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Battery-operated toy cars that kids can drive are one of the funnest toys a child can have. Unfortunately, some children must deal with various circumstances that inhibit their ability to use the acceleration pedal. This problem can be resolved by replacing the pedal with a hand-activated switch mounted to the steering wheel. Safety is also a big factor, so adding a relay protects the child by isolating the current in the motor from the child.

For this project, you will need the following parts/materials:

1 Big Red Ablenet Big Red Switch (or a switch similar to it) (https://www.ablenetinc.com/technology/switches/big...)

1 DPDT Relay with Plug-in terminals (The relay specs should allow it to operate with the battery voltage. For the 6V battery in our car, the relay frome Digi-Key with part number PB1559-ND worked well. The link to it is http://www.digikey.com/product-detail/en/7-1393769...)

1 Diode (I believe we used a 1N4001 diode, but most any diode should work)

1 1/8" Mono Jack (female)

1 1/4" Mono Audio Jack (male and female)

2 Quick Splice Connectors

Electrical Tape or Heat Shrink Tubing

Cable Ties

Wire (Red is power) (Black is ground) (Green is connected to the relay)

Wire Strippers

Drill

Pliers

Soldering Iron and Resin Core Solder Material

*Note: Make sure the car is powered off and unplugged from charging when making any modifications.

Step 1: The Basic Circuit

Step 2: Adding the Kill Switch

To add the kill switch you will need:

1 1/4" Mono Audio Jack (male and female)

Wire

Electrical Tape or Heat Shrink Tubing

Soldering Iron

Drill

The kill switch is added as a safety factor. If the child seems to be getting out of control while driving, the overseer can pull out the kill switch, stopping the car.

The first step of adding the kill switch is to complete the connection inside the male piece of the jack. Open the jack up by unscrewing the black housing from the metal connector. On the metal piece, you will see two terminals, as shown in the first picture above. Connect these two terminals by soldering a short piece of wire between them. Screw the housing back on and the male piece is ready to go.

Next, you want to prepare the female piece by soldering a short section of red wire onto one terminal and a short section of black wire onto the other terminal.

Next, you need to look under the car and find the red wire coming from the positive post of the battery. This is the wire you will cut to install the kill switch into the circuit. Follow that red wire towards the back of the car and cut the wire into two pieces. The part of the wire coming directly from the battery should be connected to the red wire on the female piece of the jack. The other part of the wire should be connected to the black wire on the female piece of the jack. You can simply twist each pair of wires together and either wrap with electrical tape or enclose with heat shrink tubing (you can also solder the wires together after twisting them to make a more permanent connection). Refer to the second picture above for how it should look.

Now, you need to mount the kill switch to the back of the car. The amount of excess wire you have attached to the kill switch will determine how high you can place it. Determine an easily accessible place to mount it and drill a hole through the back of the car that is just large enough for the female part of the jack to fit through (make sure the washer is off the female piece). Next, slide the female piece into the new hole and tighten it down with the washer. You can now plug in the male piece and the kill switch has been installed. The second picture above shows what it should look like from underneath the car, while the third picture shows the view from the back of the car.

Before moving on to the next step, confirm that the kill switch is functioning properly. Turn the car on and press the accelerator to make the wheels start turning. Without releasing the accelerator, pull the kill switch out. The car should stop functioning.

Step 3: Remove the Pedal and Add the Relay

For this step, you will need the following:

1 DPDT Relay with Plug-in terminals (The relay specs should allow it to operate with the battery voltage. For the 6V battery in our car, the relay frome Digi-Key with part number PB1559-ND worked well. The link to it is http://www.digikey.com/product-detail/en/7-1393769...)

1 Diode (I believe we used a 1N4001 diode, but most any diode should work)

Wire

Pliers

Soldering Iron

As mentioned before, the relay helps protect the child from the current buildup in the motor by isolating the current.

The first thing you need to do is remove the existing accelerator pedal. Unsnap the pedal from the car and inspect how the wires are plugged into it. Mark the position of the wires (front/back, left/right) and take a picture (this will help in troubleshooting issues with how to connect the wires later). Now, you can unplug the wires and set the pedal aside -- you will no longer need it unless you have to determine a connection issue.

Now, it is time to prepare to install the relay and diode. On the relay, there is a set of 2 terminals and a set of 6 terminals. You should solder the diode across the set of 2 terminals. At this point, the direction of the diode (as shown by the arrow on it) does not matter, but be aware of how it is oriented. Next, solder a long piece of wire onto each of the terminals with the diode (we used 2 green wires). Take a piece of tape and label the green wire that the arrow on the diode is pointing to as positive (+)(This is very important that it is labeled correctly, or the car won't run after you make the connections). See the second picture above for how the diode and green wires should look (*Note: The second picture above does not show the relay that we used. This picture is for example only.)

