Page 1 of 3 123 LastLast
Results 1 to 10 of 26

Thread: Controlling Servos with a servo controller

  1. #1

    Controlling Servos with a servo controller

    Hello everyone!

    I am new to the forum and to robotics in general. Nevertheless, I decided to jump right into action; relying on my basic understanding of programming and beginners luck.

    I already have a project in mind. To make it work I need to be able to control 6 to 10 motors from my computer. I thought the best, easiest and cheapest way to accomplish that would be to buy the following:

    a. Pololu USB 16-Servo Controller
    (using this because I want the convenience of USB and the ability to connect many servos)
    b. GWS S35 STD Continuous Rotation Servo Motor (6 – 10 of those)
    (because its more or less cheap and supposedly it can be controlled by the pololu servo controller, unlike a RC motor that needs also a motor controller attached)

    My questions:

    1. provided I have a power supply for the servos - would I be able to control these motors through this pololu servo controller without needing anything else? (the usb cable will connect my pc to the controller and the controller will connect to the servos. I will then be able to write some code to control the servo movement back and forward?)

    2. what program can I use to write the code for controlling the movement of the servos? I preffer a free and downloadable software, and something easy or similar to C / VB.

    3. to power the servo motors, would I be able to connect the following regular battery holder: http://www.robotshop.ca/home/products/robot-parts/power-systems/batteries-chargers/sfe-battery-holder-4xaa.html
    And load it with 4 regular and rechargeable energizer batteries?

    4. is there a simpler / cheaper / better way of accomplishing what i'm trying to do?

    This was a long write up, but hopefully my questions are clear and someone can answer them - I would really appreciate it!

  2. #2
    Join Date
    Apr 2008
    Location
    Sacramento, CA, USA Area
    Posts
    5,341
    Rep Power
    173

    Re: Controlling Servos with a servo controller

    1. As long as you don't need a lot of torque or speed. Those servos are super wimpy.

    2. You can write in any language on any operating system that can open a serial port and force data down it - yes, C and VB are definite candidates!

    3. You'll want a 5 cell battery pack if you're using 1.2v batteries. Remember that a battery is only going to deliver its top voltage for a very short period of time before it falls off. At 6v you start at the max servo input and fall from there. At 4.8, you're starting at the bottom and your runtimes will end-up nil.

    - WELCOME TO THE TRC!
    I Void Warranties�

  3. #3
    robot maker Guest
    i dont know if you know it the current of the servo is .3 amp at full speed no load with very little torque 39 oz,better to go to servocity.com for a better one and using 10 of them can be up to 3 amps no load,so if you are running from a computer also better to use wall transfomer
    i think why you might be using it is because it is continuous rotation,but its only a guess
    but any servo can be modified for continuous rotation and most servo's at servocity can be bought that way too or have done by a tech at servocity
    hs-311 is only $8.99 and has a little better torque 45oz and 180ma no load and easy to modifed

    parallax has another that is continuous rotation 45 oz torque for $12.99 8ma idle
    Last edited by Adrenalynn; 09-23-2008 at 01:03 AM. Reason: Seriously. Start using the edit button.

  4. #4

    Re: Controlling Servos with a servo controller

    Thanks for your answers guys!
    So at least you guys agree with my choice of controller (pololu) – that’s a start!

    Adrenalynn - I chose the servos and the battery packs I mentioned because:
    1. I’m looking for a cheaper solution, since I don’t have too much money to spare (too many other expenses), and
    2. I live in Canada, so I was looking at what robotshop.ca has to offer. If I order from trossen or servocity then the shipping and the border taxes will increase the cost substantially.
    3. I’m new to this, so even after a lot of research and reading there are many things I don’t know/understand/forget to take into account

    For the battery, I guess the “Lynxmotion 6v 2800 mAH NiMH Rechargeable Battery BAT-05” do better than my previous choice of 4 AA batteries, but for some reason the robotshop.ca website doesn’t seem to sell a charger for this or most of its battery packs.

    Robot_Maker – you are absolutely right – I am looking for a continuos rotation servo, because I am not sure if I would be able to modify a regular one – looking for the easy way out; trying to buy one that’s already set for continuous rotation.

    Where can I find instructions on how to modify the Hitec HS-422 Servo Motor for continuous rotation? If I could do that, I would buy it – it seems to have a good amount of torque for the price.

  5. #5
    Join Date
    Sep 2006
    Location
    Carol Stream, Illinois
    Posts
    1,695
    Images
    118
    Rep Power
    105

    Re: Controlling Servos with a servo controller

    Hi bodhibuilder, welcome to the TRC!

    My one major concern is overlooking just how weak and slow these cont. turn servos are. We have n00b customers call us up all the time with projects in mind using these servos, only to find out about 10min into the support call that the servos are no where near their requirements.

    You mention that you are wanting to use 6 - 10 of them, but no mention of what your project actually is and what you are trying to accomplish. The more details you provide all of us, the more able we are to give you the best possible answer

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

  6. #6
    robot maker Guest

    Re: Controlling Servos with a servo controller

    i going to make tutorial on making you own servos to have a higher torque with less current and how to modify them ,but it will be awhile since i have many projects to finish,but
    to modify hs-311 is fairly easy ,just a matter of removing a pin or nub on the main gear and remove the area in plastic gear where it attaches to the pot or remove the pot
    seattlerobotics has a tutorial on modifying one http://www.seattlerobotics.org/guide/servohack.html
    might also try ebay.ca for servos at a cheap price


    Quote Originally Posted by bodhibuilder View Post
    Thanks for your answers guys!
    So at least you guys agree with my choice of controller (pololu) – that’s a start!

