To me the appeal of the vintage Tamiya RC cars is their accurate scale appearance, but this is let down though by the lifeless plastic drivers. Fortunately it is a simple and cheap task to inject a bit of life into them, in this Instructable I will show you how.
My instructions are based around the Tamiya Super Champ, but they will match very closely to other vintage Tamiya cars, and with a little bit of thought, the techniques can be applied to any other car.
Here is a bit of footage of the mod in action.
And some bonus footage, just in case you're like me and can't get enough vintage RC action
Step 1: Parts Needed
All you really need is a micro servo and the horns that come with it, everything else can be figured out depending on what you have on hand. Here is what I used, but I recommend you read through the steps and see what you have on hand that you can use.
- Micro Servo (EMAX ES08A)
- Servo Y-harness (or two male-female cables)
- 2x Miniature Bearings (3mm inner diameter, 8mm outer diameter is perfect for the vintage Tamiya drivers)
- 3mm screw (about 20mm long)
- Hex Standoff/Spacer (also known as pcb spacer)
- Epoxy (I used Pratley's Steel Putty)
- Hot Glue
- Loctite (or a spot of nail polish)
- Screw Driver/Allen keys
- Side Cutters or similar
- Craft Knife
- Drill Bits (I used up to a 6mm)
- Soldering Iron (only if you need to change servo direction the cheap way)
Step 2: This Step Is a Pain in the Neck
I discovered that the hole in the neck of my Tamiya driver was exactly the right size for a miniature bearing (3mm inner diameter, 8mm outer). This happy coincidence led me to what is quite possibly an over-engineered solution to mounting the head.
First I drilled out most of the neck, the goal here is to make sure the bearing is only supported on its outer edge, since the inner part will be turning.
In retrospect, if you cannot get hold of a bearing, I think one could just use a short hex standoff, or even an m3 nut, glued into the neck. The head will raise/lower ever so slightly as it turns left/right, but I doubt it would even be noticable.
Step 3: My Head Feels a Little Screwey
A close shave
Your head may have been glued in place, although according to the instructions on mine, it should have just been screwed in, obviously the previous owner thought that wasn't sufficient, so he glued it in too. A good twist popped it off though.
Since the bearing in the neck uses up the space where the neck stump used to go, I shaved it off with a craft knife. I then drilled a hole into the head. Since the plastic was a bit old and potentially brittle, I just slowly turned the drill bits by hand, each time stepping up to a larger size, until the hole was big enough to put in a hex standoff.
Filling your head with rubbish
I decided to put a threaded insert into the head, in this case I just used an M3x16mm hex standoff (often sold as a "pcb spacer"). I filled the head with hot glue and then stuffed the standoff in. I put a long screw into the thread to help me see whether it was lined up correctly, since the glue takes a while to set I was able to view the head from all angles and make little adjustments.
Step 4: Get Your Head on Straight
In order to attach the head to the servo I connected the center of a servo horn to the end of a long M3 screw, and then put the screw through the bearings, into the head. The screw does not need to be too tight otherwise the bearings will bind, but this means you need to use locktight (or a drop of nailpolish) on the threads to prevent it coming apart.
I tried a few methods to attach the center of the servo horn to the screw
A short piece of silicone tube is stretch over the head of the screw and the other end goes over a servo horn who's arms I had chopped off, cable ties keep it all in place. This method has the benefit that the silicone tube is a little flexoble, so if the servo is not perfectly aligned, it's no problem.
This method was exactly the same as the silicone tube plan, except worse, the heat shrink was slippery, but I guess cable ties would have fixed that.
I simply epoxied the center of a servo horn to the end of a screw. I roughed up both pieces to make sure that the epoxy had something to adhere to. This was the way I went in the end, it has the benefit of being more compact.
Step 5: Everything's Resting on Your Shoulders Now
The benefit of this over-engineered bearings solution of mine is that the head assembly stays put, spinning around like a scary movie, even without a servo attached.
All that is needed is something to prevent the servo turning around. I used two off-cuts of 1.6mm aluminium, bent at a 90 degree angle, and stuck them to the baseplate with double-sided tape.
I would also recomend a little tape or adhesive on the servo itself, to prevent it falling out.
Step 6: Wiring
The wiring is dead simple, all you need to do is get the head-turning servo to respond to the same commands as the steering servo. Assuming you don't have a spare channel on your transmitter/receiver, the easiest way to do it is with a Y-harness, which allows you to plug two servos into the same port on the receiver.
You can buy one, or if you don't find one, make it out of two extension cables (i.e. male-female cables) as shown in my pictures.
There is a chance that your servo will turn in the wrong direction with respect to your wheels, if that is the case, there are a few ways to handle it.
- Use a fancy 3 channel tx/rx, where you can link and invert and all that stuff (I don't have one, so I can't help you there).
- Get a servo reversing cable and put it inline, just google "servo reverser"
- Or the cheapest and easiest (if you ask me), just modify the servo. I'll cover that in the next step.
Step 7: This Is All So Backwards
As I mentioned in the last step, there is a chance that your servo will turn in the wrong direction with respect to your wheels, if you would like to modify the servo to fix that, this is how.
- Swap outer leads on potentiometer
- Swap leads on motor
I want to understand version
First, a very high-level bit of theory on how servos work, you can feel free to ignore this if you like, the modification is extremely simple, even if you don't want to know how it works.
The servo receives a control signal from your receiver, which tells it what angle it should set the output shaft to.
The servo has a motor that drives the gears clockwise or anticlockwise, the direction it turns is dependant on the polarity of the voltage applied to the motor.
The servo detects what position the output shaft is at by means of a potentiometer (a rotary variable resistor).
The servo is continuosly checking the output position (via the potentiometer) with the requested position it got from the receiver, and applies either positive or negative voltage to the motor, to get it to the right place.
Reversing the Servo
In order to reverse the direction that a servo turns we are really just swapping "minimum" and "maximum" position, which is easily achieved by swapping the outer leads on the potentiometer. However, this will break the control logic. When the servo attempts to correct a difference it will actually apply the opposite polarity to the motor, making the situation worse. The easy fix is to swap the polarity of the leads on the motor too.