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Magnetic Resistance

Magnetic Resistance

Magnetic Resistance

Good Morning,

I am seeking the guidance and wisdom of my fellow peers. I am stuck with half fulfilled theories and more questions than answers. My goal that I have been tasked with is to come up with various forms of constant resistance that is adjustable in a push and pull format. I have looked at brakes, drums, magnetic resistance, constant force springs, springs in general, and have been trying to avoid electric applications due to unfamiliarity. However, I am trying anything novel as of late.
1. Length of sliding mechanism 3 feet
2. Width 6-8 inches
3. Choice of guidance is open... (plate, railing, etc)
4. Forms of contact for sliding wheels preferred but not definite. (as I stated my narrow mind is blah)
5. Resistance option locations: Opposing pulleys for variance in push-pull resistance, brake pads to either wheels (size limiting .25-1.5 inches) or tread like system, plate and sliding component (magnetic)

I have looked at various forms of magnetism from the permanent to electric but just don't have all of it pieced correctly. I don't want to use external power source if possible.
My first post/thread, If failed to state something or give proper amount of information please forgive.

Thank you in advance for the guidance and assistance.

RE: Magnetic Resistance

Great question I failed to add that in the parameters as well.

Speed is limited to an individuals ability to stand or sit. Much like a leg press.
So some devices (some magnetic setups but not all) that are directly related to resistance wont be as effective.
Cost target hasn't been set; however, I am sure they will say the same as always be frugal but not cheap.

Dashpot is pretty cool link, but the length of resistance is the puzzle I dont see fitting within the distance of sliding around 3 feet bidirectionally.
It looks like this may be an option. Will the amount of force applied cause the levels of resistance to change?

Sorry that is more likely due to my lack of detail to the goals. Visualize a sled that an individual would push or pull with varying resistance and on a smaller scale.

RE: Magnetic Resistance

Yes Sir, the movement will slide horizontally much like the rowing machine. Actually that is a good visual as well.

Lever or adjustment knob of some kind is definitely in the picture.

RE: Magnetic Resistance

I first thought of the old carbon pile controller. A set of carbon disks pressed together and used as a series resistor for generator excitation. The reference value was set by a spring and the actual value was applied in the other direction (voltage caused a magnet to pull in the other direction.

I tried the same principle on a force sensing platform but used plastic with carbon particles in it. The kind used for ESD sensitive devices, black bags.

It worked quite well and when I look for the principle I find this:

Seems to be a more developed version of the principle. Simple to apply and don't seem to be very expensive. Accuracy? Probably a few percents of full load. But still.

I am not quite sure if I understood what you are looking for. But have a look all the same.

Gunnar Englund
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Magnetic Resistance

I am envisioning some type of pulley system coupled to the sliding mechanism with one of the pulleys connected to a magnetic particle brake.
Such brakes are adjustable based on voltage/current that is controllable via knob.
Such an example:


"It's the questions that drive us"

RE: Magnetic Resistance

Got it!

You are not after electric resistance in ohms? But rather mechanic resistance in N - or lbf or what is used. A set of magnets with a piece of aluminum as a keel" between them will produce a counter force (the eddy currents) when you move it. Problem: the force will increase with speed.

That problem can be solved if the "keel" can move when the force gets high. A spring with a knob keeps it down etcetera etcetera. Not a complete solution. But food for thought.

Gunnar Englund
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Magnetic Resistance

Eddy current brakes are interesting.

A good demo is a neodymium supermagnet being dropped down a 1/2-inch copper pipe.

RE: Magnetic Resistance

Some common methods of providing mechanical resistance
> aerodynamic drag - paddlewheel-like
> air resistance - Dashpot
> eddy current resistance
> friction
> back EMF -- without active circuit
> back EMF -- with active commutation circuit
> spring

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Magnetic Resistance

Use a simple closed loop timing belt that spans the distance you need to control resistance over, like used in large format printers. At one end the belt goes around an idler pulley and on the other end the shaft of a DC brushless motor (BLDC). Use a brushless motor controller to directly control braking torque of the motor and hence the entire belt span.

The torque could be profiled any way you can imagine and several ways you probably can't imagine. This would allow the resistance to be adjusted continuously over the entire stroke. It could be adjusted over speed too, both even, and other variables too. It could be directly controlled by heart rate.

Done carefully and depending on the setup it might be possible to not power the system externally but by having it use the energy culled by the resisting torque.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Magnetic Resistance

I like that last sentence, Keith. Clever.

Gunnar Englund
Half full - Half empty? I don't mind. It's what in it that counts.

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