Re: Error when attempting to plot with AxiDraw

Home Evil Mad Scientist Forums AxiDraw Error when attempting to plot with AxiDraw Re: Error when attempting to plot with AxiDraw

#22526
CraigTheFabricator
Participant

The overall table may or may not be level, but I did rethink things and i now have 2 feet x 2 feet 3/4″ machined MDF board acting as the surface for everything.  So, with respect to its own little universe, things are flat.  All 4 rubber bumpers are “installed” in the 2 base block machined elements (though I had to find two of these rubber feet rolling around in the box when it arrived).

What I have noticed (testing with the above setup with everything powered off):



1) With the carriage moved to the (per the docs) “home corner” position – carriage at left-most and back-most position – I can lightly apply front to back pressure to the top of the left-most stepper (by EBB board) and the machine will rock front to back accordingly. It looks to be at least a couple millimeters of movement.  I can visually see the front and back of the “left base block” move up and down as I alternate the front-to-back pressure and then release pressure to the left stepper motor top (back of motor pointing upwards).  I see similar movement (during the same testing) to the “right base block” – the rear of that block visibly moves downward a few millimeters and then returns upward upon release.  The front side of the “right base block” does not move nearly as severely, though.  It appears to just slightly pivot.  It should be noted that applying the same testing pressures to the RIGHT-side stepper motor offers identical results to the overall machine. In other testing configurations, this is not always the case as will be noted later.

2) Next I move the carriage such that it is centered along the X linear shafts and still left at the rear-most position along the Y shaft (so, from the Home Corner, we only changed the X position).  In this case, the behavior is the same but REVERSED.  I now have to apply pressure to the left stepper from back-to-front and now the machine will rock back-to-front accordingly
with a couple millimeters of movement.  I can visually see the back and front of the “left base block” move up and down as I alternate the back-to-front pressure and then release pressure to the left stepper
motor top.  Again, similar movement to the “right base block” – the rear of that
block visibly moves upward a few millimeters and then returns downward
upon release.  As before, the front side of the “right base block” does not move
quite as bad.  THIS TIME, when I attempt to put pressure on the right-side stepper motor, I do not get similar results.  The machine sits rock steady on all 4 corners.

3) For proper due diligence, I move the carriage to the far right position on the X shafts and again leave the carriage in the rear-most position along the Y shafts.  Putting back-to-front pressure on the left-side stepper motor still allows movement tilting the base forward.  The backside of the “left base block” does not seem to be moved by much in this scenario.  Both the front and back side of the “right base block” have more severe (couple millimeters) movement back and forth.Oddly, putting any pressure on the right-side stepper motor does not seem to provide any tilt on any of the base blocks.

4) Moving on….returned the carriage to the left-most position along the X shafts and (for the first time) have moved the pen mechanism about halfway out along the Y shaft.  The testing procedure is the same as before with use of light pressure either front-to-back or back-to-front to the top of the stepper motors.  In this case, inducing pressure on the left-most stepper induces no tilt/movement on any of the 4 base block corners.  However, front-to-back pressure on the right-most motor causes downward movement on the rear side of the right base block and significant upward movement on the front side of the left base block.

5) Full center test.  The carriage is centered on the X shafts and the pen (as in #4) is centrally located along the Y shafts.  In this case, I get pretty identical results with front-to-back pressure placed on either of the stepper motors.  The entire front side of both base blocks (and thus translated to the now extended pen position) was pushed upwards by at least a couple millimeters.

6) With the carriage now at the right-most position along the X shafts and the pen in the same position (as above in #4 and #5) along the Y shafts.  Now, back-to-front (opposite of #5) pressure on either of the stepper motors causes the front side of both base blocks to push downward….thus causing the extended pen on the Y shafts to dip several millimeters downward.

7) Carriage at left-most position on X shafts.  Pen is now extended to its farthest reach away from the carriage on the Y shafts.  Pressure to the left-side stepper motor has no impact on any of the base blocks.  A fair amount of front-to-back pressure on the right-side stepper motor causes the rear of the right base block to dip, the front of the left base block lifts a bit, and the fully extended pen on the Y shafts goes up several millimeters.

8) Carriage is not centered on the X shafts. Pen is still extended to its farthest reach away from the carriage on the Y shafts (as in #7).  The results are identical to test #7 except that the pressure required on the right-side stepper motor was far less to achieve the same outcome.

9) Final mechanical positioning test…. Carriage is at far right position on X shafts. Pen and Y shaft positioning is same as in #7 and #8. The results were actually identical to #8 where light front-to-back pressure on the right stepper motor (only) caused the same results.


So, this is a lot of information and I don’t blame most folks for not giving up… but I’m hoping it can help guide EMSL (or others) to help identify what will ultimately cause very jerky and poor motion when this machine is actually attempting a motorized plot.  Is this twist in the base design (which is essentially the 2 base blocks mechanically connected by the 2 X shafts and a hollow black aluminum tube)?  Is this a physics issue caused by levers/cantilevers with the way the pen mechanism(s) hang on the end of the Y shafts (maybe counterweight required on Y Tail Block)?  Just throwing some thoughts out there.

I have some ideas to try to reinforce the mechanical connection to a working platform, but I worry that this will still allow some less evident flex and put wear-inducing pressures on some of the components if the fundamental geometries and physics aren’t worked out.

I’d appreciate any suggestions.

-craig
AxiDraw Serail #0004