    Adrenalynn - I chose the servos and the battery packs I mentioned because:
    1. I’m looking for a cheaper solution, since I don’t have too much money to spare (too many other expenses), and
    2. I live in Canada, so I was looking at what robotshop.ca has to offer. If I order from trossen or servocity then the shipping and the border taxes will increase the cost substantially.
    3. I’m new to this, so even after a lot of research and reading there are many things I don’t know/understand/forget to take into account

    For the battery, I guess the “Lynxmotion 6v 2800 mAH NiMH Rechargeable Battery BAT-05” do better than my previous choice of 4 AA batteries, but for some reason the robotshop.ca website doesn’t seem to sell a charger for this or most of its battery packs.

    Robot_Maker – you are absolutely right – I am looking for a continuos rotation servo, because I am not sure if I would be able to modify a regular one – looking for the easy way out; trying to buy one that’s already set for continuous rotation.

    Where can I find instructions on how to modify the Hitec HS-422 Servo Motor for continuous rotation? If I could do that, I would buy it – it seems to have a good amount of torque for the price.

  7. #7

    Re: Controlling Servos with a servo controller

    Alex – that’s a good point, I should tell you more about my project, I just didn’t want to make my post too lenghty.
    My project: I want to build something like a Vexplorer: a wheeled rover with a robotic arm on top of it. But I want the arm to have more joints and more control. Initially I just want to have all the electronics and mechanics work and be controlled being attached to my computer – that’s my first goal. When I ‘master’ that, I will add more complexity.
    I think this is an appropriate first project, both in complexity and in resources required.
    I always thought that if the motor was weak I can just add some gears, of course it will decrease the speed, but I’m not racing anywhere.
    Robot_Maker - I looked at the link you post on how to modify the motor. The use a different motor there than the HS-422 – would it be the same procedure modifying the HS-422? In any case, I think this will complicate things too much in terms of a noob’s project. Maybe the easier way is to just buy an already modified servo. At the same time – maybe I don’t need a continuous rotation motor for at least half of my project – the robotic arm, but that’s another topic.

  8. #8
    Join Date
    Apr 2008
    Location
    Sacramento, CA, USA Area
    Posts
    5,341
    Rep Power
    173

    Re: Controlling Servos with a servo controller

    The arm is where you need the torque. If you're wanting to pick up more than a feather, you'll either need a LOT of gearing (ie. very slow) or better servos. MUCH better servos.

    Those servos unmodified wouldn't lift the weight of an arm more than a couple inches log, let alone the weight of the servos out on the end of the arm. Adding more degrees of freedom means more servos means more overhung weight. Even a single HS645 won't lift the weight of four more servos out 10" from the center line of the first. There's, unfortunately, a reason arms are expensive. You can go the vex big gear route, but the more weight you add the more gearing it takes the slower it goes - at some point you'll get old and die waiting for the arm to lift a pingpong ball.

    Sorry - not trying to be discouraging, just trying to help you consider where and how you'll spend your [limited] budget.
    I Void Warranties�

  9. #9
    robot maker Guest

    Re: Controlling Servos with a servo controller

    look at the parallax link they have one already modify for $12.99
    adding gears is a good way to have more torque,look at the pan and tilt designs for ideas and how much speed changers on adding a gear ratio,you always make a cheaper design,since i made many
    only problem with adding a gears is that you need to remove the pot from the servo and put it on the main gear for feedback
    i would buy like 1 or 2 just to see if modifying them is easy then buy the rest ,and at the same time see if you have enougth torque for your project

    Quote Originally Posted by bodhibuilder View Post
    Alex – that’s a good point, I should tell you more about my project, I just didn’t want to make my post too lenghty.
    My project: I want to build something like a Vexplorer: a wheeled rover with a robotic arm on top of it. But I want the arm to have more joints and more control. Initially I just want to have all the electronics and mechanics work and be controlled being attached to my computer – that’s my first goal. When I ‘master’ that, I will add more complexity.
    I think this is an appropriate first project, both in complexity and in resources required.
    I always thought that if the motor was weak I can just add some gears, of course it will decrease the speed, but I’m not racing anywhere.
    Robot_Maker - I looked at the link you post on how to modify the motor. The use a different motor there than the HS-422 – would it be the same procedure modifying the HS-422? In any case, I think this will complicate things too much in terms of a noob’s project. Maybe the easier way is to just buy an already modified servo. At the same time – maybe I don’t need a continuous rotation motor for at least half of my project – the robotic arm, but that’s another topic.

  10. #10
    Join Date
    Sep 2006
    Location
    Carol Stream, Illinois
    Posts
    1,695
    Images
    118
    Rep Power
    105

    Re: Controlling Servos with a servo controller

    Also, if you're looking for positioning control, which I'm assuming you are with the robotic arm, you won't have this capability with continuous turn servos. When a servo is modified to continuously turn, you loose positioning control.

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Question(s) servo and motor controllers
    By csdude in forum Arbotix, Microcontrollers, Arduino
    Replies: 7
    Last Post: 06-15-2008, 08:23 PM
  2. Still Confused With 4 Servo Controller
    By mterm in forum DYNAMIXEL & Robot Actuators
    Replies: 1
    Last Post: 02-08-2008, 09:41 AM
  3. Easy Programing of servos and play back
    By hotrodled in forum DYNAMIXEL & Robot Actuators
    Replies: 1
    Last Post: 01-30-2008, 03:18 PM
  4. Kondo web page translated.
    By Droid Works in forum Humanoids, Walkers & Crawlers
    Replies: 4
    Last Post: 10-06-2007, 05:49 PM
  5. Controlling a MAXI Motor Controller
    By shobley in forum Arbotix, Microcontrollers, Arduino
    Replies: 2
    Last Post: 02-02-2007, 12:59 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •