Bearings, dusty plastic sleeves, greasy metal balls..

[rodiponer]

I am making a strange transportation machine for my daughter. The machine will use 108 bearings operating at low loads (<75 pounds) and low speeds (<20 RPM). The axles are 1/4 to 1/2" in diameter.

When I sailed we slathered lanolin on practically everything that moved, to keep salt from getting inside and seizing things up. Does this work at Black Rock, or is thick grease just fly paper for the dust to stick to, which then forms a thick sludge?

Do normal steel bearings last OK? Last year I brought a mild steel thing I welded, and I am a little surprised how much it has corroded since I've returned. It never got wet, but it looks like I dipped it in the ocean. I can't afford 108 stainless steel bearings.

Also, does anyone have experience with plastic sleeve bearings in Black Rock? I read on an engineering website that roller bearings are better in gucky environments, that sleeve bearings get sticky more easily. This is opposite of my sailing experience, where roller bearings would get packed with salt crystals and freeze up completely. Are the nerds right when it comes to the fine dust?

And, one last bearing question. The nerds say that ball bearings have much less friction than sleeves. But I have not been able to figure out in reading them if this is only at higher loads. Both the plastic and steel bearings are rated for thousands of pounds at thousands of RPM, and this machine will only be doing a fraction of that. If the friction at light loads and ability to put up with dust is about the same, I like the plastic bearings since they are less expensive and won't corrode. But a little difference in friction can add up to a lot over a hundred bearings.

[Sail Man]

Will the bearings be used like wheel bearings in that the wheels move freely of a stationary axle, or are they used as axle bearings, meaning the whole axle/wheel assembly is fixed and will rotate as one unit?

While I am not a mechanic nor do I play one on TV, I will attempt to impart a nonsensical idea in the hopes that it may make sense or at least spark new ideas

Could the trick not be in using a lube that either repels and/or minimizes playa dust adhesion, and instead using a system that allows for easy ability to clean out the bearings and repack them with new grease?

i.e. the bearing buddy: http://www.bearingbuddy.com/

Or in using various types and/or "mixes" of lubricants?

http://www.wikihow.com/Grease-Bicycle-Wheel-Bearings
http://www.green-oil.net/
http://casanovasadventures.com/catalog/bike/p1562.htm
http://forums.bicycletutor.com/thread-435.html

These are just a few suggestions off of the top of my not so lofty head, I'm sure those here with more experience will chime in.

Have you considered discussing this in art car forums, tribes, groups?
Elliot here in the forum may also be a very good source of info.

HTH.

[TomServo]

Not a mechanic either. But, here's my experience. A few years back a friend of mine helped me build a chopper bike, that I designed. It was just over 11 feet long, with the front forks being about 6 feet long. The bearings we used for the forks, in the triple tree, were motorcycle bearings. A bit heavier than bike bearings. They were not sealed. Greased up pretty well, by the time I took the bike apart AFTER burning man, they were completely destroyed. I blame the weight load on the bearings more than the playa dust...but I'm sure that it played a part. If I were to ever build another bike, id try to use industrial sealed bearings.
Playa dust is strange stuff. After slicing my foot open on a buried tent stake, I noticed the blood almost immediately clotted with all the dust on my feet. I can only imagine it finding its way into engine grease, and mucking things up.

[rodiponer]

There are art car forums? I will find these, they are the next step in my evolution.

The bearings are for legs on a small walking machine. I am using the Theo Jansen linkage, which has more of a rolling horse gait than the stomping spider gait of the enormous walking machine:

http://www.mekanizmalar.com/theo_jansen.html
http://www.mechanicalspider.com/comparison.html



So the bearings are all used on clevis pins attached to the various linkages. Only the two bearings attached to the drive shaft will rotate completely around like a car wheel, the others are only moving back and forth through somewhere between twenty and eighty degrees.

A little bit of clogged playa dust in each bearing will add up, since there are six legs and 54 bearings per crankshaft. The bearings will be buried inside clevises, so to clean them I would have to completely disassemble the machine.

[motskyroonmatick]

use industrial sealed bearings.

