Explore4x4AZ
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- - Long Post Disclaimer - - Skip to the video below if you just want to understand what a motorized license plate is
I’m not sure how many other people have a similar situation as me, but I have been a bit disappointed with the aftermarket options for license plate mounts. I know, this probably sounds a bit strange… but the aftermarket bumper my wife bought did not have a license plate mount, and the only options either had the plate hanging off the LH side of the vehicle (seemed easy to catch on brush), or mounted off-center in the spare tire (just looks a bit strange IMO). So being an engineer, and having a knack for overcomplicating things, I decided to make my own motorized license plate.
The concept is simple: mount the license plate in the center of the spare tire and use a servo to move it out of the way when you shift into reverse.
There is a bit more to it than that, but that's the gist.
I have had it on the jeep for 6+ months now, and it's still working strong. ALMOST the entire design is made of off the shelf or 3D printed materials, with the exception being the base bracket and the lug nuts adapter, which I got from a different license plate relocation kit. I had originally hoped to productionize the design and attempt to launch it as a product, but that's not in the cards at this time. So with that said, I figure I should share the design files with anyone else who may enjoy them! I'll also post a simple BOM with links at the end of the post.
The design is broken down into 5 main tasks:
1. Signal / Communication
I’m not sure how many other people have a similar situation as me, but I have been a bit disappointed with the aftermarket options for license plate mounts. I know, this probably sounds a bit strange… but the aftermarket bumper my wife bought did not have a license plate mount, and the only options either had the plate hanging off the LH side of the vehicle (seemed easy to catch on brush), or mounted off-center in the spare tire (just looks a bit strange IMO). So being an engineer, and having a knack for overcomplicating things, I decided to make my own motorized license plate.
The concept is simple: mount the license plate in the center of the spare tire and use a servo to move it out of the way when you shift into reverse.
There is a bit more to it than that, but that's the gist.
I have had it on the jeep for 6+ months now, and it's still working strong. ALMOST the entire design is made of off the shelf or 3D printed materials, with the exception being the base bracket and the lug nuts adapter, which I got from a different license plate relocation kit. I had originally hoped to productionize the design and attempt to launch it as a product, but that's not in the cards at this time. So with that said, I figure I should share the design files with anyone else who may enjoy them! I'll also post a simple BOM with links at the end of the post.
The design is broken down into 5 main tasks:
- Signal / Communication
- Microcontroller / Breadboard
- Power
- Mounting
- Mechanism
1. Signal / Communication
The signal for this device comes from the driver's side tail lamp wire harness. More specifically (at least on the '18 JLU), pin 5 of this connector is the power to the reverse lamp, so we can use this as the signal for the system (This Forum post is an EXCELLENT source of info).
Now I didn't want to just splice into this harness, since dealers love to void warranty over these types of things, so I went ahead and made my own bridging adapter using an inline 12 pin Molex MX-150 connector with a T split for pin 5. You can find these for ~ $3 / piece on websites like digikey, or even Amazon for that matter. All you need to do is remove the driver's side tail lamp (https://youtu.be/ORm-ZnbdCoQ ...skip to 1:11), disconnect the tail lamp from the vehicle side harness, connect your bridging adapter, and replace the tail lamp.
Simple Diagram (green connectors is custom harness):
You will now need to run your wires from the rear driver's side tail lamp into the storage area of the rear compartment, where the OEM spare tire jack is. I found the easiest way to do this was to run the wires under the rear of the vehicle and up through the drainage port at the bottom of this compartment. Within this compartment is where I have the microcontroller stored. From this point, you will need to run another wire harness from the microcontroller out to the spare tire (you don't NEED to talk the interior trim out as shown in the image below, it's just a bit cleaner install that way).
At this point, all the connections should be made onto the breadboard housing the microcontroller (details in next section).
2. Microcontroller / Breadboard Originally I was using an Arduino Uno for this project, but it was pretty big and overpowered for what I was needing to do. To reduce cost and space, I down sized to an Arduino Nano. This is still far more capable than is needed, but it gets the job done for only about $3 / controller, which is very reasonable. Unfortunately, the only schematic I have is of the old Arduino Uno setup, so I'll post that below and if there is enough interest I'll create one for the Nano too:
Something VERY important to note on this... the step down resistors from the custom bridge harness (circled in red). The vehicle runs on a 12V system. The maximum voltage input on the Arduino is usually around 5V, or less (for an analog input pin). After destroying two uno's I realized these resistors are rather important, so don't make my mistake! The final layout looks like this:
I'll add an upload link for the Arduino code in the future, but it's pretty simple. The only tricky part about it is ensuring that the servo range matches the physical servo position, but more on that later.
3. PowerNow this is where the instructions may deviate depending on what model you have. To make my life easy, I'm using the 12v cigarette lighter in the back storage compartment (I believe this is only on vehicles w/ the rear subwoofer). I simply bought a 12V plug (with a DC connection on the other end), and a 12V to 7.5V transformer. I chopped of the DC connection, spliced in the transformer to reduce the voltage to something Arduino will be happy with, and then added the necessary connectors to mate to the power connector in the image shown above. The last thing I had to do was switch the 12V outlet from always hot to ignition based (Tutorial here...Also in the manual).
4. MountingThis is the portion which is not so off-the-shelf. The one component I could not find easily, and which would be expensive to produce in low volumes, are the lug nut adapters for the spare tire. I happened to have these available from another project, so I used this and the base mounting bracket (shown in the below image as pink and purple, respectively).
5. MechanismThe mechanism itself is pretty straight forward. I'm using a 4-bar link with a single servo driving the system. In order to make the up/down actuation smooth (due to having only one servo), the bottom links are connected via a torsion bar. This torsion bar is snapped into the mounting bracket for quick access to the lug nuts if needed. The link arms are retained by external retaining rings to keep things cheap, light, and simple. All of the parts you see (minus the servo, hardware, base bracket, and lug nuts) are all 3D printed in ABS using a desktop FDM printer.
The image below is the "Down" position. This is the default position which places the license plate in the center of the spare tire.
And once shifted into reverse (or manually overridden via the switch), it will move to the "Up" position, shown below:
The rest is pretty straightforward. I'll return to post the Bill of Materials, links to OTS components, and files for the 3D printed parts another night, and depending on interest, add more detailed instructions. Thank you guys for reading! - Kyle
Images of it mounted:
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