Servos

From RobotCombatWiki
Revision as of 03:59, 25 May 2021 by Chklnk (talk | contribs) (More selection factors and link to SDB)
Jump to navigation Jump to search

Combat robots use servomotors as actuators, positioning devices, and sometimes as drive motors. These servos are the same type used in remote-controlled devices such as model aircraft flight control surfaces, steering for boats and cars, as well as other hobbies. Most common radio-control receivers have built-in connections for several servos, allowing them to be remotely operated by moving the controls on the transmitter with very little setup required.

These devices take a pulsed electrical signal (usually PWM, or Pulse-width modulation), and respond by moving a lever, slide, or shaft to a specific position. This motion is usually over a range of rotation such as 90° or 180°. This motion can be used to operate flippers, lifters, self-righting mechanisms, and other features of the bot.

How to select a servo

In combat robotics, limiting factors for servos are weight, voltage, torque, and cost. For each servo you plan to use, obtain a specification sheet to find out whether it is suitable for the purpose.

  • Weight: A very durable servo with metal gears may be far too heavy for a small bot, but one with plastic gears may break quickly when the bot is struck or dropped.
  • Voltage: Many small hobby servos run on a limited range of voltages, often 4.8~6.0 volts. If your servo can't run directly from your bot's battery voltage, the receiver might need a battery eliminator circuit (BEC) module that generates enough power to run both the receiver and the servo(s).
  • Torque: Usually stated in kg-cm or ounce-inches. The servo needs to have enough strength to accomplish its task in the bot.
  • Cost: High quality servos cost more.

In addition, here are some other factors you should consider.

  • Dimensions and mounting method
  • Rotational speed and response time
  • Signal required (some servos may have more features with a digital signal)
  • Availability (you will want to have spares on hand in case of damage)
  • Continuous rotation ability (be careful not to order one of these if you need only a short range of motion)

ServoDatabase.com lists specifications for thousands of models.

How to connect and use

Nearly all servos have a common type of 3-wire connector, although the wire colors vary:

  • Ground wire – Black (or Brown)
  • DC power wire – Red (or Orange)
  • Signal wire – White (or Yellow)