Next, you should take the wires you unplugged from the accelerator pedal and connect them to the set of 6 terminals on the relay. The relay should have a diagram on it for how the pins are connected. You should connect them in the same manner that they were connected to the pedal. For our car, the terminals on the relay were smaller than those on the pedal, so we had to use pliers to bend the connectors so they would make a tighter fit on the relay terminals. It is likely that you will need to do the same. The first picture above shows the relay that we used with the connectors and wire attached (Note: the diode is not connected in this picture).

At this point, you are almost done, but before moving on, we suggest getting a 9V battery and touching it to the green wires you soldered onto the relay to make sure the car is still functioning properly at the end of this step. To do this, make sure the kill switch is in, the car is turned on, and the direction (forward, reverse) is set. Next, touch the ends of the green wire to the posts on the battery. The green wire that was previously labeled as positive should be touched to the positive post. The other green wire should be touched to the negative post. With both wires touching the battery, the car should run. If the car is not running, confirm that the connections are correct. If they are, confirm that the relay is flipping properly (you should hear a clicking sound as soon as the battery is connected to the green wires). (*If the car started running before you even touched the green wires to the battery, you have an issue with how the connectors previously on the pedal are connected to the relay.)

Before moving on, turn the car off.

*We 3D printed a box to enclose the relay, diode, and connectors. The STL files are uploaded here for your use. If you want to use these, you will need to feed the connectors through the hole in the top of the box prior to connecting them to the terminals on the relay. The box top piece slides into the groove on other piece of the box. The last picture above shows the box taped to the bottom of the car (we just used double-sided tape).

Step 4: Adding the Big Red Switch and Splicing Wires

For this step, you will need the following:

1 Ablenet Big Red Switch (or a switch similar to it) (https://www.ablenetinc.com/technology/switches/big...)

1 1/8" Mono Jack (female)

2 Quick Splice Connectors

Wire

Electrical Tape or Heat Shrink Tubing

Cable Ties

Wire (Red is power) (Black is ground) (Green is connected to the relay)

Drill

Pliers

Soldering Iron

First, you need to determine where you want to plug the switch in. We chose to plug it in on the side of the car under the side view mirror. The spot you determine is where you should drill a hole. The hole should be just large enough for the 1/8" mono jack to fit through. Before putting the jack in place, solder a red wire onto one of the terminals of the jack and a black wire onto the other terminal. The red wire should be long enough to easily reach the on/off switch and the black wire should be long enough to easily reach the green wire from the relay labeled positive (+). Now, you should put the jack into the hole and tighten it into place with the washer from it. See the first and second picture above for how it should look.

Next, you need to connect the black wire from the jack to the green wire from the relay labeled positive (+). This can be done by simply twisting the wires together. You can also solder these together for a more permanent connection. Wrap electrical tape around the exposed connection or encase it in heat shrink tubing. The third picture above shows this connection.

You are almost done! The last part of this step involves splicing into power and ground with Quick Splice Connectors as shown in picture 4 above. Follow the wire (red) coming from the positive post of the car battery to where it goes into the on/off switch and find the other red wire coming out of the on/off switch. The red wire that comes out of the on/off switch is the one you will splice. This red wire will go into open channel of the Quick Splice Connector. The red wire from the jack will go into the other channel. Use the Quick Splice Connector to make the connection. The fifth picture above shows this connection.

Next, trace the wire (black) coming from the negative post of the car battery. This is the other wire you will splice. You will need to cut a section of black wire to connect to the second green wire coming from the relay. The wire needs to be long enough so that it can reach from the green wire back to the black wire you just traced coming from the car battery. The newly cut black wire and green wire from the relay can be connected by twisting them together and wrapping in electrical tape or heat shrink tubing. Again, you can solder this connection to make it more permanent. Now, run the black wire from the car battery through the open channel of the Quick Splice Connector and the black wire you just cut into the other channel. Make the connection. The last picture above shows this connection.

Now for the last step: use cable ties to attach the Big Red Switch to the steering wheel and plug it into the jack. The switch attached to the steering wheel can be seen in the last picture above.

Test the car to make sure it functions properly. With the kill switch in, the car on, and switched to a direction, the car should move when you push the switch.

Step 5: The Open Road Awaits!

Congrats! The car is ready for children to have fun driving!

<p>Nice mod</p>

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