Balancing tires with magnetic levitation

While the use of an air bearing will make the wheel and axle spin more freely, that by itself will not enhance your ability to do anything more than balance the wheel statically.

A device that is balanced when at rest is of little value unless you intend to park the model and walk away.

Dynamic balance addresses the fact that the opposing weight could be placed anywhere along the axle on either side of the rim and while it might balance it statically, if the weight is not exactly opposite the heavy spot, it will actually make dynamic imbalance worse.. So, where to put the weight is key.

Air bearings or magnetic bearings, by themselves, contribute nothing to solving the problem however, they might prove to be more sensitive and thus contribute towards identifying how much and where to conterbalance. That will require a detection system with suitable circuitry.

Sorry to rain on your parade but science and technology take no prisoners.

L.J.

Route89--

You probably want to do single plane balancing (static balancing). Two plane balancing (dynamic balancing) usually used where the wheel is relatively wide; maybe more than 10-15% of the diameter or speeds are very high. Two plane balancing can only be done by rotating the wheel and sensing the unbalance with some kind of instrumentation, which I won't go into here because do-it-yourself 2 plane balancers are best left to someone with good engineering knowledge and the ability to set up instruments and circuits needed to make it work. By the way, this will be a lot harder to do with your small R/C wheel and tire than it would be for something like a flywheel or a motorcycle wheel.

I'm thinking that with your R/C cars you won't need any more than a good single plane setup as well as a good dial indicator setup to measure tread and sidewall runout.

For a single plane setup you need very friction free bearings of some kind, a fact you already know and are working on. The classic method for single plane balancing is to mount the wheel to be balanced on a hardened shaft that will run on two parallel and level knife edges with the wheel in between. To set this up you'll need to make a mount for the knife edges that allows them to be adjusted parallel using a flat plate. Once parallel the plane of the two blades needs to be made level. Without access to the precision tools of the machinist the hobbyist could probably make do with two single edge razor blades, a long hardened steel 1/8" dowel pin or maybe the round shank of a broken 1/8" drill or a 1/8" diameter needle bearing from an old American stick shift transmission. A small pocket level should do to keep the wheel from rolling downhill while the heavy side is finding bottom as you experiment with adding balance weights to get it so it won't roll.

Now something you must be aware of is that if the tire isn't round it will cause unbalance-like vibration when it rolls on a surface no matter how perfectly balanced it is. This is where you need a dial indicator rubbing (smoothly) on the OD of the tire tread as you rotate it. This can be done right on your model car preferably when mounted on an axle rather than the front steerable spindle which is liable to have some looseness in it from the steering.

Put the dial indicator on the sidewall to measure sidewall runout also. This can produce a 2 plane unbalance, a most likely source that the dial indicator is able to spot.

Note that low quality tires or poor mountings can cause these troublesome runouts. But they can also come from wheels that are poorly machined, a bent axle or an axle or bearing bore in the wheel which is worn or damaged.

A tread runout can be trimmed to roundness by grinding. We do it on full size race car tires with specialized machines. On your model tires it could easily be done on a small bench lathe with a tool post grinder.

A sidewall runout is compensated for in real tires by adding weights in the 2 plane balancing process. Grinding tire sidewalls is impractical due to the thin structural sidewalls on pneumatic tires. But if the tires in your models are solid and you think your vibration or performance problems with the car might be corrected by improving the 2 plane balance then trimming the sidewalls is worth an experiment.

With regard to some kind of low friction bearing I don't think you can easily make a magnetic levitating bearing that will hold steady enough to be useful. Probably possible but it would require some pretty sophisticated magnetic circuit design. A hydrostatic air bearing is possible but even that requires a good bit of knowing what you are doing. Of course an air bearing is a lot easier to experiment with than a magnetic bearing. Make the bearing pair pretty close clearance to the shaft, like on the order of a thousanth of an inch and in perfect alignment. So assemble them in the mounting frame and ream them to size together. then drill a tiny air hole(no bigger than 1/32" and preferably smaller) at the bottom of each bearing making sure you don't leave any burrs. You'll feed air through each hole and set the flow with a valve so that the wheel floats and rotates freely. If the bearings are full circle holes the shaft will have to be inserted through the bearings and the wheel together. If you cut the top half off each bearing the setup may still work well and then you'd be able to mount the shaft in the wheel and just drop it already assembled into the "half" bearings.

Another possible way jeweled pivot bearings maybe out of an old pocket watch. But you'd need a special shaft with precision conical ends.

