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robotic arm project — Parallax Forums

robotic arm project

shoman95shoman95 Posts: 3
edited 2012-12-08 09:03 in Learn with BlocklyProp






Hi everyone!

I'm am Hamza. I want to make a robotic arm and In order to do that I need to use a couple of servos:

1. Do you recommend me to use a continuous servo, or a standard one? i know the difference i just need a list of the pros and cons of both of them.
2. If i want to control the arm on my iPhone, what applications do you recommend me to use?

Thank you for your help.








Comments

  • Martin_HMartin_H Posts: 4,051
    edited 2012-12-08 07:48
    Generally people just starting out use standard servos for arm building. That way no additional position feedback is required and there's several forum members who've used this approach. Indeed most people use this approach.

    While rc servos work great for basic robot arms, their accuracy isn't high enough for precision applications. At this point stepper motors with precision mechanisms tend to be used. The reason is that steppers allow control over both position and velocity of the robot's joints.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-12-08 07:58
    Martin_H wrote: »
    The reason is that steppers allow control over both position and velocity of the robot's joints.

    I agree with Martin's opinion about the limitations of RC servos, but you can also control the velocity of the robot's joints with regualar RC servos. You just tell the servo where to be 50 times a second and control the speed through software. Here's an example.

    Hanza, Do you have a microcontroller you plan to use? I think you'd be very limited in the type of arm you could make if you were to use a Basic Stamp. A Propeller chip would be able to control an arn without a problem.

    If you wanted to interface your iPhone to the Prop, I'm guessing Bluetooth would be the way to go. I don't know of any "apps" for this though (that doesn't mean much since I don't have an iPhone).
  • Mike GreenMike Green Posts: 23,101
    edited 2012-12-08 08:01
    Regarding your 2nd question:
    Mocha Telnet or Mocha Telnet Lite is an application that allows you to open a Telnet connection and acts as a text terminal for that connection. You will need some kind of wireless interface on the other end. Parallax's Spinneret can be used for this, but only has a wired Ethernet connection. You'd need some kind of wireless Ethernet bridge. You can also use a Roving Networks' RN-XV wireless module along with some kind of microcontroller. I've done this with a Propeller as the microcontroller ... works fine. Bluetooth is useless with the iPhone. The only serial Bluetooth interface they support is incompatible with all of the Bluetooth serial adapters I've seen.
  • Martin_HMartin_H Posts: 4,051
    edited 2012-12-08 08:24
    Duane Degn wrote: »
    I agree with Martin's opinion about the limitations of RC servos, but you can also control the velocity of the robot's joints with regualar RC servos. You just tell the servo where to be 50 times a second and control the speed through software.

    I've tried that sort of thing, but there's always uncertainty about exactly where the arm is versus where you think it is. For many applications you won't notice, but for closely following a path the limitations show up. Doodlebots being a classic example as there's jitters in the line.

    Erco's three servo BS2 powered robot arm was fairly functional and capable of tower of Hanoi. So starting simple can yield good results. More than that and you'll need to tackle inverse kinematics.
  • ercoerco Posts: 20,256
    edited 2012-12-08 08:33
    Martin_H wrote: »
    While rc servos work great for basic robot arms, their accuracy isn't high enough for precision applications.

    I wouldn't say that. Precision is relative to the application. I was quite pleased with my results using cheap servos. http://www.youtube.com/watch?v=kF6TwbIT384&feature=player_detailpage#t=76s
  • Martin_HMartin_H Posts: 4,051
    edited 2012-12-08 09:03
    Pick and place is fine. I was reading through the build log of Aaron Fan and his delta drawing robot.

    http://aaronbot3000.blogspot.com/2011/10/pythagoras-drawing-delta-robot-math-and.html

    He used servos for the first few iterations but abandoned them for steppers when he couldn't get his lines smooth enough.
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