More H Bridge work

March 20th '06

Today I made the double NOT gate circuit for the motor controller.

For the first time I tried one of those blank predrilled PCB's from radio shack. What a total pain in the butt. It looked nice though and was less expensive and more sturdy than the acid etching stuff I've done before.

Here are the plans and the finished board.


Here it hooked up. It seemed to work for a bit but something went horrible wrong and fried the L298 H bridge chip. *cry* What a huge waste of time, I ordered a handful of NOT gate IC's that afternoon, along with a replacement L298 chip. The not gates are about 60cents a piece for a 8 gate chip, so why fight for hours building my own?


Thank goodness for the suction iron....


Per a request here are the notes I made for the H bridge and NOT gate stuff.
http://www.pasqualy.com/landraider/stepperplans.jpg

There may be errors on that page so make sure you double check anything I wrote down before you use it yourself.

Replacing the RDFR with a dual H bridge

March 17th '06

Alyssa and I worked on the robot today. I'm taking out the underused and overpriced RDFR speed controller and replacing it with a simple dual H bridge.


Alyssa says, "That's a price savings of about 300 bucks!"

The unit will mount in the front bay like the old one did, but forward of the motors.


Its is much smaller as you can see.


"Dad! Those motors draw 980 milliAmps each! You should add a heat sink!"


Right, here is the board with heat sink mounted on the L298 chip.


Fortunatly the motors have little fans on the back that kick out air in the direction of where the H bridge will be mounted, and there is an air vent just underneath of where the heatsink will stand.


Here it is mounted.


Here is the SV203 board driving the inputs on the H bridge, Alyssa was pretty close with her current draw estimate. The L298 can handle 2 Amps per motor.


Now here comes the tricky part.
The L298 has 6 inputs.
Left motor Forward
Left motor Backward
Left motor Disable
Right motor Forward
Right motor Backward
Right motor Disable

My SV203 controller only has 8 inputs total and I need 2 of them for the gun's pan tilt and another one for the trigger device on the gun. Plus I'd like to have another two for a second camera's pan tilt.

So I had to use some electronics wizardry(joke) to minimize the number of outputs used up by the H bridge (the RDFR used only two outputs Left/Right channel and Forward/Back channel all with automatic mixing).
So what I did was get it down to three outputs like this:

Left Motor Direction
Right Motor Direction
Left and Right Disable

For the left/right motor direction I simply used one line going to forward, and then did a logic inversion of that line same going to backward. So if forward is on, backward is off, if forward is off then backward is on.
Then I connected both sides disable to a single line, so either both are on, or both are off.

You can see me testing this with a NOT gate (or inverter) built from a resistor/transistor circuit built on the bread board. It worked great so all I have to do is build a board for it and stick on the robot.

Replacement motherboard is in

The replacement motherboard came in for my tank today.

I added lots of switches, buttons and LED's while I waited for it over the past few weeks.

Thank goodness it all worked!









The red and yellow bottom LED's are for motherboard power LED and HDD LED.
The big red switch at the top right is for master power.
Below it is a green LED and switch for motor control power.
Below that is an amber LED and switch for servo controller power.

To the right is a power(red) and reset (black) buttons for the motherboard, and between them is a 12V DC jack for when I dont want to run off the battery.

Replacement drive wheel

21st Century toys was kind enough to send me a free replacement drive wheel for tank. The original was cracked and tended to slip off of the brass drive nut and then the nut would just spin in place inside the plastic housing. The corners had worn away so bad that it was becoming a big problem.

You can see the small crack here.


This is the brass nut that drives the drive sprocket. The drive sprocket is held on only by the tension of the plastic around the shaft and the tendancy of the tracks to keep it in place.

Installing switches, buttons, and indicator lights.

While I was waiting for a replacement motherboard, I decided to work on adding some switches and what not to the back of the tank.

First off I was cleaning up my wiring and making things nice and neat when I started to consider where I was gonna put all the switches etc. I realized that my mounting board was going to have to be modified or else I could never fit all the switches in, and even if I did, I could never get the board out without pulling out every LED and switch I installed.


So I had to yank out the mounting board and modify it.


I removed a notch that would end up being the place for the mobo LED's and removed the two 'wings' that filled the gap toward the back of the tank. I had to take those off because they would have sat under the switches and stuff and made it impossible to remove the board without first removing the switches.

Let me tell you, this was a HUGE pain in the ***. I wish I had accounted for it before, because I had to take all kinds of crap apart to get it back out and then modify it.

Now that I had that taken care of, on to the switches etc.

Master Power Switch
When it was off, the power line to the batteries and 12V jack was broken, however it did not break the connection of the 12V jack and batteries, so the batteries would still charge off the jack when the main power switch was off.
When this switch is off nothing has power.

Motor Controller Power Switch
This broke the power to the motor controller in the front of the tank. This would allow me to work on the tank and not have to worry about the thing running away on me.

Servo Controller Power Switch
This one is a little tricky. The Servo controller doesn't run off of 12V. I't is a 5-6V system. Instead of adding its own DC-DC voltage regulator, I just ran it off of the power supply that runs the motherboard. If you don't know it, PC power supplys give 5V(red lines) and 12V(yellow lines).
So the switch is simple in that it just breaks power to the servo controller from the motherboard power supply, but tricky in that the motherboard supply has to be on to give power to the servo controller. Not that big of a deal really.


Here is an image of the switches installed.


Next, I needed to install indicator lights for the Motor Controller, and Servo Controller switches. The Master Power Switch has its own built in light.

The two LED's had to be connected correctly with the switch and then resistors added. Unlike lamps, LED's don't have built in resistors, and you must be mindful of polarity.


I put the resistors inline with the wire just behind the LED.


Then I covered them up with some heatshrink.


Next I drilled holes and mounted some LED holders. The plastic was way to thick for them to catch right so I had to modify them and glue them in place.


Here they are mounted etc.




Now as mentioned before, the Servo Controller has no power unless the motherboard is on. Since I had no motherboard, how did I power up the power supply to test the light?
Like this..


To power an atx power supply simply short the green wire on the motherboard connector to ground.

Motherboard Power Button
This is just a momentary switch that turns on the motherboard. It connects to the built in pins of the motherboard itself.

Motherboard Reset Button
Same as above, just a momentary switch that connects to the reset pins of the motherboard.

These two switches were very straight forward, just drilled the hole and mounted them. Again, I yanked the wires from old computer hookups and wired them to the switches I got at Radio Shack. The green button will be replaced with a red one.

Power on and HDD Activity
These were just straight forward LED's that I actually yanked from an old computer someplace (I have a huge box full). They connected to the pins made for them on the motherboard. I didn't have to add resistors here because that was taken care of on the motherboard.

Here is an image from the inside view where LED sockets mounted. This is what the gap in the mounting board was made for.


Here they are mounted inside and outside views.