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Re: [SeattleRobotics] testing robot

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  • ListServ
    Clippard has a pretty complete product line, and some good documentation on pneumatics. Look at their knowledge base and catalog for what is possible.
    Message 1 of 20 , May 17, 2013
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      Clippard has a pretty complete product line, and some good documentation on pneumatics. Look at their knowledge base and catalog for what is possible.
      http://www.clippard.com/

      The symbols you see are likely pneumatic ansi symbols. A google search will describe them. If you can read a schematic, the pneumatic drawings should be understandable.



      On Thu, May 16, 2013 at 8:50 AM, Peter Balch peterbalch-at-btinternet.com |Listserv| <lf4fhwmmot@...> wrote:
       

      I want to fatigue-test some load cells. For instance, apply 100kg for 1
      second 50,000 times and apply 1000kg 1000 times; total travel 10mm.

      In our local Ikea store, there's a demonstration device that uses pneumatics
      to open and close a cupboard door all day long. That's the sort of thing we
      need.
      http://www.youtube.com/watch?v=fPTyGGGaWq8
      (OK, I know that's a demo not a real test.)

      I can find lots of pneumatic stuff in catalogs, e.g.
      http://uk.rs-online.com/web/c/pneumatics-hydraulics-power-transmission/pneumatic-cylinders-actuators/pneumatic-compact-cylinders/

      But it's very hard to get started. What should we buy? What pressures do we
      use? How do we do the sequencing: via electric solenoid valves or pneumatic
      logic?

      What I need is a beginner's guide. Is there a website or a book? A DIY
      explanation?

      Peter


    • 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
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        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 3 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 4 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
          • Peter Balch
            Thanks Kevin. I think I m beginning to understand what we need to buy but the valves are still a mystery. If I want active retraction of the cylinder (i.e. a
            Message 5 of 20 , May 19, 2013
            • 0 Attachment
              Thanks Kevin.

              I think I'm beginning to understand what we need to buy but the valves are
              still a mystery. If I want active retraction of the cylinder (i.e. a
              double-acting cylinder) then maybe I'll need a 5-port 2-Way, 3-way or 4-way
              solenoid valve. Or maybe a 5-port air-spring valve operated by two 3-port
              2-way solenoid valves. Or maybe just use two 3-port 2-way solenoid valves.

              When I look at the catalogues, there's an enormous range of valves to choose
              from with no clear way of making a decision.

              Then I look at the photos of the valves and realise the connectors for the
              hoses need to be the right type. Are there different ranges? Which is bect
              for what we want to do? Presumably, it depends on pressure and airflow. And
              so on and so on.

              I can see what I need in theory and I can see where to buy Stuff. But
              there's still a big gap between those two.

              Peter
            • mark@kenworthymachine.com
              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
              Message 6 of 20 , May 19, 2013
              • 0 Attachment
                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

              • 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 7 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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