Jorge's random things

A couple of weeks ago, I took my daughter Keira who is under two years old, to a playground nearby. When we got there, two kids who seemed at least five years old drove all over the place in a Power Wheels Jeep. Of course, Keira wanted to join them, but they never stopped.

That evening I searched online for Radio Control (RC) ride-on cars. The one thing they all shared in common was negative reviews, so I decided to put my many years of RC experience to good use and ventured into building one that would make her and me happy.

Need for speed

I've seen several 12V ride-on cars, and they're all slow! Don't get me wrong, slow might be suitable for a child, but if I do this, I want the option of having a little more oomph.

I have a couple of Ryobi lithium batteries at home. I decided to use them because the increased voltage would make the car faster without going overboard for ~12V rated electronics. Unfortunately, they're only 1.5 Amps each, so I decided to connect them in parallel for a total of 3 Amps for longer ride times.

I searched the web for Ryobi battery holders. Still, I couldn't find any, so I went over to Thingiverse and found just what I needed: A 3D printable model for Ryobi batteries model; so I printed two battery holders using PLA filament and used these clips on them.

One problem was that the clips wouldn't stay secured to the battery terminal, so I had to design a cap to keep them in place. I glued the cap using CA glue and electrical tape.

Building Keira's RC ride-on car

I purchased a Kid Trax 12-Volt Sports Coupe Ride-On Car because it's pink and small enough to fit in a small-size SUV.

I unpacked the car and inspected all of its components, but to my surprise, it's fundamental and has no added features such as sounds, horns, lights, etc. however it seemed pretty well built.

The most complicated part of converting a ride-on car to RC is figuring out the steering mechanism. First, I thought about using high torque servos, but the number of custom pieces and mechanics required to make it work quickly got me looking into other directions.

The Steering Mechanism

I chose an actuator for the task and decided on a 12V 35lbs Feedback Actuator from Firgelli. These actuators are equipped with a built-in potentiometer so one can determine the position of the actuator at any point in time.

The actuator alone can't be connected to an RC receiver (RX) directly, and an interface capable of converting position readings from the actuator's potentiometers to RC pulses is necessary. I looked into building an Arduino-based interface, but I randomly stumbled into an already made product. The Actuonix Linear Actuator Control Board (LAC) does precisely that and has a few added features, so I decided to get one.

I connected the actuator to the LAC and the LAC to the RX. Once the actuator was extending and retracting to RC Transmitter (TX) input, it was time to mount it.

One thing I noticed about the steering mechanism is its relatively constrained range of movement. Of course, this is on purpose, and the stoppers in the mechanism are to blame:

Unfortunately, I didn't take a picture, but I reduced the width of both stoppers by almost 70%, and that increased the range of movement.

Mounting the actuator took quite a bit of work and was not entirely trivial. I first removed the steering mechanism from the car and devised a plan to mount the actuator.

I didn't want to reuse the existing steering brace because maybe someday I'll yank out the RC and enable power-steering on the car, so I had to build a new one.

I headed to Dunn Lumber, purchased a bunch of different-sized screws and spacers for mounting the actuator, and I ran across a Simpson Strong-Tie APDMW56 made out of G9 steel. So I bought two of them and modified them to make them work.

I initially thought that a piece similar to the original brace would do the trick, so I created something similar using my cordless Dremel and several cutting wheels. However, cutting G9 steel is hard, so I later opted to reuse the original hole instead drilling a new one.

Below are a few pictures of the actuator and steering mechanism mounted and in place.

The Electronics

With the actuator mounted, it came time to install all the electronics and convert the car to RC.

The first thing I did was strip out all of the existing electronics and see what could be reused, and the only things I ended up reusing were the main Switch and both of the motor connectors (white connectors in the second picture).

Below is a diagram of how each of the electronic components is connected:

The Ryobi lithium batteries are connected in parallel to provide double the Amps. There is also the original 12V lead battery that the car came with, and the power source is determined via a Gardner Bender GSW-13 Heavy Duty Toggle Switch (ON-OFF-ON). Then it goes to the car's original switch and into a STETION Car Audio 30 Amp Resettable Fuse. From there, there's a bifurcation (Y) where one side goes to the Electronic Speed Control (ESC), and the other powers the LAC and the toy steering wheel.

The car has two motors: 1 for each rear wheel, so I used a QUICRUN WP 880 Dual Brushed ESC speed control because it supports dual motors. I connected the ESC to the power supply and then connected both of the motors to it. I used some old audio banana plugs lying around to connect the wires to the ESC.

I already had a Futaba 4PLS TX, so I just needed a compatible receiver (RX). I got a Futaba R203GF S-FHSS 3-Channel 2.4GHz Receiver and connected it directly to the ESC, and tested things out. Unfortunately, when I pulled the throttle, one of the motors spun in the opposite direction, so I had to reverse the wires.

From the other side of the Y supply, I created another bifurcation where one side went to a 12V Regulator that powers up the LAC and, by consequence, the Actuator. If I were doing this project again, I would have used a 13V regulator for the LAC. The other side went to a 4.5V Regulator, which powers up a toy Interactive Steering Wheel.

All the connections were done using Deans connectors which are standard in the RC industry.

Putting Everything Together

Installing and connecting all components was pretty straightforward, but special attention was needed for the battery holders. Unfortunately, there wasn't much room to install them, but I found a way where they got fully secured and didn't interfere with the steering mechanism.

Here are the motors installed:

At first, I used double-sided tape to stick the components to the base, but then I realized I had made a mistake and had to remove them. That's when I decided to 3D print enclosing cases stuck to the car, allowing easy removal of the components.

I also 3D printed a base for the Toggle Switch so that it could be placed in a convenient and easy-to-access position.

Here are the 3D models that I created:

By now, the car was ready, and I gave it a few test runs! It was so much fun! 18V makes the car shine, though at 12V, the speed is plenty for indoor fun.

The Steering Wheel

Having the ability to control the car via RC was super fun and exciting. Still, the lack of horns, sounds, and baby-friendly gadgets wasn't something I was proud of: This project was supposed to be fun for my daughter and me, so I had to fix that and make it baby-friendly.

When I first saw pictures of the Battat - Geared to Steer Interactive Driving Wheel, I knew it was exactly what I needed: A steering wheel-shaped toy with all the electronics enclosed in a frame that could easily be modified to fit in the car:

I was surprisingly lucky with this one because very little work was required to make it work.

All I had to do now was make an adaptor or modify it in such a way that it would allow itself to be secured into place.

I created another 3D model for this which turned out really well. Here is a link to the 3D model that I used for this.

With the adapter built and perfectly fitting, all left was to power it via the 4.5V regulator terminal to avoid using AA batteries. This also ensures the wheel gets turned on when the car is turned on and vice versa.

Mounting and connecting the steering wheel.

The grand finale.

I hope you found this post instructive and fun. I really enjoyed building this car and I hope Keira likes it as well.

List of Parts and 3D Models

While building the project, I purchased a Ryobi 4 Amp 18V battery. I would not have put two batteries in parallel to increase amperage if I had initially owned this battery.

Here is a list of all the parts and components that I used for building this car:

These are the 3D models that I used: