Loading ...
Sorry, an error occurred while loading the content.

Re: [SeattleRobotics] testing robot

Expand Messages
  • 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
      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.



      Visit the SRS Website at http://www.seattlerobotics.orgYahoo! Groups Links
    Your message has been successfully submitted and would be delivered to recipients shortly.