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Author Topic: Electrical Main Engineering Notebook 2008  (Read 158898 times)


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Re: Electrical Main Engineering Notebook
« Reply #30 on: March 04, 2008, 09:45:24 PM »

Updated Pneumatics
<3 Jessica Lynn


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Re: Electrical Main Engineering Notebook
« Reply #31 on: March 25, 2008, 11:55:54 AM »

Here is the updated pneumatic schematic.

Summary of changes to current schematic and existing hardware:

  • Removal of one (or more) storage vessel(s)
  • Removal of both arm actuator flow control valves
  • Reduction of operating pressure
  • Addition of one 5-way valve and sub-base
  • Addition of pipe plug in "B" port of new 5-way valve
  • Addition of 90 air line fitting to cylinder rod end port
  • Addition of single air line to arm cylinder rod end port
  • Open (or remove) the gripper flow control valves to increase speed
  • Addition of power relay (spike?), wiring, and controls as required

Notes on changes summarized above:

Storage Vessels:  One or two storage vessels can be removed as required to reduce weight.  Amount of on-board air storage required depends on operating pressure of the working circuits - the lower the working circuit pressure, the less air storage (at pump pressure) is required.  Enough air must be stored to allow the arm to raise fully without slowing - the lower the pressure at the cylinders, the less air volume (at atmospheric pressure) is required to cycle the arm, and the shorter the recharge time.  Lower working pressure equals more arm cycles per unit time, and less recovery time between arm cycles.

Flow Control Valves:  These are simply adjustable restrictions that regulate the flow rate of air leaving the cylinder (but not entering - the restriction is bypassed in that direction), and since the addition of an air line and valve to the rod end port of the arm cylinder will result in additional restriction, it would be prudent to remove the existing flow control valve.  The bore-end flow control valve was already removed at the last competition.

Operating Pressure:  Geometry of the arm, cylinder, wrist, and ball combinations dictates the lowest circuit pressure that will raise the arm and hurdle the ball.  The highest pressure required in the working circuit is dictated by the hurdle position, with the ball and gripper outstretched.  Changes in the control routines and driver technique will allow the arm to raise with lower air pressure due to the ball and grab centers of gravity being closer to the shoulder pin, followed by hurdling the ball (rolling the wrist forward) only when it is in close proximity to the hurdle.  Keeping the ball and gripper rolled back while approaching the hurdle can result in a substantial reduction in required air pressure.  As long as the ball does not have to be supported by the arm and cylinder alone at full extension (max radius) during hurdling, the air pressure can be lowered to save energy.  The minimum workable pressure is best determined by trial and error, and driver technique will have to be adjusted to compensate for reduced ability to support the ball at long reach without the arm sagging.  Rolling the wrist forward to hurdle in such a way that the hurdle prevents the arm from sagging during the last 45 of wrist roll may prove beneficial. 

5-way Valve:  Reinstall the poker valve in it's original mounting location.  Install a pipe plug in the "B" port.  From "A" port, install new air line to rod end port of arm cylinder, using new 90 air line fitting to replace flow control valve.  Recommend strapping new air line to cylinder body, but don't crush the line.  Keep air line as short as reasonably possible to reduce flow restriction.

Open Gripper FCV's:  Hurdling with a coordinated wrist roll and gripper open command may be improved by increasing the speed at which the gripper opens.  Open the FCV on the bore end of the gripper cylinder to increase opening speed.  If the speed is still not enough, the FCV can be replaced with a plain fitting.  Same thing applies to the closing speed, but the rod end FCV is adjusted or removed.

Electrical power and control elements:  The "power down" valve should default to the "A" coil being energized (continuously) unless and until the "B" coil is momentarily energized to pressurize the rod side of the arm cylinder.  Recommend interlocking (either at the control or at the power level) the two arm cylinder valves such that the arm driver can pre-engage the arm down button in anticipation of the need for rapid arm lowering after a hurdle (for instance).  Consider utilizing a presently unused button on the X-box control, or on the console.  Pre-engaging the lower valve will result in BOTH valves shifting when the normal arm lower command is sent.  The arm will start downward almost immediately upon engaging the normal 'arm lower' control since a charge of air will be sent to the rod side of the cylinder, but only a small amount of air will be used if the power down button is released shortly thereafter.  Experimentation by the drivers, of course, would determine the optimum sustain time for getting the arm under the hurdle as quickly as possible (if desired), with the least stored air volume used.  Of course, it doesn't have to be used at all for normal arm lowering, but game play may be enhanced for those instances where it's crucial to get the arm down as quickly as possible.

Tuning Suggestions:  Recommend experimenting with working circuit air pressure starting at a substantially lower pressure than it is now (it's at 50 psi presently), and working up from there.  Driver technique will have the greatest affect on operating pressure, as relatively little pressure is needed to raise the ball with the wrist rolled back.  High pressure is only needed to support the ball at long reach, so if the drive team hurdles the ball by rolling the wrist only in close proximity to the hurdle, the structure can support the arm for the brief time the forces on the cylinder overpower the air pressure.  The lower the air pressure they can work with, the more arm cycles they will have available to them during the 2-1/4 minute match. 

It's easy to simply set a high pressure and call it good, and with three storage vessels (down from four) there is not likely to be any noticeable difference in performance.  But if frequent hurdling is needed, as in one recent match at RIT, the less air that is used for each hurdle, the more hurdle cycles will be available during the match without waiting for the compressor to push the arm up.
Be seeing you . . .
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