Dissecting a Milton Bradley Big Trak.

Locate a Milton Bradley Big Trak that you will be willing to dissect. You should be able to reassemble the dissected vehicle without any problem as long as you don't break anything. The tools needed to dissect the vehicle are a #1 Philips screwdriver, two small slotted screwdrivers, a wrench, a pair of long nose pliers and some tape. Also, before dissection, it would be nice to know if the vehicle is working correctly. To test it, purchase 4 D-sized batteries and a 9-Volt battery, install and program a small program by pressing the following 4 buttons; CLR, FIRE, 3, and GO. The Big Trak should make an announcement that it is running its program, fire its laser 3 times and then announce that it is finished running its program.

Image: Milton Bradley Big Trak.

Before dissecting the Big Trak, remove the batteries! You will find two battery covers on the vehicle; a round one on the top towards the front, and a rectangular one on the bottom towards the back. The round one on the top covers the 9-Volt battery compartment and is removed by twisting it 90 Degrees counter clockwise followed by pulling it straight up. The one on the bottom covers the 4 D-Size battery compartment and is held on by two hook like tabs. Remove the battery covers and the batteries and set them aside.

On the front of the vehicle, you will find two screw hole covers disguised as overly mechanized headlights. These are held in place by friction and come off by prying them straight up. If you do not pull them straight up, you run the risk of breaking off one or more of the 3 pins that hold them down. Using the two small slotted screwdrivers, pry the screw hole covers straight up until they come off.

Image: The front of the Big Track with the 9-Volt battery cover and the two screw hole covers removed.

The shell on the top of the Big Trak is made up of two parts. The nose section of the shell is removed by unscrewing the two screws that are found under the two screw hole covers that were removed in the last step. Once the two screws are removed, the Nose Shell can be pulled up 1/2 inch and then forward until it comes loose. You will find that the "Laser" is a regular light bulb and that it is attached to both the Controller Board and the Nose Shell. The connection to the Controller Board is done with two snap on terminals with can be disconnected by pulling straight up on them. The attachment to the Nose Shell is done with a single screw. I opted to remove the screw, and leave the Laser Light connected to the Controller Board. You will also need to work the 9-Volt connection out of the battery compartment.

Once the Nose Shell is removed, the Speaker, which was held in place by the Nose Shell, is now loose along with the Laser Light and the 9-Volt battery clip. Use some tape to hold these items down so that they do not fatigue their wires while we disassemble the rest of the Big Track.

Image: Big Trak with Nose Shell removed.

To get to all of the screws that need to be removed, the outer 4 wheels will need to be moved out of the way. Of the 6 wheels on the Big Trak, only the center two are used for driving. The outer 4 wheels coast along when the Big Trak is in motion. These 4 wheels are held in place by two Wheel Guard Rails which will need to be removed. Using a screwdriver pry the back of the Wheel Guard Rails straight out and off of the back axel. They are on tight, so it will take some work.

Image: Rear end of the right side Wheel Guard Rail pulled off of the back axel.

The Front Axel is a free-floating axel that is held in place by the two Wheel Guards and a notch in the front of the Gear Box. Since the backs of the Wheel Guards are already loose, then only thing that needs to be done to remove the Front Axel is to move the Gear Box out of the way. Note: You will not be able to remove the Gear Box at this time because of the attached wires. To move the Gear Box out of the way, remove the 4 screws found on the bottom outer edge of the Gear Box. Pull the Gear up just enough to let the Front Axel slip past the notch in the front of the Gear Box. Once the Front Axel has been removed, replace the 4 screws holding the Gear Box down. It will be removed in a later step.

Image: The front Axel removed with the Wheel Guards still attached to it.

The remaining part of the shell on the top of the Big Trak is held down by 6 screws. It also has the connector for the Transport Unit, which is wired to the Controller Board, attached to it. Remove all six screws and pull the Top Shell away from the Base.

Image: The three Top Shell screws on the left side of the Big Trak

Before the Top Shell can be removed, the connector for the Transport Unit must be disconnected from it. The hex nut that holds it in place can be found between the Top Shell and a Keypad Frame. These parts must be separated in order to get to the hex nut. The Keypad Frame is held to the Top Shell by 6 locking tabs. Press these tabs inwards and pry the Keypad Frame away from the Top Shell.

Image: The bottom of the Top Shell with the Transport Connector connected and the Key Frame attached.

Once the Keypad Frame has been removed, the hex nut holding the Transport Unit's connector can be accessed. Using a wrench, remove the hex nut and push the shaft of the connector out of its hole.

Image: The top of the Top Shell with the Key Frame removed, exposing the Transport Unit's connector.

With the Top and Nose Shell removed, all of the components can be accessed.

Notice that the speaker, the laser light and the 9-Volt battery clip have been taped down to prevent fatiguing.

To remove the Gear Box, the wires connecting the Motors to the Controller Board must be disconnected. On the Controller Board you will find two sets of two wires that go through the base and down to the motors. These are held onto the Controller Board by two sets of two snap on terminals. They can be disconnected by pulling straight up on them. Be sure to make a record of the color coding of these wires, or you will find yourself guessing which way they go back on. When you do reconnect these wires, If you get them backwards, then the motors will run backwards. Using a pair of long nose pliers, pull the snap on terminal straight up.

Image: The Controller Board.

The designers at Milton Bradley must have decided that at least on part of the vehicle must be difficult to disassemble because the Optical Encoder that is used on the gear box is hard-wired directly to the Controller Board without any connectors of any kind. This leaves two options for removing the Gear Box; cut the wires -or- detach the Optical Encoder. Of course the proper way to do this is to NOT cut the wires. However, the Optical Encoder is not that easy to detach either.

As in Step 5, remove the 4 screws that hold the Gear Box in place. Pull the Gear Box down about 1 inch and look at the left side. You will find a circuit board that has 4 color coded wires attached to it. This is the Optical Encoder circuit board which is held in place by a single bracket with a single screw. Remove the screw and carefully work the Optical Encoder out of the Gear Box. When the Optical Encoder is clear, the Gear Box can be removed.

Image: The Gear Box pulled down about 1 inch exposing the Optical Encoders Bracket.

The Gear Box that Milton Bradley used for the Big Trak is magnetically clutched. This is accomplished by placing a magnet on the motor's shaft. The two halfs of the gear box hold the magnets together and when both motors are energized so that both wheels are turning the same way, the magnets lock together synchronizing the wheels to turn at exactly the same rate. This is a very simple, yet ingenuous way of moving the vehicle forward in a straight line.

As shown here, in 1/2 of the Gear Box, the last gear in the gear drive has holes which are used for the Optical Encoder, and the magnet on the end of the motor's shaft is rectangular.