Maestro and Brookshire's RAPU

So I am building an animatronic and am planning to use the Brookshire RAPU running the VSA software. I have a prototype routine running on VSA on my PC (the maestro connected by USB and the servos powered by a battery pack). As I understand it, and as I have it set up now, VSA is sending commands via the virtual “command” COM Port (COM 3 in my case) through the USB connection. That works fine (at least so far).

My question is, how do I migrate to the RAPU? The RAPU has both a Serial Out DB9 and a 3-pin “TTL Port.” Which one do I use? The Serial I think? I hook that up to the Rx and GND pins on the Maestro, correct? Any addressing issues I need to be aware of? Should I use the Mini SSC or the Maestro Servo protocol? Also, if I want to control a couple LEDs, how do I set up VSA? The Maestro docs explain how to configure the channels, but not sure for VSA. I asked Brookshire, but no reply so far.


We are not that familiar with Brookshire’s RAPU board. From a quick scan of its documentation, it looks like you should be connecting your Maestro to the RAPU’s TTL serial port (which I expect to include RX, TX, and GND connections). Unfortunately though, I do not know how you should proceed beyond that.

- Patrick

Thanks… perusing the manual more carefully, it suggests the TTL port on the RAPU should work with the Maestro. The pins on the TTL port are labeled +, -, and S. So that confuses me a bit. I have a message out to Brookshire, but they have not been great at responding. Is there a risk of damaging the Maestro if it is hooked up incorrectly?

Yes, making incorrect connections to the Maestro could damage it, so it would be ideal if you could get some information for Brookshire.

However, if you have already waited a long time, here is a hypothesis that might help you make some progress (a reminder though, I have not used the RAPU board myself). I suspect the intention might be for the + and - pins to power the target device (e.g. be connected to the Maestro’s VIN and GND respectively). Then the S pin might be acting as TX, so it would be connected to the Maestro’s RX pin. They might be forgoing the connection from the Maestro TX to RAPU RX pin. You could check if that hypothesis seems reasonable by looking at the + and S pins with an oscilloscope, to see if they have the expected behavior. The + pin would provide a constant voltage (probably 5V, but it should be between 5V and 16V for the Maestro), and the S pin would provide a data signal (square waves when sending commands).

- Patrick

I was thinking along the same lines as your hypothesis… S for signal. Later tonight I’ll power the RAPU and see if there is a steady voltage across the + and - pins. Currently planning to power the Maestro through the Servo power connector. The Maestro and the RAPU will he powered by the same battery, so the grounds should be the same.

I thought I’d follow up, since this might help other folks. Brookshire got back to me and confirmed your hypothesis and said to connect the Maestro Rx to the S (Signal) pin and to tie the Grounds together, just to be sure. No need to connect the “+” pin if the processor is otherwise powered.

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I am glad to hear that Brookshire got back to you! Thank you for letting us know, and good luck with your project!

- Patrick

I seem to have it kinda +working on the RAPU… after I remembered to change the serial mode! I selected fixed BAUD UART. But although it seems to be working (servos are moving in any case), I am getting the red LED lit indicating an error. Any ideas? I mean, it SEEMS to be working, so maybe just ignore the check engine light? Just worried (a little anyway) about damaging the board.

If you are talking about the red LED on the Maestro (not something on the RAPU), then you might try connecting it via USB to a computer running the Maestro Control Center. Once it is connected, you can monitor the “Errors” tab while your RAPU is sending commands to get more information about what is going on.

- Patrick

Final update (for now, anyway). After I disconnected and reconnected all the wires, it seems to be working without the error condition. Maybe an error state that cleared.

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