Accelerometer Controlled Car (Need RC Xpert)

Discussion in 'The Projects Forum' started by simplytuff, Aug 11, 2010.

  1. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    I am building the following project as My FYP

    http://www.symbianresources.com/projects/shakerracer.php


    i cannot seem to understand the schematics, as i am new to RC Cars !


    [​IMG]

    i have the Blutooth Module and the Olimex Development Board, The RC car i have got only 1 Servo for steering, Servo 2 = ESC , i dont get what is RPM Sensor?

    Any help would be appreciated


    Regards,
     
    Last edited: Aug 11, 2010
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Just guessing: RPM--maybe motor revolutions per minute?
    Seems incomplete--might sensor & seryo pins 1 go to ground, & all three pin 2's be connected?
    Do you have speed control--needs servo or equivalent?
     
  3. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    As ESC is responsible for supplying power, so PIN 1 is GND, PIN 2 is +V, PIN 3 is Control Singal Input !

    Following is a basic diagrame of ESC,

    [​IMG]
     
    Last edited: Aug 11, 2010
  4. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    Following Pics are available on the project website, ! there are three 3PIN connectors in the Board, ESC (servo 2) Steering Servo (servo 1) and 3rd is unknown...(electric rcs dont have rpm sensor)??

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited: Aug 11, 2010
  5. nickelflipper

    Active Member

    Jun 2, 2010
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    Second servo could be for 4WD, Tank drive, or as mentioned previously a throttle control for a gas engine. The rpm sensor could be for a governor control or feedback loop.
     
  6. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    is there a component which gives RPM Value in the car?
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I didn't go through the code, but I am reasonably sure those servos won't work regardless of what code you use. 1) Pin 2 is probably V+ for the servos (it can be ground in some earlier, now rare servos). Were does the power come from? 2) Pin 1 is probably ground. It is not connected to anything either. 3) SV1 is a switch/jumper. It is not at all clear how the signals get to Pin 3 of each servo. 4) Where are the signals being decoded/demultiplexed?

    John
     
  8. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    Servo 1 = Steering Servo
    Servo 2 = ESC (Throttle/Speed Control)

    SV1 = Micro Controller
    BlueNiceCom = Bluetooth Module

    Below is a standard ESC

    3 pin plug that looks like a servo cable. The white wire is the signal wire, the black is GND and the red is the regulated or unregulated output from the ESC

    [​IMG]
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Where do servos 1 and 2 get V+? Where does any servo get ground? My point is, your schematic does not show what you describe. Unless the servos have a common ground with the signal, they will not work.

    John
     
  10. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    ESC (Servo 2) Provide V+ & GND to Servo!

    ESC act as a power source

    Servo 2 is not actually a Servo Motor, it is used to represent ESC PINs!!


    the thing confusing me is the RPM Sensor, whats its use? will the project work if i dont use the RPM Sensor ?
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    OK, let's just assume your schematic works when wired as shown. An RPM sensor in a model car translates to a speed transducer, as you do not usually have the ability to shift gears. I suspect any autonomous or RPV would want speed and time data to help calculate location. If it is visually piloted, then a speed sensor is probably not needed.

    John
     
  12. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    The project tutorial says and i quote "The microcontroller on this board (MSP430 by Texas Instruments, http://www.ti.com) receives commands from the mobile phone via Bluetooth and generates the PWM signals needed to control the RC servos"

    There is no feedback required its open loop, and also no position or speed monitoring, then why need RPM SENSOR ?
     
  13. retched

    AAC Fanatic!

    Dec 5, 2009
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    Unless it used different motors on each wheel, or a 4-wheel drive setup, I dont see a need for a RPM sensor. IF you are using separate motors, you would want to ensure, using a feedback loop and RPM sensor, that the motors (wheels) are spinning the same speed.

    I dont see a need otherwise.
     
  14. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I waded into the source article and am not so sure the rpm sensor is dispensable. Also got a 404 when I tried to dig deeper, so I can't be sure of anything really. The picture of the modified RC car shows one motor and, apparently, two steering servos. I am assuming the numbered servos are for steering and the "RPM sensor" is required for operation of the motor. NB: This project appears to require two-way communication. The commands to the motor seem to be "accelerate" or "decelerate." In other words, the motor speed is not set to a certain percentage of full speed, as it is in regular RC controls. There is also a failsafe program that stops the motor in the event communication is lost.

    To get to an explanation, dig into ShakerRacer-Hardware.zip. Unzip and find Bluetooth Remote Control.pdf version 0.2, figure 1.

    I had to spend 45 minutes accessing, wading through sponsor advertisements, and downloading materials from an outside source just to get a glimpse of what the OP's question might be. It would be far more helpful, if the OP could better define what his question is and present his own analysis of the system.

    In sum, I think you need the rpm sensor. This is an acceleration-based device. I am not sure whether the sensor input is derived from back emf from the motor or is a separate device attached to the motor.

    John
     
  15. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    thnx for the insight,

    I have posted the same topic on several RC Car Expert Forums, they all seem to agree that Servo 2 is ESC which is controlling the Forward Motion Motor Speed (Acceleration)

    There is no such thing as Two Steering Servos, Only 1 Servo is used for steering!

    I just want to be sure that it will run if the RPM Sensor thing is ignored, because i have yet to order the equipment and i dont wana waste 500$ (which is the est. cost of the project including car)

    I emailed the Project Creator, he said

    "Hi,

    I'm on vacation right now and don't have access to the documents. I'll
    get back to you as soon as I'm in the office again.

    Best regards,
    Stephan"

    So i guess i have to wait
     
  16. retched

    AAC Fanatic!

    Dec 5, 2009
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    After looking through the documents myself, It also seems like you need the RPM sensor.

    jpanhalt, I was also thinking along the % of full speed lines. I believe you are correct.

    It seems like the RPM is detected, then the bluetooth signal is read to see if the operator wants to go faster or slower, then adds to the speed, checks against the RPM sensor, and loops.

    If there is no response or CD (carrier detect) type signal from the bluetooth, it ramps down the speed to a stop, or until a signal is detected again.
     
  17. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I just hope some inventor doesn't install "body English" controls in a real car. It might appeal particularly to a certain type of driver who is on the cell phone constantly. The possibilities are endless. ;)
     
  18. retched

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    Dec 5, 2009
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    I can see the thread now... ;)
     
  19. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    the rpm sensor should be a separate device attached with the motor,but the 3 PINs (Blue, Yellow & Green) of RPM Sensor doesn't seem to be connected with motor
     
  20. simplytuff

    Thread Starter Active Member

    Mar 21, 2008
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    Finally Got reply from the project creator

    "Hi Safy,



    the RPM sensor (revolutions by minute) was used to implement an automatic transmission (we have a truck with a 3 gear transmission). If you don’t have that then you won’t need the RPM sensor at all (which was also built by us, based on an infrared diode and transistor).



    Best regards,

    Stephan"

    So which car should i buy to make it work without RPM Sensor? Single Gear Transmission?
     
    Last edited: Aug 17, 2010
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