3/18/2021

 

A significant milestone was passed recently. The walking feet were fitted and lift and slide tested. The lifting units performed fine and confidently lifted the machine onto the four pseudohydraulic lift units. However at the first attempt the tub was being left about 3mm behind. The cause of this was the tub itself flexing by that amount when its 140 kg weight was suspended by the central support rod. When adjusting the pretensioning of the tub at an earlier stage I had tried to estimate what the tub would do by stepping onto the floor of the mainframe. My 85kg weight could not cause movement at all. This was not a good indicator of the way the tub would behave since the latter is only 11 holes deep while the mainframe( which is all I was testing) is 22 holes deep. The cure was simple and just required me to climb partially inside the hall, undo the locknut on the rod keeping the two units together and then tighten the nut 4mm and relock it. This effectively pretensioned the tub some more so that on retrying lift the tub followed the rest of the machine up off the ground. On lowering the machine I retested swing to see that I had not jammed it but it was fine. The eight swing units are tremendously powerful and easily handle the effective extra weight of about 180 kg. Figures 87 and 88 show the overall view of the machine from two slightly different elevated positions. The full width of the machine has been reached now, 9 foot. Figure 89 shows me inside the machine adjusting the tension on the bolt.

 

Fig. 87: Elevated front view showing walking feet installed

Fig. 88: Dittom moved slightly to one side

Fig. 89: Me inside adjusting tension!

Initially I had been worried that there would be some rock to the machine when it went up on its four lifter “stilts” but there was none at all. The action of lifting is slow, taking about eight minutes from fully retracted to fully extended for the feet, but the motors remained cool during this time and so did not seemed overstressed. The booms, bucket and ballast will add about 300 kg to weight but I do not expect problems because of the above observation.

Figure 90 shows the two walking feet on the left side, and figure 91 is a closer view. In these pictures the 20mm horizontal stainless steel rods on which the machine slides are clearly visible. Also visible is the upright brass fitting with an M20 thread into which the rotating M20 rod drives up and down driven by two 12V motors geared down to give huge torque. As usual I bolt pinions to gears to avoid torque going through grub screws on axles. They would just rip loose. The large vertical brass unit has a transverse 20 mm hole milled so that it can rock slightly in the slide piece. This is to allow the feet to be planted on slightly uneven ground. I had thought this might be a source of machine rock but the rigidity with which the lifter units are bolted to the machine is preventing this from happening. The slide piece itself is a box made of 2mm material with a pair of   brass rods bored out to a fraction more than 20mm. In fact the whole of the central section of the walking foot is made from 2mm plate except for the bottom which is made of 1mm plate, which is fine since the weight is spread out over a large area.

 

Fig. 90: Two walking feet on left

Fig. 91: Ditto, but a clearer view

To accommodate uneven ground the front and back feet on either side are hinged in the centre. Figure 92 shows this hinge, a 10mm rod with an aluminium machined disc to imitate the look of the prototype.

 

Fig. 92: Central hinge between walking feet

The walking feet will be finished off by installing a boxlike hydraulic pump housing on each. All four are shown in figure 93. The units are plated with recycled coffee tins which were easy to bend into small radius curved corners to continue the theme of such corners started on the hall. The small box at the rear of each I believe contains air filtration equipment so that filtered cooling air is made available to the powerful hydraulic pumps. The air intakes point downwards to prevent rain from being taken in. There is also a door opening on each, opening out onto a walkway which will allow staff to enter from the top of the foot which in turn is accessed from the ground by ladder. Although I am not modelling the inside of the pump stations they would also hold tanks for hydraulic fluid. There was a total of 200 000 litres of fluid on the machine for all the hydraulics. That would fill 4 normal sized domestic swimming pools!

 

Fig. 93: Four hydraulic pump houses

Before I close up the hall I am going to install 10 ersatz swing motors shown in figure 94. The employ recycled paint cans and coffee tins. I think the small device at the top is some kind of electrical unit in reality. Maybe a capacitor?

Fig. 94: Ten ersatz swing motors