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Which rotational sensor... — Parallax Forums

Which rotational sensor...

Paul ShermanPaul Sherman Posts: 11
edited 2006-12-27 01:04 in General Discussion
...would be best for my project?

I need to make a BS2 aware of direction and RPM (this will be a very slow rotation, 30-40 RPM). I can use either a shaft, sprocket, idler sprocket, or flange bearing to get the info from, so I have options there.

My machine will most likely be pretty jerky & lumbering, so something delicate that needs to maintain a precise distance from sensor might not be ideal. "Forgiving" would be a good feature here.

So, photoelectric, infrared, hall effect; which would be suited best?

Thanks
Paul

Comments

  • T ChapT Chap Posts: 4,249
    edited 2006-12-26 23:13
    If you are firm on the BS2 and not open to the Propeller then you would most easily do this with an quadrature encoder rom USdigital.com. They have a chip that will translate the encoder pulses to a two pins, Count and Direction, which can be pluggeed drectly into the BS2. The BS2 would read two pins, Count and Direction, from which anytype of info can be derived by the right code. They are closed til 1/1/07 but call them and describe the requirement and they'll get you the part numbers. The E2 encoder will be a good bet. You'll have to fab a 1/4" shaft to be mounted on some precision bearing, this shaft will mount the encoder. RPM can be derived from counting the input pulses over some time period, and doing the math from there.
  • Paul ShermanPaul Sherman Posts: 11
    edited 2006-12-26 23:21
    Hello, and thanks-

    Not necessarily "firm" on the BS2, I just have a BOE so it's easy to test with what I've got. Sounds like the BS2 will be fairly useful here, I'll check out the quadrature encoder.

    Would the Propeller be a better choice here?

    Thanks
    Paul
  • T ChapT Chap Posts: 4,249
    edited 2006-12-26 23:34
    The only reason I suggest the Prop is that is has a Rotary Encoder object already done, ready to plug in the encoder and start counting. The obvious advantage is speed and cost, but at speeds you described the Stamp can handle it I think. The thing is, what are you going to do with it when you get it working? For a one-off, cost isn't a concern to prototype with a Stamp, but if you are going to sell it then the Stamp is pricey for a production part. The Propeller could handle 16 encoders at once, and could do a hundred other things too at the same time. Your Stamp will be all tied up looking at Direction and counting, so if it has to go do something that requires much code then the Stamp is going to not handle many things at once. So yes the Prop is a better choice all the way around, and even for someone new, this usage is very basic for the Prop.
  • Paul ShermanPaul Sherman Posts: 11
    edited 2006-12-27 01:04
    I had intended the machine to be entirely mechanical/hydraulic, but it becamse obvious that a microcontroller could handle my leg synchronization & steering issues fairly simply, so I started researching how to control my hydraulic pumps with servos.

    This won't be sold. I just wanted to build & develop a large walking machine; learning the programming is a recent development.

    I will check out the Propeller...

    Thanks a lot-
    Paul
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