# I'm stuck: Trying to set up Diagonal Rod Arms

Posted by disneytoy
 I'm stuck: Trying to set up Diagonal Rod Arms December 12, 2013 08:45PM Registered: 12 years ago Posts: 138
Okay.

Still not sure about the carbon fiber arm lengths. the so called Delta_Dagonal_Rod. (These are mag arms if it makes a difference).

My primter is based on the Cerberus Pup which is 500mm tall ans 170mm build circle. Mine is 650mm tall, and a 220mm build circle. I've measured the important configs below. Can anyone help me calculate this last dimension?

#define DELTA_SMOOTH_ROD_OFFSET 160 // mm

#define DELTA_EFFECTOR_OFFSET 30 // mm

#define DELTA_CARRIAGE_OFFSET 27 // mm

#define DELTA_DIAGONAL_ROD ?????

Thanks
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 13, 2013 03:04AM Registered: 11 years ago Posts: 732
```#define DELTA_RADIUS (DELTA_SMOOTH_ROD_OFFSET-DELTA_EFFECTOR_OFFSET-DELTA_CARRIAGE_OFFSET)

[forums.reprap.org]
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 13, 2013 10:34AM Registered: 11 years ago Posts: 110
You'll need to measure the actual length of your rods. There is a very helpful picture here: [forum.seemecnc.com]
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 13, 2013 04:42PM Registered: 10 years ago Posts: 99
Calculating......
Disneytoy has a delta_radius of 103 and a delta_diagonal_rod of 206.
But these are calculated values or limits in real space?
If the 220 mm is the build platform, then the actual build space has a diameter of 206mm.
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 14, 2013 01:22AM Registered: 12 years ago Posts: 138
Thanks, My sideways calculating came to a rod length of around 200mm. That was based on taking the image provided and knowing the build radius. I saw that the arms were 30 degrees. I then drew the triangle in Illustrator and measured the diagonal length. About 200mm.

 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 14, 2013 01:27AM Registered: 12 years ago Posts: 138
RTurnock,

I measured all info provided real world.. I have not assembled my rods yet. That was what I was trying to determine. I have 150mm CH tubes. But my metal ball ends are on 1.5" 6/32 screws. So I have a certain amount of adjustment. I will put the arms together tomorrow once the JBweld cures. I'm go with your 206mm . Thanks.

Edited 1 time(s). Last edit at 12/14/2013 01:28AM by disneytoy.
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 16, 2013 08:22PM Registered: 11 years ago Posts: 110
I'm on a tablet now, so I can't provide a picture. If you want to make full use of your bed diameter, setting the rod lengths based on a. 30 degree angle when the head is centered won't allow you to use the full diameter. Here's why. If the rods are at 30 degrees from the vertical when the head is centered, you have a 30-60-90 triangle. So if the rods are 200 mm long, the print head might be 100 mm away from the outside of the circle. When one of the arms is perfectly horizontal, you'll be at the full travel, which therefore would give you a theoretical maximum print diameter of 200 mm. However, when the rods are horizontal, you have a bad condition as just a tiny additional movement of the carriage down will result in the print head moving back toward the center.

So you want to make sure that at the maximum travel of the print head, the rods are not horizontal. You'll therefore want to pick an angle from the horizontal that is noticeably greater than zero for full extension. Assuming the rods can be vertical when the head is at the edge closes to your vertical slides and are at 30 degrees from the horizontal at the maximum diameter, your rod length will need to be 1.16 times the bed diameter. So if your bed diameter is 220 mm, you'll need rods that are at least 255 mm long. I'm just about to get on an airplane, so I did these calculations in a hurry.

-- John
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 16, 2013 11:42PM Registered: 11 years ago Posts: 66
Delta Rod length needs to be measured and most important is that all rods are as close to the same length as you can get them.
You need to anchor your dimensions in the real world and delta rod length is the one dimension you can measure accurately. All the other dimensions are much trickier to measure
As well the other 3 (DELTA_SMOOTH_ROD_OFFSET, DELTA_EFFECTOR_OFFSET and DELTA_CARRIAGE_OFFSET) are combined into one measurement (delta radius) and are never used again.

If you are using the magnetic ball joints with the balls on the carriages and cups on the rods then fit a ball on each end of the rod and measure overall length from ball to ball and deduct 1x ball diameter.
The dimension you want to measure is the distance between the centres of the balls.

Once you've got things moving you then need to adjust delta_radius so that the Z height in the center of your build plate matches the Z height near the edge in front of the towers.
Since DELTA_RADIUS is calculated you actually need to adjust one of the DELTA_SMOOTH_ROD_OFFSET, DELTA_EFFECTOR_OFFSET or DELTA_CARRIAGE_OFFSET
It doesn't matter which one you adjust but choose one, make a change and check the Z again.MAKE NOTES as you go.
The values you start with are the theoretical values but it's not unusual to have to adjust them by a few mm to get the the Z-plane flat.
Automated bed levelling can compensate for a lot of this error. I think for best results you should have the printer calibrated reasonably well before the bed levelling.

Regards,
Mike P

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 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 16, 2013 11:48PM Registered: 11 years ago Posts: 66
Quote
hercek
```#define DELTA_RADIUS (DELTA_SMOOTH_ROD_OFFSET-DELTA_EFFECTOR_OFFSET-DELTA_CARRIAGE_OFFSET)

