Sunday, September 07, 2008
RepStrap Build - Laser Cut Parts Kit - Z tensioner modification
Here's a diagram:
The modified design places the tensioner in the center.
Here are a couple of pictures of the modification:
I took the 2 diagonals and mounted them horizontally, 1 above and 1 below the centerline of the belt. I think that the cartesian robot is rigid enough to deal with the lack of diagonals on the tensioner side. It will still have support in the horizontal direction on the tensioner side. If more support was required, diagonals could still be mounted on this side if the horizontal rods in the Y dimension were longer such that they are long enough for both sets of diagonals. The lack of diagonals becomes a feature though because when your part is complete you can just reach in and pull your part out without the diagonals in the way.
When mounting the horizontal supports for the tensioner take care to place them such that they do not hit the Z pulley flanges. With the motor off, move the belt by hand to make sure there are no clearance issues. When everything moves without interference you can fire up the electronics and test without breaking anything. Here's a picture of the clearance I'm talking about.
Mine are not perfectly aligned because this was merely a test to see if the design worked. I am going to replace the broken acrylic parts that mount the diagonal support rods with machined delrin or aluminum. I feel that these parts need to be stronger and made from a less brittle material. I have broken more than 8 of them. Haven't thrown any tools yet though! I must be getting mellower with age...
One last note: The parts that mount the tensioner to the rods, item number 89 on the Z Sub-Assemblies drawing, were originally designed for the rods to pass through them diagonally and could be re-designed specifically for their use with the rods mounted horizontally. They seem to be sturdy enough and are working fine but they could easily be re-designed to accommodate mounting on horizontal rods if a problem comes up.
Links to this post: