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What to use for spinning "radar". — Parallax Forums

What to use for spinning "radar".

NWCCTVNWCCTV Posts: 3,629
edited 2015-03-21 11:15 in General Discussion
I want to put something similar to a radar on my Wild Thumper. The idea is to have a servo spin either a ping sensor or a PIR sensor mounted to a slip ring/servo. I am wondering which would be better and also should I use just one or would 3 in a triangle work out better. The idea is to fly my quad over the Wild Thumper and have the sensors detect it and then have my Laser Range Finder "lock in" on it and shoot it with mini missiles!!!! Quite a long shot I know but it has been an idea that has been brewing in my head for a while now and I am just getting around to the planning stage. My ADD does not let me finish one full project without starting several more!!!

Comments

  • Mark_TMark_T Posts: 1,981
    edited 2015-03-20 03:25
    In processor design that's called pipelining and leads to more efficient (mis)use of resources!

    I guess a scanning servo mount would enough and quite simple - or a stepper motor.
  • abecedarianabecedarian Posts: 312
    edited 2015-03-20 06:54
    For 3d scanning, you could use a pan and tilt mount. One servo / stepper controlling the horizontal pan and another controlling the vertical tilt.
  • RagtopRagtop Posts: 406
    edited 2015-03-20 07:10
    If you do go with something that rotates you might want to look at these slip rings for running the sensor wires. I made a feeble attempt at
    making one for a POV project, but if I had the money I think I would just buy one.

    https://www.sparkfun.com/products/13064
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2015-03-20 07:17
    Two sensors back to back and rotating 180 degrees on a standard servo would probably work; 3 would provide more overlap coverage, but might be overkill if your servo can travel 180 degrees anyway.

    Slip rings like the Sparkfun product are fine but if these are standard IR or ultrasonic sensors you're talking about, a second sensor might be cheaper.

    If you go the 360 degree spin route, a stepper motor with an index signal (so you always know where "home" is), or a gear motor with an absolute encoder would be required, so you know which way the thing is pointing.
  • ercoerco Posts: 20,256
    edited 2015-03-20 08:13
    Perfect laser sensor tracker project if you can put some Scotchlite under your quad! Use Duane's $2 Pan & tilt servo bracket.
  • kwinnkwinn Posts: 8,697
    edited 2015-03-20 08:47
    You could make it simpler (no slip rings) by having the ir or ping fixed and a reflector mounted at 45 a degree angle to the sensors rotating to perform the scan.

    A pir sensor would be triggered continuously if it was rotating so I am guessing that you were referring to a reflective ir sensor.
  • xanaduxanadu Posts: 3,347
    edited 2015-03-20 08:51
    I'd imagine without traditional radar, machine vision and or cameras, you'd need an array of sensors.

    I've been trying to use PING and IR to track a copter and it doesn't work well at all. The area that you need to scan is massive considering the size and sweep of a single beam and the size of the copter. Using an array of sensors would alleviate a lot of scanning.
  • ercoerco Posts: 20,256
    edited 2015-03-20 08:56
    No need for slip rings, as you're only looking upwards from the WT (upper half sphere view). An XY pan setup gives full 180 degree coverage and doesn't need to spin.. Probably easier to write realistic tracking algorithms for XY than polar coordinates, too.
  • ercoerco Posts: 20,256
    edited 2015-03-20 09:02
    xanadu wrote: »
    I've been trying to use PING and IR to track a copter and it doesn't work well at all. The area that you need to scan is massive considering the size and sweep of a single beam and the size of the copter.

    What this country needs is a good 5-cent blimp target. Big & slow, easy to detect, track and hit.

    On a copter (indoors or at night) you could have it emitting a 38 khz IR signal, which would make it easy to detect & track. Not sure if an emitted ultrasonic signal would get messed up by wind & propwash.
  • kwinnkwinn Posts: 8,697
    edited 2015-03-20 09:12
    A flying Wild Thumper??????
  • xanaduxanadu Posts: 3,347
    edited 2015-03-20 09:19
    erco wrote: »
    What this country needs is a good 5-cent blimp target. Big & slow, easy to detect, track and hit.

    On a copter (indoors or at night) you could have it emitting a 38 khz IR signal, which would make it easy to detect & track. Not sure if an emitted ultrasonic signal would get messed up by wind & propwash.

    A beacon on the copter would help tremendously. Probably easy enough to use a wii camera, of course not ideal on a bright day outside :(

    Also if you need some rockets to shoot check this out -
  • LawsonLawson Posts: 870
    edited 2015-03-20 15:05
    Might also be able to track the quad-copter with a passive sonar rig. I'd expect it to be particularly loud at the PWM frequency. Based on PhiPi's RF work with the counters, I bet a pile of counters could be configured to do most of the ADC and correlation work. (PhiPi's IR proximity sensor multiplexing demo would also be relevant) Some 74AC164 chips could be used as digital delay lines to give electronic beam steering as well.

    Marty
  • NWCCTVNWCCTV Posts: 3,629
    edited 2015-03-20 18:06
    Thanks for all the great ideas!!! I already have the slip rings, several pings and several PIR sensors. I was kind of wanting to make it look as realistic as possible which is why I was thinking of using a CR Servo. However, I like the idea of using two PING's on a standard servo. I am not wanting to take it outside and would only be flying a couple feet over the WT. It's basically just a project I thought of that I want to prove to myself I can do. I bought a spinning missile launcher from Amazon that I plan to hack to use as the launcher!
  • NWCCTVNWCCTV Posts: 3,629
    edited 2015-03-20 20:38
    Next question. I think the answer is no but will ask any how. Can I use the same signal pin for more than 1 ping if they will be doing the exact same thing?
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2015-03-20 22:02
    Andy, When you say PIR sensor, are you really talking about a passive infrared (motion) sensor, or do you mean an IR sensor like the Sharp units Parallax sells? A PIR is totally useless on any moving platform. Interesting sensors, but quite ineffective for what you describe in your project.

    As for sharing pins, if you're going to use a CR turret with a slip ring, you'd only need or want one Ping, yes? I'd think you'd either use multiple Pings on a non-360 servo (separate signal pins), or a single Ping on a CR servo (one signal pin). In the end, though, it's one Ping, one pin. While one pin could fire two Pings, how do you detect the echos you get back, and know which is which?
  • NWCCTVNWCCTV Posts: 3,629
    edited 2015-03-20 22:26
    Gordon, As I stated in post 14, I like the idea of 2 Pings on a standard servo instead of a CR. As for the PIR I was talking about the ones Parallax sells but I have nixed that idea. What kind of height can I expect to cover with the Pings?
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2015-03-21 08:15
    NWCCTV wrote: »
    Gordon, As I stated in post 14, I like the idea of 2 Pings on a standard servo instead of a CR. As for the PIR I was talking about the ones Parallax sells but I have nixed that idea. What kind of height can I expect to cover with the Pings?

    I wasn't clear you were not using a continuous turret, because you then asked about using just one signal pin, as might be the restriction if you had a slip ring.

    I seem to recall Parallax publishes the beam pattern of the Ping, which would answer the question regarding height. You will also need to consider the use of ultrasonic sensors outdoors, and the effects of wind, especially at the max echo distance of approximately 12 feet.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2015-03-21 11:15
    Sorry for the confusion. Any how, I do not plan on using this outside. It is just an indoor "waiting for it to stop raining" project!!!
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