Still another approach might be to use the wheels and conical pivot bearings in a pair of larger scale, maybe S, O or ON30 gauge (1/4' to the foot) freight car trucks. Ask a knowledgeable model railroader which are the most free running trucks. You might even find 1/8" axles with conical ends that would be a perfect fit to your wheels to act as a balancing arbor. Use of sprung truck frames that can flex and then return to position would allow you to load and unload a balance job quickly. A variety of precision model train truck axles are available from a small Montana company named Northwest Short Line.

Ed Weldon

I know nothing about the balancing, but please be aware that all the rare-earth magnets are extremely hard and brittle. It will take great care, and possibly a carbide or ceramic drill bit, to drill a hole through one without breaking it, and the dust created in the drilling process may be significantly toxic.

Dremel. Thanks for the warning about toxicity, I didn't know that...

Magnetically levitated wind turbine

Another one

There is no way you are going to use a Dremel tool to produce accurately centered holes in those magnets! If the holes are not accurately centered, then the magnets will be off balance, and it will be impossible to balance the tires correctly.

You need a lathe or a milling machine with someone who knows how to center accurately.

The answer to your question on how much to oversize the holes depends on how accurately centered and how accurately vertical they are. If they are accurately centered and aligned, then a few thousandths of clearance should work. If you try the Dremel, you'll need considerably more.

Would this actually work? Wouldn't it depend on the orientation of the magnetics fields in the magnet? If you are referring to a bar magnet with a North and South pole at each end, wouldn't there be null or no magnetic force if it was in the exact MAGNETIC center? Would their be opposing magnetic forces in such a hole or would there be a lack of them because they are balanced out? The center of a bar magnet has very little, if any, magnetic force.

Also are the magnets made that the filed lines in them are that consistent that the exact physical center would be this 'null point'?

Frankly I'm not sure what kind of a magnetic configuration could be used that would achieve this? Putting it between two magnets? If it moved out of the exact center of the 'balance point' between the two magnets, it would immediately get pulled to that magnet.

The configuration that might work was if the axle itself was magnetized like a bar magnet, and then use two circular magnets that had had one pole in the hole and the other pole on the outside. Then stick the 'North end' of the axle between the round magnet that had the South pole on the inside of the magnet and vica versa.

Is their even such a thing as circular/torus magnet configurations that I am referring to? Would it be possible to have a magnet with this magnetic orientation? I suppose it could be done, but finding such magnets might be difficult as I would think that this is a rather rare configuration?

As far as drilling the hole, as someone who worked as a machinist for over 15 years, as stated a milling machine would be the best way to go. It could be done on a drill press if one was VERY careful about locating it to get the exact center.

As for using a dremel tool, if you are talking about doing it with a grinding burr and have any experience with it; you know what happens when the grinder binds and starts rebounding all over the place inside the hole. You could put a drill bit in the Dremel tool though. But most of them rotate WAY to fast for a drill bit. If you intend on trying to grind a hole with a dremel tool, wear proper protective gear for your eyes and hands etc as their is a good chance you may need it. Especially in some of the more powerful rare earth magnets where the material tends to be quite brittle and shatters and breaks quite easily compared to magnetized steel ones. If you are drilling such materials and don't want it to shatter the magnet when the drill bit breaks through the surface, place it on a piece of wood or mild steel and drill right through it into the material below. 'Steady' is the 'watch word' with a consistent, steady feed rate for drilling such materials including glass. Another factor in favor of a mill. Unless one has a drill press with automatic feed rates. Hard to beat the mill for getting the exact center though.

Clearance? IF the theory is sound then a few thousands of an inch would be plenty of clearance. The general rule of thumb for bearing clearance and shrink fits is 1 thousands of an inch for every inch in diameter.

The axle is probably a standard size. It's not hard to get an over sized hole while drilling, quite the opposite. But their are 'standard' letter and number drills made for just such purposes. Metric drills sometimes are the right size for such jobs as well.

FYI: They can and do DRILL triangular and square holes! Anyone with experience drilling a large diameter hole in material that is quite thin relative to the diameter of the hole (sheet metal etc) by hand has probably ended up with holes that have a distinct triangular shape to them.

FYI: 'Step' drills where their is only one flute and a series of steps that go up one standard drill size in diameter each step are great for making nice holes in thin materials. If done carefully, one can even chamfer and debur one side of the hole at the same time with the same tool.