Ring Sled Design Discussion

[mexicomillionaire]

I decided to start a new thread to avoid hijacking the “link” sled discussion.

I wanted to share my current progress on the “ring” sled modification and get some input. If life doesn’t get in the way, I hope to be cut testing sometime this next week if not sooner.

While I do like the link idea and really enjoyed the discussion, I was immediately interested in Bar’s original idea and had immediately sourced parts. I missed the link discussion until a about a week ago…

My main concern was ensuring that the ring was centered on the bit. I accomplished this by creating a V groove jig that centered itself in the router hole and held the ring in place.

The ring was sourced from my work. It has a ~8.75 Overall ID and a cross section of 12.6 mm. I separated it to create a 200 degree ring section. I measured the height of my current change and created brackets for the sled that could be welded to the ring.

Once it was welded and attached to the sled, the router was reattached. In order to center the chuck, I took the same jig and inserted the circles into the hole in the sled. I then attached the router base and Z-axis.

I chose V groove bearings. These were mounted to a adapter I designed out of aluminium. The chain attachment is currently the struggle. The idea was to ensure easy removal and installation of the sled.

I left a groove that should place the center of the chain exactly at the center of the V groove. I plan to trap 1.5 chain links and use the natural joint in the as the pivot.

Happy to answer any questions on creating this ring set-up.

I would love to hear everyone’s thoughts who has tried this setup or has some ideas for chain attachment.

[blurfl]

I like your jig for centering the ring. That ring is plenty stout, it must take quite a machine to bend that ring!

[pillageTHENburn]

@mexicomillionaire

I plan to trap 1.5 chain links and use the natural joint in the as the pivot.

Are you talking about allowing a chain link to be a pivot?
I may be wrong but I believe that in this design the only pivoting that happens is where the roller meets the ring. The line of the chain and the center of the roller should always be in the same line (which should always point directly at the router bit).

Maybe I misunderstood what you mean by “pivot”?

Looks like a nice build! Be sure to share how it turns out!!
-Logan

[Nathan_Miller]

I find this really interesting. I’d like to get started on building a “ring sled” but centering it around the bit has baffled me. This looks like you’re heading the right direction! I’ll be curious to see how it goes for you.

Thanks for your work on this.

[Nathan_Miller]

for what it’s worth, I believe this is what @bar used for his experimental ring (it comes in various sizes): http://www.sailrite.com/Hoop-Stainless-Steel-12

Seems like the price is reasonable, doesn’t it?

[bar]

Beautiful build!!

Keep us posted as it comes together

[mexicomillionaire]

I got the chain attachment completed!

I want to start testing it tonight!!!

One thing that I have a question on is the setup in Groundcontrol.

How should I compensate for the ring assembly length? Is this added to the chain length? (Assumption for the software is that the chain are attached at the router bit.)

My initial thought, is that it shouldn’t really matter as long as the sides should be equal but, any thoughts would be really helpful.

[bar]

Beautiful build!

The settings you want are in the advanced settings page of Ground Control. You want to change the kinematics type to ‘triangular’ and set the rotation radius to be equal to the distance from where the chain attaches to the center of the bit.

I’m excited to see your tests!!!

[Nathan_Miller]

I’m dying to see how this turns out!

[mooselake]

Me, too. YouTube video?

[MattPDX]

Hi,

Just a lurker here. I don’t have a Maslow, i’m not an engineer and my understanding is basic but calculating the position becomes much more precise when a triangle is created, right?

So just make a triangle. Connect both chains to a single point above the router and then calculate the distance from the center to the bit below it.

See my horrible drawing. The chains are black and the router would is light blue.

Now that I think about it, you wouldn’t need to make any adjustments as long as it was calibrated and the design accounted for the offset position of the router.

[dlang]

and the result is going to be that the router is a pendulum, it will lag behind
and move up when you want to move it side to side, and it will keep swinging
when you want to stop.

unfortunantly, it’s not that easy.

[Gero]

Funny, but I’m building exactly that with 4 bearings. Did not dare to post until tested for the reasons @dlang mentioned. I’m in hardware exile land and all I can find online does not ship to here, so until I have my desktop cnc back up and running, I’m stuck with limited options. One more motor, 2 gears and a snippet of arduino-self-balancing-robot might be an aproach, if gravity is not enough.

[mexicomillionaire]

Sorry guys for the delay. So, I got it running. I had also purchased longer chains so I was actually able to complete the calibration routine… Motors are a touch under 11 feet apart and the kit chains are just a touch over 11… new chains are at 15 feet

Anyways, the sled seems to work as expected. I was getting some jittery movement from the chains. Perhaps some more weight or change the angle of the table.

The bit is not perfectly centered. However, I found that the router moves quite a bit when not locked down. I initially positioned the router without it locked and I think this is my error. I will be re-mounting the router base with the router snuggle held in place.

