Help With Motor Boat Race

Discussion in 'The Projects Forum' started by LegendofZeroOne, Feb 23, 2008.

  1. LegendofZeroOne

    Thread Starter New Member

    Feb 23, 2008
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    Hi I'm needing help with a project for school. The project is to build a miniature motor boat that will carry a Navel Orange through a fountain-pond. I'm having trouble specifically with the electronic and circuit elements in my design as I have very very very little knowledge of circuits, but if someone could explain it to me from the ground up I could learn it (i.e. I'm not an idiot).

    The pond is semicircular in shape with a fountain in the center of the pond. The object is to get from one corner to the other. The two viable routes are obviously straight through or following the arc. However, there will be a mesh that blocks the straight path twice. The mesh starts at the base of the pond, wraps around the fountain and returns to the base. I want to consider the curved trajectory. The hard part is that the boat must be self-propelled and self-guided. So after I turn it on and set it in the water, it must reach the end on its own.

    I plan on using DC Motors and propellers (duh) to send the boat on its course. The boat will head straight from the finish and at a specified time, either turn off or turn on a motor to enable the boat to turn and after another period of time to do the opposite and let the boat go straight again. But how to I deliver the timed action?

    I'd like to reemphasize that i really only need help with the circuit elements of the boat. I'd like to keep my source voltage at or below 12VDC so I don't have to carry too many batteries on board. The total length of the run will also not exceed 1 minute (it is a race after all).
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
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    Timing is best accomplished with a nifty little gizmo we call the "LM555 timer." It is a tried and true favorite of designers. You can learn about it at Tony Van Roon's web-page: http://www.uoguelph.ca/~antoon/gadgets/555/555.html

    This will let you turn on your "steering motor" at a specified time after launch, and for a specified time. It will be up to you to figure out how much time is needed for both.
     
  3. LegendofZeroOne

    Thread Starter New Member

    Feb 23, 2008
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    Will I be able to accomplish turning on the motor and then turning it off with just 1 555 timer?

    Another thing is I know that the time constant is t=RxC. Is there any difference in which is more preferable for resistance and capacitance? That is, is it better to have low resistance and high capacitance or high resistance and low capacitance or is there no difference in practice? Otherwise, which would drain less power from the battery?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    You may be better off to use a single larger motor/prop, and a rudder to steer the boat, instead of trying to steer using speed differentials on twin screws. This would simplify your construction, as you would only have one propellor shaft to deal with. Or is the boat design "fixed?" (ie: you cannot substantially deviate from a given design)

    You'll want to have the motor very low in the boat for maximum stability.

    If you're looking for a really fast boat, you might consider a hydrofoil or ski design.

    As far as timers - no, a single 555 will probably not be adequate. This seems to be a task more suitable for a microcontroller, like a PIC. You could use the PIC for functions like turning the main motor on and off, and changing rudder steerage angle at predefined times. A microcontroller (MCU) can do these things very precisely; but you will need to write a program and design the interface circuits.
     
  5. LegendofZeroOne

    Thread Starter New Member

    Feb 23, 2008
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    I am considering a hydrofoil design because I'm trying to make the run in well under 60 seconds and the fountain is rather large. The problem is I won't be able to test the boat directly in the fountain until the race. I chose not to use a rudder because it would be way too complicated. But if I ever figure out how to design the circuit (which I can't even do for a simple timer right now) then I'll work on the rudder. But are there any simple solutions for a predefined fixed rudder input?

    The race is also very competitive and its nearly impossible to make it with a single motor. Although that has nothing to do with steering. I haven't really decided on whether to use a rudder or steering motor yet.

    *A side note, the vessel cannot leave the water at any point with only one exception, if you pile straight through the barricade and JUMP the mesh. I thought it would be really cool to do that, and it would similar circuits but I haven't thought of a way to make a boat leap yet. Especially since the location of the mesh will be very unpredictable. Ive pondered about a photosensor but my maximum spending for this project is $60.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    There is a "simple PWM circuit" in the Projects Collection forum I put up a month or so ago. It would work fine on anywhere from 10V-14V. With some additional circuitry, you could use that to vary the current supply to your motor(s).

    You seem pretty set on using two motors. It may be a good idea to have them running in opposite directions, to cancel out each other's gyroscopic effect. Otherwise, the boat will turn very quickly in one direction, and be difficult to turn in the opposite direction. However, precision props may be pretty expensive. In any event, will be important to have them running very close to the same speed, or your boat will quickly go off course.

    You're going to have to figure out a bunch of things; how quickly the boat will accelerate from a dead stop to top speed, precisely when you need to begin the turns, how sharp the turns must be. The sharper the turns are, the more momentum you will lose.

