by LoboCNC, published

Gyroman by LoboCNC Apr 11, 2015

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Watch the video: https://youtu.be/8qM3Bao3zJQ

This fiendishly clever walking toy was invented by my friend John Jameson back in 1981. It mechanically couples a spinning gyroscope (thru some gearing) to a pair of feet that stomp up and down. When one foot goes down, the body actually lifts up and then starts to precess clockwise. Then when the other foot comes down the body lifts again but this time precesses counterclockwise - and voila, it walks!

All the parts you need (bearings, screws, etc.) are listed in the instructions, including the 104 pennies used for the flywheel mass. I've included a 3D PDF file which will let you view the entire assembly from all angles, hide components, etc.

This 3D printable version that I designed is kinematically a little different from the original, but you can read the history of the original at: http://cyberneticzoo.com/walking-machines/1981-the-walking-gyro-john-w-jameson-american/


UPDATE: I've added a flywheel that works with 0.02 Euro coins. Also note that RobertCL has done a flywheel remix for 1p UK coins: http://www.thingiverse.com/thing:794106

You will need the following parts:
2 side.stl
1 flywheel.stl
1 retainingring.stl
1 pulley.stl
1 eccentric.stl
4 bar.stl
1 link.stl
2 leg_short.stl
2 foot.stl
1 collar.stl
1 hook.stl
1 pullring.stl
20 4-40 x 3/8" pan head screws (McMaster 90272A108)
1 4-40 x 5/8" pan head screw
10 3mm bore, 10mm OD, 4mm thick ball bearings (623ZZ)
......(I purchased 10 for $2.15 at http://www.ebay.com/itm/161255478926)
4 #4 washer, 0.22 OD x 0.031 thick (McMaster 90295A359)
1 3mm rod x 1.9" long (McMaster 5544T222)
1 3mm rod x 2.5" long (McMaster 5544T222)
4 O-rings 1/16" thick x 1 7/8 OD (McMaster 9452K118)
3ft 30# test Spectra braided fishing line
104 pennies

Before starting, take a good look at the 3D PDF file gyroman3d.pdf. It will give you a good idea of how everything goes together.

  1. Acquire all the parts. You can buy most of the hardware from mcmaster.com (I've listed their part numbers), although it may be cheaper if you can find some of the items in a hardware or hobby store. For the pennies, I'd recommend getting 2 rolls of brand-new pennies. Pennies are suppose to weigh exactly 2.5g, but I've found a number of them tipping the scale at 3g.

  2. Print all of the parts. I used PLA, 0.2mm layers, 3 perimeters and 30% infill, except for the flywheel where I used 20% infill. All of the parts need to be pretty flat, so if you don't have a heated bed, use a raft 3-4 mm tall.

  3. Press 2 bearings into each side, one bearing into each foot, and 2 bearings (stacked) into the eccentric. Use a vise or arbor press because you don't want them to get cocked as you are pressing them in. If you don't have either, you can carefully tap them in with a hammer.

  4. Fit two of the O-rings into the grooves on the feet. This is kind of tricky. Once in place, run a tiny bead of superglue along the top edge to hold the O-ring in place.

  5. Screw the feet to the bottoms of the legs with a washer between the bearing and the leg. Screw the 4 bars onto the legs, and then screw the link between the 4 bars. Tighten the screws all the way and then back off 1/8 turn so that the legs can pivot up and down freely.

  6. Assemble 13 pennies into each slot in the flywheel. Make sure the entire stack it sitting flat (it's a tight fit). Fit the retaining ring over the pennies, snapping it into place (another tight fit). The retaining ring should be flush with the top of the flywheel. Use a few drops of superglue on each stack of pennies to hold them in place. (If the pennies rattle, you'll lose flywheel energy.)

  7. Press the short 3mm rod onto the pulley, with one bearing thickness of the shaft sticking out one end. Press the collar onto the other end of the short shaft, again, with one bearing thickness of shaft sticking out the end. Press the long 3mm shaft into the flywheel, with one bearing thickness plus one washer thickness protruding from one end. (If you don't get a tight fit with flywheel on the rod, you can secure the rod with a 4-40 setscrew.)

  8. Put a washer over the short end flywheel axle and insert into the center bearing on one side. Place one O-ring over the small pulley on the flywheel. Insert the collar-end of the pulley axle into the other bearing, going thru the O-Ring. (Don't try to fit the O-Ring into the pulley groove yet.) Place another O-ring over the small diameter groove in the pulley and also over the flywheel axle. Now slide the eccentric onto the flywheel axle. (Don't try to fit the O-ring into place yet.) Put one more washer on the end of the flywheel shaft.

