Updated 12/20/2011

Safety first! Wear eye protection and never touch a powered robot!

Note: This tutorial uses the Bot Board II, BASIC Atom Pro 28, a wireless PS2 controller/receiver, and two PicoSwitches (DE-03).

Software:
  - BASIC Micro Studio
  - BRAT Servo Offset Finder Program (09/17/09)
  - PS2 Mech Control Code v1.2 (11/11/2009)

Overview: This tutorial will show how to build a BRAT-based mech using the hardware and components that we used in our build. This is NOT the only way to do a BRAT-based mech, though! Keep in mind that if you deviate from the components we used, you may have to make changes to the code we've provided, and the assembly instructions listed here may not match exactly. Have fun, and experiment!

For the Mech project, you'll need to make sure the aluminum channel is oriented as shown in Figure 1. If yours is different, you'll have to rebuild it.

Figure 1.

Figure 2.

The bracket will be off-center, but the servo horn will be center aligned.

Figure 3.

Remove the servo horn. This servo will rotate the gun platform turret. Plug the servo in to P11 on the Bot Board II. A wiring diagram is shown below.

Figure 4.

Use 2-56 screws and nuts to attach the brackets as shown using the innermost holes. You will need to use a 5/64" drill bit to add holes for the outermost screws as shown. Do this carefully! Make sure everything is aligned properly before drilling!

Use 2-56 screws and nuts to attach the HUB-08s to the ASB-06s.

Figure 5.

Wiring instructions are shown in Figure 12. Don't worry about connecting the guns until you get there.

We had to drill the center hole of the HUB-08s to .25" to accommodate mounting the guns we used. The gun's mounting posts have ridges that need to be filed or cut down, in order to fit into the HUB-08.

We attached our guns to the HUB-08s using epoxy. Hold or clamp the gun tightly to the hub, and make sure to give it plenty of time to set before moving on.

Figure 6.

This completes the mechanical assembly. Because every servo is unique in its center position, we need to calibrate the software to the servos. To do this, follow the next steps.

Figure 7.

You MUST have the buttons enabled in order to proceed.

 
Figure 8.

Program the Atom Pro, and follow these instructions to find your robot's offsets.

• Press A to decrease the servo offset by 5us.
• Press C to increase the servo offset by 5us.
• Press B to change which servo is being manipulated, and to save your offsets. The order of the program is shown in Figure 9.

Note, if you have the Speaker enabled, when you press the B button you will hear a short tone. The tone will raise in pitch when you change from servo to servo, and will lower in pitch and be longer when you get back to Start.

Figure 9.

Use the A, B, and C buttons to straighten the BRAT as shown in Figures 10-1, 10-2, and 10-3.

Note, if you are building the robot with HS-422 servos, you will notice the hip servos oscillate if the robot is lifted off the ground. This is normal, and is due to the lower power servo. When the robot is walking, the effects are minimal. Using a voltage that is higher than 6vdc will make the oscillations worse. When building a robot with more powerful servos such as HS-475, HS-485, or HS-645, you will not see this effect.

After you've cycled through the servos and adjusted them to match Figures 10-1 through 10-3, pressing the B button again will save your servo offset values to the Atom Pro's EEPROM.

Figure 10-1.

Figure 10-2.

Figure 10-3.

The gun's black motor wire goes directly to ground. The red wire goes one side of the PicoSwitch. From the other side, run a wire from the PicoSwitch to + on the Bot Board II.

For the motor's internal switch, cut a 24" servo extender cable in half and strip some from the end of the cable. Strip about a finger's width extra on the RED wire, and solder a 10k resistor onto the wire. Solder BOTH the yellow wire and the other end of the resistor to one side of the switch. Solder the black wire to the other side of the switch.

 
Figure 12.

The command set has changed slightly from the one in the PS2 control tutorial. Make sure you read the list carefully.

We removed the camera's outer casing to make it lighter, and used double-sided foam tape to attach it to the MPSH-01.

Our camera is powered by a 7.4vdc LiPo battery with a 5vdc switching regulator.

Figure 14.

Figure 15.