    Simply varying the speed of one motor may not be enough to turn the boat. You would have to have the motors as far from the keel centerline as possible in order to generate sufficient torque differential to turn it; but the wider the boat is, the more loss from friction against the air you'll have.

    A rudder design can be a bit tricky in itself. It should have a slight positive stability. By that, I mean slightly less surface area forward of the vertical rotation point than aft. By keeping the stability low, it will take less force to move the rudder.

    You could consider using a pair of solenoids to steer the rudder, attached by lightweight springs. This would tend to keep the rudder centered when neither solenoid was energized. A servomotor under PWM control would be a more elegant solution, but you're trying to keep the costs down.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    Have you considered an air-boat?

    That would keep all of the complicated parts above the water-line. You could still have a rudder if required

    hgmjr
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
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    What material is the mesh made from?
     
  9. LegendofZeroOne

    Thread Starter New Member

    Feb 23, 2008
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    @thingmaker3: the mesh will be the orange construction mesh.
    @everyone else: i only needed help with the circuits, you guys are thinking way too hard about this.

    but how to jump a wall of construction mesh would be interesting, haha.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    So the sequence of events is:
    Boat is turned on manually.
    1) Boat runs for "i" seconds straight ahead.
    2) Boat enters a turn to one side for "j" seconds.
    3) Boat resumes a straight-ahead path for "k" seconds.
    4) Boat enters a turn in the opposite direction of the turn in step 2) for "l" seconds.
    5) Boat resumes a straight-ahead path for "m" seconds.
    6) Motors off; full stop.
    Need some numbers for i, j, k, l and m.
     
  11. LegendofZeroOne

    Thread Starter New Member

    Feb 23, 2008
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    skip steps 4) 5) and just for the sake of simplicity ignore step 6)
    i+j+k cannot exceed 60s. But the smaller the sum is the better.
    But just so i can understand this circuit lets say 10,10,10 or 10,20,10 or something like that.

    So I have the 555 ic, a 1000 microF capacitor and a few 10k Ohm resistors. So the external RC circuit with 1 capacitor and 1 resistor has a time constant of ~10s. So now what?

    Uhh the pins on the 555 timer are not numbered and I cannot find any obvious way of identifying which pin is which, is there something I should be looking for? It's a 555CN
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    You're going to need more than just one timer.

    Put the 555 IC on the desk in front of you, so that you can read the text printed/etched in the top of it. You should notice that one end (most likely the left end) has a bump/divot/dot in the lower left corner, and/or a notch out of the left end.

    The pin in the lower left corner is pin 1, then to the right is 2, 3, 4 - cross over straight up, and continue counting to the left, 5, 6 7 8.
    If you rotate it 90° to the right, it'll look something like this crude ASCII representation:
    Code ( (Unknown Language)):
    1.     +--U--+
    2.  1 =|o    |= 8
    3.     |     |
    4.  2 =|     |= 7
    5.     |     |
    6.  3 =|     |= 6
    7.     |     |
    8.  4 =|     |= 5
    9.     +-----+
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    You need a much smaller cap. 1000uF will suck up lots of current. You need the power for the motor(s).

    Instead, get a 47uF cap for timing, and a 0.01uF cap for pin 5, and a couple 0.1uF caps to bypass the power pins. It would not be a bad idea to use the 1000uF capacitor as a filter cap where the power connects to the board; those motors will be making a lot of electrical noise.

    You're also going to need the following resistors:
    10k (2)
    47k (1)
    And for each timed event, you'll need one 500K pot, one 10K trimpot, and one 1N400x (x=1 to 7) or 1N914 or 1N4148 diode, along with 1 extra diode.
    You will also need a 4017B CMOS 5-stage Johnson counter. It MUST have the B suffix. You will use one of the 0.1uF caps to bypass the Vdd/Vss pins on each IC.

    It will be very helpful to you if you get a circuit board with pre-drilled holes.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    OK, I changed tactics just a bit. Now using a 4093B quad NAND gate w/Schmitt inputs rather than the 555. This actually simplifies the circuit, while giving you more options than you would've had with just a single 555.

    Upped the 10k trimpots to 50k, but if you've already ordered some you can use them. Need a 100uF cap instead of the 47uF.

    See the attached schematic with O-scope representation of output signals. You may need to click on it to blow it up to full size, otherwise it'll be hard to read.
    Note that the IC's Vdd/Vss pins and the 0.1uF bypass caps are not shown, but are required - along with your 1000uF cap to use as a filter cap.
     
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