Faller Indiago 140438 & Homemade Control Box - Construction Log



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Several months after finishing the model, I decided to have a go at creating a proper Control Box to replace the one supplied by Faller...

Phase 1 - Prototyping


This is the original wiring diagram for the Indiago.
Faller's supplied Control Box simply switches on the power to the 2 motors via the blue wires. After 70 seconds the power is shut off, but because of the permanent power connection via the purple and red wires, the 2 arms on the model continue to rotate until the magnets on the end of each arm pass the reed switches, at which point there is a break in the circuit and the arms stop rotating.

What I wanted to do was control each motor separately, randomly stopping and starting each motor so as to alter the angle of the car suspended between the 2 arms.
After some investigation and design, I decided to use 4 relay switches - 2 for each arm/motor. One to power the motor directly for the duration of the ride, whilst the other would only be switched on at the end of the ride and would power the motor via the reed switch.
Here's the revised wiring diagram:



The relays would be controlled by a programmable Picaxe chip, with each relay connected to an output pin on the chip.
I created a prototype circuit, mounted it on a breadboard and downloaded a 31 line program onto the Picaxe chip. I tested this setup with the Indiago model - and it worked great.



The next task was to take the above components and arrange them on a stripboard.
I want to use a single power source, so I would need to add some additional components to transform the power source from 16v AC (for the motors) --> 16v DC --> 5v DC (for the Picaxe chip).


Phase 2 - Stripboard Design

Using the free TinyCAD software I converted the mess of the above prototype circuit into the mess of the following flowchart.



TinyCAD allows you to export the flowchart into a file that can be imported into the low-cost VeeCAD Stripboard Editor software.
Using VeeCAD, I went through many different stripboard layouts, but eventually settled on the following design (even though it probably goes against the general rules of circuit board layout).
(Note: During prototyping, I found that one of my Relays (K1) was wired differently from the others, so the output (J10) for this relay is on a different side to the others)



Key Component Value Purpose (as I understand it)
K1 / K2 / K3 / K4 Relay 5v SPDT To control flow of 16VAC to left and right motors.
D1 / D2 / D3 / D4 Diode 1N4001 To prevent back EMF damage to Transistor when the Relay switches off
T1 / T2 / T3 / T4 Transistor BC337 A switch, activated by Picaxe chip, to control the Relays
R1 / R2 / R3 / R4 Resistor 10k Restrict current flow through chip
R5 / R6 / R7 Resistor 4k7 / 10k / 20k Recommended connections / values by Picaxe
BR1 Bridge Rectifier W02M Converts AC to DC - in this case 16vAC to 16vDC
U2 Voltage Regulator L7805CV Converts input DC (in this case 16vDC) to 5vDC.
I've left room on the stripboard for a Heatsink, but it may not be necessary.
C1 / C2 Capacitor 100nF / 100uF Smoothes the DC output from the Voltage Regulator


The next stage was to add all the components to the stripboard and solder them in place.


Phase 3 - Building


Cuts applied to the stripboard tracks.

Once the circuit had been built, I ran into a problem - the AC -> DC conversion didn't work as planned.
The Voltage Regulator would get very hot, very quickly and eventually fail. I don't know whether the 16v -> 5v conversion was just too much for it, but I eventually had to abandon this idea.
Instead, I decided to have two separate power supplies - 16vAC for the motors and 9vDC (converted to 5vDC by a new Voltage Rectifier) for the chip and relays.
I was able to make the necessary adjustments to the stripboard (as it existed at that stage) without having to start from scratch.
I left the Bridge Rectifier in place, but now it is superfluous to requirements and has no impact on the circuit.
Here's the revised layout:











This is the program that I downloaded on to the Picaxe Chip:
symbol counter=w0               
main:                           
        low 3			
        low 2			
        low 1			
        low 0			
        pause 2000		
ride:			        
	high 3		
        high 2 			
        for counter = 1 to 4	
                pause 7000	
                low 3 		
                pause 700 	
                high 3 		
                pause 6000 	
                low 2 		
                pause 1200 	
                high 2 		
        next counter 		
        pause 7000		
        high 1			
        high 0 			
        pause 1000 		
        low 3 			
        low 2 			
        pause 17000		
        low 1			
        low 0 			
        goto ride 		


;power to left motor off - main circuit
;power to right motor off - main circuit
;power to left motor off - reed circuit
;power to right motor off - reed circuit
;wait 2.0 secs
;start ride
;power to left motor on - main circuit
;power to right motor on - main circuit
;loop 4 times
	;wait 7.0 secs
	;power to left motor off - main circuit
	;wait 0.7 secs
	;power to left motor on - main circuit
	;wait 6.0 secs
	;power to right motor off - main circuit
	;wait 1.2 secs
	;power to right motor on - main circuit
;repeat loop
;wait 7.0 secs
;power to left motor on - reed circuit
;power to right motor on - reed circuit
;wait 1.0 secs
;power to left motor off - main circuit
;power to right motor off - main circuit
;ride completes - wait 17.0 secs
;power to left motor off - reed circuit
;power to right motor off - reed circuit
;start ride again


And here's a video of the model in action:

Video@YouTube



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