5.1 gearboxes for tanks

[Son of a gun-ner]

An example of motor torque.
Hornby produce scalextric cars and OO trains.
The cars are light and need to be quick. The locomotive needs to be able to pull weight at slow speeds.
The scalextric motor has 2 very weak magnets and three poles on the armature, and can spin quite freely. The locomotive motor has two stronger magnets, with a minimum of five poles on the armature.
Forgetting the gearing in these two toys, and just looking at the motors. The car motor doesn't need much torque within its design to achieve what it needs, therefore it doesn't require many amps. The locomotive motor however has to pull weight at slow speeds, which requires more torque in the motor, which needs more amps.
Either motor will want to take as many amps as it needs. Therefore if there isn't enough amps being supplied because whatever is supplying the amps can't supply enough it will get over heated and burn out.
A further example. Have you ever used scalextric controller that got hot? Burnt out maybe? That is because the controllers are just resistors, and resistors restrict the amp flow. The car motor, although doesn't need many amps, always demands its full quota of amps, and therefore the controller gets hot trying to stop the flow of amps.
Just like a standard tank MFU will overheat because it can't supply more amps than it was designed to supply, and will burn out with motors that want more amps than are available.
So, tank manufacturers use higher revving motors that don't need more amps to try to work with their higher ratio boxes (because these boxes are designed to be used with their standard MFU's), but sadly these boxes need higher torque motors instead that will need more amps.

[Max-U52]

I put a set of these in a King Tiger and it fried the mfu.

[Son of a gun-ner]

I put a set of these in a King Tiger and it fried the mfu.

Yep, over straining the motors will also overload those standard MFU's.