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I need to design a long (6-7m) pole for plucking fruits from tall trees.

The following are the requirements:

  1. The pole material needs to be as light as possible.
  2. The pole should not be flexible meaning it should not swing in air due to its own weight or the weight of the front attachment or the fruits.

I need to know the following:

  1. What would be the ideal material for the pole?
  2. What mechanical properties ( strength/ stiffness/ cross section etc.) affect the rigidity of the pole?
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    $\begingroup$ Things that do not bend will break. Figure out how much "movement" (deflection) is acceptable under what load (wind, fruit, accel/decel from swinging, etc). Also figure out what size you want this thing. You say pole, but depending on your material, you may need to make it thick (and maybe that's not a bad thing to have your fruit rolling down a half-pipe or something) $\endgroup$
    – Abel
    Jun 5 at 16:11
  • $\begingroup$ maybe, a rigid pole is not an ideal solution ... a semi-rigid pole with attitude control, similar to a spacecraft, could work ... the pole could be pressurized with air ... several controllable air jets near the manipulator to move the pole into position $\endgroup$
    – jsotola
    Jun 5 at 22:15
  • $\begingroup$ Buy one of those pole things people used to run cables. It's a telescopic fiberglass rod thing. $\endgroup$
    – DKNguyen
    Jun 7 at 4:10
  • $\begingroup$ Prune to an open center, do not let trees get tall. $\endgroup$ Jul 18 at 23:00

1 Answer 1

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You will want a material with a high stiffness, and strength to weight ratio.

If cost is no object, then carbon fiber is probably the best option.

Fiberglass, titanium and aluminum are also good options, with aluminum and fiberglass being the most realistic if you're on a budget.

The next question will be how to structure the "pole" to increase the rigidity. You can look at cranes and other tall/stiff constructs for inspiration.

enter image description here

The simplest option that will still give decent results would be a tube. Using a larger diameter will increase the stiffness, but will increase the tendency to buckle (assuming a fixed qty of material for unit length).

You can decrease the droop by using a cable to support the picker end similar to the crane pictured.

The non-picking end of the pole will be subject to greater bending forces than the end. Therefore a tapered design would be optimal, if it's feasible.

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