Shop OBEX P1 Docs P2 Docs Learn Events
Linear Actuator or Servo? — Parallax Forums

Linear Actuator or Servo?

BullwinkleBullwinkle Posts: 101
edited 2005-09-12 14:00 in General Discussion
I haven't bought a Stamp yet. But Im pretty certain it is the way to go for a few interesting projects I have in mind.

One of these projects is a smart cat door that reads our cats RFID tags and only lets them in and out. I don't want to have an automatic door ( at least no in the first instance ). I was thinking I would have a regular cat flap with a latch on either side. The latch would drop, or swing out of position to allow the cat door to move once the cats RFID tag and been read and confirmed.

I am a total newbie to all this robotic stuff. I imagined a sliding metal pole for these "latches", one either side of the cat flap, that simply prevents the flap from swinging. I have looked around the Internet and found devices called "Linear Actuators" that look like they might to this job. Servos also seem to be a good option.

What would be better for this application, servos or linear actuators?

Comments

  • John R.John R. Posts: 1,376
    edited 2005-09-12 04:27
    How about a simple spring loaded electrical solenoid. In the "relaxed" or un-energized state, the plunger could stop the gate from swinging. When energized, the plunger could be held out of the way. If you needed a different form of travel, a linkage could be used. You might even be able to use an actual electrically released door latch, just like on a security door when someone has to "buzz" you in. The "buzz" is the solenoid releasing the latch.

    If you go this rout, make sure the solenoid has a long enough duty cycle so that you can keep it on long enough for the cat to open the door.

    If you did the latch mecanism "right", it could work like the doors described above. You'd only need to keep the latch open until the door was ajar, then when the cat came through, and the door swung shut, it would relatch without the solenoid being activated.

    John R.
  • John R.John R. Posts: 1,376
    edited 2005-09-12 13:04
    One more thought on the RFID part of the application.

    The stated read range is only about 4" with the RF reader from Parallax. Will that be enough range to even read the tag on a cat (or other pet).?

    The smaller tags have an even shorter read range, and at the low frequency these particular tags use, the "water" in the pet's body may reduce the range even more, depening on the "angle of approach".

    John R.
  • BullwinkleBullwinkle Posts: 101
    edited 2005-09-12 13:29
    I don't know John.

    The RFID chips are embedded between their shoulder blades, which is only about 10cm behind the tip of their nose. As they head-but the door, the chip should be within 4 inches of the antenna, in theory.

    Does antenna size improve the reception distance? I plan to lay an antenna coil right around the cat door.

    I am not using the Parallax RFID reader, but the TI Series 2000 Micro Reader ( http://www.ti.com/rfid/docs/manuals/pdfSpecs/RI-STU-MRD1.pdf ) This unit operates at 134.2 kHz and should read our cats RFID chips.

    I guess I'll have to suck it and see! If it works great, if it doesn't - bugger it - I'll still be having fun! smile.gif
  • John R.John R. Posts: 1,376
    edited 2005-09-12 14:00
    I'm not an RFID expert, but have been looking into it (and will be purchasing and testing soon) for a model railroad application.

    Antenna size, frequency, tag configuration/orientation and surrounding environment are all part of read distance. I assume the tags are "passive". If this is the case, upping the power on the antenna may also help. I don't know what the limits are for that. The TI stuff looks interesting.

    Let us know how things work out. I may need to do some of my own antenna work for my railroad project.
Sign In or Register to comment.