Different purpose for motor

Hi everybody,

I am completely new to the world of e-bikes, so bare with me. I've done a fair amount of research online but I was looking for ideas on a slightly different type of "e-bike".

As part of a capstone project, I'm trying to harness power via regenerative braking to power external devices such as a speedometer. This isn't like your everyday e-bike because I will NOT be using the motor to generate any sort of electric assist for the bicycle. All the energy captured via regenerative braking will be stored to power small, external devices. I have access to the front wheel on the bicycle.

From what I've read, it seems like only direct drive hub motors provide the opportunity to harness energy via regenerative braking at the expense of having the motor always engaged (causing some drag). As this project is an experiment, I'm not too worried about the drag.

My best guess at the moment to tackle this would be a small front direct drive hub motor w/ a controller that is somehow only activated via a brake toggle (programmed via controller??) that can generate power from the biker's momentum and relay that to a battery pack. I don't have the specs on the external devices yet but you can go ahead and assume that I will have to have some external circuitry to regulate the voltage supplied from the battery pack to the external devices.

My questions are:

- Is my thought process on the right track? If not, why not?
- How would you tackle this yourself?
- Do you have any recommendations for motors/controllers for powering smaller electronics?
- Any recommendations for a battery pack? I'm okay if the device dies ever so often (power generated through braking depends on path traversed)

Thanks for all the help!

A capstone project is a large project that is meant to be the final piece of an undergraduate degree. It will usually require a great deal of research and effort, and is supervised by a professor or teacher.

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You can use a geared hub motor if you modify it to defeat the internal freewheel. That would give you more small motor choices.

sure you can use a motor to do that. but it is a huge energy waste using a large motor to do the work a small bicycle hub dynamo can do. Shimano and SRAM both make ones that output 6V AC @1.5W. pedaling a 300W or larger motor takes a lot more effort than a 1.5W dynamo. even without a load the 300W motor has a lot of mass to move. I'm out of breath just thinking about it.

the output of the dynamo could be fed to a rectifier, to produce DC, filtered by a couple of super caps and used to charge a small Li-Ion battery to power lights.

if 6V is not high enough the rectifier could be replaced with a voltage doubler to produce 12V before the super cap/battery storage unit.

by using a small amount of energy to constantly charge a battery, the power unit can be small. the energy stored in the batteries can be quite large.

i see no reason why not use both a small hub dynamo in the front wheel to charge a battery and run small devices and keep the motor drive separate.

on my trike i use a dynamo to charge a 4 cell LiFePO4 pack to power the NuVinci Dev Kit automatic shifting system. it also has a couple of USB charge ports for my cellphone, GPS and some instruments. I do charge the 12V system at the same time that i charge my main pack, the dynamo keeps it almost fully charged at all times. this way i can be sure that my auto shift still works even if my main pack or motor drive is down.

rick

gogo said:

A capstone project is a large project that is meant to be the final piece of an undergraduate degree. It will usually require a great deal of research and effort, and is supervised by a professor or teacher.

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I'm completely aware of this. I started my capstone project last spring and was supposed to complete it this fall/winter with my team. However, I landed an internship I couldn't turn down and am struggling to focus all my energy to the project after 12 hour workdays. I sincerely appreciate all the help.

Rick, that does sound like a more plausible idea. I was thinking of dynamos initially but wasn't aware that they could produce power outputs as you mentioned. I'll look into this asap.

Thanks again, I appreciate it.

to really impress with techie mumbo jumbo, how about proposing a dynamo that uses eddy currents at the rim an has absolutely no physical contact with the wheel.

Magnic produces such a light.

http://www.magniclight.com/MagnicLight/index.php/en/startseite

this video may be in German but it does explain how it works:
[youtube]2JsNxOX34cE[/youtube]

and a copy of the "Concept" filing. a concept is registering the idea before the actual patent. but i think there is sufficient prior art in numerous other gadgets like the "LED Shower Head" gadgets that work on the same principal to make an actual patent impossible.

http://worldwide.espacenet.com/publ...cale=en_EP&CC=DE&NR=202011107060U1&KC=U1&ND=9

rick

I saw the kickstarter! It looks really fascinating. Is there a version in English?

Is a dynamo hub always engaged? Or could it be used only when the brakes are applied via some sort of toggle?

mechanically it is always engaged. but electrically the power can be turned on and off. switched off, there is very little drag. but when switched on the dynamo is doing work so it needs energy put in. the higher the electrical load, the higher the mechanical load as well. with a small alternator/dynamo the mechanical drag alone is negligible, so a clutch is nice but not really needed.

with the eddy current dynamo, since there is no mechanical connection, when turned off the drag introduced would be miniscule.

rick