[forums.reprap.org]

Not sure where that code comes from. I haven't seen it in any of the firmware I use.
Johann's original Rostock used 250mm and 124mm for rod length and radius. and I worked out that a 2:1 ratio was optimal to give you the largest build area for a given rod length.
But there is no requirement that the rods are exactly 2x the delta radius. That is purely a design choice.

Regards,
Mike P

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[www.makershop.co.nz]
Makershop - Reprap parts, adding new stock almost daily.
+++++++++++++++++++++++++++++++++++++++++++++
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 17, 2013 04:39AM Registered: 11 years ago Posts: 732
Quote
mikep-nz
Quote
hercek
```#define DELTA_RADIUS (DELTA_SMOOTH_ROD_OFFSET-DELTA_EFFECTOR_OFFSET-DELTA_CARRIAGE_OFFSET)

[forums.reprap.org]

... I worked out that a 2:1 ratio was optimal to give you the largest build area for a given rod length.
But there is no requirement that the rods are exactly 2x the delta radius. That is purely a design choice.

Yes, one can put diagonal rod length to whatever value he likes ... and then fill the right value in Configuration.h. I even claim that in the link I provided just below the piece of code. I'm curious whether anybody followed that link at all

You probably will not find the code anywhere because I put it there as a default for the post only.

2 x deltaRadius is just a good default which still covers the whole built area and does not decrease built height more than necesarily needed. It also makes sure the effector cannot hit towers. One can make them considerable longer than 2 x deltaRadius and achieve somewhat bigger built width (at expense of lower built height). But it will not be a circle any more because you need to avoid the space around towers.
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 17, 2013 05:49PM Registered: 10 years ago Posts: 515
Richrap, in his latest 3DR blog, advocates 0.8 of the distance between the towers as the optimal rod length. I used that formula in my 'Cherry Pi' design and it works well. My rods are 277.5mm and with 800mm tall towers I get a 212mm circle that's 350mm tall to build in. I can go well past the 106mm radius between the towers but limit the firmware to avoid a tower crash. There must be a way to alter Pronterface, Repetier, Cura, etc to take these weird delta build platform planforms into account to maximise build area safely?

Andy
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 18, 2013 01:03AM Registered: 11 years ago Posts: 110
I completely edited this post after I discovered I'd measured the wrong design. On my 3DR "Simple" the distance between the posts is about 246.55 mm, so 0.8 times this = 197mm, which is very close to the 200mm that I used, and I found it worked quite well.

Edited 1 time(s). Last edit at 12/18/2013 01:11AM by JohnSL.
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 18, 2013 05:57AM Registered: 11 years ago Posts: 732
Quote
AndyCart
There must be a way to alter Pronterface, Repetier, Cura, etc to take these weird delta build platform planforms into account to maximise build area safely?
KISSlicer allows you to specify STL of your built area.
If you use deltaDiagonalRod = 2*deltaRadius then it is just a cylinder with the top like this (pictures are for deltaDiagonalRod=250mm):

 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 22, 2013 03:05PM Registered: 11 years ago Posts: 66
Sorry to contradict you but the build envelope is not cylindrical.
The attached plot shows the build envelope for the original Rostock dimensions.

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Makershop - Reprap parts, adding new stock almost daily.
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 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 22, 2013 04:06PM Registered: 11 years ago Posts: 732
Quote
mikep-nz
Sorry to contradict you but the build envelope is not cylindrical.
You are correct. It is not cylindrical. Thanks for the correction.
 Re: I'm stuck: Trying to set up Diagonal Rod Arms December 15, 2015 11:56AM Registered: 8 years ago Posts: 2
arm length is 250 including jaws or not??????
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