Tamiya Solar Car, R/C Steering

So, I've been meaning to make a remote-controlled steering solar car using Tamiya's Solar Car (Kit @ Tamiya's site) kit for a long while. A mom had come into the store where I work, looking for a project for her kid, and we got onto this project idea. I ended up talking about it in detail enough that I decided to build one that same night, and I did. I'm doing this instructable "early" and draftish for a friend and for that mom :)

Items Needed:

Tamiya Solar Car Kit - around $30-40 (TAM76012 is the part/item #)

R/C Transmitter (radio, Tx) and receiver (Rx) - anywhere from $20 and up, or used/garage saled from old hobby-grade r/c cars/planes/etc. The Toys'R'Us and Radioshack style stuff is possible, but much more complicated to use for this project. I'm using a Spektrum DX4 transmitter and a Spektrum AR400 receiver (about like DX5 w/AR400), these are normally used for planes/helis. You can also use car-focused systems like this - Spektrum DX2E w/Rx. I'm not trying to plug this particular brand, but they do have great customer service for new hobbyists. There are nearly a million options for this 'component', and if it works, it works. These two items can be used on a variety of projects, they are not single-use. I also use this radio/tx for flying r/c planes and using a flight simulator program.

Servo (servomotor) - anywhere from $5 to $20, I used a Hitec HS-55 (HRC31055S) because I had it, $12. Mine is a size standard called "micro". I recommend getting a servo that lists it's size as micro, as it fits well for the size of the car. Sub-micro or mini can work too, though submicros are going to tend to be weaker and mini size will be a little heavy and hard to attach to the frame.

Battery - I use a battery to power the Rx, which powers the servo. The solar panel that comes with the Tamiya kit does not provide enough voltage (0.5v) for my setup, and doing the wiring would be more complicated. An entirely panel-powered car is my next project. The battery I am currently using is a 1s/3.7v 500mAh LiPo. I have also used a little NiMh because I have them. If you do not already do r/c stuff, you probably do not have a battery charger capable of charging these little guys! I then suggest a 2x AAA holder w/wires and a 'pigtailed' plug of some sort that you can plug into the receiver, like this pigtailed JST plug, and just twist the wires together and wrap individually with tape. You may need to strip extra wire to get something twistable.

Small phillips (X head) screwdriver.

Masking tape.

Moderately stiff wire, I used some brass 22 gauge.

Build the Solar Car kit according to the instructions in the box. You'll need the phillips screwdriver. Its helpful to have either an Xacto or small scissors handy as well, but not necessary.

You may want to go outside and test it as is, before you add the radio control stuff to it.

When I built my first one in June (car by itself) I had to jog to keep up with it.

Tape the receiver onto the solar car's frame. You'll want the area that has the pins to be clear of tape. I used some masking tape and cut it in half lengthwise, since it was too wide. This does not have to be on snuggly, as it does not move or have force applied to it.

I put mine up by the servo, but I think in the back on top of the motor is a better spot. Also make sure to keep the antenna wire that comes out of the receiver out of the way of the wheels. If you lose or cut the antenna, it won't work or won't work very far away from you.

Look at the diagram on this page - How It Works - Servo - if you've not worked with servos before.

When you buy a new servo, you usually get a set of "arms" or "horns" with it. These are extra plastic pieces usually in a X, T or I shape with a hole in the center. If there is a "I" shape one, that's the one you'll want to use. If there is not, you can modify the X by cutting off two 'legs' to make an I shape. Set it aside for now.

Tape the servo onto the frame of the Solar Car. I have mine with the servo's top (with the output gear/spline) pointing up to the sky. You could also have it facing down. I may be doing that in my second version.