I think that is your answer right there. Probably the more expensive answer though.

[Captain Goddammit]

For cost-concern and playa-corrosion reasons I'd give it a go with the plastic ones.

[theCryptofishist]

use industrial sealed bearings.

I think that is your answer right there. Probably the more expensive answer though.

I could have sworn he said industrial salad bearings.

[carmatic]

i also suggest the plastic bushings for cost concerns...

here's an interesting idea:
http://en.wikipedia.org/wiki/Dry_lubricant ... i wonder what combination of plastic and playa dust will work?

::edit:: well to sound abit more serious, i think that dry lubrication would fill the tiny seam between your axle and the bushing, and not trap playa dust like grease would...

[Elliot]

Hoo, boy. I have no expertise, but I can offer my thoughts. These are simply the first things that pop into my head after reading the question.

I did not look at any of the links, but I have seen the Human Powered Walking "Ant" in Corvallis, Oregon, in action, so I think I have an idea about the weird loads and accumulation of friction in such a machine.

With so many pivot points, all that friction will add up to a lot, so I would go for minimizing friction. Off the top of my head, that means sloppy ball bearings, running almost dry. Field maintenance would consist of flushing the dust out (if needed) with WD-40 -- which is mostly a kerosene-like solvent plus some light lubricating oil. (You could clean with water, but then corrosion would get you.)

I repair bicycles on the Playa, and a lot of the problems are caused by the bearings (crank and wheels, sometimes steering -- all simple ball bearings) being just a little bit too tight. (The kid at WalMart apparently sets them up "nice and snug".) There just isn't room for the dust particles to share the space with the bearing balls. The quick fix is a wash-out with WD-40 -- or in an emergency, water. The permanent fix is to loosen the bearings a tad, so there is room for dust to live in harmony with the steel balls.

I have Bearing Buddies and lots of grease in my trailer wheel hubs. Gotta love Bearing Buddies. But the thought of 108 of them full of grease in a walking machine... good dawg, the total friction!

Sealed bearings -- also a great invention, but every single one of them has two seals trying to keep it from turning. Walk into your local auto parts store and ask to see a sealed bearing, like for an alternator. Try to rotate it with your fingers. 108 of them!

There is a reason why bicycles are made with nothing but ball bearings -- and all but some very fancy one with no kind of seals at all. That yields the lowest friction -- rolling resistance. Still handymen like me walk around with cone wrenches in our pockets to loosen them up so they resume spinning freely.

So... cheap ball bearings and nothing but a drop of light oil -- is my thought.

If you had said 5/8" shafts, I would have suggested wheel barrow bearings. Don't know about smaller sizes.

I'm looking forward to seeing this thing!

[AKAparttime]

I am making a strange transportation machine for my daughter. The machine will use 108 bearings operating at low loads (<75 pounds) and low speeds (<20 RPM). The axles are 1/4 to 1/2" in diameter.

When I sailed we slathered lanolin on practically everything that moved, to keep salt from getting inside and seizing things up. Does this work at Black Rock, or is thick grease just fly paper for the dust to stick to, which then forms a thick sludge?

Do normal steel bearings last OK? Last year I brought a mild steel thing I welded, and I am a little surprised how much it has corroded since I've returned. It never got wet, but it looks like I dipped it in the ocean. I can't afford 108 stainless steel bearings.

Also, does anyone have experience with plastic sleeve bearings in Black Rock? I read on an engineering website that roller bearings are better in gucky environments, that sleeve bearings get sticky more easily. This is opposite of my sailing experience, where roller bearings would get packed with salt crystals and freeze up completely. Are the nerds right when it comes to the fine dust?

And, one last bearing question. The nerds say that ball bearings have much less friction than sleeves. But I have not been able to figure out in reading them if this is only at higher loads. Both the plastic and steel bearings are rated for thousands of pounds at thousands of RPM, and this machine will only be doing a fraction of that. If the friction at light loads and ability to put up with dust is about the same, I like the plastic bearings since they are less expensive and won't corrode. But a little difference in friction can add up to a lot over a hundred bearings.

