Drawbot Quick Change Pen Holder
by UechiMike, published
For a counter weight is uses 2 dead AA batteries (or what ever else you want to mount on it).
The servo arms are positioned to hold a Turnigy TG9e 9g servo. As of right now I don't have one of these to test pen up/down functionality but it should work with an appropriately positioned servo arm. For now I've added a couple washers to my servo arms where the weight contributed by the servo should be.
I'll be posting up another one capable of holding a Sharpie Magnum (the really big sharpie).
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I just used OpenSCAD to mirror arm2 and it worked for me. But I do thank you for the detailed explanation!
It all goes together as shown and documented in the instructions page. The spacers as rendered out look a little odd/off due to shadows and optical illusions. The instructions tab and images has a good picture and explanation of how to put it all together. I've made a half dozen of these and they certainly go together corretly. Are you sure you have the spring arms on the correct side of the body. The pinch tabs when holding the servo mount away from you is on the left. If you put the pinch tabs in the wrong order or on the right it will not work and you'd have to flip arm2. There's no harm in mounting arm2 upside down…it just won't provide any gripping force and the pen might be a little wobbly. An alternative would be to thicken the holder arms so they provide more surface contact with the pen. If this was done it would eliminate the need for the other braces as well (It would also make assembly easier.
Frame with arms facing away.
Arm with spacers facing back of frame
Spring Arm with spacers facing arm
holder arm with pinch tab on the same side as spring arm
arm2 with big spacer opposite to the holder arm
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1) Print the entire gondola. Mine is printed with 1 extra shell and 25% infill and plenty sturdy.
- the gondola consists of the following parts: frame, arm, spring_arm, holder_arm and arm2
2) Assemble the gondola (referring to the labeled picture):
- face the frame with the servo arms facing away from you insert 2 M3x30mm screws from the servo arm side
- place the "arm" with the spacer side towards the frame
- place the "spring_arm" with the spacer side towards the frame
- place the "holder_arm" with the lever on the same side as the spring arm
- place the "arm2" with the larger spacer opposite the side the "holder_arm" is mounted
- affix 2 M3 nuts to the ends of the screws
3) Attach "spring" - I used a smaller elastic band - which can be purchased in a drug store in bags of 100. Elastics from dental braces may work as well (untested).
4) Attach counterweight - I used an M3x10mm screw and nut to hold the battery weight on. The weight should be "fixed" to the gondola - using something tethered by a wire/string causes wobble when the pen changes direction.
5) Affix gondola to drawbot. You can utilize the two holes in the spring arm. Depending on your pen and the weight of the servo you balance point may differ. I ran the loops through the holes and hooked them ver the screw ends so I could detach it easily. You may have to adjust the weights - although I found 2 AA batteries are sufficient mass to keep the gondola's center of mass so the pen remains perpendicular to the paper even on a completely vertical surface.
6) Mount a pen and have fun. Pinch the levers on the holder_arm and spring_arm to open up the grip and slide your pen in.
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