OT: Small diameter magnetic roller between wheels to provide frictionless braking resistance?

DC injection brakes apply DC to the windings of an AC induction motor

Hysteresis or eddy current brake

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Consider the concept of conservation of energy. You have to do something with the energy that is gained by going down hill, right?

Dynamic or regenerative braking.

Electric forklifts use the generated current of the drive motor to stop a coasting truck before reversing direction without use of the brakes. This is known as "plugging" the truck. Motor becomes a DC generator when coasting.

Some manufacturers of electric trucks use this force to enhance the braking system to the point that brake shoes wear for extreem extended times between replacement of the shoes. The brake pedal reacts as if it has power brakes, when in reality this is an electrical adjustment to increase or decrease the amount of (regenerative) braking as the pedal is being pressed.

Eddy-current braking would be interesting, but I don't know if the speeds/forces would work out. It would involve an electromagnet or a permanent magnet in proximity to a spinning aluminum or copper disc or cup. But I suspect the braking force might be small, given the speeds and geometry.

John

Check out stepper motors. Spun around and they are alternators. Very cheap and easy when you just need an amp or two.

I played with a few to make cheap alternators for some engines (where one needs 24 V DC and only has a rotating shaft)

The downside is they "cog" (slight "friction or detent" from one pole to the next). A skate rider probably wouldn't notice it. Twist it by hand and you would definitely notice it - very hard to turn with a shorted winding.

Apply a short to the wheels connected to the windings (via something like a mosfet) and you could make an electronic brake.

They already use this technology in "bait casting" fishing reels. Apparently "bait casters" can't master, or can't bother to master the subtle thumb pressure on the reel as the line spins out when open reel casting. - so they apply a kind of magnetic brake - similar to a speedometer mechanism.

Several magnets spin on the shaft and their close proximity to a aluminum ring tends to take the ring along in the same direction as the spinning shaft - the ring works against a spring and indicates the speed.

Take a sheet of aluminum or copper (or non-ferrous metal) and drop a magnet (strong magnet - nevoid) so it slides down the nearly 90 degree sheet - it will slowly drop until it reaches the end of the sheet - then Newton takes over.

Point is . . some spinning very strong magnets on the wheels, would make some decent brakes as the aluminum rings got closer to them.

And you didn't think of it first, so don't try to patent the idea.

Controlling speed doesn't take much force, probably much less than the

36 V DC motor I connected it to. When the motor speed control trigger was released and it did the electronic braking thing, it abruptly kicked my leg backwards. Not talking about hysteresis or eddy current braking, but in my estimation a small DC motor (think RC car) would be enough magnetic power.

If it only requires the small part, doesn't require power, and is adjustable (either resistance or top speed) like at the following link provided by Ned Simmons, that would be great.

Now I can find places to buy the things.

Thanks to the replies.

What about a pony brake... Use a small water pump and restrict the flow...

The first thing that came to my mind is an eddy current clutch or brake, using permanent magnets. You have a few permanent magnets mounted to some reasonably sturdy plate (has to be able to resist the opposing torque) and you move it close to an aluminum or copper (or any conductive metal, depending on braking power needed) disc that you want to slow down. Keep in mind that the disc might get really hot, and could possibly come apart from the eddy current losses melting it down, so mind that for extended braking situations. I asked a fellow who has worked with the North American Eagle on some design issues about a related question awhile back (poke around

until you find a video of the brake bringing a full sized lathe to a full stop by eddy current braking--I couldn't find it when I went looking last couple times, though) with the question about how much axial force one had to push the magnets, which he didn't think was much, but couldn't quantify it. The faster the parts move, the more of a difference it makes, especially when there's a large speed differential between them. I'm not the physicist, so I couldn't offer much more on the topic, other than it's fairly easy to implement, but at low speeds the brake makes little difference, so a light duty final brake is required.

That's good.

Yeah, I think a small non-powered device that increases resistance as RPM increases (but is adjustable) would be great, even if it requires heat sinking.

I'm still looking for places to buy.

This is a little off what you asked for, but may be useful anyway. This guy makes brakes for skateboards / longboards:

Not sure what they call it but some smaller class B and K dieslel trucks use a magnetic braking system on the drive shaft to help control downhill accelleration.

CJ

1) You need to absorb energy (equivalent to friction) to do any braking, so reducing friction appears to be a poor choice. 2) Adding a motor wheel and using it as a generator is a start in the right direction; use of a variable resistor across that generator to dissipate energy is an improvement.

Some trains do too, according to a History Channel (USA cable TV) show, and they dissipate lots of heat.

I was thinking somehow I wouldn't need a heat sink since a DC motor requires force to turn even with the leads disconnected. I'm not disputing any of the expert opinions here, I know things aren't always simple as they seem.

Thanks.

Thanks, I can grasp that idea, the force that generates heat is the force pushing back against the vehicle rolling down a hill.

I'm sure you're correct, but I'm not sure what you're saying. I am sure that a heat sink would last a lot longer than a rubber friction brake, and the braking should produce little heat anyway.

Not that this is what you mean, but for what it's worth. For this application at this time, just using a ready built device that can be rolled against the wheel is probably better then trying to turn a wheel into the device itself. And using a smaller scale device would probably produce smoother rolling (I suppose that has to do with the magnet configuration), and smooth rolling matters a whole lot. When standing on a skate/board, unnecessary jerking motions play havoc with my reflexes.

Someone else with the same hobby might consider adding flashlight bulbs as a side benefit. Personally, I'd really rather just buy an eddy current brake, like the ones in the links, if I can find them for sale. Hopefully they aren't just OEM parts.

If you look at the bottom of the page you will find a link to "sales representatives" Gerry :-)} London, Canada

I'm not an OEM.

Apparently also called "permanent magnet brake". Thanks.

So they will probably send you a free sample if you ask ;)

Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/

That depends what you mean by "little heat". Suppose you are skating down a 10% grade of length 50 ft (15.2 m). If you are going 10 mph (4.47 m/s), and you weigh 160 lb (73 kg), and your speed is held constant, you are generating about 320 W for 3.4 seconds.