If the arms were built as “sandwich” stacks of three you could eliminate any sideways flexing. This would greatly reduce friction at the joints and probably help things stay a little more accurate too.
@krkeegan’s test with the crossing 45˚ version shows basically what I mean (link). I have designed a stacking arm version for each of the linkage designs, I will try to post those tomorrow at some point (I made them on a different computer and don’t really want to double work).
This method should reduce or eliminate the need for low-friction washers etc. (I do love the idea though!).
Also, it appears that your horizontal bars are not quite parallel to each other, I ran into this problem as well and found that much of that error was born at the anchor points (where the arms anchor to the sled). You might consider adding a thin spacer block between the two anchors to keep them from pushing toward each other. You can see an example of what I mean in this post.
Dollar store cutting boards are really cheap and could be used to fabricate the arms of the linkages. They will provide the anti friction and should not warp due to weather/heat. As wood can. They adhere well with many epoxies, are just as easy to work with as wood. If you want thicker material it’s readily available and decently priced for larger pieces.
So a question for some of you that have tested this Triangular Kinematics. In the settings for the Rotational Radius for Triangular Kinematrics… the default is 100. BUT in the top arm design it would seem that this would be zero even though the chains are attached to the arms. The chain length would need to be compensated for to add the distance from the pivot point on the arm to the center of the bit. Am i Corrected or Confused!!
@Blsteinhauer88 Here’s that linkage stack I was talking about.
This is just a mockup for the stacked idea, the measurements and clearances would likely need to be adjusted if one were to build this.
While this complicates the build slightly the benefits are:
Keeps chain and pivots on the same plane (as each other and as the linkage joints)
Eliminates arm bowing due to link offsets
Reduces friction at all joints
Note: the hot-dog shaped pieces on the left two horizontal arms are not needed but could be added for strength if you’re using thinner material. Really only the top arm could have a tendency to bow under compression. The bottom arm is always under tension.
I’m working on designing an easy and cheap “kit” to make linkages, I bought hardware today and things are looking quite promising (price-wise). With laser cut (accurate) wooden arms and hardware etc. it looks like it might be around $10-15. Could be even less, I haven’t timed the cutting process for the parts yet… I’ll keep y’all posted!
And it’s a circular issue for making them on your Maslow, or perhaps that’s iterative
Moot for me, there’s that whole hung on the wall over a bunch of too rough to walk on rocks problem. By the time it’s sorted out you (all) should have a much better sled design, and maybe parts to just fasten together
I have considered the iterative… I mean my device seems pretty accurate and quite repeatable (it’s inaccuracy stays the same :-)) as it is. I expect I could get pretty close making these with it as it stands.
But if @pillageTHENburn comes up with a cheap, pre-done solution - well. Easy button time
@pillageTHENburn, Very nice, could each layer be 5mm board and still have the strength?. Are all the lengths the same, except for the spacers of course? Also I like the addition of your spacer between the two anchor points for added strength. Nice Job. Have you found an easy mount for the chains?
I feel like 5mm plywood would suffice but it’s hard to say without testing it.
After a second look at the clearances for the top mounted design it is apparent that much of the bracing and double layered sections of that stacked mockup would have to go away.
Here’s the linkage in it’s most extreme position (with .75" wide bars), the red triangles are the only places that the arms don’t cross over each other. Those red triangles would be the only places we could add extra material on the vertical bars.
…unless we change arm shape! (I mocked up some weird variations that increase that surface area but the arms get a little silly)
The vertical linkages (“vertical bars”) can be C-channels cut from
aluminium or steel.
The C-shaped cross section gives the linkages rigidity in bending and
torsion, yet it’s not a closed section so should have no clearance
problems. The open side of the C cross section should be installed
towards the moving linkages (the “horizontal bars”) to allow the
pivoting linkages to move freely.
pillageTHENburn[1]
September 5
I feel like 5mm plywood would suffice but it’s hard to say without
testing it.> After a second look at the clearances for the top mounted design it
is apparent that much of the bracing anddouble layered sections of
that stacked mockup would have to go away.> Here’s the linkage in it’s most extreme position (with .75" wide
bars), the red triangles are the only places that the arms don’t
cross over each other. Those red triangles would be the only places
we could add extra material on the vertical bars.> …unless we change arm shape! (I mocked up some weird
variations that increase that surface area but the arms get a
little silly)> top mount extremes overlap
I plan to use 5mm plywood for the 45˚ kit test, it has much more
overlap on the bars.>
Visit Topic[2] or reply to this email to respond.
In Reply To
Blsteinhauer88[3]
September 5 @pillageTHENburn[4], Very nice, could each layer be 5mm board and
still have the strength?. Are all the lengths the same, except for the
spacers of course? Also I like the addition of your spacer between the
two anchor points for added strength. Nice Job. Have you found an
easy mount for the chains? …>
Visit Topic[5] or reply to this email to respond.
The problem with that is the chain would hit that curved bar when the sled is at its extreme. There are some simple solutions with non-straight bars but the material use is not as efficient.
I’ll try to post what I was doing at some point.
Somewhere in this thread I posted drawings of some of these linkages at their maximums, you can see where the chain is in these drawings. If you are playing with clearances those drawings might save you some work.
I believe that this number is the distance from the bit to where the chain pivots (and that needs to be the point where you put the chain over the sprocket for calibrating the length)
I’ve contacted a local metal supplier to get an idea of what it would cost to cut the arms as I posted earlier (complete with clearance for the chain at the extreme angles), I haven’t heard back yet.
due to starting a new job, I probably won’t be able to afford to do this until after the 15th (hopefully I can do it this month), but I hope to get a handful cut and check if 3/16 aluminum or stainless steel is strong enough. If not, my fallback is to cut the shape on one side of 3/16" thick 1" angle metal (again aluminum or SS to try and avoid metal that is liable to rust if moisture gets at the joints). I see no reason to believe that it won’t be able to handle the loads.
not really, the dimensions need to be consistant, but not a particular number
If you are setup to cut all the bars in the same place, in a vertical
orientation, and move the wood under the sled rather than moving the sled to a
new location, you can cut the holes in precisely the same spots each time. If
you also cut the holes in the sled this way, they will also match up precisely
(works for top mount, not for the 45 mount)
(I mocked up some weird variations that increase that surface area but the arms get a little silly)
