# Powering electromagnets with bicycle power

## Main Question or Discussion Point

Would it be possible to operate an electromagnet using the power produced by pedaling a bicycle? The electromagnet would need to be strong enough to lift up the training wheels of a bicycle.

## Answers and Replies

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SteamKing
Staff Emeritus
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Would it be possible to operate an electromagnet using the power produced by pedaling a bicycle? The electromagnet would need to be strong enough to lift up the training wheels of a bicycle.
Would you by chance be trying to see if you could make a self-levitating bicycle using these electromagnets?

mfb
Mentor
Lift up in which way? You can certainly make something like a human-powered elevator. Just don't expect it to be fast.

CWatters
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What do you mean by "lift"?

Google can find a 6V 1A electromagnet that can "lift" 40lb. What they mean is it consumes 6W just suspending 40lb of weight at a constant height. If you want to raise the magnet (and whatever is attached to it) vertically at some speed then you have to add more power. Exactly how much will depend on the weight and the vertical velocity you want.

Humans can generate 200-250W reasonably easily. Trained cyclists perhaps double that for quite long periods.

Basically, I want the pedal power to be able to lift up training wheels as the bicyclist pedals faster. And then, they will come down when the bicyclist moves slower.

russ_watters
Mentor
That's clever. Certainly, it could be done. I think the bigger problem would be making the transition between functional and non-functional, since if you are lifting the wheels off the ground, nothing is pushing them down to make them keep the bike upright. I think you'd need a locking mechanism that disengaged above a certain speed.

Wouldn't the person cycling be able to keep the bike upright? The four wheeled bike would just turn into a regular 2 wheeled one.
Why would you need a locking mechanism?

CWatters
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I think he means they need to be locked when down.

CWatters
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Gold Member
Rather than lift the wheels why not allow them to remain down all the time but lock/unlock a hinge so that they do/don't provide support?

For example the wheel on one side could be connected to the other via a hydraulic pipe and two pistons (like a shock absorber or gas strut). Put a valve in the middle of the pipe. With the valve open the bike can lean from side to side as hydraulic fluid would pass back and forth through the valve. With the valve closed the training wheels would be locked in position.

Wouldn't the person cycling be able to keep the bike upright? The four wheeled bike would just turn into a regular 2 wheeled one.
Why would you need a locking mechanism?
If the training wheels aren't held rigidly in place when you want to use them they won't hold the bike upright when weight is placed on them.

Also: If the rider can keep the bike upright, why would they need training wheels or your mechanism?

I'm not sure why you want to engineer this system. Normal training wheels are mounted to be off the ground somewhat anyway, and only come into play if the bike leans too much. Their function is to prevent completely falling over if the rider loses balance. Otherwise, the rider should be balancing the bike most of the time. I think the goal is to rely on them as little as possible.

Oh I see, yeah a locking mechanism would be necessary then.
The point is to specifically use electromagnets, so that's why I'm using them.

Oh I see, yeah a locking mechanism would be necessary then.
The point is to specifically use electromagnets, so that's why I'm using them.
So, it's just an assignment requiring you to use electromagnets in some gizmo. This isn't some invention you think will revolutionize training wheels.

It's not an assignment. But rather an invention I want to try.

It's not an assignment. But rather an invention I want to try.
OK. I don't get the point, but it's perfectly possible to raise the training wheels with electricity generated by the rider. You can reduce the power needed to almost nothing by counterweighing the training wheels. That is: the wheels would pivot forward or backward and they'd be balanced by a counterweight so a very small amount of force would move them. You should be able to generate electricity by mounting a generator that contacts the side of either the front or rear main tires, just like the old school bicycle headlight generators. The faster the rider goes, the more watts they put out.

russ_watters
Mentor
What are the constraints here? If it isn't an assignment, what qualifies as an "electromagnet"? A solenoid/linear actuator? Servomotor? Or just a nail with a bunch of wire wrapped around it?

I haven't ever used electromagnets before, so I wanted to try them out. I guess it would be something like a metal rod with wire around it? Or just something that can attract metallic objects from far away.

I haven't ever used electromagnets before, so I wanted to try them out. I guess it would be something like a metal rod with wire around it? Or just something that can attract metallic objects from far away.
If you don't have any practical experience with making electromagnets yourself I suggest you put the invention on hold, step back, and simply play with making a variety of them in various configurations. Start with wire wrapped on a nail like Russ mentioned.

Your "metal rod" has to be a ferrous metal, of course. Aluminum or copper wouldn't work. And the wire has to be insulated copper wire. You can't use uninsulated steel wire, such as is made for picture hanging or bicycle brakes. Steel has too much resistance and will result in dangerous heat. And insulation is required so that each turn around the core doesn't short to the other turns or to the core itself. Uninsulated copper or aluminum (or any conductor) wire would just short out.

This is the wire you want:

Rule of thumb: if your ferrous core is x in diameter, wrap enough layers of the insulated wire such that the final outside diameter of the electromagnet is 3x. Less than that and you're not taking full advantage of your core. More than that and you get diminishing returns. All other things being optimal, your core will be saturated.

Use wire that is thin enough that you have to wrap at least 4 layers to get your 3x outside diameter. Fewer layers and the inductor may not have enough resistance to prevent undue battery drain. It could get hot enough to burn your hand just from all the amperage going through it. I'm told the battery, itself, can heat up and burst if there's not enough resistance in the circuit. For safety's sake, start with AAA batteries. If there's no problem with your test, move up to AA. If all's well, move up to D cells. They're all the same voltage, but you can draw greater amperage from the larger sizes and the strength of the magnetic field is partly dependent on the amperage the inductor draws. Conversely, don't use wire that is so thin you have to wrap a gazillion layers to make your 3x O.D. That's just a waste of time.

It would be a good idea to get, or rig up, a switch that is only closed when you're physically pressing on it, that will open the circuit by itself when you release your pressure. That's another way to prevent battery drain and overheating.

Wow, thank you so much. That's very great advice.

Wow, thank you so much. That's very great advice.
Aright, then. Go make some electromagnets.

Basically, I want the pedal power to be able to lift up training wheels as the bicyclist pedals faster. And then, they will come down when the bicyclist moves slower.
This sounds like trying to help a child learn to ride a bike. Give them a two wheeled scooter to ride for a while. They can step off of it to either side easier than with a bicycle. It will help them learn the concept of steering the scooter/bicycle beneath them to maintain balance. After riding the scooter for a while, my daughter was able to hop on the bike and just ride off.