My ongoing 'biggee' Kossel development July 25, 2015 12:28AM |
Registered: 9 years ago Posts: 280 |
Re: My ongoing 'biggee' Kossel development July 25, 2015 03:06AM |
Registered: 10 years ago Posts: 14,672 |
Re: My ongoing 'biggee' Kossel development July 25, 2015 08:40AM |
Registered: 8 years ago Posts: 49 |
Re: My ongoing 'biggee' Kossel development July 25, 2015 08:55AM |
Registered: 10 years ago Posts: 14,672 |
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wfcook
I recently completed a large delta; here are a few things I learned:
(1) 2020 is likely to be too wobbly for the vertical towers. I'm using 2040 and it is borderline.
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wfcook
(2) After doing a LOT of analysis of bed size, printer size, rod length, etc. (including using the quite handy kinematics visualization scripts here) I came up with a few dimensional rules of thumb which I am sure will ruffle everyone's feathers but which nevertheless are working well for me:
given a print radius DELTA_MAX_RADIUS, in my case 150mm, I got what I felt produced the best tradeoff between size and print quality at the outside of the radius with:
DELTA_DIAGONAL_ROD = 2.5 * DELTA_MAX_RADIUS = 375
PRINTER_RADIUS = (4/3) * DELTA_MAX_RADIUS = 200
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wfcook
(3) I bought motors that had WAY more torque than necessary and drive them at 80% of the rated current. They don't get hot.
Re: My ongoing 'biggee' Kossel development July 25, 2015 09:03AM |
Registered: 9 years ago Posts: 346 |
Re: My ongoing 'biggee' Kossel development July 25, 2015 09:30AM |
Registered: 10 years ago Posts: 14,672 |
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LarsK
Hello,
I don't have much delta design experience but the following things strikes me:
The carriages are really wide. I understand what you say about aspect ratio (rod spacing to rod length) but will the tolerance in your rails not create problems with slack in the setup? As tried to illustrate below.
For that reason it seems attractive to have the rods closer together unless your rails are really good.
Re: My ongoing 'biggee' Kossel development July 25, 2015 10:46AM |
Registered: 9 years ago Posts: 346 |
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dc42
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LarsK
Hello,
I don't have much delta design experience but the following things strikes me:
The carriages are really wide. I understand what you say about aspect ratio (rod spacing to rod length) but will the tolerance in your rails not create problems with slack in the setup? As tried to illustrate below.
For that reason it seems attractive to have the rods closer together unless your rails are really good.
I don't think the wide carriages will make things worse. If a carriage rotates due to slack as you have illustrated, then the effector will rotate by the same angle as the carriage, no matter what the rod spacing is. OTOH, a wider rod spacing will improve rigidity of the spider assembly, and will also make the system less sensitive to tiny differences in the lengths of the diagonal rods in a pair.
It occurs to me that if 2040 extrusions were used with the long edge in the tangential direction, then wide carriages with rollers running on the outside of the extrusions should provide very stable system.
Re: My ongoing 'biggee' Kossel development July 25, 2015 01:01PM |
Registered: 8 years ago Posts: 49 |
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dc42
Looking at your photo, I think you could use a much larger print bed. XY resolution improves as you get farther from the centre. Compare my photo here:
Re: My ongoing 'biggee' Kossel development July 25, 2015 04:28PM |
Registered: 9 years ago Posts: 280 |
Re: My ongoing 'biggee' Kossel development July 25, 2015 06:23PM |
Registered: 10 years ago Posts: 14,672 |
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shadowphile
@DC42:
-I don't see any kind of cooling on the duet stepper drivers, which seems counter to the usual heats sinks on RAMPS (although that is probably why there is no cover?)
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shadowphile
-It looked like you mounted your bed using metal standoffs (in your blog) attached to the heat spreader but that seems like that would cause cold spots where the standoffs attach. (althought ceramic standoffs might work well)
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shadowphile
-I agree about up-sizing the bed radius for the reasons mentioned.
-XY resolution does increase at the edges but isn't there a big tradeoff with speed as one of the rods goes nearly horizontal? That is one reason I scaled the frame (and rods) to completely surround the bed.
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shadowphile
-I really wanted a more polished solution than the popular clips to hold the bed down, although I admit their simplicity is hard to beat. It's just so temporary looking...
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shadowphile
-Do you ever plan to enclose your rig for heating?
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shadowphile
-The SeeMeCNC deltas have an enclosed bottom, what have they done to mitigate trapped heat down there? I was thinking of using forced air venting.