Hi

For the last 6 burns I've been using Honda O-ring lube on all the moving
part's of my chopper bike, head stock,cranks,ect.. some year's I don't
clean it at all and leave till the next burn, the last time I looked at the
bearings they were in good shape.
Now if you can get some polypenco nylatron slip plates made you will be OK.

[Captain Goddammit]

I'm not a walking-machine expert either, but like Elliot, I had a bike-repair shop at BM, from '00 to '04 and can vouch for the things he had to say.
He didn't brag about the cool human-powered Kinetic Sculpture Racing rigs he builds (so I'll do that for him!) that I'd say qualify him as an authority on this kind of stuff.

I'm not sure if you specified whether this is a human-powered contraption or if it has a motor.
If it's got power, you can probably afford the potential extra friction of the cheaper plastic bushings.
But - if it's human powered, with 108 friction points, then the ball bearings with loose tolerances and frequent WD40 Elliot recommended baths sounds right to me.

[rodiponer]

You guys are awesome. Thank you all so much.

Wheelbarrow bearings-- cool. I am machining the joints and so can use any size bearing.

The machine will be powered with two motors, one on each side, driving six legs each. Probably 300-500 watt motors with internal reduction gears: I helped a friend motorize his very heavy four wheeled bicycle thing for last years burn with a motor like this and it had plenty of power. Actually, too much, he had to slowly add throttle or it would bend the steel mount I made for him. It will probably need some kind of torque fuse or slip clutch so that I don't accidentally bend the machine into a pretzel. Maybe a piece of thick rubber hose between the motor shaft and the crankshaft? Or a belt that can slip instead of a chain somewhere in the drive system?

The loads at the crankshaft are weird on the prototype legs I've made. The linkages are sometimes trying to lift the leg by pushing on it sideways, so it is harder to turn the crankshaft than you'd expect from the weight of the leg. The next leg I make will use thin walled aluminum tubing (1/16"), to weigh less than 6 pounds at the target 4' height. This should reduce the loads on the crankshaft a lot.

I'll try a combination of a loose ball bearings on the joint that takes the weight of the machine and plastic sleeves on the others (where the weight is split between 4 bearings). And skip the heavy grease for WD-40 and maybe futuristic dry lubricants (I used stuff called McLube while sailing, and it was magic with plastic bearings).

Thanks again.

[Captain Goddammit]

I'll make the suggestion to look more at your idea of a bit of rubber hose inline with the drive shaft, that sounds like it would work and would be easy to replace or substitute with a solid part if necessary.
One year a friend and I had a mutant vehicle made from a riding lawn mower chassis... it had a vertical-shaft 11 horse with a very small pulley under it, driving a large pulley at the rear transaxle via a standard automotive-type v-belt. It was way too slow, so we welded on equal-size auto water-pump pulleys at each end, expecting belt traction issues but to my surprise it would pop wheelies, the belt didn't slip at all.

I used old auto steering column rag-joints in a few places on my mutants, they're virtually free if you're a little resourceful.

Oh... hey... post pictures! This thing sounds extremely cool!

[Elliot]

FYI: The Corvallis Human Powered (two people) Mute-Ant.

http://www.rwtechservices.com/MuteAnt/index.html

It officially worked -- I saw it walk (or stomp) a short distance -- but rather poorly. Getting it moving from a standstill seemed to be the hardest part. I believe I heard that they finally dismantled it and made a hybrid walking/rolling vehicle, but not sure.

[rodiponer]

Thank you for the links and encouragement. With your words, I've found the right term for a 'slip clutch' and think I will add one to each crankshaft to keep the machine from twisting itself into a pretzel if a leg gets stuck.

Here is a video of the legs I am using, on a smaller Segway sized machine. It supports a 300 pound person and moves pretty fast with two drill motors.


The 2010 Dynamic Walking conference is July 8-11 at MIT. I will try to go, because I think it's important for people with our perspective to attend these things. No one else will make these machines as they should be made, which is large and with flame throwers.

