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robotic:arm [2020/02/10 23:08]
tony [Hardware description]
robotic:arm [2020/05/04 11:24] (current)
tony
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 ===== Overview ===== ===== Overview =====
  
-To build a computer controller robotic arm capable of moving with at least three degrees of freedom. ​ It would seem attractive to re-use a mechanical assembly, like an extendable desk lamp arm, as the basis for this:+To build a computer controller robotic arm capable of moving with at least three degrees of freedom. ​ It would seem attractive to re-use a mechanical assembly, like an extendable desk lamp arm, as the basis for this.   My first attempt was using a [[:electronic:​equipment:​lights:​superluxc|Superlux Model C]] desklamp.
  
 <​HTML>​ <​HTML>​
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 On this particular arm design the '​hand'​ end of the arm can only reach the ground from a radius of about 33cm from the base out to 50cm with the arms fully extended horizontally. ​  The under beam of the fore-arm prevents it from bending enough to reach the ground at closer distances. ​ Other lamps that have a square or pentagonal plate at the elbow, can bend without obstruction. ​ Removing the under-beam of the forearm allows the '​hand'​ to reach the ground from the base out to 50cm, unobstructed. On this particular arm design the '​hand'​ end of the arm can only reach the ground from a radius of about 33cm from the base out to 50cm with the arms fully extended horizontally. ​  The under beam of the fore-arm prevents it from bending enough to reach the ground at closer distances. ​ Other lamps that have a square or pentagonal plate at the elbow, can bend without obstruction. ​ Removing the under-beam of the forearm allows the '​hand'​ to reach the ground from the base out to 50cm, unobstructed.
 +
 +====Exploded parts====
 +{{robotic:​robotarm:​dsc_0310a.jpg?​800|Exploded parts view}}
 +
 +=====Construction=====
 +After a bit of trial and error I selected components from the lamp arm to construct my robot arm.  The springs and support struts didn't seem to be useful here and would just add weight.
 +
 +{{robotic:​robotarm:​dsc_0314a.jpg?​400|Selected components}}
 +
 +{{robotic:​robotarm:​dsc_0316a.jpg?​800|Assembled components}}
 +
 +=====Servos=====
 +I didn't have a huge choice of actuators to use to articulate this arm, the first I tried is an old eject mechanism from a CD-Rom drive, [[:​electronic:​actuator:​servo:​xm3301b-1|XM-3301B eject mechanism]]
 +
 +<​HTML>​
 +  <div class="​shadows"​ style="​text-align:​center;​ margin-left:​ auto;  margin-right:​ auto; ">
 +    <a href="/​dokuwiki/​_detail/​robotic/​robotarm/​dsc_0164a.jpg"​ class="​media"><​img src="/​dokuwiki/​_media/​electronic/​actuator/​servo/​p3029632a.jpg"​ width="​90%"​ class="​media"​ title="​XM-3301B eject mechanism"​ alt="​XM-3301B mechanism"​ /></​a>​
 +    <div class="​container">​
 +      XM-3301B eject mechanism
 +    </​div>​
 +  </​div>​
 +</​HTML>​
 +
 +The servo was mounted so that the axle of the last servo gear, went through the pivot point of the arm.   A drive pin was then inserted through the gear and further up the arm, so that as the gear turned, the arm was raised or lowered.
 +
 +=====Servo mounted on base and attached to arm=====
 +{{robotic:​robotarm:​p2279603a.jpg?​800|Side view}}
 +
 +=====Movement of servo gear and robot arm =====
 +{{robotic:​robotarm:​p2279607a.jpg?​300|Side view}}
 +{{robotic:​robotarm:​p2279609a.jpg?​300|Side view}}
 +{{robotic:​robotarm:​p2279610a.jpg?​300|Side view}}
 +
 +=====Assembled mechanism=====
 +{{robotic:​robotarm:​p2279613a.jpg?​400|Side view}}
 +{{robotic:​robotarm:​p2279614a.jpg?​400|View from above}}
 +
 +Although the servo could raise and lower the arm, it didn't have enough power to lift anything else (not even the next segment of arm made from the desklamp). It could be used as a crane, the worm drive means it holds its position well, even without power on.  The lifting would be done by cable running over a pulley at the end of the boom, and powered by another motor with spool, attached to the base.  It still needs some form of positional feedback, for example a rotary potentiometer,​ shaft concentric with the axle, and body turned by the arm.  Alternatively limit switches to detect the top and bottom positions being reached - after calibration the duration that the servo motor is powered on could be used to estimate the arm position.
 +
  
 ====== References and Additional Resources ====== ====== References and Additional Resources ======