Take it's wired plug, and plug it into the receiver. Most receivers have a row of 3-pin slots for things to plug into. They are usually marked in some way, either with numbers 1-4 or more, or with abbreviations or full words. Throttle or THR, Steering or STR, AUX, BAT, etc. Plug the servo into a numbered slot (1-4, not 5+) or into THR/throttle or STR/steering. Aux/Bat/etc may work, but also may not, depending on your radio. It will usually also have markings of + - and a little 'bump' symbol, along the other side of those pins. + is positive/power, - is negative/ground and the little bump means 'signal', which is the instructions your radio/tx sends to make it move/do certain things. The lightest colored wire (white or yellow) is usually signal, and the darkest colored wire (black or brown) will be ground. Plug the connector in the right way! Take some extra time to make sure. Your servo will probably live if you do it wrong, but its possible it may not.

I wrapped the extra length of my servo's wire around the power wires from the solar panel. If you have a lot of extra wire length, just wrap it around something or tape it out of the way.

This linkage was my 3rd attempt, and works, though is not optimal. Its good enough for how fast the car goes though.

Make 2 lengths of wire approximately 3"/75mm.

Make 2 lengths of wire that are the distance between the front axle and your servo. You do not have to be very accurate with this, and too long is better than too short. You can always clip/cut off excess.

I pulled the front wheels off when I did this, though its possible to do while on.

Start by wrapping the wire around the wheel's inside axle-holding bit. I did 4-5 wraps.

Now make a U shape, and bring the wire back to wrap around the blue plastic near the center. I held my screwdriver in the U shape so that my U wouldn't get pulled flat. Wrap the wire around the center. I only did 3 wraps, but that's not on purpose.

Do for both sides.

Take one of the longer pieces of wire. At the 'back' or 'bottom' of the U, do a small twist of this wire to attach it to the U shape. Let it dangle, and do the other side as well.

At this point, we're nearly done.

Its almost time to put the horn/arm on the servo, and pop the wire into the holes, but not quite yet.

First, plug your battery into the receiver. Since your battery likely only has 2 wires/pins, you need to make sure you know which "pins" that is for the receiver. For *most* receivers, the negative/ground/black wire will be the one furthest to the right-hand side - if you're looking at the receiver and can read the writing on it like normal. Check for that little +/- and 'bump' symbol though. Make sure when you're plugging in the battery, that the black wire goes to the - 'row' of pins, and the red/positive/power wire is going to the + row. The 'signal' row will be empty.

When you plug in the battery, your servo should make a little noise and then stop. If it didn't, either its already where we wanted it to be, or you'll need to turn your radio on before plugging in the battery again. Unplug the battery.

What we did was to re-center the servo. We want to make sure that the servo is at it's "natural" center point before we attach all our steering stuff. It just makes everything easier.

Now, that plastic horn/arm piece you set aside, needs to go on the servo again. If there's a screw in the servo already, take it out. If there was a horn/arm on your servo already, unscrew it and pull it off. If you move that top-gear on the servo while taking it off, do the battery plugging in thing again to re-center.

Place the horn/arm on the servo, so that its 'ends' of the I shape are the same/parallel to the solar car's axle. You can see that in the picture. The white 'bar' is the servo horn. My servo is a dark blue, and the tape is yellow.

Now, take those dangly bits of wire, and with the wheels as straight as you can keep them - loop the wire into the holes of the servo horn/arm. Then loop or twist it around the arm once. Perfection is not required for functionality :)

Turn on your transmitter/radio.

Plug in your battery to the receiver.

Take the car out into some sunlight.

Twist or push all the sticks or knobs on your radio and find out which one will steer the wheels.

DRIVE!

If you don't like which part of the controller you need to use to steer the wheels, plug your servo's connector into a different slot. If you want to know ahead of time which one does what, skip down a bit and read.

Air or "Stick" radio, like I've used. Mine is "mode 2", which is the default usually in the United States. "Mode 1" is swapped sides for the stick. So right-stick is throttle/etc.

Left-side stick is usually - Up/Down = Throttle/THRO or 3, Left/Right = Rudder/RUD or 4

Right-side stick is usually - Up/Down = Elevator/ELEV or 2, Left/Right = Aileron/AILE or 1

On a surface/car or "pistol grip" radio - the turny wheel is steering or STR or 1, and then the trigger is throttle or THR or 2. 3 or more is usually just for powering things, like lights.