February 2002

Friday 1st February 2002

I had two bits of good news today. The Headmistress of the local infants school contacted me following a letter I sent to her asking if I could use the school playground to practice driving the robot. I chose the playground because it was surrounded by walls and metal fencing, which mean it was a safe environment should the Hog go out of control. It was also about 200 yards from my home so I would be able to wheel the Hog down the road, even if there was a bit of a hill en-route. Katherine was happy to let me use the playground provided I gave them enough notice so someone could open the relevant gates. The school is on the village high street so I'm not sure how comfortable I will be being under the watching eyes of every passerby while I become familiar with its driving idiosyncrasies!

The second bit of good news was that I eventually talked the Futaba support team into showing me part of the transmitter circuit diagram. I needed this so that I could work out how best to extract the controls to a remote unit for someone else to operate the weapons from. It took a bit of persuading (about 5 emails) because Futaba have a policy of not giving out circuit diagrams. The way I got by this barrier was to offer them a circuit diagram of how I thought the controls were wired, and then ask them if it was correct. As it turned out my assumptions were wrong, but they sent back the relevant section of the circuit showing how it actually was wired. I now have a good idea how to tackle the task of building a remote weapons controller.

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Sunday 3rd February 2002

I worked on the self-righting tail over the weekend. The first job was to cut two strips of aluminium that would go to make the T section of the tail. It took the best part of an hour using a jigsaw, and by the end of it my hands were aching and tingling with the vibration from the jigsaw tool.

I also made some brackets and hinges that would hold the self righting tail to the rest of the body. I wasn't sure how long to make the tail, so I made it longer that I thought was necessary for the moment, and would shorten it later. as and when I could try it out.

The srimech tail hinge with the ram attached

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Monday 11th February 2002

My order of miscellaneous pneumatic unions arrived from RS Components. I was pleasantly surprised to find that where Southern Pneumatic's normal supplier couldn't source a suitable NPT threaded union for my American CO2 paint ball bottle, RS had a number of unions that fitted just right. This now means that I should be able to complete the pneumatics after I've first finished making a few more mounting brackets for the rams, valves, bottles, etc.

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Saturday 16th February 2002

I completed the supports for the self righting tail, and bolted the ram in position. Since the ream was a little larger that I had first anticipated, I had to mount it slightly inclined. With a lot of jiggling around of the mountings, I found an optimum position where I got the correct angle of elevation from the tail so the hog would be pushed passed its point of balance, and with enough leverage to lift the weight of the robot, well according to my calculations anyway.

A view looking down onto the pneumatic bottles and the srimech ram The main CO2 reservoir on the right, and the buffer bottle on the left

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Sunday 17th February 2002

Today was the moment of truth with the self righter. I managed to fill my CO2 reservoir from one of the old CO2 fire extinguisher, and was then in a position to see if all my maths were correct. I wheeled the Hog out of the garage, turned it over onto its back and then connected the bottle directly to the ram.

The hog on its way back on its wheels

I gingerly opened the bottle valve and watched as the hog started to rise. With seemingly no real effort the hog rolled over onto it's wheel without any problems. What a relief! I did it a few more time just to prove is wasn't a fluke, but each time it self righted fine. If you want to see a short video of it in action, go to the new video page on the web site.

The kids then persuaded me to give the Hog a quick run around the front garden too while things were going well. We all stayed on the other side of our front gate just in case it went out of control and I drove the hog around on our gravel front. The controls were smooth and I was able to control the movements quite well. The way I had designed the motor controller to give fine control at low speeds seemed to work well and I was able manoeuvre it with reasonable precision. After about five minutes the batteries started to go, so the kids helped push in back into the garage.

The hog on its first real outing in the front yard
The hog's first real test drive
  The kids and the hog after the batteries had been exhausted during testing
Pushing the hog back after
the batteries run flat

Later on I looked at plumbing in the pneumatic valves. After half an hour of positioning and then repositioning various components, I came to the conclusion that I needed a few right angle unions if I wasn't going to strain the pipe work. I did however manage to find a way of mounting the CO2 bottle and buffer bottle on the framework. Not being able to do any more on the pneumatic front today I decided to order some unions from RS, as well as the components I would need to build the remote self righter and flipper controls with.

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Wednesday 20th February 2002

The parts arrived from RS so I had a go at finishing off plumbing the pneumatics together. By late in the evening I had the piping in place and had wired up the valves to the controller as well. The moment of truth came as I opened the bottle valve. There was a small leak from the buffer bottle union that was quickly cured with some PTFE tape. I also noticed that the pressure release valve was operating and letting gas out of the buffer tank. This was the first time that I had had it in circuit, so I presumed that I needed to adjust the regulator a bit. I unscrewed the regulator and gave the adjustment screw a tweak and tried again. This time the pressure release valve remained closed

After that I turned on the power flicked a few levers on the radio transmitter. To my relief the valves operated at expected, so my next job is to build the front flipper and mount the ram to it, but will be for another day

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Saturday 23rd February 2002

I went to my local Air products gas supplier who was George Rose in Buxted, to hire a CO2 gas bottle with which to refill the main robot reservoir. I came away with a PT10 sized bottle that holds just over 7kg of CO2, and is about three feet high. It's the size that you can lug about without a trolley and I felt was just about the ideal size for roboteering. The arrangement I made with George Rose was to have a monthly standing order that covered the hire charges of the bottle, becaue you can't actually buy these bottles, you can only hire them. You can opt to pay a year's hire up front, but I opted for a monthly payment so that should I not want any gas for a month or two, I simply return the bottle and the standing order stops. A CO to gas bottle containing 7kg of gas

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Sunday 24th February 2002

We had some friends round who were keen to see the Hog, so I wheeled it out of the garage and took it for a spin in the front garden. I turned it over and showed how it self righted, but only managed to do it once. The second time I had to nudge it to start it of, and I guessed it was because the gas bottle was getting empty, and thought nothing more of it.

Later in the evening I checked the pressure in the system (as you do) with the pressure gauge in circuit, and discovered it was 8 bars instead of 10. I decided to set the regulator to the maximum pressure the pressure release valve would tolerate, which was 11 bars. This all worked well on the bench, but when I put the components back on the robot, the pressure release valve started to open again. After a bit of head scratching and fiddling I discovered that when I first pressurised the system the pressure release valve operated. After a short while it would settle down and everything would be okay. This might explain why I only got one self-righting action earlier in the day because I had misguidedly wound the regulator down too much the day before. The proof of the pudding will be in the eating, and I will have to see how it goes on the Hog's next outing.

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Monday 25th February 2002

While grovelling over the Hog I noticed that the bottom of some of the rear struts were a bit misshapen. This seemed to be due to the Hog's whole weight coming to bear on the ends of the struts as it self rights. I cut the offending bent bits off, and then angled the edge before welding a plate across it. I hope now that the weight will be spread more evenly, and not buckle the struts any more.

The bottom of the strut is bent after a few self righting actions
The bottom of the strut is strengthened to spread the load  during selfrighting

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Last updated 4th March 2002