July 2001

Sunday 8^th July 2001

In an idle moment I decided to casually go over the Robot Wars rules again, but later on wished I hadn't. (Well actually I guess it was just as well in the end, but what I found was a bit depressing.) I was reading the section on radio control gear and spotted a reference to the frequencies used, which were 40Mhz. This raised alarm bells because I thought the radio gear I had been donated was 35Mhz. With a quick inspection of my controller the situation was confirmed. It was the wrong frequency!
I fired a query into Derek Foxwell at Robot Wars asking if there was a quick solution to upgrade my radio gear to 40Mhz. He responded quickly by saying "No", and referred me to the forum pages of the RW site where this subject had been raised before. After a bit of surfing I located an incredibly useful site with loads of quite technical info about different areas of robot building. It covered weapons, radio gear, motor controllers, embedded micro-controllers, to mention just a few of the topics. It was run by Paul Hills, and was very technical is some areas, so be prepared if you visit it. In the area of radio gears, it gave reasons why it was very difficult to upgrade a 35Mhz system to a 40Mhz system. That was a bit disappointing because it meant that I would have to source another radio kit. However, the site had a lot of other useful links that talked about reducing radio interference, and how to ensure you installed your system to get the best results. Despite this whole exercise being a bit of a "downer", I can still continue to use the radio gear I have in the short term to check the robot operations. It just means for the moment I won't be able to enter any events!

Thursday 12^th July 2001

I received a 40Mhz transmitter and receiver from those nice chaps at Sussex Model Centre. They were willing to send me only the transmitter and receiver without the servos, so I saved a bit of money from the normal kit price.

I discovered that the 40Mhz systems are allocated to land-based models, and the 35Mhz band for air-based models. Apart from that, there was no real technical reason why my old system wouldn't work equally as well as the new one.

The next thing I had to do was take the receiver apart and locate the point in the circuit were I could extract the serial data stream for the micro controller to decode. After a bit of poking about with the oscilloscope probe, guess were the connection point was that I needed to get to.

That's right, on the chip with the big blue capacitor glued to the top of it!

Realising that I was about to completely invalidate the warrantee, and also risk permanently damaging the circuit, I gingerly cut away at the glue until the capacitor was loose, and then I gently de-soldered and removed it. This modern day surface mount technology is all very well, but it does mean the chip contacts are very small and soldering a wire onto them is particularly difficult. I wound a bit of copper wire around the soldering iron and used this as a very small soldering iron bit so that I could get onto the board without damaging any adjacent tracks.

Once I had soldered the wires on, I managed to put the capacitor back and then held it in position with instant silicon gasket.

The receiver looked like this after the job was complete, and what's more, it all seemed to work! The next thing I needed to do was modify the micro-controller software a bit because the channels allocated on this transmitter were different to those of the Pulse Core system. This should be a simple job of changing the value of a couple of variables, and downloading a new version to the controller. (I hope!)

Saturday 14^th July 2001

I decided to try and hide all the delicate, low powered motor control circuit in a single box, (a) to provide some shielding , and (b) to make it easier to fit into the robot. I got the receiver, the gyro, the micro-controller, and interface board in there. The Receiver and micro-controller batteries will have to be mounted outside the box, likewise the power MOSFETs on their heat sink "bricks."

Thursday 19^th July 2001

I made a few small changes to the motor control software to match the new radio gear characteristics. There was a small offset in the joysticks range that meant that the mid position was off centre, and the maximum range couldn't always be achieved. After a few changes, the joystick operations were back in range with the trimmers set to mid position.

Sunday 22^nd July 2001

I managed to squeeze a bit of time in a very busy weekend to make the fourth axle mounting bracket. The welding was still not perfect, but improving. On a couple of seams I don't know what I did, but the weld just flowed freely and easily and it was difficult not to end up with a nice looking weld. On on a couple of others it wasn't until I had chipped off the slag that I realised the weld had only taken to one side, and I needed to go over the weld again. I would like to know what it is that I do each time that makes all this difference!

Tuesday 24^th July 2001

I collected the motors shafts and bearing spacers from Bill at Settform. The spacers now allowed the bearings to hold the shaft in the right place for it to mesh with the stub end of the motor. The studding used to mount the bearings on will also come in handy to help mount the motors onto the chassis of the robot.