yes, have the spools outsize the Z axis and anchored to the sled instead of the
router.
the result would require a large diameter tube for the arms to ride on, which
would be a shipping problem, so I can understand why the current method was
attractive.
David Lang
@WFD @arjenschoneveld
I updated my spreadsheet to calculate the angle between the opposite anchors when at a top corner (using c^2=a^2+b^2-2abCos(c))
please check that my math is working correctly and is matching your simulations
This is David Langs spreadsheet
sorry, I’ve been tinkering and now have it so you can set the min angles for adjacent or opposite angles. it doesn’t currently handle the case of differences between top and side angles
working frames appear to be:
153" x 127"
3880mm x 3220mm
it looks like if you clip the ears off the top anchor, trim the screws holding the leadscrew nuts, and add a slight spacer below the bottom arm (allowing the arms to get closer to vertical) you can get away with a 144" x 101" frame
Hi David,
I have been tinkering as well, and it appears that I have made a mistake about the optimal frame size. I said 4500x3800, but that is too large.
If we allow for rotating of the sled, the limitting factors are:
Opposit arms have a Minimum angle of 130 degrees, the corners of the workarea get affected by this.
Adjacent arms have a Maximum angle of 140 degrees, the middle of the long sides get affected by this.
I put that in a sketch:
and I get an optimal frame size of 4492 x 2855. I didn’t check, but is this what you get in your spreadsheet?
I don’t know how to put this method in a formula or a spreadsheet, but graphicly it is easy to do.
of course if the dead zones could be made smaller, the optimal frame size could be smaller too.
Arjen
I just looked at the spreadsheet, and it seems it doesn’t take into account the maximum angle of adjacent arms, 140 degrees
Arjen
it looks for the top/side angles to be no less than 20 degrees from horizontal/vertical at the centers, which is the equivalent of the 140 degree limit
here’s one taller, but not as wide 3880 x 3220
I tweaked it to also show the angle between arms
3880x3220
this gives an angle of the opposit arms of 125.5 on the corner of the work area
should be 130 or more
arjenschoneveld wrote:
3880x3220
this gives an angle of the opposit arms of 125.5 on the corner of the work area
should be 130 or more
please see if you can spot the error in my math on the sheet, the sheet shows
an angle of 130.237
I calculate that this is a triangle of:
frame diag (c) 5042,102736
lower near anchor to top corner (a) 2220,324301
top far anchor to top corner (b) 3314,453198
then
c^2 = (a^2 + b^2 - 2abCos(C)
becomes
Cos(C) = (a^2 + b^2 - c^2)/2ab = -0,6459540719
C = 130,2372462
David Lang
i misunderstood
so the triangle should be frame diagonal, topcorner frame right to bottomcorner workarea right,
bottomcorner frame left to bottomcorner workarea right
arjenschoneveld wrote:
I see the error: that point is not on the frame diagonal, but on the diagonal of the workarea
it is the corner of the work area
but the triangle the belts make is from the corners of the frame (the frame
diagonal, c) to the top corner of the workpiece (each leg of which is a triangle
of offset from workpiece as one leg, the other leg being offset + workpiece
dimension a and b)
David Lang
correct. I’ll check to see if I can spot the error. in the mean time , here is the sketch of the 3880x3220 frame
a is not correct, should be 2334
(1220 + 1000)^2 + 720^2 = a^2
found it, I had * instead of ^ in the formula
