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  • Need help to construct telescopic light stand with motor

    Discussion in 'The main mechanical design forum' started by Mastino, Aug 22, 2012.

    1. Mastino

      Mastino New Member

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      Hello everybody,
      So what we have is the studio light stand like this one:
      [​IMG]
      I need somehow mount a motor or servo or stepper to it, which will lift up and bring down the stand. I need to operate it from PC. All electrical schematics is not the problem for me, only I have problem with mechanical part. How should I attach the motor and how will it lift all the pipes up and down?.. I thought to put a threaded pipe inside or something.. but no idea how..
      Working conditions:
      When the stand goes up the pipes can not spin around, it must lift max 5kg.
      When the stand is down it should be something about 1000mm.
      When the stand is up it should be something about 2500mm.
      If somebody has idea or mind please help! :)
      Here are couple pictures with dimensions:
      [​IMG]
      [​IMG]
      [​IMG]
      [​IMG]
      [​IMG]
       
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    3. marine&hydraulic

      marine&hydraulic Member

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      You may consider having a low pressure telescopic air cylinder for this .... single stage air out ..solenoid controlled with regulated air from a seperate air cylinder ...stability on extension may be a issue here and also costs of the telescopic cylinder
       
    4. smartguysml

      smartguysml New Member

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      Construct it like an automatic car antenna, that extends and retracts.
      Run a nylon cord up the tubes and attach it to the top of the smallest diameter tube.
      The cord winds on to a motorized spool at the bottom. Winding the cord out will raise the lights, winding the cord in will lower the lights. The amount of weight the stand can take depends on the stiffness of the nylon cord. I would guess you can get 15 to 25 lbs of load.
       
    5. AndrewNew

      AndrewNew Well-Known Member

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      That's a good thought, although you would need to run the plastic strip (not actually a cord) inside a guide channel to stop it buckling (it's hard to push with string!)

      Do you need to be able to set the height at intermediate positions, or does it only need to be "raised" and "lowered"?
       
    6. marine&hydraulic

      marine&hydraulic Member

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    7. kjwissing

      kjwissing New Member

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      I think you could do it with threaded rods - its a concept that is gonna be hard to really explain without a drawing, but I can try anyways.

      The hard part would be finding (or machining) a threaded pipe that has threads on the outside and inside surfaces. The threads on the inside would only have to be at the very bottom - maybe the last few inches. This pipe would have to have an outside diameter (OD) of, say, 15mm. (I'll call it Pipe1). Screwed on, near the bottom of Pipe1, on the outside, would be a threaded nut, with an OD of 23mm. Welded onto the very end of Pipe1 would be a washer with an OD of 30mm. Insert this threaded pipe into the smallest of your telescoping pipes (the red one). Make sure the red pipe rests on top of the nut, and the green pipe rests on top of the washer.

      You'd also need a solid threaded rod that would mesh with the inside threads of Pipe1. I'll call this Rod1. Rod1 should fit snugly inside Pipe1, but it should be slightly longer so that it sticks out the bottom. Couple a stepper motor to Rod1. As you turn the motor, Rod1 turns, and Pipe1 will move up. When the bottom of Pipe1 approaches the top of Rod1, there needs to be something to block Pipe1 from rising any more. (Maybe a clamp that activates when it gets to the top. You could just have Rod1's threads stop for the last few inches). When the clamp is engaged, if you continue to turn the motor, Rod1 and Pipe1 will move in unison. The nut attached to the outside of Pipe1 will now rise up, pushing the Red telescoping pipe up until it gets to the end.

      I haven't come up with a way to make sure the nut doesn't rise during stage 1. You'll need some sort of channel that engages only during stage 2. You want the nut to rotate freely with Pipe1 at first, then to stay straight as Pipe1 turns during stage 2.

      Confusing I know. If I had any decent software on hand I'd draw something up for ya.
       
      Last edited: Aug 30, 2012
    8. Dave B

      Dave B Active Member

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      Another alternative might be to rig a cable on pulleys located inside and near the top the center pipe run attach the cable to the bottom of that pipe run it up inside to the pulley and back down to second pipe which has a similar pulley at it;s bottom. Cable runs around it and back up a space between the two pipes to final pipe which is the outside pipe with a pulley on it;s outside.
      cable runs over this pulley and back down to base where a cap stand or winch arrangement can wind up the cable. With proper guiding
      of pipes with bushing between them to hold centricity while allowing axial freedom they will telescope out of each other with the shortening of the cable. Allow gravity with load to retract provided the guide are not binding .
      The assumption here is the load is relative centered over the pipes.

      If not the concept for the muscle is valid but the guiding may need to be small rollers.
      Pushing a rope is not easy I agree so pull on it.

      Thread and nut will definitely work for the first stage of the telescope with plenty of force available. Problem becomes a bit more complex as mentioned with he 2nd stage engagement.

      No solution exist without some complexity. I like the idea of an three stage air cylinder if it were nitrogen charged gas spring it would lift the load then you just had to figure out how to pull against the spring to lower it. That could be done with a cable if the two cables 180 from each other went up the side of the extend cylinder to a bracket and were again wound on small a winch below.
      I say winch because this would require a worm drive and possibly a brake to prevent unintended release of tension.
       
    9. Mark Stapleton

      Mark Stapleton Active Member

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      Personally I would do it with a rack and pinion arrangement ... the rack on the pole, naturally, and you can use the rack itself as a key to prevent rotation inside a keyed collar attached to the outer tube. To lift the weight and keep the size of the motor down you may have to design or buy a small gearbox (small spur gear to larger gear which acts as the pinion on the rack), but I doubt that you need to worry about lubrication or sealing because of the low frequency intermittent operation.
       

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