Already making full size prototypes out of wood.
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Brandon thanks for volunteering please get in touch with @rcktdr she’s working on doing some modeling
Thursday @HoarseHorace will be burning a screen for the shirts
Shirts to be printed at a later date
You (and everyone) an always promote the gofundme - we are close to the goal! please send this out @Team_PR
There are pictures above of some stuff being cut out, what was that used for, a demo of basic linkage mechanism?
We cut out one full scale leg and were going to start to assemble it, but realized that it wasn’t the right size to match up with the bike that was donated.
Is the design using the recommended jansen linkage dimensions? What’s the scale of the legs for the bike? Any details on the joint construction (bearing/bushing/axle/etc)?
Yes - all the dimensions are according to jansens formula.
I’m not sure of the exact scale - I do have the measurements for the bike. Chuck is correcting one measurement - all the other things will fall within the proportion.
Bushings - that all falls under @Photomancer wheelhouse. We’ve 3D printed some basics.
Our objective is to pull off this bike that anyone can create - were going to open the files up to everyone once we know they function properly. Everyone had much more advanced ideas of this but we felt we should focus on a very doable “maker-centered” bike for anyone who was interested. I’m sure bike 2.0 and more will be right around the corner.
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Here is an idea if this is useful, (can go to Assembly 2 tab, then right click animate on the MainCrank joint) was wondering how skinny the leg could be made but still keep the joints rigid enough
It’s scaled so that the mechanism is about 3’ tall, which is what I guessed would be about roughly bicycle seat height
This would be entirely out of 1/2" plywood, the thick parts are two 1/2" sheets glued together to make 1" thick leg sections
The struts are each 1/2" plywood with a piece of plywood connecting the two side to make them like an I beam
All joints could be 2" delrin with 1/2" steel shaft going through them. The delrin would be lathed down and pressed / gorilla glued into the wood. The steel shafts would be drilled / taped on the ends so that a bolt + washer would retain the joint
Could additionally be some thin delrin sheet between where it would otherwise be wood on wood motion
The main crankshaft would be welded together with the linkages in situ, making it not possible to remove without cutting it back apart
The main frame is not shown, but could be 2" steel box
Could fit each leg in 6" of horizontal space with the additional frame, so you could pack 4 in less than a few feet wide
The fixed triangle parts are not fully defined, the bottom leg probably needs to be thicker all the way to the foot
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- Do you have interest?
- Are you curious enough to attend?
- Are you willing to add your enthusiasm to to project?
Any of the above qualifies. Besides, other skills thank building are needed and used. One member has designed a logo and tee-design. PR?
Please come join in … you may not know how to do things NOW, but … you might learn something!
I just did an unrelated (sort of) linkage experiment this past weekend and used 608ZZ bearings (cheap, like $0.30 each) and 7/32 (I think) plywood and laser cut it. That and a chopped up dowel rod for axles and I’m super happy with it.
I feel like:
- compression loaded things (I’m guessing bottom blue and dark grey, def. bottom orange) should be designed fatly
- triangles need to be actual triangles; what kind of engineer doesn’t use triangles when they could use triangles?
5 minute mspaint job:
Note the triangles.
This would be mounted on the jagged line, which come to think of it probably isn’t ideal. Probably needs something out of plane to prevent buckling out of plane (depending on load).
Dunno. Hard to tell what to enbeefen and what to make smaller without a solid idea of the loads on this guy. I’m spitballing on your dark grey and orange links being the weak ones.
I could probably cut something that worked tonight if I felt like it. I … am seriously thinking about this.
I do all my work on the laser, so if I needed something thicker I’d use glue, pinning layers together like I did on my test article, or castle joints (?) or somesuch. I would be using Solvespace, because it is God’s CAD software, and anything else for 2D is wrong.
This has been: 30 seconds with the peanut gallery. Now back to your regularly scheduled project chatter.
Edit: laser line is too long and I have work tomorry. I have all the .dxfs for the pieces ready to go. Probably tomorrow or Friday I’ll cut it and a warped-plywood-and-bearings version will exist.
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My rough estimate would be that each leg would only ever see about 100 pounds of static load, my assumption is that the solid plywood peg leg should be strong enough (I iterated the design to make it a bit thicker than pictured above), my main thought was just doing something that looks a bit different than typical linkage which is build out of pipe
I’m printing out a 1/4 scale model of this design, The total design would be 27" wide with 4 legs. My initial estimate of bill of materials would be around $350 to build this design
Remaining questions for this design, should main axle be 1/2" or up sized to 3/4", should main crankshaft ball bearings be welded into crankshaft and then sandwhiched onto a square tube frame? Or could put the main bearings inside a tube when building crankshaft, and then just weld struts directly to that outer tube to build the frame around the crankshaft (making it even harder to deconstruct and fix anything)
2’x4’ 1/2" birch plywood $22 x 2 = $44 per leg (https://www.homedepot.com/p/1-2-in-x-24-in-x-48-in-Birch-Plywood-Actual-0-476-in-x-23-75-in-x-47-75-in-1503004/202088758 much cheaper to get 4’x8’ but 2’x4’ is what I can fit in my car)
delrin rod 1.5" diameter 24" $32 (https://www.amazon.com/Acetal-Copolymer-Plastic-Diameter-Length/dp/B01N7U74GO)
1/2" x 36" smooth steel rod $14 x 2 = $28 (https://www.amazon.com/National-Hardware-N179-804-4005BC-Smooth/dp/B002CTUBM4)
1/8 x 3" x 36" steel flat bar = $17 (for crank sections https://www.homedepot.com/p/Everbilt-3-in-x-36-in-Plain-Steel-Flat-Bar-800227/204325647)
1/2" ID ball bearings $16 (for crank https://www.amazon.com/R8-2RS-Premium-Sealed-Radial-Bearing/dp/B078TN7LMZ/)
Not listed are frame sections, would either be steel square tube or triangulated steel pipe
These prices are all from home depot / amazon, would be cheaper to source from other suppliers, but I like the convenience of picking up or next day delivery
Could cut all the materials next week (at least the 56 pieces for 4 legs) and try to assemble it the following week, completing the first strandbeest by October 13th
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One specific issue (at least with the stackup as I have drawn it to minimize width and with using plywood where the joints will be much wider) is Strut K colliding with the main fixed joint, here is the position when its picking up the leg during peak of backstroke
And there is 1/4" of clearance
Of course there would be more space if I didn’t make the joints 3" in diameter, but with a 1.5" bearing that leaves only 3/4" border of plywood around the bearing which is the minimum that I think seems reasonable.