  9. Slide the other side onto the two axles and loosely screw the two sides together. Work the first O-ring up and over the large diameter groove in the pulley. The second O-ring is a little trickier. There is a little nub on the eccentric that you can hook the O-ring on. Then rotate the eccentric around until the O-ring is pulled around the diameter of the eccentric. Tighten the screws holding the two sides together. At this point you should be able to spin the flywheel and everything should rotate smoothly.

  10. Screw the leg assembly onto the body with the link on the side with the eccentric. Now place a bearing in the eccentric slot and push it so that it exactly lines up with the slot in the side piece. Tip the body on its side so that the bearing drops into the slot in the side piece. Slide the bearing up or down so that it stays captured in the slot in the side. Stick a second bearing in the eccentric slot and push it so that it again lines up with the slot in the side. Now push the first bearing so that it exactly overlaps with the second bearing. Insert the long 4-40 screw into the link and screw it in so that it goes through the bores of both bearings. The screw should be almost touching the bottom of the slot in the eccentric.

  11. Tap the hook onto the end of the flywheel axle. Tie a loop in one end of the fishing line. Tie the other end of the fishing line to the pullring. CAUTION - Do not pull on the fishing line with your bare hands. It is extremely strong and extremely thin, and it will cut your hand to ribbons!

  12. Hook the loop end of the fishing line over the hook and then spin the pulley to wrap the line up on the axle. Try to keep the wraps neat. Now let-er rip!

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Great item, very detailed instructions. Please update the parts list to mention 'nuts' for the screws. Seems like it was implied for everybody else except me - I thought the groves for the screws will be in the 3d printed parts.

LoboCNC - in reply to Kon

This design does not use nuts. The screws thread directly into the printed parts. Note that 4-40 threads are much to small to 3D print, but the holes are sized so that if you force the screw into the hole, it will form its own thread in the plastic.

Great. Makes sense now that you explained. Thanks.

I have no pennies, can I substitute with cents?
The diameter of the cents should be 19mm

A penny diameter is 19.05mm, so your 19mm dia. coins will probably work fine.

No Pennies in Canada :( we ditched them.

Might be time for a border run.

I made it, that's why I am here, Not going back EVER.

What is the groove for on top of the flywheel running from the centre to the edge....?

There is a hole in the hub part of the flywheel for a set screw to secure the flywheel to the shaft. The groove is for allen wrench access.

I see, thank you for your quick reply. Am building one but made some slight adjustments. I have 4mm ID bearings and 4mm steel shafts so will make it fit them. (from RC motors) Also designing a flywheel for Australian 2c pieces. It will take 88 coins and should come out at around 480g. Will keep you informed....

Looking forward to seeing your "make"

The flywheel part file includes a conical hollow. Is there a reason for this geometry?

The hollow part is just to reduce the mass in the center of the flywheel, which in turn, maximizes the ratio of the rotational inertia to the overall mass.

That's what I thought, but wanted to make sure. My system filled that in with support material, which is a pain to dissolve (and I didn't want any leftover small plastic chips rattling around on the inside). I instead adjusted the interior to be "solid" with a bit of a gap for axle clearance, and am rebuilding the part at low interior density but thick wall. Should provide the same outcome.

Hi, the pdf-file is empty. Do You know why?
Do I something wrong?

The PDF file is a 3D PDF - you need to use a PDF viewer that supports 3D files.

Oct 15, 2015 - Modified Oct 15, 2015

Thank you for uploading this fantastic little toy...

But!!.....when you designed this, why did you use a currency as your weight ??? ... could you not have used something a bit more widely accessible to the rest of the world? Say... a stack of washers??? or better yet..maybe ball bearings ?

Check out the remixes - there are a number of adaptations for different coins around the world.

Or you could try putting 3/4" (19mm) dia steel balls in the coin slots. I haven't tested this, though, so it may not work.

I decided to use coins because they are much more consistent than washers and they have a better packing density than spheres. And if you are in the right country, they are more commonly available than either.

where do I find the pdf file?

The file gyroman3d.pdf is in the Thing Files, 4th from the bottom.

Jul 31, 2015 - Modified Jul 31, 2015

Thanks very much, LoboCNC! I just made one and I love it! I added a little pulley wheel and it can gain much faster speed. Initially it can hardly walk, now it can do a fine job :D https://www.youtube.com/watch?v=Y-aFRy1UGOM&feature=youtu.be

Comments deleted.

Hello, LoboCNC

Mine went together perfectly, and it runs well, but i'm bummed out that it doesn't keep speed anywhere like yours, and doesn't even have enough to take a step :/ This bums me out a lot! Are your bearings greased or ungreased? Mine came greased and i feel this may be taking a lot of the energy away?


