Bed size calc based on Arm length

Help......

I'm trying to determine the bed size and hence the base measurements for my new Delta based on the actual arm length and effector sizing. I think I have it worked out but the printable area has turned out larger than I expected.

Arm Length: 520mm
Delta Effector Offset: 45mm
Delta Carriage Offset: 33mm.

Total available smooth rod travel will be around 1400mm (1.4M) so build height will be more than I ever expect to use

Minimum arm angle no less than 20 degrees and maybe 25 degrees

the Carriage will allow the effector for go past the vertical, but I have no idea if that is a good idea but it means I can get within 10mm of the vertical rods.

I ended up with a circular printable diameter of just over 500mm without hitting any towers in the design,

Hope I've provided enough info for some help to be given.

Cheers
Phil

Here is a simple approximation. If the arms are vertical when the head is as close as it can get to a tower, then cos(angle_at_max_distance) = print_diameter/arm_length. Putting in your figures of 500 and 520mm gives the angle as 16 degrees. So for you to get 500mm with not less than 20 degrees angle, the arms would have to go well past the vertical when the head is close to a tower. So I suspect your figures are wrong.

In most carriage designs I have seen, the joints on the carriages are in line with or behind the belts, and this means that the rods are not quite vertical when the effector is as close to a tower as it can get. This reduces the print diameter.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
Here is a simple approximation. If the arms are vertical when the head is as close as it can get to a tower, then cos(angle_at_max_distance) = print_diameter/arm_length. Putting in your figures of 500 and 520mm gives the angle as 16 degrees. So for you to get 500mm with not less than 20 degrees angle, the arms would have to go well past the vertical when the head is close to a tower. So I suspect your figures are wrong.

In most carriage designs I have seen, the joints on the carriages are in line with or behind the belts, and this means that the rods are not quite vertical when the effector is as close to a tower as it can get. This reduces the print diameter.

Cheers and thanks.. you put in so much time and effort to help and respond.

With 20mm rods spaced 80mm apart i have plenty of room to run the belt cleanly centred between the rods with the only limit then being the vertical rods, this gives the Effector offset distance plus a few millimeters as the tower to print edge distance, this assumes that all wiring/cooling for the hotend is contained inside the effector sizing.

Really what i'm trying to reverse engineer is my base extrusion lengths for the hex design to maximise the build area for the chosen arm lengths..... 520 was picked only because 500mm long CF tube is easy to source.

Why didn't you run the OpenScad simulator here : [github.com]
It does have simulation with rods, so that could be pretty accurate . Note that with rod simulation, the reference radius is the plane which goes in the rod axis. Look the Rostock max data set.
It can run arms over 90° .

However, what will not be shown and is very important for printable diameter is part cooling fans. They often conflict with columns.
If you know to use OpenScad, you may add them in the Buildeffector function. If you want to see how to build specific component in the simulator, have a look here : [github.com]

My advice was wrong, better to use the Fisher as a base data set.
I made a quick simulation with rod diam 20, spaced 80, arms spaced 80, effector offset 36, carriage offset 35, arms 520 center to center.
I found with mini angle 22.5 and max 62.6 a usable diameter of 483mm. With effector offset of 36mm , you may have in principle space to set three 40mm fans without conflicting with rods.

Here is the test file. data_X.scad

This is a ten minute test, so you may improve simulation on details, notably height and extrusions

Corrected with your values for effector offset : 45mm and carriage offset 33, I had to increase a bit the diameter of the printer
With 22° mini and 62.3° max, the usable diameter is 480mm, which is near perfect for a bed 500mm dia.

data_X.scad

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Pierre

- Safety [reprap.org]
- Embedded help system for Duet and RepRap Firmware [forums.reprap.org]
- Enclosed delta printers Lily [rouzeau.net] and Lily Big [rouzeau.net]
- OpenScad delta printer simulator [github.com]
- 3D printing on my site [www.rouzeau.net]

A bit more fun , but a bit more complexity, I made a simulation for a boxed version, in the 'Lily' form factor.

That gives that :


The simulator version to use (with associated utilities) is the Lily version here : [github.com]

The data set (with added programming for components) is data_Lily_X.scad

Beware : the data are not the default of the file, you shall browse down to the Lily 'X' parameters .

Not yet published, but I have a utility for extracting all panels in dxf

Edited 2 time(s). Last edit at 04/07/2016 08:21PM by PRZ.

Thanks PRZ,

That is helpful and actually quite awesome, sadly driving OpenScad is something I haven't worked out.

I'll model the base dimensions to get 480mm circular clearance for the effector to all towers with a 500mm circular build plate.

Cheers and Thanks

Phil