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-   -   Dynamo Hub to power Solenoid Actuator Clutch (http://www.diychatroom.com/f18/dynamo-hub-power-solenoid-actuator-clutch-154306/)

RookieAtThis 08-20-2012 04:05 PM

Dynamo Hub to power Solenoid Actuator Clutch
 
I'm designing a clutch for a pedal bicycle that will be engaged by the actuation of a solenoid linear actuator. The actuator is to recieve its power from a battery pack charged by one or two Dynamo hubs as the rider pedals.

My question, being a mechanical engineer, is what advice or comments would the electrical world have in terms of obstacles I may run into on such a project.

Thanks.

curiousB 08-20-2012 04:35 PM

Quote:

Originally Posted by RookieAtThis (Post 992854)
I'm designing a clutch for a pedal bicycle that will be engaged by the actuation of a solenoid linear actuator. The actuator is to recieve its power from a battery pack charged by one or two Dynamo hubs as the rider pedals.

My question, being a mechanical engineer, is what advice or comments would the electrical world have in terms of obstacles I may run into on such a project.

Thanks.


Be careful sizing the dynamo's. If you oversize them you'll put significant mechanical drag on the bicycle and make the rider waste a lot of energy just to charge a battery. Also the charging scheme for the battery is also of concern for the same reason.

You don't mention the travel distance required for the actuator to engage or disengage the clutch. A regular plunger solenoid will have limited travel and have high peak current. This is why automotive electric door locks don't actually use a solenoid, they use a gear reduced motor to drive up and down the lock mechanism, lower peak current, higher torque. Similarly dishwashers don't use solenoids to open up the soap dispensers. Instead they use wax motors which is a piston filled with wax. The wax is heated with a resistor and after a few seconds to minutes the wax softens and greatly expands in volume to provide a very strong piston force even with low power input. Both of these schemes achieve higher mechanical power with reduced peak power. They do it by spreading the energy across time, think of the area under the curve.

Oso954 08-20-2012 05:02 PM

What is the rest of the story ?
Clutches generally are not needed on pedal bicycles. Coaster gear hubs and coaster brake hubs work quite well. You don't need an electrical clutch, unless you are doing something quite different.

RookieAtThis 08-20-2012 05:26 PM

Great point Curious. I would like to be able attain reasonable torque maintained for a few seconds to keep the synchro/gear mating surfaces against the higher ratio stack until the lock engages, holdig it in place until the rider presses the unlock linkage level. The rest of the story is that the gearbox will allow the bike to achieve highway speeds with a single external chain.

curiousB 08-21-2012 08:32 AM

Quote:

Originally Posted by RookieAtThis (Post 992919)
The rest of the story is that the gearbox will allow the bike to achieve highway speeds with a single external chain.

At higher speeds doesn't the wind drag and mechanical losses of the rider/bike becomes larger than the energy the rider can deliver, even Lance Armstrong. If this weren't true then simply putting in high ratio gears would allow anyone to ride very fast....

It seems electrically actuating a clutch is the least of your concerns.

RookieAtThis 08-21-2012 09:04 AM

You're very right again, however speeds of 80-100km/h are nothing new on a bicycle. Any off the shelf bicycle can reach 60km/h down a 15 degree grade, the only question then becomes: are your off the shelf quick release axle pins under enough tension.

curiousB 08-21-2012 09:15 AM

Quote:

Originally Posted by RookieAtThis (Post 993327)
You're very right again, however speeds of 80-100km/h are nothing new on a bicycle. Any off the shelf bicycle can reach 60km/h down a 15 degree grade, the only question then becomes: are your off the shelf quick release axle pins under enough tension.


I think I'll stick to walking. Sounds safer... :laughing:

BShow 08-22-2012 10:53 AM

Quote:

Originally Posted by RookieAtThis (Post 993327)
You're very right again, however speeds of 80-100km/h are nothing new on a bicycle. Any off the shelf bicycle can reach 60km/h down a 15 degree grade, the only question then becomes: are your off the shelf quick release axle pins under enough tension.

I don't really have much to add here, but I am curious about your project. So you are planning to use the hubs to generate a charge for the battery and then the battery will drive an electric motor that will assist the rider like a pedal moped? It'll be interesting to see if you can produce enough power to sustain the speeds you're looking for. The gearing is there on your run of the mill road bike, it's just that most riders lack the power to get to those speeds - let alone sustain it.

Don't neglect the brakes... If you're able to achieve these speeds on the flats, you'll need a way to reliably stop you from 80-100km/h repeatedly. Heat will be an issue with normal bicycle hydraulic brakes and is a hurdle with regard to the current push for disc brakes on road bikes.


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