Medium Tank
My second tank, features a drivetrain with the subtractor, more advanced suspension, a headlight, rotated turred and elevated cannon.
Datasheet:
Completion date: 22/07/2007
Power: electric (wire-controlled)
Dimensions: length 30 studs / width 20 studs / height 12 studs
Weight: 0.82 kg
Suspension: pendular bogies / independent with shock absorbers
Motors: 2 x RC, 2 x 71427
Second take on the subject of the tanks. Very similiar in size to the first tank, but lower and wider, which makes for a more realistic look. The drivetrain is exactly the same – two RC motors with a subtractor between. The suspension is somewhat more advanced, by the addition of an amortized rocking levers in front. The turret is rotated by a motor inside the hull, and inside the turret is a motor that elevates the cannon. All the wires exit through the hull this time, and the hull’s sides are protected by the openable side courtains. I have bought a black 8×8 plate with grill specifically to place it above the motors, so that some internal parts could be seen. There is also LED brick from the Exo-Force sets located in the front part of the hull.
@Mihály Stépán
No, it should be fine, but it also depends on the size of the drive wheels and the surface you’re driving on.
@Sariel
Does a 1-1,5 kg vehicle give a hard time for an XL motor? Using say, 20t to 28t diff ratio.
@Mihály Stépán
Depends on what you do with the motors. If they are heavily loaded, they drain batteries pretty fast. The new 8878 battery is supposed to last to up to 4 hours when fully charged.
@Sariel
Speaking of which, if you have a model with like 6-10 motors, how often do you need to recharge the batteries? I guess those XLs use up quite a load of energy..
@Mihály Stépán
Exactly. Additionally, with a subtractor you can use 2 different motors and the tank will always go perfectly straight. You can use a strong motor for drive and a weak one to steer, which is more efficient than using two strong ones.
@Sariel
Aha! So that’s the trick! 😀 The subtractor lets you control the tank in a precise manner, and the speed control just refines that.. I get it now…
@Mihály Stépán
Yes, it is difficult as there are delays when you speed-control two motors at the same time. It’s very inaccurate, e.g. starting straight ahead is almost impossible. I have subtractor + speed control in my new tank and it works like a charm.
@Sariel
Ok, but seems to me that you can do exactly these (turning in arch etc) with speed controlled motors for the individual tracks. I was asking because as I know your work, you tend to use the simpler mechanism if it can do the same as the more complex. Is it difficult to speed control the motors in a precise manner?
@Mihály Stépán
Read this and you will know: http://sariel.pl/2009/01/subtractor/
It might be a stupid question, but if you already have two motors for driving a subtractor, then why not power the treads independently by their own motors? I mean, then you don’t have to mess with a lot of gears the subtractor needs…