16 SERVO 12.2017
securing everything, I needed to make sure that it was
clocked properly. To do this, I turned the servo manually to
its counterclockwise limit, manually closed the gripper, then
pushed the driven arm onto the servo
spindle. This seemed to do a nice job
of making sure the assembly would
close completely and open as widely
I did notice that the whole assembly seemed a bit
loose; like it might have problems holding onto anything. To
help with this, I glued the servo horn into the pocket of the
Once the glue was dry, I was ready for a test. I hooked
the servo up to a receiver and battery on my bench (Figure
5). At first, the whole thing just shuddered and made some
After a bit of playing with the tension of each
connection and a bit of filing here and there, I had a
working gripper. It wasn’t quite as strong as I’d hoped, but
remember this is a small servo without a lot of mechanical
advantage on the system.
Adding some double nuts to keep things from backing
off seemed to help (Figure 6), as did adding a small
amount of white lithium grease to the sliding surfaces
I’m still not sure if that’s the best solution as it will
attract debris, but it did help the motion of the gripper.
If you don’t have a 3D printer at your disposal, there
are a few designs that could be pattern cut from wood or
You could also investigate some of the designs in the
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and/or downloads, go to www.servomagazine.com/index.php/magazine/issue/2017/12.
Figure 7: Adding a
small dab of
sliding joints and
greatly reduce the
friction and make
the operation of
the arm much
Figure 8: A few minutes in Fusion and this mounting bracket was
ready to print.
Figure 5: A quick bench test setup helped tune the gripper a bit
and made sure that everything moved properly before mounting
it on the quad.
Figure 6: Using two nuts back-to-back
helped reduce self-loosening of the
hardware during flight and operation.