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Re: [SeattleRobotics] testing robot

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  • Kevin Ross
    Compressor duty cycles are often times specified in 10 minute intervals or in 1 hour intervals. You need to check with the specific model you are looking to
    Message 1 of 20 , May 18, 2013
    • 0 Attachment
      Compressor duty cycles are often times specified in 10 minute intervals or
      in 1 hour intervals. You need to check with the specific model you are
      looking to use. A common value is 30% / 10 minutes, which means you can run
      it for about 3 minutes then it needs to cool down for the next 7 minutes.
      There are a lot of variables in this. You are also going to find compressors
      which claim to have a 100% duty cycle. Be very wary of that claim, it isn't
      actually true in most cases and especially at the pressure you are going to
      need for your device. (We have 100% duty cycle compressors for use on FIRST
      robots, but if you attempt to run them for too long they heat up and fail.
      You have to let them cool down, meaning they are not really 100% duty cycle!
      It is marketing BS.)

      I see you have some of the math below. I don't really understand the details
      for your design so I am not able to verify your numbers at the moment, but
      you seem to get the idea. If you are generating 2200lbs of force with a 10cm
      stroke, my guess is that you are going to use much more air than what you
      have stated. I base this on a gut feeling from a guy who does a lot of
      pneumatics on FIRST robots and watches the compressors heat up very quickly.
      However, if you do the math, you get to tell me I am wrong and I won't feel
      bad at all.

      Pneumatics are a full of little variances. If you need more precision, you
      should consider hydraulic. Air acts like a spring, and is full of all sorts
      of surprises. It is not instant power, nor is it linear. It is, however,
      easy to work with and pretty reliable once you get it setup. The regulators
      do a good job at not allowing the pressure to exceed a certain amount, so
      they are usually pretty accurate at limiting the pressure.

      Friction will be an issue in any device you make. The fewer moving parts,
      the fewer sources of friction.

      -----Original Message-----
      From: Peter Balch
      Sent: Friday, May 17, 2013 11:43 AM
      To: SeattleRobotics@yahoogroups.com
      Subject: Re: [SeattleRobotics] testing robot


      > Compressors have a
      > series of different ratings you need to consider, most important is the
      > expected duty cycle. They will get very hot if you exceed their duty
      > cycle.

      I hadn't considered that.

      At 700kPa that's a piston area of 14sq cm which at one operation every 2sec
      is 4 litres/min. (I think my math is right.) Even if I assume a 10% duty
      cycle that's only 40 L/min. A small compressor you'd use to paint your fence
      is 150 to 200 L/min. Even a desktop compressor can give 70 L/min.

      Would that be enough?

      > I would expect this to take a larger (60 or 80 gallon) unit to keep the
      > thing from running every couple of minutes.

      That's 200 to 200 L. Seems quite large if I'm using 4 L/min.

      > You could use the same large cylinder and have two regulators and two
      > solenoids. One regulator might run at 10psi to generate 220lbs of force,
      > the
      > other would run at 100psi to generate 2200 lbs of force.

      Interesting idea. I was assuming that the cylinder lifted a lever which
      passively dropped to provide the force. The force would depend on what
      weight we hung on the lever.

      You're suggesting that the cylinder provides the force directly (or via a
      lever) and the force is determined by the air pressure.

      How accurately can you control the force that way? Doesn't friction and
      stiction affect the force? And how accurate is the air pressure?

      It would be nice if we could use the same rig for calibration as well as
      fatigue testing so a force accurate to a couple of percent would be good.

