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Thread: Biped. What Controller, Gyro, Pressure sensors to use?

  1. Biped. What Controller, Gyro, Pressure sensors to use?

    Hi im building a large humanoid using wck servos at the moment. 26 servos all up. I have just been working on the mechanical side of things for the last 3 months but now i have to start looking at the controlling side.
    I have few questions for you guys. The biped is 680mm high and weighs only 1.5kg (minus controller, gyros battery etc)

    I have a robobuilder controller box. Can i have a gyro and pressure sensor input?

    Do pressure sensors on the feet actually work? Or do i need a 6 axis sensor in the ankle?

    Are pressure sensors really need if you have a gyro with accelerometers?

    What gyro/accelerometers work the best? What is the CH Robotics - IMU 6 DOF Board like? It has 3 gyros 3 accelerometers.

    I would like the robot to be completely wireless. So i don’t want the controller on the robot. Are there boards that would be able to drive 26 serial servos, have gyro pressure sensor inputs and be wireless (Bluetooth or xbee or something)?

    Would there be any advantage to having gyroscopes in the feet for positioning?

    I have no idea how i am going to program this. It is a huge task. Any info would be greatly appreciated.

    Heres a photo a one of the older designs. Im not able to show you the final one.

  2. #2

    Re: Biped. What Controller, Gyro, Pressure sensors to use?

    The Robobuilder control box has the advantages of plenty of wck compatible connectors and a clock frequency easily dividable to give the highest 921.6K speed of the wck. The disadvantages are that the number of outputs on the Mega128 which are pinned out are few and you probably want to ditch the batteries in favour of LiPo. The standard Robobuilder software is probably of no use to you. I have taken the batteries out of mine and reduced the case size, put a connector where the accelerometer goes to bring out the I2C for sensor interface, and run off LiPo. So overall, lowest cost but limited.

    What board can run 26 servos ? Well the serial protocol does allow all 26 on a single serial port, but it depends on how often you update or read the servos. The normal wck bus speed is 115200, but can run up to 921600 if you have a crystal on the controller which provides that speed. However there is also latency in the wck response, so even at higher speeds, you will only get about 1 ( 4 byte TX ) bus transaction per millisec, less at lower baud. You can use the sync move ( about 3 millisec for 26 servos @ 115200), but it really depends on how often you want to read position of the 26 servo as to whether one serial port is enough. I would say that 26 servos on a single wck at 115200 is OK provided you are not obsessive in reading position.

    For a controller better provided with IO, maybe the Arbotix, the serial baud will be a bit out, but might work OK even at 921600. Do look at pypose as well.

    After that anything like ARM or Roboard might be best.

    For the IMU, one with a built in processor is an advantage in preprocessing and filtering the data. You may have to do some stability control local on the bot if you are using remote control over xbee or bluetooth from a PC due to latency. The new low cost 3 axis SPI interface gyros and acclerometers look interesting if you want to build you own IMU.

    I see no value and great complexity in gyros or accelerometers in feet. pressure sensors or IR sensors would be of more value.

    On Xbee vs. Bluetooth vs. Wifi topic, there is lots of discussion here already.

  3. #3

    Re: Biped. What Controller, Gyro, Pressure sensors to use?

    Also it would be of help in advising if we can understand your programming skills and knowledge.

  4. #4

    Re: Biped. What Controller, Gyro, Pressure sensors to use?

    That's a really neat design. It's cool how you are using double-servo indirect-drive joints. If you can actualy get this to work, it would be most impressive.

  5. Re: Biped. What Controller, Gyro, Pressure sensors to use?

    Thanks heaps Ibot thats some good info. Can the Robobuilder controller use a xbee on it? Theres an 8 pin plug in the board for wireless but i cant find anything on what the pins represent.

    What is the Bioloid FSR pressure sensor like? Do they work very well, and would this work with the robobuilder board?

    My programming is not great but its alright. Can use C+ VB6 and .net ok, also a few others but theyre not worth mentioning. Iv done a lot of work with a 8051 micro using c+ but i would like to us VB if that is possible with the RoboBuilder controller?

    Sorry for the 'noob' like questions. Just getting my head around things.

  6. Re: Biped. What Controller, Gyro, Pressure sensors to use?

    The Bioloid FSR boards only work with Bioloid robots. The FSR sensors, however, are general purpose analog pressure sensors, and you can use them with any microcontroller that has analog inputs.

    - Jon
    "The best way to predict the future is to invent it." - Alan Kay, inventor of Smalltalk

  7. #7

    Re: Biped. What Controller, Gyro, Pressure sensors to use?

    My schematic for the RBC is here:

    The 8 pin connector is compatible with the Parani ESD200, though the reset pin is not presented. It should be OK to wire in the Xbee here.

    I did hardwire analog gyros direct to the ATMega pins of the RBC, you might do the FSR this way in an initial setup.

  8. Re: Biped. What Controller, Gyro, Pressure sensors to use?

    Cheers iBot. Much appreciated. What do you use to program your RBC? C+?

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