One thing that was not noticed when I placed everything together is that the weight is not vertically opposed to the ring diameter… (Its crooked) I will need to move the weights to ensure it hangs correctly.

However, I made the test shape (I made several but, had the wrong radius entered…) and found that I was quite a bit off. I have 5.78 vertical and 6.1 horizontal on the square on the first (real) test.

My radius of the triangle is about 5.875 inches. (8.75 diameter ID rings, ~1.5 adapter).

I moved the measurement from 8.875 to 10.25 and the test shape was 6.4 vertical and 5.76 in the horizontal.

At this point, the neighbor started yelling at me and I had to stop testing. I will hopefully get more testing done tonight.

Question: I am measuring to the first pin on the chain. Is this correct?

Also, how do I interpret the test shape. Is there a guide? It would seem that if I get the measurements equal, the square would not be exactly 6 inches. Is this motor spacing or some other item?

I have a few videos and a some additional photos here for those very curious.

“https://goo.gl/photos/B7pDkbsW3Yrk9vYK9”

[mexicomillionaire]

@MattPDX, I have seen this suggested before but, I think Dlang is correct. The router would swing and not be very stable.

I see this with my set-up as well. I believe a larger ring would be needed to improve the stability situation in my setup.

[blurfl]

@bar

set the rotation radius to be equal to the distance from where the chain attaches to the center of the bit.

Have you tried the distance from the center of the router bit to the inside surface of the welded ring? What was the result?

[bar]

We don’t have an automatic calibration procedure yet for the ring type of system, but the simulation is working if you change the kinematics type to triangular:

With the triangular kinematics, errors in either the motor spacing or the size of the ring cause very similar distortions. Because you measured the ring very carefully, I would assume that number is right and adjust the motor spacing until the test shape is correct.

I’ve also found that better for calibration than the 6 inch test shape is a long straight line near the top of the board or a two marks of known distance apart near the bottom.

[dlang]

what you actually need to provide is the distance from the center of the router
bit to a link in the chain (I believe the first hole, but that may be off 1/8"
since the measurement starts with the chain straddling a tooth)

[pillageTHENburn]

EDIT: I was totally confused and off base about the actual question being asked here. Therefor my answer below is pretty stupid. What I totally missed is that what is needed is the distance from the end of the chain tip to the router bit so that Maslow can calculate the triangle correctly (since chain length is apparently already known). I’ll go ahead and leave my ignorance here so y’all can have a laugh today. Just pay no attention to me.

// begin stupidity //

@mexicomillionaire

Question: I am measuring to the first pin on the chain. Is this correct?

As I mentioned before, the point at which the chain attaches to the rolling bracket would not be a pivot point. Your chain and bracket should act as one piece until they reach the point where they would pivot, in this case they “pivot” around the point where the roller meets the ring. The math doesn’t care if there’s a chain in that line or a bracket or a wire or a rope or a twinkie, it doesn’t matter as long as it doesn’t stretch.

Since I have not set up and calibrated a Maslow yet I don’t know exactly what you’re measuring but I do believe that the point where the chain meets your bracket is mathematically invisible, and therefor should not matter in any measurements. (It would be like measuring to a point on the chain 13 links from the attachment point, there’s no need for that number anywhere)
// end stupidity //

Your build documentation is great! Thanks for sharing those pictures and videos! That jumpy roller phenomena is a tough one. Maybe if you could polish the inside of your ring that might help?

It’s a difficult problem to solve from a physics standpoint because of the way the tensions and frictions work; imagine a tight clothesline strung between two houses with a pulley on it with a rope hanging down to the ground. Imagine the clothesline is just above your shoulders. If you grab the hanging rope and give it some tension and walk from one house to the other the pulley will follow you pretty well. Now imagine the same clothesline is 20 feet in the air, if you do the exact same thing you’re going to have a very hard time getting the pulley all the way across the clothesline (without using momentum, that’s cheating!). This is because the point where the pulley touches the clothesline is actually a pivot point so in order to get the pulley to roll at all you need to overcome the lateral friction in the system, the further you are from the pulley the harder it is to imply lateral forces to it using a rope. This is why I would guess that the Maslow chains are the most jumpy when they are the longest (lower corners of the work area)…

Thanks for keeping us posted! It’s looking awesome!
-Logan

[mexicomillionaire]

Yeah, the jumpyness in the right bearing is explainable by a mistake I made installing it. Press bearings on kids and use the right tools… I got the bearing crooked on the first try installing it at home and had to resort to solving the issue with a hammer. I already ordered a replacement…

So, should I use the inside surface of the ring in your opinion. I think the only thing that would effect is the chain length but since it is equal on both sides of the machine… How can I adjust the chain length after calibration to add in the adapter length?

I will try it out again tonight and make some more scientific tests to report back.

@bar thanks. I had forgotten about that simulator. Should be helpful.