      Peter



      ------------------------------------

      Visit the SRS Website at http://www.seattlerobotics.orgYahoo! Groups Links
    • Kevin Ross
      Compressor duty cycles are often times specified in 10 minute intervals or in 1 hour intervals. You need to check with the specific model you are looking to
      Message 2 of 20 , May 18, 2013
      • 0 Attachment
        Compressor duty cycles are often times specified in 10 minute intervals or
        in 1 hour intervals. You need to check with the specific model you are
        looking to use. A common value is 30% / 10 minutes, which means you can run
        it for about 3 minutes then it needs to cool down for the next 7 minutes.
        There are a lot of variables in this. You are also going to find compressors
        which claim to have a 100% duty cycle. Be very wary of that claim, it isn't
        actually true in most cases and especially at the pressure you are going to
        need for your device. (We have 100% duty cycle compressors for use on FIRST
        robots, but if you attempt to run them for too long they heat up and fail.
        You have to let them cool down, meaning they are not really 100% duty cycle!
        It is marketing BS.)

        I see you have some of the math below. I don't really understand the details
        for your design so I am not able to verify your numbers at the moment, but
        you seem to get the idea. If you are generating 2200lbs of force with a 10cm
        stroke, my guess is that you are going to use much more air than what you
        have stated. I base this on a gut feeling from a guy who does a lot of
        pneumatics on FIRST robots and watches the compressors heat up very quickly.
        However, if you do the math, you get to tell me I am wrong and I won't feel
        bad at all.

        Pneumatics are a full of little variances. If you need more precision, you
        should consider hydraulic. Air acts like a spring, and is full of all sorts
        of surprises. It is not instant power, nor is it linear. It is, however,
        easy to work with and pretty reliable once you get it setup. The regulators
        do a good job at not allowing the pressure to exceed a certain amount, so
        they are usually pretty accurate at limiting the pressure.

        Friction will be an issue in any device you make. The fewer moving parts,
        the fewer sources of friction.

        -----Original Message-----
        From: Peter Balch
        Sent: Friday, May 17, 2013 11:43 AM
        To: SeattleRobotics@yahoogroups.com
        Subject: Re: [SeattleRobotics] testing robot


        > Compressors have a
        > series of different ratings you need to consider, most important is the
        > expected duty cycle. They will get very hot if you exceed their duty
        > cycle.

        I hadn't considered that.

        At 700kPa that's a piston area of 14sq cm which at one operation every 2sec
        is 4 litres/min. (I think my math is right.) Even if I assume a 10% duty
        cycle that's only 40 L/min. A small compressor you'd use to paint your fence
        is 150 to 200 L/min. Even a desktop compressor can give 70 L/min.

        Would that be enough?

        > I would expect this to take a larger (60 or 80 gallon) unit to keep the
        > thing from running every couple of minutes.

        That's 200 to 200 L. Seems quite large if I'm using 4 L/min.

        > You could use the same large cylinder and have two regulators and two
        > solenoids. One regulator might run at 10psi to generate 220lbs of force,
        > the
        > other would run at 100psi to generate 2200 lbs of force.

        Interesting idea. I was assuming that the cylinder lifted a lever which
        passively dropped to provide the force. The force would depend on what
        weight we hung on the lever.

        You're suggesting that the cylinder provides the force directly (or via a
        lever) and the force is determined by the air pressure.

        How accurately can you control the force that way? Doesn't friction and
        stiction affect the force? And how accurate is the air pressure?

        It would be nice if we could use the same rig for calibration as well as
        fatigue testing so a force accurate to a couple of percent would be good.

        Peter



        ------------------------------------

        Visit the SRS Website at http://www.seattlerobotics.orgYahoo! Groups Links
      • Mark Kenworthy
        That should be “any other type that is rated for continuous service”. Our rotary screw compressor has two operational modes. One where it just runs
        Message 3 of 20 , May 19, 2013
        • 0 Attachment

          That should be “any other type that is rated for continuous service”.  Our rotary screw compressor has two operational modes.  One where it just runs continuous and bleeds off excess air, and another mode where it cycles off when reaching the preset pressure level.

           

          They are fairly expensive, as compressors go, so you might want to try to find a business that has one and work out a deal to do your testing there.

