Building a bigger robot by hacking the controller board of a smaller one.
My Scribbler hacking project should be winding up soon. Which means its time to start thinking about a new project! Since I've only worked with small robots, I'd like to build something a little bigger for my next project. I plan on mining this forum for ideas on the mechanics of building a platform and motor selection.
Now I happen to have a Basic Stamp 2 board that would be almost perfect for building a robot. I say almost because there's a small problem. The controller board is from a TAB Sumo-bot I got cheaply a few years back. It was a cheap way to get a BS2 board, even if the rest of the robot had problems.
In many ways this board is ideal. It has a BS2, 11 free I/O pins, a motor controller, a pair of h bridges, light sensors, IR sensors, and a remote control. Not to shabby! But the h bridges don't look like they could power a motor large than they toy motors it came with. Not good for building something more substantial, but circuit hacking might solve this problem.
Does some kind amplifier exist which can amplify current and polarity of a signal from the small h bridge to drive a bigger motor?
Could four diodes be used to rectify the output of the h bridge and use them as inputs to another h bridge?
If either of those don't work then cutting traces on the board to tap into the inputs to the existing h bridge and connect them to an off board h bridge might work, but that seems tricky.
As a last resort I could forget about the on board circuits and use the remaining eleven pins. But that seems like a waste.
Now I happen to have a Basic Stamp 2 board that would be almost perfect for building a robot. I say almost because there's a small problem. The controller board is from a TAB Sumo-bot I got cheaply a few years back. It was a cheap way to get a BS2 board, even if the rest of the robot had problems.
In many ways this board is ideal. It has a BS2, 11 free I/O pins, a motor controller, a pair of h bridges, light sensors, IR sensors, and a remote control. Not to shabby! But the h bridges don't look like they could power a motor large than they toy motors it came with. Not good for building something more substantial, but circuit hacking might solve this problem.
Does some kind amplifier exist which can amplify current and polarity of a signal from the small h bridge to drive a bigger motor?
Could four diodes be used to rectify the output of the h bridge and use them as inputs to another h bridge?
If either of those don't work then cutting traces on the board to tap into the inputs to the existing h bridge and connect them to an off board h bridge might work, but that seems tricky.
As a last resort I could forget about the on board circuits and use the remaining eleven pins. But that seems like a waste.
Comments
http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-circuit.html
I also put it into Visio and attached as a bitmap. I can upload the Visio file if desired, but it might be bigger than 2 MB.
Essentially I think you could connect the on board H bridge's red and black wires to the FWD and REV inputs of the external H bridge. Because the opto-isolators contain LED's they'll act as diodes, so when the current direction matches the diode bias that bring that input of the H Bridge high. Conversely when the diode is reverse biased that should set that input low. The ENA is tied to ground and you rely on the PWM of the current in the existing H bridge to switch the external H bridge and PWM that motor. Ignore the circuit at the bottom, I was noodling around trying to figure out a way to pulse ENA instead of the H bridge inputs.
The downside of this approach is that you only have three settings coast, forward, and reverse. The external H bridge also supports dynamic breaking but there's no way to signal that as near as I can tell.
What's cool about this approach is that the opto-isolators mean the motor power system is separate from the logic power system. So the 4 AA batteries powering the basic stamp should last longer and noise from the motors won't get into your logic circuits.
Dynamic breaking, bad. Very bad. [noparse]:)[/noparse]
You're on the right track. Depending on the size of your robot motors and what you want to achieve, you may be better off starting from scratch. You could go far with a BS2 (which could be upgraded later to an BS2SX or BS2PE) and a simple speed control, like a Pololu micro dual serial controller or such.
I'm a fan of using relays in H-bridges, as my recent posts suggest!
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·"If you build it, they will come."
I guess dynamic breaking is when your H bridge doesn't support dynamic braking and you bring both inputs high. ;^)