Hitec Servo Preparation Guide

Updated: 18-Aug-2008

Before attaching servos to your robot, it is necessary to check that the servo horn is fitted correctly and in the center position. This guide will explain how this is achieved.

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Number02 Servo Horn Position
Number02 Servo Horn Centering




Number02 Servo Horn Position


Figure 1.


When you first remove your Hitec servo from the packet, the servo horn should be fitted in the position shown in Figure 1. This should be the servo center position, however, this is not guaranteed so we suggest this is checked before you begin kit assembly. (See Setting Servo Center)

The holes indicated by (A) & (B) are used for attaching the horn to other mechanical assemblies. This is done with No.2 self tapping screws. Although not necessary, you may wish to open these holes up with a 1.5mm or 1/16" drill for easier assembly.

Hitec servo splines have 24 teeth, which means the servo horn can be moved around in 15° increments.


Number02 Servo Horn Centering


p.Brain-hexEngine: 6V dc is supplied to the VS terminal via a switch, with JP3 1-2 link in place to supply VL from VS.


To check if your servo horn has been fitted in the mid position (center of rotation) correctly as shown in Figure 1. you will need to power up the servo with a 1.5ms positive pulse sent every 20ms (50Hz). This can be done using an R/C style transmitter/receiver, a p.Brain-HexEngine or SSC.

Using p.Brain-HexEngine
Connect a 6.0V power supply or battery pack via a switch to the SMB board, V+ to the VS screw terminal and V- to one of the GND screw terminals. Install a jumper on JP3 across pins 1-2, this sets VL = VS for single power source supply. Remove any jumpers on CN18. Connect the terminal port RJ11 4/4 connector to the serial port of your host computer using a suitable lead such as a p.Brain-RJ232.

Open up a connection in your terminal software on the host system, set the baud to match that of your HexEngine ( default = 115200,N,8,1). Switch on power to the SMB, you should see a RED led near the terminal block illuminate (if it does not, switch off power immediately and check your circuit). When powered up you should see the HexEngine display message in the terminal window, enter the SERVO TEST screen by typing "SERVO TEST" within your terminal screen. Once in SERVO TEST mode, select the servo you wish to test using the left/right cursor keys, press the '2' key to send the servo to the required 1.5ms mid position. The servo horn should now be in the position indicated by Figure 1.

Using Lynxmotion SSC32
Please visit the following link: http://www.lynxmotion.com/images/html/build046.htm

Once you have your servo powered up with the required 1.5ms signal, If you find your servo horn is not in the expected position remove the servo horn and move it as close to the position indicated in Figure 1.