It seems like it should be possible to get a leg out of a single 2’x4’ sheet (and thus all 4 legs out of one 4x8), but manually packing this is about as good as I can get
Edit, 3rd attempt got it
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I prefer this right now:
(Image from https://commons.wikimedia.org/wiki/File:Solvespace_workspace.jpg by user “Stringybark”, licensed CC 4 BY-SA)
Puts things in their own plane and avoids interference issues. Only issues involve the torque it generates on the shafts / bushings / bearings, which I have (for reasons relating to laziness) decided to disregard for the forces expected.
Note the triangle.
Edit: also consider the grain of the plywood. I run my links with the grain in an attempt to improve the out-of-plane bending performance.
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My 3d printer ran into issues so I had to finish this with foamboard, one thing I just realized, typically the direction of walking ‘forward’ is with the crank in the trailing position, but with the legs behind you on the bike to go forward the mechanism is going in reverse. Which will limit ability to climb over obstacles as the foot swings past the point of contact with the ground first, the motion of the bike would be to the right in this picture
At full scale (4x this model) the foot would be in contact with the ground ~16"
Edit, on second thought, its probably the imprecise drilled foamboard alignment causing the step motion to be less symmetrical than ideal, this is the ideal foot path:
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Does this look plausible? For scale this is a 2’x4’ piece of plywood using 3/8 bit for all cuts, because of how close I made everything to fit it in a tiny sheet of plywood lots of the tabs get cut off / have nothing to connect to, so not sure if I will run into issues with the pieces moving around. (Most of the struts are 14" long and 3" in width at largest spot)
On the plus side, cut time is only 25 minutes
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Kris helped me skirt my luddite no-smartphone-having issues and get a pic of this:
I’m at the space now and plan to cut the last link while I’m here. (Ran out of wood 2 nights ago.) I’m thinking of doing a little load testing to see if it has out-of-plane flex issues and if so I’ll cut some finger joints (I think that’s what they’re called) and make the flexing bits into X / + beams.
The entire reason I went to plywood + bearings for linkage prototyping was because my foamboard straight line mechanism prototype was hot garbage.
I wish I could say something about the rest, but I haven’t used the router. Also, I don’t actually know what I’m doing, so beware my input 
.
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Got a full size prototype assembled, here it is along with some things I learned
It’s fairly heavy, could probably go even smaller to 2.5" diameter knuckle (around the bushing) and 1" min strut width instead of the 3" knuckle and 1.25" min strut width seen here
My first attempt I had a wavy piece of plywood that didn’t completely suction down on cnc table and I tried to skimp on the tabs, the second attempt with more and bigger tabs worked well
The delrin bushings worked amazingly well, the smooth rod I got ended up being about 2 thousandths less than 0.500", so I just used DMS’ 1/2" reamer and then parted out pieces the thickness of the plywood. Another big win with the delrin besides being 1/3 the price of ball bearings, is that the doubled up 1" thick section of plywood have a single 1" thick delrin bushing. Add a little bit of silicone ptfe grease and there is very minimal friction.
Another plus was using a 3/8" bit in CNC router so that all the holes are interpolated, but they came out to be about 10 thousandths less than what I expected, making a 25 thousandths interference fit between the bushings and plywood. Only about a 15 thousandths press fit would have been better, I had some minor splitting / layer separation because I didn’t clean out the holes well enough before pressing in the bushings (arbor press was faster, was excessive to use hydraulic press)
I originally designed all ends to be the same diameter with the thought that the extra plywood would provide more rigidity for the joint, but really I should make the strut ends that simply retain the 1/2" axle be smaller to reduce weight as the plywood itself isn’t rubbing, just the delrin bushings make the joints rigid enough that there is no sag when its mounted horizontally
Didn’t have time to do a destructive load test, need some good ideas on how to rig that up
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If the group wants to fund building this design (would be good to build more than one design if possible) then we just need to pick a weeknight build day to start meeting on, would be about a 1.5 hour initial cnc cut time for all the pieces. There are lots of parts that different people could help out with, welding / (optionally) cnc cutting crank pieces, lathe work to make bushings, sanding / prepping all the pieces, glueing / assembling leg pieces, welding frame pieces to bike, etc
The longest lead item (not on amazon prime or in home depot) would be more delrin / acetal rod https://www.ebay.com/itm/Rod-Acetal-150-Wht-1-1-2-In-Dia-x-6-Ft-L-DELRIN-2XMR7/382336920901
Now with 16% less mass, from 200 cubic inches of plywood to 167 cubic inches by reducing width of struts and going for more straight lines.
For reference, and one reason why I think this is probably still overbuilt, it took ~4,000 pounds of force to snap a 2"x3" laminated birch plywood beam in this video, the struts in this design here are 1" wide in an I beam configuration and they will face practically 0 bending moment
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Dang dude. You put a lot of work in before we had our next meeting.
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