No, seriously, there was a session at last years conference about reducing the torque and energy requirements of the type of legs I am using. Maybe something applicable will be at the next one. Information on the last one: http://www.dynamicwalking.org/dw2009/?q=node/3

And, if you have not yet seen the walking machines that will stomp on your corpse in the coming robot apocalypse:
http://www.youtube.com/results?search_q ... le+dog+mit
http://www.youtube.com/results?search_q ... n+dynamics

[Captain Goddammit]

By the way, I totally love what you're doing. This is REAL mutant vehicle building, not the decorated golf cart or flatbed trailer stuff.

[gyre]

Very low speed bearings are the most difficult to lubricate and build.
Check out steering bearings on racks.

You may want to look at bronze or other self lubricating material.
Then there is delrin, nyon and composite teflon.

Pegasus and some other race suppliers should carry the bronze parts.
I don't think ball bearings are essential, especially if you use a wide surface.

[carmatic]

i wouldve thought that someone somewhere runs a hardware shop which has a corner full of rotating joints , where you could pick up and play with different bearings and bushings and stuff... that would be quite fantastic, i would think...

[rodiponer]

Thank you everyone for your help. You all probably saved me from blowing way too much money on bearings, or buying the wrong kind.

I ordered nylon sleeve bearings for nearly every joint (only $0.45/each!), and a set of the open style of ball bearings that Elliot suggested. I will also try the needle roller bearings, which have a higher load capacity but might on clog up with dirt easily. I settled on 3/8" clevis pins for the shafts because the bearings for them were less expensive than the adjacent sizes. 1/8" shafts are theoretically strong enough but just feel ridiculously small.

Each leg is only going to cost about $60, which is much more economical than I originally thought possible. $25 for off the shelf parts: 20 sleeve bearings, 2 roller bearings, clevis pins, and cotter rings. ~$22 for aluminum stock to machine the joints: each half joint will take about 1.25x3" of aluminum stock, at ~0.1 pounds/cubic inch and ~$3.60/pound = $1.35/half joint, with 8 joints. And finally, $10 for the ~15' of 1" 1/16th" thick tubing at $0.69/foot.

My wife thought of a more efficient way to machine the joints, with only having to clamp the parts in a vice twice to make each one and no need to make a jig or fixture. I'll see when I run the program, but it should take about 3 hours to machine the parts for each leg. And then welding and assembling the legs, making the crankshaft, motor mounts, frame, and then the finger protectors to keep hands out of the pinchy bits, the electrical system, motor controller, lights... The good news is that if this set of legs works, I feel the most complicated part of making the whole thing, the part that took the most planning, weird parts, and uncertainty of whether it would work or not, will be behind me. But even with Burning Man nine months away I feel like I have to work quickly to do all the stuff that will turn the legs into a rideable machine.

A friend said this morning that hobbies are for under achievers, that I have obsessions.

Do you guys who have made other weird vehicles, do you get nerdy and do math to figure out how much structure you need? Whether you should use 2x2" or 1x1" tubing or 1x3" angle bracket or how many cross braces there need to be and etc, or do you just kind of eyeball it? This is my first vehicle, and only the second thing I am making out of aluminum (the first was essentially a piece of furniture), so I don't have an intuitive feel for the strength of a design. I can't just look at it and think-- yeah, a three hundred pound man could jump up and down on that.

Matt.

[gyre]

I just ask someone that knows.
But I know the giraffe was checked for 1500 pounds.

[Elliot]

I use the eyeball-and-gut-feel method. Of course, I have to, because I know no other way.

People tell me that my designs tend to seem heavier and stronger than necessary.

But a couple of years ago, a frame collapsed (racked) because I had simply forgotten/neglected to include adequate triangulation. So my method is not perfect!

Only recently have I begun calculating Gear Inches for my chain-drivetrains. This I find very helpful.

I suppose I have picked up some basics of engineering over the years, from things my father told me to stuff I've read in books.

Do it however works for you. So long as you DO IT!

[gyre]

http://www.engineeringtoolbox.com/
I think this is a site that has been useful.
And there are probably forums for the subject.
Triangulation is not always intuitive.
I tend to put door braces on backwards and it matters.

There is suspension engineering software and design books that come with the software.
May be overkill for what you're doing but will work.
http://www.sae.org/