As I have already announced, at my test drive is a more or less major problem occurred. Since a while I drive a new track tensioner, same principle as used in Tamiya Tiger 1.
But while I have my Tiger tested in really deep sand, he stopped at once suddenly. Okay I thought, fuse blown - no problem, for that is she there. But indeed was not only blown the fuse, but broken both idler wheel arms. A view at my damaged idler wheel arms...
So first once take the tank in my car, drove home and analyzed at home this problem. Two causes could I found beside the crucial extreme driving conditions. But first was complete disassembly at my agenda.
From my supplier for the track tensioners (RC tank) I've got after description of the problem immediately and free replacement. However, not only the broken arms, but also equal to the counterpart, the internal tensioner.
First I was surprised, but then I saw the reason for that - the idler wheel arm was about 1 mm in diameter stronger than its predecessor. So that was a weak point and also a reason for the failure.
An additional cause was the big lever that could be effective on idler wheel arm, because an external support is missing. For this problem I have found my own solution, I turned on my lathe two jacks of aluminum. The inner diameter of the sleeve corresponds to the outer diameter of the idler wheel arms, now they sit sucking in the sleeve.
The aluminum inner part of the lower hull had to be adjusted a little in the rear, so that my sockets could be inserting from the inside. Pictures...
And so looked the whole thing from the outside.
So were two vulnerabilities reinforced, but not quite enough to me. If I drive again in deep sand takes the track (again) between the guide teeth a lot of sand and small stones and it will run over the idler wheel. As result increases the tension of the track until there is nothing more and this tension is then passed on to the drive sprocket and idler wheel.
Nothing to do against that problem at the drive side, a good help could be a chain tensioner, who isn't rigid; so in case like a spring, according this principle. This tensioner then as small as possible because I haven’t enough space in my tank. So I've made first a sketch, then a CAD drawing and then the construction; as building material was used copper sheet and brass tubes.
Four slices of copper sheet 0.4 mm thick cut, drilled and screwed together for further processing. For this purpose, each with 2 husks of 6 mm in length (corresponding to the width of the clamping nut) cut from brass tube with 3 mm inside diameter and fits for that two pieces of pipe 10 mm long, 3 mm outer diameter. The two small pieces of pipe were then placed in the two husks and will later receive the spring.
The whole thing then repeated once more with brass tubes of 4 mm inner and 4 mm outer diameter; this holds the tensioner on the common shaft.
Here they are sanded and assembled temporarily.
Then the four copper plates processed together.
From these parts were assembled two new tensioners and soldered together as follows.
However the springs still missing. These I have then bent out myself of spring steel rod with 1.8 mm diameter and for that I've built a small bending tool. Pictures...
That was the preliminary result.
After a few adjustments follows the installation, on the track side for receiving the spring and for a good force transmission I've soldered still two little tubes. Pictures say more than words, that's why...
With my self-made tensioner I increase the preload of the spring, this gives the preload then directly to the track tensioner and the track shall tensioned.
The spring may seem a bit weak in the photos, but is actually very strong. So the tensioner does only a little bit springs, this should mean, that he does not operate during normal use, but is capable to rotate a bit under high pressure.
Well, I've tested a few spins on a doormat, so he works a minimum, the chain tension still remains, as it should be.
But nevertheless I have considered to build another spring from spring rod with 1.6 mm diameter and a bigger inner diameter for a better working range.
A specific statement about functionality may follow later times after detailed testing, perhaps outdoor.
