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How do I monitor an angle?

Former Member

Hi all,

 

To say that I am new to robotics would be an understatement.  My first "mini project" is putting a camcorder on a turntable-style bearing.  The turntable has (will have) wires fed through the center, so I would like to limit the movement of the turntable to 360 degrees in order to avoid twisting up the wires.  I would also like to be able to find out the exact angle in which the camcorder is pointing so that I can chart the angle in an application.  From the searches I've done, it seems like the right tool is a absolute position encoder.  Am I on the right track?  Can anyone recommend a good product that I could use in conjunction with a turntable?

 

Thanks!

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  • You can buy 360 degree turning potentiometers, or you could use encoders, accelerometers or a simple led/detector and place a grey scale strip of paper around the turntable base.  You set up the scale so that it gives separate values for each degree.  Just about any graphics program will print you a strip to the correct change.  You could also use tic marks on a paper, but you need to have a zero angle point and keep active track of going right or left to keep track of your position.

     

    Basically, you just need to define how much accuracy you need and repeatability you need and then find a solution that works.

     

    Engineering 101.

     

    DAB

Reply

  • You can buy 360 degree turning potentiometers, or you could use encoders, accelerometers or a simple led/detector and place a grey scale strip of paper around the turntable base.  You set up the scale so that it gives separate values for each degree.  Just about any graphics program will print you a strip to the correct change.  You could also use tic marks on a paper, but you need to have a zero angle point and keep active track of going right or left to keep track of your position.

     

    Basically, you just need to define how much accuracy you need and repeatability you need and then find a solution that works.

     

    Engineering 101.

     

    DAB

Children
  • in reply to DAB

    Hi DAB,

     

    I think I liked your idea about having a grayscale ring (I'm attaching a file I created based on how I interpreted your reply).  I do have a follow-up question: If I at some point put a night-vision camera on the turntable, would the grayscale ring approach still work?  If not, maybe taking the linear potentiometer approach would be the better route.  The biggest problem I'm seeing right now with the linear pot (as described by Peter and Raimondas) is that I'm still unclear how to attach it.  My current design has a vertical "drive" shaft coming through the center of the turntable and it's getting in the way of how I thought the linear pots would attach.  Maybe I should just order a couple different kinds and play around with it.

     

    Thanks.

    image

  • in reply to Former Member

    You mean you have connected a turntable directly to the motor? What type of mottor is it? You do not use any dears? you could use some gears to make the potensiometer turn when the table turns. And then you can ujust gera ratio (size ot table gear / size of potensiometer gear) to get the maximum acuracy of your potensiometer. For example if you have potensiometer that is turning less then 360 deg, just 270 deg for axample. then you can chose the gear ratio to be about 0.7 then 360 def of table rotation will turn 252 deg for potensiometer. And you'll have spare 18 deg not to breack it. image and still have a good resolution.

    As for connectin potensiometer and mesuring its resistens, you can use arduino analog input. And if you controll talbes rotation motor with arduino, then it will be perfect.

     

    So what  will control the turning motor and what wil send comands were to turn? Is it pc over usb or what? image

     

    By the way, do you know how to connect potensiometer for mesuting it?

  • in reply to Former Member

    If you set up a LED and light detector over the ring, it would work in any lighting condition as it is only focused on the ring.

    You determine position by measuring the amount of reflectance from the ring based upon the level of grey that the detector sees.

     

    You can use gears to turn a potentiometer or an encoder to measure movement.  It all depends upon how much you intend to move and how accurate you need to know the position.

     

    Attaching the encoding device depends on access and resolution.  Most application would use the encoder on the primary turning access with a reset when you go 360 degrees.  However, you can use a series of gears or other connections and derrive your position from the movement of the table.  Again, accuraccy and repeatability will drive you to the best solution.

     

    Have fun,

    DAB

  • in reply to DAB

    Yes it depends on how acurat you want it to mesure. As for axample for this robot:
    image

    For hand position we ussed 2 regular potensiometers. It is not even a liner potensiometer, but still does the trick.

  • in reply to DAB

    I agree DAB but I think a Magnetometer may give more long term accuracy than the acelerometer unless the device is moving quite fast .. Mind you Ebay does an entire 10 DOF magnetometer, Gyro,Accelerometer for £10 so I don't think  sensing is a problem here image