Week 7 : Circuit Board

This week we initiated work on the circuit board and lathe work for the project. The GENIE 18 motor board PCB418 kit was soldered together and tested to see if it worked during the 1 hour lab this week. During the 2 hour lab, we began manufacturing of the stilts for the sumobot.

Soldering is a method of joining similar to that of brazing. Here, we use a solder iron and filler wire (solder, a mixture of copper and zinc) to join the components of the GENIE board to the board. On the reverse of the GENIE board you can see a series of copper tracks and holes surrounded by a copper circle. The intention is to feed the wire of each component through its respective hole and drop the melted solder onto the wire joining it to the copper circle surrounding the hole.

On the front of the GENIE board is a pictorial of what component goes where. There are 30 parts on the GENIE board, not including the additional terminal blocks we added. These components include the GENIE 18 microchip and the L293D microchip which make up the core processors of the GENIE board. Together with the selection of resistors, capacitors, diodes, LED’s and other hardware, the GENIE 18 PCB418 proves to be a very efficient, reliable and easy to use piece of hardware for our application.

As you can see from the 2 images below, the revers of the GENIE board has all the components soldered to the contact strips. However, if you look closely to the top left corner, there is a silver circle 2 holes down from the top. This is a contact circle where we would drop solder onto. The wire of the corresponding component would be fed through the hole in the center of this contact.

The image on the right is of the front of the GENIE board. Here we can see all the components and what they look like and where they went. If you look closely you can see it is written on the board where each part goes.

After soldering up the GENIE board, it was important to test the board to ensure it was working. To do this, a simple program was developed on circuit wizard and uploaded to the board. The circuit I choose was to send power to an output for 5s. In this case I choose Q7. I then connected a multi-meter to the board to measure if the board was sending power to the output. The multi-meter read a high of 5v for a period of 5 seconds. it then dropped for 2 seconds and repeated the program. This is what i intended to happen. Below is the simple program i uploaded to the GENIE:

After much discussion within the group we have decided on how we are going to control our sumobot. We intent to attach the following hardware to our project:

• LDR x 3
• 2 geared DC motors
• Ultrasonic sensor

LDR

We intent to include 3 LDR’s on our project. 2 of these LDR’s are at the front of the sumobot and the remaining LDR is situated to the rear of the sumobot.

The LDR’s to the front are used to sense the outer ring of the battle field so that our sumobot does’t drive straight out of the ring. If these LDR’s sense they are on the ring (the values picked up by the LDR’s will be below a certain value, probably 90 ohms)  the program will runt he motors against each other so that the sumobot will turn around and move in the opposite direction.

The LDR situated to the rear of the sumobot will act as a fail safe in case it is pushed to the edge by our opponents. In this case, 1 motor will shut off and the other will drive turning the sumobot 90 degrees and allowing it to drive away from the danger.

Below is a schematic of how to wire up 2 LDR’s onto the GENIE board. However, I have not yet wired on the 3rd LDR which goes to the back.

Below is the flowchart for controlling the LDR’s. In this case, the LDR’s are directly controlling the 2 motors.

Ultrasonic Sensor

The ultrasonic sensor will be used to sense where our opponent is. The sumobot will slowly rotate until the ultrasonic sensor picks up a reading and it will then briskly move towards the object. It is important to define the maximum distance the ultrasonic sensor picks up reading to. For instance, if the ultrasonic picks up a spectator outside the ring who is 5ft away, it will move towards that object. So we must define that the ultrasonic sensor can only pick up readings form a maximum distance of the diameter of the battle field.

Below is a schematic of how to wire up an ultrasonic sensor. We intent to place our ultrasonic sensor on the main body of our design so that it is sending signals directly in front of itself.

DC Motor’s

We intend to use 2 geared DC motors. These motors run on volts varying from 4.5v to 15v. The ratio of the gear is 5:1. If we can send enough power to the DC motors, we can have high speed motors driving 2 wheels. If we want to use 9v to power our DC motors we must include a sub system as the GENIE board only allows a maximum of 5v through.  To accomplish this we can use an L293D on a separate board as a relay or sub system to send 9v to the motors.

Below is a circuit wizard of how to send 9v to a motor using a DPDT switch and an L293D. But in our case, we would be controlling this sub circuit by the GNEIE board. We could send the control power to the sub system from an output on the GENIE meaning we can get rid of the DPDT switch. In this instance the DPDT is used to change the direction of the motor. however, we can control all this from the GENIE board.

Lathe Work:

We started to turn down the stilts for under the GENIE board today on the lathe. These stilts are being made from 8mm diameter aluminium. The stilts consist of 2 parts, the lower part will be secured to the base of our project and the GENIE boar will then be secured to the top of these stilts. The idea behind this is to keep our board up out of danger from shock and vibration caused by collision with our opponents. The stilts act as a sort of shock absorber. The second half of the stilts has 2 functions. Firstly, it acts as a lock onto of the GENIE board to hold it in place and secondly, we will be attaching a ‘roof’ to the top of the project.

The manufacture of these parts is difficult as they are small with fine threads. As you can see from the sketch below we intend to have the top half of the stilt screw into the second meaning that 1 side must be drilled and tapped, the other must be turned down and threaded with a die for the male end. We tried this, but difficulties ensued with the threads on the male part of the first part. As we were starting with 8mm aluminium and turning this down to 4.5 to run a 4mm die on it, we had very small thin and weak thread.

So alternatively we decided to scrap the idea of the male end and put a female end on both halves and use 4mm threaded bolts. We cut the head of the bolts and then threaded these into the ends of both the stilts as seen in the below sketches and pictures.: