the teeth. If you have ever seen the coupler on a washing machine motor to it's gearbox, it'd be like that. See this post:
http://www.endless-sphere.com/forums/viewtopic.php?p=268579#p268579
for pics of one possible version of such a coupler (although I'd make it out of metal, not plastic, for the shaft-finger pieces).

 

[jmygann]

Too complicated

I feel better to do this ...http://tinyurl.com/2fljj79

 

[amberwolf]

Well, there are tradeoffs for everything. Sometimes making something less stressed may require a more complicated system of applying power thru it.

Since the large chainring is going to give the chain even more torque on that SRAM as a wheel hub, it's going to have more stress on it at startups than it would if the SRAM were farther forward in the driveline (not in the wheel). Depending on the power levels you'll be putting thru it, it might not be an issue, but remember that it has to move more weight than usual (probably double that of a single-rider bicycle) when on a two-person trike, so the system as a whole must provide even more startup torque than normal. That generally means more stress on the SRAM gearing inside, so you'd probably have to run even less power thru it from the motor at startups from a stop, only gradually feeding it in as the system ramps up.

Now, if you were to at least use something like that shock-absorbing coupler at the motor end of the chainline, it would probably help with the shock loading of the SRAM's gears' teeth in such situations, and maybe prevent problems even with higher power levels.

I guess you can first build it without the coupler, and if it doesn't break anything you're ok. If it does, then replace the SRAM with a new one, and then try it with the coupler, and see if it fixes the problem.