It's more typical for small, high speed bearings to have a very light oil rather than grease. If they seem gummed up, you could try soaking them in something like WD40 and see if that loosens them up. There's not much of a load on them so they don't really need much lubrication. You should also check to make sure that nothing is binding or rubbing anywhere (you shouldn't hear any scraping).

Super cool!!!!

In step 3 we put all the bearings in all the pieces, but then in step 10 it mentions putting bearings in again. I tried it the first way, putting bearings in on step 3 and found step 9 to be very hard. I measured the rod that McMaster sent and it measures 2.99-3.02 (depending on how firm I am with the calipers) and the bearings measure 2.99mm so it's possible McMcaster just sent me a rod that's a little too big. Would that 0.02mm be enough to make it impossible to use this rod and slide it through the bearings on the side piece?

Yes, you can definitely get problems with the shafts not sliding smoothly onto the bearing, both from the shaft being oversized and the bearings being undersized. (I had one set of 3mm bearings that wouldn't slide over the same shaft that worked fine with a different set of 3mm bearings.) Usually, though, it is pretty easy to reduce the shaft diameter by a tiny amount with some 400 grit emory paper. I'll put the shaft in a drill and then sand a bit and then test with a bearing until the bearing will just slide over the entire length.

I sanded them down, but I still don't quite understand what happens in step 10. My side of the eccentric is only deep enough for 1 bearing on the side (2 are in the middle - the ones put in on step 3), but it sounds like step 10 wants you to put 2 bearings on the side as well?

In step 10, you have one bearing that rides in the slot in the eccentric, and the second bearing rides in the slot in the side piece. The two bearings end up side-by-side, but they are sliding in slots in different parts. If this is not clear, look at the Gyroman3D.pdf file. With the 3D PDF, you can selectively hide some parts (or even make them transparent) so that you can see what's going on inside the assembly.

Side note for anyone outside the United States:

McMaster Carr do not ship anywhere outside the US unless you are an established business. This means that anyone from countries other than the US won't be able to source any parts from McMaster Carr. Unfortunately I can't find the gaskets anywhere on Ebay and such websites, so I'll be improvising with something.

You can now collaborate on a thing and get help on customizing a thing with this App:http://www.thingiverse.com/app:796

I just remixed this for any Aussies who want to make one with 1 cent coins! http://www.thingiverse.com/thing:858508

Gyroman - AU 1c Coin Compatible Flywheel

Quick, someone try to get this to work with LEGO bricks! - Brilliant build and design. Perfect video too.

May 28, 2015 - Modified May 28, 2015

Be careful selecting your pennies.

  • Mass of a solid "copper" (95% copper, 5% zinc from 1962 to 1982) penny = 3.11g
  • Mass of a clad penny (97.5% Zinc clad with copper from 1982 to present) penny = 2.5g

That's a significant difference. Note the overlap year; 1982 had a mix of the two in production. Make sure you distribute the old pennies evenly, if you have them.
These numbers are for the U.S. cent.

Thanks so much. SCIENCE!

May 28, 2015 - Modified May 28, 2015

Could you please upload the coins flywheel in dxf or another editable format? Thanks!!!

I've just added the Solidworks files flywheel.sldprt and retainingring.sldprt for those wanting to adapt this for other types of coins. Note that the total mass of pennies I used is 260g. Generally, the more mass the better.

+1, I'd like to do this with Israeli currency :)

It would probably run for months if you sent it on a Mars expedition.

Super cool. Even just swaying back n forth was fun.

are those coins the same size as 0.01 euro?

The US pennies are actually closer in size to the 0.02 euro coins, and I've just added a version of the flywheel with a slightly smaller diameter so the 0.02 euro will fit snugly. Also note that RobertCL has done a flywheel remix for 1p UK coins (http://www.thingiverse.com/thing:794106).

Gyroman - UK 1p Compatible Flywheel
May 25, 2015 - Modified May 25, 2015

You mention 4 O-rings 1/16" thick x 1 7/8 OD but the o rings on the foot don't look the same size as the two used on the flywheel mechanism. Is this an error or do they stretch that much?

No error - all the o-rings are all the same size. The ones used for the belt drive reduction are stretched quite a bit. You may be able to use larger ones for the belt drive that are not stretched so tight, but the 1 7/8" ones were the largest available in my local hardware store, and they seem to work. They are pretty cheap, so you could try some different sizes and see what works best.

May 26, 2015 - Modified May 26, 2015
thecrazy - in reply to LoboCNC

Didnt know o-rigns could be stretched that much, i guess its not the same kind I use on my pool

Thanks for clarifying! and Thank you for the model!

That's a brilliant design! And great job on making it printable

Excellent !!!! Love it!