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Cheaper, simpler Oilpan

Posted by Jonathan Lussier on January 5, 2011 at 7:32am
I'd like to propose a new, cheaper oilpan with (much) cheaper sensors embedded.  The goal would be to have an oilpan (that probably couldn't be used for quads, but for gliders or some planes it would be OK) that is priced at around 30-40$ instead of 160$.  It would be pin-compatible with current oilpan.
Features (modified from Oilpan specs)
  • Single 3.3V regulator
  • Relay switch for cameras, lights or payloads
  • LSM303DLH 3-axis Accel / 3-axis Magnetometer (~5 dollars) (I2C communication)
  • LYPR540AH 3-axis gyro (~5 dollars) (analog)
  • 3-channel, 12-bit ADC for gyro
  • No Data logger
  • No DIP switch
  • Built-in FTDI, making the board native USB. [can this be removed?]
  • No OSD port.
  • No extra I2C port
  • No user-programmable buttons
  • No analog expansion ports
  • Reset button.
  • No voltage dividers
  • One status LED
  • Airspeed sensor port (optional, sold separately).
  • Pressure sensor and temp for accurate altitude (can this be made optional?).

I'm going to start working on the EAGLE files this weekend, what is everybody's thoughts on this?

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Comments

  • bGatti January 6, 2011 at 10:06am

    @Marshall, Op amps (741) are nearly the first circuits commercially implemented as an "integrated circuit"

    Kilby_solid_circuit.jpg?width=270First Integrated Circuit -  Scale: 1/16 of an inch wide

    Op amps have undergone two important changes: 1, the price has dropped from like ~$1000* per chip to < $0.15 cents per amplifier. and 2. The initial requirement for a split power supply (+- 15V) has moved to single side supply.

     

    A Wheatstone Bridge is pretty cool; it is the basic component of nearly all force sensors and illustrates a basic concept in temperature compensation. By using the same circuit twice (one inverted) the effects of temperature are linearized. The challenge of Wheatstone bridge is that the signal is not high as it turns on small changes in the dimensional cross section of stretched wires. (I've implemented a similar sensor - Plan on initial gain of ~100x)

     

    *Todays dollars IIRC

  • Jonathan Lussier January 6, 2011 at 7:22am

    Marshall,

    yes we could start with your board, but it'd be good to have its footprint and pinout identical to Oilpan so that all those with APMs can now have a cheaper option.  I think the price of APM is pretty good and the board is obviously very well designed so I'd like to maintain compatibility with it.

     

    bGatti, that pressure sensor looks good.  I'm not familiar with designing with opamps, I guess I can look at a tutorial on how to implement one, like an MCP6021?

     

  • bGatti January 5, 2011 at 8:02pm

    h.800,s.1,w.800,yajmikura.true,m.a8e7503960909520da44d7f24d9a430e,8472,tdr_120.jpg?width=250There is a pressure sensor for $1 while you're looking for low-cost. (Speed not altitude) 

    http://www.allelectronics.com/make-a-store/item/TDR-120/PRESSURE-TR...

    It needs an OpAmp because it's a Wheatstone bridge. 

     

  • Mark Grennan January 5, 2011 at 7:33pm

    If you/we put the PPM encoding in the main chip (code) does this give us access to the PPM output?

     

    Could we record an in flight maneuver and replay it? If so, maybe we don't want to git rid of the data logger.

  • marshall scholz January 5, 2011 at 6:57pm

    pete, I am making a board similar to what is requested on this page too, only for the regular ardupilot, if you are willing i could use your help too, also I could adapt my board designs for use on the ardupilot mega.

    my project page can be found here: http://diydrones.com/forum/topics/ardupilot-imu

    thanks

  • Moderator
    Roberto Navoni January 5, 2011 at 3:00pm

    Hi Jonathan ,

    if you need only gyro and acc you can hack wii :) See multiwii project only .. it's a good toy:)

  • Jonathan Lussier January 5, 2011 at 1:18pm
    Chris, does that mean the PPM input/output on the APM is driven by the FTDI of the IMU shield?
  • 3D Robotics
    Chris Anderson January 5, 2011 at 10:37am
    @Thomas: what we're doing with the next APM/IMU combo is moving the PPM encoder chip to the atmega32u2 so it can also serve as the USB interface. That means the IMU shield doesn't need to do it and we can remove the FTDI chip and connector.
  • Thomas Saunders January 5, 2011 at 10:30am
    You could try replacing the FTDI chip (and maybe even the main micro controller?) with one of the usb avr chips, e.g atmega32u2.
  • 3D Robotics
    Chris Anderson January 5, 2011 at 9:01am
    As I announced yesterday, we will be releasing cheaper, simpler IMU shields early this year.  This is an open source project, so you're very welcome to use our designs and we love people make variations that suit their own purposes better than what we make. But we will have something in the marketplace that addresses your price concern, at least.
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