My Simpson Build

Re: My Simpson Build

Postby machinofacture » Fri Jun 27, 2014 8:02 pm

The hole distance is a critical parameter for the kinematics.

I think the kossel-like base is easier to make than the plates. You only need a hacksaw and a ruler to make it. It was easier to make FOR ME, anyway. Plus I want to mount a bunch of stuff on the platform so I felt like having the extrusions would allow more flexibility.
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Re: My Simpson Build

Postby Nicholas Seward » Fri Jun 27, 2014 8:47 pm

There is no wrong way. I just wanted to point out that getting <250um hole placement is pretty easy to do by hand.
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Re: My Simpson Build

Postby Niggle » Fri Jun 27, 2014 9:46 pm

Two points.
1) The hole distance is not critical, although the kinematic logic does need to know the relative positions of the bolts.
2) The bed does not need to be fastened to the bolts. Looking at your pictures, the positions of the bolts is fixed by the rails and the printed corners. Fastening a bed to the rails doesn't affect the bolt positions. Unless you need to print something with a first layer that covers every scrap of space on the bed, you do not need to get it perfectly centered.
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Re: My Simpson Build

Postby machinofacture » Sun Jun 29, 2014 8:52 am

Check it out guys!! It moves


I changed a lot of things from your marlin fork, Niggle. I re-wrote all the formulas to transform the co-ordinates so that 0,0 is in the bottom left corner of the build area as well as re-writing the homing code so that it works now. In the video, when the printer moves to the corner the first time, that is considered [0,0] in my variant.
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Re: My Simpson Build

Postby timrwilliams » Sun Jun 29, 2014 9:15 am

That is very impressive, especially at extremes of travel. Mine has the habit of going unstable at those positions. I have been trying to keep things cool by running the motors at 0.35A/phase (25% of rated current) and this may be my problem. Its OK for mid bed printing but not enough torque at the edges when the weight of the motor has to be countered.
Have you have dispensed with tensioning springs ?, as has been discussed on the forum, but I haven't had the nerve to try. I like having a bit of compliance in case I crash the head !
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Re: My Simpson Build

Postby machinofacture » Sun Jun 29, 2014 6:25 pm

Thanks!

Right now I have some really stretchy and thick monofilament line installed, because I didnt know what spectra was. Thus, it's compliant without a spring (which makes for like 3mm of backlash).

I have actually got some spectra now, so I will re-string (waaah). But, I don't think I will need a spring because now when the head gets jammed into the bed the motors just skip steps in a horrifying twitchy motion. So it doesn't really do a lot of damage.

Springs on the bed might be a better way to do it anyway, because then you have maximum stability for your end effector while still having some give in case of crashes.
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