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From: "Steve Tyng" <SteveT44-at-comcast.net>
Subject: RE: newbie [TANKS]
Date: Mon, 4 Apr 2005 07:35:17 -0400
Reply-To: tanks-at-rctankcombat.com

Tim wrote:
> mabey if i could see some pictures of your guys tank guts. could
> you send me some pictures of your tanks inside electrical work?
> that would help alot.
Tim, here you go.  This is the original wiring setup in tank T005.  It is designed to handle much more current and higher voltages than the RC trucks your used to.  The doubled red and black wires feed current to the two aluminum busbars.  Attached to the busbars are two circuit boards (one for each motor)  with four relays attached (the black boxes).  The relays are arranged in what is called an "H-Bridge" configuration.  An H-bridge is a way to reverse electric polarity to a DC motor so you can reverse it's rotation.  Reversing ESC's you are familiar with also use an H-bridge design but instead of relays will use a type of transistor called mosfets or just "fets" (a transistor is an electronic relay with no moving parts).  There is a great explanation of how an h-bridge works here (http://www.rctankcombat.com/articles/speed-control/).  The orange/black and yellow/blue wires attached to the top of the relay boards feed current to the drive motors.  The relay boards ARE NOT attached directly to the Rx (receiver) but to a control board located in the turret.
Pictured here is the control board that controls the motor relay boards.  The black/red/white wires are going to the Rx and the cable bundle going into the black connector on the lower right are heading to the relay boards in the back of the tank.  The control board is the brains of the tank in that it mixes the signals from two receiver channels to provide you with the forward/reverse and left/right motion you are looking for.
In case you don't understand what channel mixing is all about here's a brief explanation.  Mixing allows you to control the tanks motion from only one stick of the Tx (transmitter).  Remember we are talking about airplane type Tx's with joysticks instead of the pistol grip style you may be used to.  Because a tank doesn't have any steering wheels it's direction is controlled by varying the speed and direction of it's tracks.  This requires two channels, two motors and two motor controllers.  Imagine you are pushing one stick of the Tx forward to move your tank forward.  But this one motion is only affecting one channel of your Tx and normally can only control one function like an ESC in a RC car or the steering servo.  What the mixer board does is takes this one signnal and then activates BOTH motor controllers in the forward direction so your tank moves forward.  Now imagine your moving forward and you want to turn left so your move the joystick to the left.  What the mixer board does is to start to slow or even stop the left motor (but keeps the right motor going) so that the tank turns to the left.  This is what mixing is all about.  Without a mixer circuit you would be forced to use two sticks on your Tx to control tank movement.  This would not allow you the other stick to control the turret rotation and gun elevation.
The wiring and mixer board shown here were one-off prototypes used only in the T005.  It worked very well but is not exactly what is being used today in the majority of tanks but is close enough for a general explanation.
Steve Tyng