Sunday, June 22, 2008

Week TechVideo, 2008 #25 - Sariel 'S Tank'

This week another pair of videos from Paul (Sariel), where he shows and explains in detail his 'S Tank' working principles (left side video).
The 'S Tank' itself pretends to be a Stridsvagn 103 tank from the Swedish army.








Nice video! 'S Tank' features:
  • Full pendular suspension
  • Pneumatically tilted hull (forwards and backwards)
  • Pneumatically lowered front blade
  • Internal compressor with autovalve from Paul's design (once, posted here)
  • Subtractor driven with PF XL motor, steered with PF motor
  • Detachable side skirts
  • Detachable rear fuel tanks
  • Moving commander's turret & gun

One of the most interesting video parts, turns to be the explanation from the driving and direction mechanisms, and how it was achieved with a subtractor on the drivetrain design (something I should return to, in more detail later on).

Meanwhile take a look to Paul's 'S Tank' photos more in detail, at his BS folder.

5 comments:

Sariel said...

Muchos gracias, Conchas! :)

AVCampos said...

Absolutely impressive! I particularly like the way it tilts the tracks: I bet a lot of research and trial-and-error went into that!

However, I have a question about the drive choice: a dual-differential drive is more intuitive to steer (one control goes F/R while the other goes L/R) and allows for perfect straight motion, but wouldn't a simple differential drive (like on the 8275 Bulldozer) be better? When moving forward/reverse, both motors help in propulsion instead of one of them being dead weight. Also, the additional gearing introduces more friction.

On the other hand, if you intend to "robotise" the tank, the dual-differential's straight line ability could be the decisive advantage.

Sariel said...

Actually, the 'dead weight' argument is easy to disprove. The dual-differential drive allows you to use smaller, lighter motor for the steering, and thus the 'dead weight' is actually quite small. The 8275-like drive, on the other hand, requires both motor to run almost all the time (the only exception is one of two possible turining manoeuvres), which in case of two PF XL motors powered by standard batteries means that none of them will run at full power.
It's true that additional gearing = additional friction, but I have tested subtractor drive in a Truck Trial, and it proved surprisingly effective. The reason, I guess, is that there is only one pair of bevel gears, which cause most friction. Except for that, the entire drivetrain mechanism consist of parallel gears.

Conchas said...

In case of the Bulldozer, I guess that even at turning maneuvers most users use both motors simultaneously, for faster turn a shorter radius, like in a real dozer (each motor running in opposite direction relative to the other).

Ezra Frantzen said...

Hello Paul,

My name is Ezra Frantzen. I live in Amsterdam and I am 9 years old. I think the Lego S tank you designed is really amazing and I am trying to build it but it is really really hard. Did you ever make instructions?

Thanks for your help.

Ezra

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