flying device (i call it a proto-flyer)

Discussion in 'The Projects Forum' started by mu71b, May 8, 2014.

  1. mu71b

    Thread Starter Member

    Feb 26, 2014
    43
    1
    Hi guys I am a 16 year old making a flying device which other people have called quad copter, I did not intend to copy them as i only found out about quad copters once i had started to make my flyer, i will refer to my invention as the proto-flyer, this is quite large compared to some, as this is at least 60cm x 60cm. I will be using 2 frequencies 40mhz and 27mhz instead of a 5 or 9 channel chip or 2.4ghz or 5ghz, I have both the transmitter (remote) and receiver (the chip normally inside a vehicle)

    My querie is that like in rc helicopters , would i be able to add a potentiometer in some place on the transmitter to constantly control a a channel on the reciever for altitude rather than me having to manually decelerate and accelerate repeatedly and unstoppably to keep it in a height I desire.

    e.g. would I be able to control the speed of a motor attached onto the receiver by adding a potentiometer to the remote (transmitter)

    -Thanks in advance, Kind regards...
     
    Projects Pune likes this.
  2. Little Ghostman

    Member

    Jan 1, 2014
    294
    97

    Yes.

    Look in projects at my helicopter project (in progress), I am going to implement something similar, as long as you have a micro connected to the receiver, then it can adjust the speed based on whatever commands or data you pass to it.
    I would suggest you take a look at sites like DIY DRONES, and study other quad copters and flying devices. You dont have to copy anybody (I am doing my own thing) but there are things you need to be aware of. It would be better to study some designs first, that way you have a chance to catch problems at the design stage, rather than after you have spent all the money.
    For now I am using a old RC helicopter, it came with brushed motors, in time when I can afford it I will change them to brush less. Decide up front what sort of flying time your expecting, I can guarantee you will be shocked at how hard (and expensive) it gets to get above 10 mins!
    So looking at other designs helps alot, the flying time is governed by the battery, but then you have to balance the size of battery to the amount of power the motors can lift etc! It can rapidly get into a nasty circle, so I urge you to plan it all well.

    Keep us informed and good luck

    LG
    BTW I am 14 this year, its great to see other kids doing this kind of stuff
     
    mu71b likes this.
  3. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Just some off-the-wall thinking:
    You can buy a 3 axis accelerometer chip. If you designed a circuit to maintain 1g of vertical force whenever you are not commanding it to go lower or higher, that might be feasible.

    and, no, I don't have any experience with accelerometers. This is just noodling.
     
    mu71b likes this.
  4. Austin Clark

    Member

    Dec 28, 2011
    409
    44
    Accelerometers tell you, well, acceleration. It would be difficult to use this to cancel-out vertical movement (which is speed, not acceleration), let alone maintain a constant height. Using integrals you could try to find horizontal speed, but the measurements will slowly drift away from it's real value, and doing a second-order integral (to find vertical position) would drift even faster.

    You need to use a barometer. Using barometric pressure you can find your actual vertical height. Typically within a meter or so. With this you can use a control-loop to precisely tune the output to your rotor blades to stay at a specified level.

    Oh, and it is great to see people under 20 interested in this sort of thing. I'm 20 myself and I had a very hard time finding people on my level to communicate with at that age (still sorta do). Keep it up.
     
    Last edited: May 8, 2014
    mu71b likes this.
  5. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    If you'd ever flown a plane you would know that "straight and level" is called 1g because gravity can be used as an acceleration factor in the math.
     
    Projects Pune and mu71b like this.
  6. Austin Clark

    Member

    Dec 28, 2011
    409
    44
    Yes, I know, but knowing your acceleration isn't enough to tell you your absolute velocity or position.

    Also, something else that can/will be useful later in the project. You can use the accelerometer to measure your absolute angle. This is because as you rotate, the gravity vector, which is considered down, moves as well, which you can measure with the accelerometer. The only problem is you have accelerations not related to gravity that can only really be filtered out over time. Gyroscopes have the same problem as the accelerometer, in that they only give you angular acceleration and not absolute angle, causing your estimates to drift over time. You take the Gyro, which is accurate for only short periods of time, and combine it with the Accelerometer, which is accurate over a long period of time, and you have yourself a complete system, good enough to keep your quad completely level and stable.
     
    Projects Pune, mu71b and #12 like this.
  7. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    This is the idea I was responding to. It does not mention velocity or position except for the idea that vertical movement can be measured as a velocity compared to a gravity field. If an accelerometer is not good enough for this purpose, well, that is why I brought up the idea, to find out if it is feasible.

    Visualizing the math, I can see that the difference between 32 ft per second per second must be compared to some amount smaller than 31 or 33 ft/sec/sec. That puts the needed accuracy in the 1% or better range, after calibration. I simply don't know if that can be accomplished.
     
    mu71b likes this.
  8. mu71b

    Thread Starter Member

    Feb 26, 2014
    43
    1
    Last edited: May 9, 2014
  9. mu71b

    Thread Starter Member

    Feb 26, 2014
    43
    1
    if not could you guys tell me if there is a way and if yes then how would i be able to use the potentiometer?
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,766
    1,102
    If you want the pot to command a specific altitude then you could use that as an MCU input and use the MCU to double-integrate the output of an accelerometer, resetting the integral when at ground level. It won't be easy, because of drift (as others have noted).
     
  11. mu71b

    Thread Starter Member

    Feb 26, 2014
    43
    1
    could you please tell me how to do it in simple terms e.g. attach one leg to the witch, that sort of thing
     
  12. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    So what does the accelerometer read when you climbing or falling at a constant velocity?

    Bob
     
  13. mu71b

    Thread Starter Member

    Feb 26, 2014
    43
    1
    please explain it in simple terms
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,766
    1,102
    Sorry, I can't. This is not a simple project :(
     
  15. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
  16. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    On this planet, just standing still causes a reading of 1 g. If you move upwards, you and the bathroom scale you are standing on would perceive that as being heavier. When you fall downward, you and your bathroom scale will perceive that as lighter. What the accelerometer says is what the discussion is about.
     
    Last edited: May 9, 2014
  17. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    Not really. Falling at terminal velocity, or any steady vertical rate, you still feel 1G. It only changes when you accelerate or decelerate.

    Controlling height based on barometric pressure is fraught with another big set of problems. I think ultrasonic might be a better technology if the altitudes are not too great. Combining several methods is likely the best strategy. For instance, accelerometer gives fine control to prevent oscillation, barometer and ultrasonic give ranging.
     
  18. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    So you're saying that free falling from an airplane with a bathroom scale strapped to which ever side of you is down, the scale would still display your steady state weight on the surface, and changing altitude from 100 feet up to 200 feet up will not register on an accelerometer while you're changing altitude. OK. I can live with that.
     
  19. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    It's true, amazingly. Of course air resistance is holding you up (keeping you from accelerating further) instead of the scale. If you could somehow isolate the air resistance behind only the scale, with none on you, your weight on the scale would be .... your weight. Losing or gaining altitude at constant velocity will definitely not register on an accelerometer.

    But a sudden drop in local air pressure that causes the copter to fall, will. That's why I think an accelerometer would help hold vertical position far more precisely than a barometer. The OP is going to need one anyway, to hold it level.
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Or a tiny cheap ultrasound distance sensor, pointed at the ground. :)
     
Loading...