           

          Mark

           

          From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of mark@...
          Sent: Sunday, May 19, 2013 8:13 AM
          To: SeattleRobotics@yahoogroups.com
          Subject: Re: [SeattleRobotics] testing robot

           

           

          Rotary screw type compressors are designed to run continuously.  I don't know of any type designed for continuous service.

          Connected by DROID on Verizon Wireless



          -----Original message-----

          From: Kevin Ross <kevinro@...>
          To:
          SeattleRobotics@yahoogroups.com
          Sent:
          Sun, May 19, 2013 05:25:46 GMT+00:00
          Subject:
          Re: [SeattleRobotics] testing robot

           

          Compressor duty cycles are often times specified in 10 minute intervals or
          in 1 hour intervals. You need to check with the specific model you are
          looking to use. A common value is 30% / 10 minutes, which means you can run
          it for about 3 minutes then it needs to cool down for the next 7 minutes.
          There are a lot of variables in this. You are also going to find compressors
          which claim to have a 100% duty cycle. Be very wary of that claim, it isn't
          actually true in most cases and especially at the pressure you are going to
          need for your device. (We have 100% duty cycle compressors for use on FIRST
          robots, but if you attempt to run them for too long they heat up and fail.
          You have to let them cool down, meaning they are not really 100% duty cycle!
          It is marketing BS.)

          I see you have some of the math below. I don't really understand the details
          for your design so I am not able to verify your numbers at the moment, but
          you seem to get the idea. If you are generating 2200lbs of force with a 10cm
          stroke, my guess is that you are going to use much more air than what you
          have stated. I base this on a gut feeling from a guy who does a lot of
          pneumatics on FIRST robots and watches the compressors heat up very quickly.
          However, if you do the math, you get to tell me I am wrong and I won't feel
          bad at all.

          Pneumatics are a full of little variances. If you need more precision, you
          should consider hydraulic. Air acts like a spring, and is full of all sorts
          of surprises. It is not instant power, nor is it linear. It is, however,
          easy to work with and pretty reliable once you get it setup. The regulators
          do a good job at not allowing the pressure to exceed a certain amount, so
          they are usually pretty accurate at limiting the pressure.

          Friction will be an issue in any device you make. The fewer moving parts,
          the fewer sources of friction.

          -----Original Message-----
          From: Peter Balch
          Sent: Friday, May 17, 2013 11:43 AM
          To: SeattleRobotics@yahoogroups.com
          Subject: Re: [SeattleRobotics] testing robot

          > Compressors have a
          > series of different ratings you need to consider, most important is the
          > expected duty cycle. They will get very hot if you exceed their duty
          > cycle.

          I hadn't considered that.

          At 700kPa that's a piston area of 14sq cm which at one operation every 2sec
          is 4 litres/min. (I think my math is right.) Even if I assume a 10% duty
          cycle that's only 40 L/min. A small compressor you'd use to paint your fence
          is 150 to 200 L/min. Even a desktop compressor can give 70 L/min.

          Would that be enough?

          > I would expect this to take a larger (60 or 80 gallon) unit to keep the
          > thing from running every couple of minutes.

          That's 200 to 200 L. Seems quite large if I'm using 4 L/min.

          > You could use the same large cylinder and have two regulators and two
          > solenoids. One regulator might run at 10psi to generate 220lbs of force,
          > the
          > other would run at 100psi to generate 2200 lbs of force.

          Interesting idea. I was assuming that the cylinder lifted a lever which
          passively dropped to provide the force. The force would depend on what
          weight we hung on the lever.

          You're suggesting that the cylinder provides the force directly (or via a
          lever) and the force is determined by the air pressure.

          How accurately can you control the force that way? Doesn't friction and
          stiction affect the force? And how accurate is the air pressure?

          It would be nice if we could use the same rig for calibration as well as
          fatigue testing so a force accurate to a couple of percent would be good.

          Peter

          ------------------------------------

          Visit the SRS Website at http://www.seattlerobotics.orgYahoo! Groups Links

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