My Build of the LISA

[fidlerro]

Design Goals:

1. Follow the original LISA design as close as possible

2. Use the simular lead screw/anti-backlash nut but find a cheaper version of it(.5" 5 start)

3. Use the same firmware and slicer to keep implementation as simple as possible (if needed update firmware with custom code)

4. Detail/Quality is key, 5 foot construction will be used to print electric guitar bodies

5. Speed of printing is a second to Detail/Quality of print

6. Make frame and assembly as simple as possible (even a 10 year old could do it)

7. Print as many parts as possible (frame included)

8. Custom aluminum heatbed to meet custom design surface

9. Resizing Goals (quick resizing with as few modifications to design as possible):

a. Adjustment to the vertical and horizontal aluminium 1" square tubing to gain desired print area
b. Adjustment print arm size (arm from shoulder joint to elbow joint)
c. Adjustment custom aluminum heatbed (change dimensions and number of heat resistors)
d. NEMA23 KL23H256-20-6A stepper motors so the length/weight of lead screws will not be a concern when re-sizing (within reason, 10 foot lead screws are not in reason)
e. Strong enough power supply 12V 30A so during re-sizing power consumption isn't an issue.

Here is my current progress:

Current Progress

WP_20140914_001.jpg (898.62 KiB) Viewed 733755 times

I am stuck on the arms. I'm looking for a simple equation to determine the optimal arm length.

Arm Length Issue

WP_20140923_002.jpg (1.25 MiB) Viewed 733755 times

So, any help in this matter would be much appreciated. In the meantime, my thought is to review the firmware to see if I can determine how it's calculating the coordinates. My guess is that the arm length will be important in these calculations.

Again, any help, comments, and/or concerns with my approach is appreciated,
Robert Fidler, Springfield, Missouri

[Nicholas Seward]

There is no LISA firmware (I use a preprocessor that transforms the gcode from spatial coordinates to motor coordinates.) and it won't be easy to put on a standard AVR controller. (This is not your standard delta kinematics.) Any of the new ARM controllers running Smoothieware should make it easy to put in the kinematics. (No firmware also means no automated leveling.)

The arm length is more of a personal thing. Longer arms keep the speed from dropping around the perimeter. Shorter arms get you more height. If you would like a minimum, calculate the length of the arm needed to get the effector to the far side of the print area if the arm is horizontal. Take that length and add 15% to keep the arm at least 30 degrees from horizontal.

Torsional stability of the arms is key to effector rigidity. Make sure your arms have no torsional play. Even with rigid arms, I am pretty sure the effector's rigidity is going to seem less than ideal. I was concerned but it didn't seem to mess with the prints. I think double shear joints would be better than my single sided arms. If you are going to use square tubing this will be appropriate. Just print 4 yolk pieces and then make sure the clamp the crap out of the tubing.

The screw is a huge weak point of the design. It is likely that you will have some screw wobble. Even if the screw is withing 100um of straight this will cause differences of 200um because of the rotation of the screw. 200um doesn't sound like a lot either but that might change the position of the effector by more than that. The result will be subtle waves in the print. For me, it is not an issue but I wouldn't accept this in a product. A more patient person than me could straighten the problematic screws.

Great progress so far. It looks very clean. I can't wait to see it move. Let me know if there is anything you need help with.

[fidlerro]

Thanks for the quick reply and sorry the the delayed response.
Been a busy 2 weeks

Top View

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Front Right

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Back

10649562_10152775687008516_1337512712152728729_n.jpg (60.33 KiB) Viewed 733667 times

I am looking at using Repetier-Firmware to run the printer, adding 6 end-stops and a custom aluminum heated bed.

Thanks again for all the assistance.
Robert Fidler, Springfield, Missouri

[Nicholas Seward]

Unless you write some custom Firmware the 6 end stops won't do you much good except protect you against crashes. It isn't as simple as turning a motor until you hit a limit switch to home. Once one is homed, you lose that position as soon as any other motor turns. You would need a relatively fancy homing procedure.

1) Move all arms up until one hits
2) Move all arms back down by one turn
3) Then dance like below

Code: Select all

backoff=1
acceptable_error=.001
while backoff>acceptable_error:
    for motor in motors:
       motor.driveToEndstop()
       motor.drive(backoff)
    backoff=backoff/4

[Feign]

Yeah, the Lisa seems like such a simple, straightforward machine until you start taking everything into consideration, and then the horror sets in.

[Nicholas Seward]

@Fidlerro: Wait, is that Superman's cape? Is there a LISA in the Fortress of Solitude?

@Feign: Yeah, the design was never meant to be taken too seriously. It all stems back to a forum post about using screws for a Rostock. I said that was a dumb idea for many reasons. I felt bad. I decided to come up with possibilities that using screws would provide that belts would not. Using the screw as a pivot and a linear guide was what I came up with. LISA was my best stab even though I knew full and well that it would have a few issues. (Backlash, wobble, stability, control) I really had no intention to ever build her but my students wanted to take it on as a project and I already had her fully modeled.

[fidlerro]

Yes, Nicholas Seward; that is my superman cape.

Sorry for taking so long to reply, work's been keeping me busy.

I ended up revamping the arms with Rostock arms and platform.

Front

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All Arms

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Arm and Shoulder

alive003.jpg (292.37 KiB) Viewed 733421 times

I am using Repetier-Host and it's firmware. This is taking for ever, not sure on some of the values needed. As of now, I am moving VERY slowly but moving. It appears to move about 10 mm for every 100 mm it should be moving.

So I still have a lot of tuning to go.

If you have any thoughts of why it's scale is so drastically off, please let me know.

Thanks again for everything,
Robert Fidler,
Springfield, Missouri

[Dejay]

Nice design! I actually thought about this today and I keep coming back to the LISA design for some reason.

This is a late reply and just a guess. But maybe the scale is simply off because of the pitch of the lead screws? Your lead screw have a pitch of 12.7mm and a 16 tooth GT2 pulley has 32mm. Maybe you have to adjust steps/mm and/or acceleration?

[fidlerro]

@Dejay

Good idea and I'll look into that.
Work has been crazy busy this year and I haven't had a change to revise this.
I am thinking also I might have mis-calculated the pitch used on the Repeater-Host Configuration Tool.
http://www.repetier.com/firmware/v091/

I will update this thread when I find my bug in case anyone else is using this firmware with a lead screw delta printer design.

Thanks again for the ideas?