The drive which I am planning on having tracks is going to be a very trial and error set-up as since planning on doing it I have been told its not to practical. As the track setup can be used in something else I am not to worried about it working or not, as it wonít go to waste.
I started off with drawing up some plans on my computer to get the layout for the wheels. It is going to be based on a CAT dozer set-up with the drive wheel sitting above the other five wheels. The end two will be fixed, and the three in the middle floating on spring dampers. Apparently tracks donít work very well at all if all wheels are fixed in one position, as it can make the object very unstable if it goes over a ridge. By having the three middle wheels floating, they can move up and down to compensate for uneven ground.
So the wheels are simply turned from a rod of delrin. The rod was cut into ten equal length sections, then one end of each faced off, then when all ten were done, the lathe was set up to face off the other end, and at the same time make sure they were all the same length.
When doing a run of ten like this it is best to do each stage on all the wheels in one go. This makes sure they all come out identical, and also saves having to re-set the lathe for each step of each one.
With the centre taken out for the bearings, the groove was cut in the outer surface for the tracks to run in. These are standard tamiya king tiger tracks made from plastic, but if it does work they will be upgrade to metal as they are much tougher
So with the wheels made, it was time to turn my attention to the axles. The two end wheels will be fixed, but the three middle ones floating to allow for more stable travel over uneven ground. Due to not having any dampers at the moment, I have started with the end axles. This is just a piece of 10mm brass rod, which is cut to length, then each end machined so it will fit into the side plate and finally the end drilled out and a thread cut so it can be bolted up from outside.
I also made some more identical bits out of slightly ĹĒ alloy to act as strengthen struts.
With the axles and strengthening struts done, I made the side plates from carbon fibre as its very strong but very lightweight, then started to assemble the bits. I had pre-draw plans I had done for the layout, and these were stuck to the carbon fibre prior to cutting out so I would know the correct shape and placement of all the bits.
The axles are fixed as the wheels have bearings inside them to run on, but the drive wheel has to be turned from a motor so it fixed to the shaft, so flange bearings were fitted to the carbon side panel, to allow it to run smoothly.
The two end wheels are fixed but the middle three are floating and will have sprung dampers to push them onto the ground. This will allow the tracks to go over uneven ground or objects, and prevent the unit from toppling over if on uneven ground. If the middle three wheels were fixed if for instance you drove over a cable tidy that are often run across floors at shows or conventions, the unit would rock when halfway across as the fixed wheels would not allow flex in the track. But allowing the middle three wheels to lift means if the unit runs over something like a cable tidy the first wheel hits it and bumps over then the rest rise up as they encounter the object creating a stable ride. Same principle as a real tracked vehicle.
With the main wheels fixed on place, it was time to fit the spring dampers to the middle three wheels to keep them on the ground at all times. The dampers are off a tamiya rc car, as any will do really, but these were a good length. As I didnít want the damping effect, just the springiness of them, the oil was removed, and then they were cleaned out and a single drop of silicon fluid placed inside for lubrication. They were then reassembled, and bolted to the main axle. I made a single alloy spacer to hold the top in position, then made a mould of it, so they could be reproduced in resin, as this is quicker than turning all twelve by hand.
Once done, a hole was drilled in the carbon side plate, and the resin spacer glued in position then a bolt fixes it all together and provides added strength.
Now when pushed along over uneven ground, the middle three wheels move up and down, keeping the tracks on the ground at all times.
Next was time to connect up the motor to the drive wheel. Now being electric, and as it will operate like a tank does when done, a speed controller is needed, all be it a fancy one for controlling a tank. The motor was chosen for several reasons. It was fairly chunky, and also only spins at around 6000rpm, which on its own is still to fast for practical use, but it allowed for gearing down to a sensible speed.
The motor is connected via a timing belt to stage one of the gearing, which from the motor is 10 a ten tooth pulley to stage one which is a 35 tooth pulley. The shaft then runs through to the other side, where again the drive pulley is 10 tooth to the drive wheel which is a 30 tooth pulley. This will allow my R6 to run around at about 3.2 mph, which I think is fast enough, but more importantly the motor can run at full rpm most of the time, which stops it getting so hot, and electric motors are far more economical when running at full rpm rather than slower. Also gearing down in this way produces far more torque, than just using a direct drive, and in things like this torque is more important than speed.
While it came out slightly bigger than I envisaged in the beginning, it still fits nicely inside the foot, which I had to make to check it would fit ok.
Now I just have to make another one.