Ste's Robot Project - Motor and controller selection help

Discussion in 'The Projects Forum' started by Ste_Mulv, Sep 23, 2009.

  1. Ste_Mulv

    Thread Starter New Member

    Sep 23, 2009
    Hello all,

    I have been planning to build a robot for ages now. I have drawing "cigeratte packet" designs for literally years, but although I am good in some areas, I am hopeless at actually picking a product off the shelf and getting a circuit going.

    I am going to finally take the plunge and get buying components to build with.

    I have a few questions in this topic (which i know is taboo, but they all lead on from each other)

    I intend to build a modular system, where a module is responsible for a specific area's control, these modules will then be linked with a serial bus communication newtork (probably a long time in the future!)

    So every journey must begin with a first step, and mine is the motors and motor control module.

    What type of motor should I choose? I am thinking that a brush/brushless DC motor is the best choice to start with. I plan to strip this out of a portable car compressor pump (£7.99 from ebay). Will this be a DC Br/BrLess motor?

    What type of feedback system would be best? I think that adding an encoders to gain a feedback, thus creating my own servo and design a PID to run it all. Does anyone know of some good position encoders, that are avalible off the shelf?

    Would you just shell out and buy a servo?

    I don't want to build my own H-Bridge, because I want an all in one package that does all the options i could build anyway, however, there are millions around. Does anyone have a suggestions of a controller they have used?

    Additional transistors? will I need to add transistors to allow max unregulated current to flow to the motor, or do controllers have those built in?

    So to summerise:
    Will it be a DC Brush/Brushless motor in a car compressor?
    Is that the right choice of motor for my project?
    Are there some good position encoders avalible which will work with the above motor?
    What H-Bridge controllers are good, cheap and readily avalible?
    Will that H-Bridge come with "everything I need"?

    Thanks for you time, and any help would be much appriciated...


    Steve Mulvenna :)
  2. hgmjr


    Jan 28, 2005
    It would help to know what your application for this motor is.

    Last edited: Sep 23, 2009
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    With no parameters, not much accurate input is possible.

    One thing can be answered -
    Nope - just pull in a relay and let the contacts pass the current.
  4. DieselPower

    New Member

    Sep 24, 2009
    Fanuc 0S or 5S series motors off ebay with one of jons servo amps??? ( How big are you going? Robotic arm, hexapod, crawler???? Toy or tool??? I love robotics, but only if they involve welding hundreds of pounds of steel together, use massive anounts of power, and perform a needed function when done!
  5. Ste_Mulv

    Thread Starter New Member

    Sep 23, 2009
    Hey there, sorry about being ambiguous...

    I am going to make a little bot, track driven approx 30cm long and 20cm wide.

    stage one is to get the base together with the tracks and motors running and controllable with speed and direction. I would like to at this stage add in a PID and gain precice control over the speed and angle of the motor.

    I guess that the whole thing is going to weigh around 5kg, and I would like it to have a top speed (on the flat) of 8-10mph (not really fussed about the top speed though).

    <quote>Nope - just pull in a relay and let the contacts pass the current.</quote>

    I am sure that the best way to control speed is with PWM, and a relay would not be suitable for the high frequencies required... I have just checked and the quickest response time i can find is 7ms and that would play havock if I was to use a 10kHz PWM frequency

    Thanks again...

  6. bertus


    Apr 5, 2008
  7. Ste_Mulv

    Thread Starter New Member

    Sep 23, 2009
    Hi again,

    this is the type of motor controller that I want, but I don't want to build one out for discrete components.

    I have heard that there are ready build IC that controlls the motor speed and direction based on the duty cycle of a PWM input. (10%DC = full reverse, 50%DC still, 90%DC full forward - DC Duty Cycle)

    I have been having a look, but there are too many to choose from, and I don't know which one will do the job.

    I have attached a flow diagram that may clarify what I am after:

    Recommendataions on the motor controller would be great
    Do I require a transistor arrary to get enough current to the motor?


  8. Ste_Mulv

    Thread Starter New Member

    Sep 23, 2009

    That is 100% perfect, I have been trawling through data sheets for ages now, and when I find one that looks ok, it is normally too expensive.

    This one is both in stock and reasonably priced. also example circuits in the data sheet are good.

    Thanks a lot.

    I will now be researching LIN bus controllers, LIN bustransevers and simple microcontrollers...

    Thanks again.

  9. BMorse

    Senior Member

    Sep 26, 2009
    Try the LMD18200T by national Semiconductors >> << I use this in plenty of robotics and motion control, the LMD18200 accommodates peak output currents up to 6A. An innovative circuit which facilitates low-loss sensing of the output current has been implemented also so you will be able to tell when the motors stall, it only requires a TTL compatible input for Brake, Direction and PWM.....

    I used this H-Bridge to develop a 2 speed PWM driven PM DC Motor controller (for this company for their automated recycling machines. I also use another variation of the same H-Bridge without the current sense output the LMD18201T....

    My .02
    Last edited: Sep 27, 2009