Connect AX 12+ bus

[Goldrake]

Hello,
i'd like to connect the ax12 bus directly to a UART of an embedded board (arm9 board), all without CM5.
What type of interface?
I think i need 2 type of boards. One: AX12 bus -> UART, Another about the alimentation of the servos (with battery recharge).
Anyone can help me?

Thank you

[Goldrake]

UART is the serial port.

None can help me?

[billyzelsnack]

There is a small circuit in the AX-12 manual.

http://robosavvy.com/RoboSavvyPages/Support/Bioloid/

[JonHylands]

There are a pile of posts in the past couple months talking about how to do this. I have an extensive tutorial on how to build a ATmega128 interface, including all the code, here:

http://www.bioloid.info/tiki/tiki-index.php?page=pc+serial

An ARM9 would be very similar, although it si doubtful that you could get 1.0 Mbps out of the normal UART from most ARM9 boards, since they are typically set up with a crystal for more typical baud rates, like 921 kbps.

If the ARM9 you're talking about is a gumstix, I have a page that describes how to do that as well:

http://www.bioloid.info/tiki/tiki-index.php?page=gumstix

That is using the Robostix as a go-between, and it gives you 115K access to the AX-12 bus from the gumstix.

If your ARM9 has USB host, you could use this setup:

http://robosavvy.com/modules.php?name=Forums&file=viewtopic&t=990

There are lots of options...

- Jon

[Goldrake]

Thank you for your feedback.
I was thinking about buying this board:

http://www.robot-italy.com/product_info.php/cPath/1_94/products_id/676

It has usb, rs232 ed UEXT connector.

What do you think? Shoud i use usb? It's better to reach 1mbit?

[JonHylands]

For that board, which has USB host, I would definitely recommend the USB solution. Check into the drivers first, to make sure that the USB -> TTL board listed in that post will work under whatever version of Linux they are using.

I would recommand you contact ArnaudBuy as well, since he is the one who did the work and got it working, to see if there are any caveats.

- Jon

[JonHylands]

Here's another, smaller, cheaper, faster, SBC that runs linux and comes with Wifi, and has USB host:

http://www.compulab.co.il/x270/html/x270-cm-datasheet.htm?gclid=CMvwzJ_Y8IkCFSJNPgod-AJZLA

In single quantity that one is about $130 USD.

As an additional bonus, it also has an analog video in port.

From my perspective, if you took that board, and combined it with the USB -> TTL board mentioned earlier, you could then easily write all your robot control code on your PC, talking over Wifi to this board, which pipelines all the data to and from the AX-12 bus over the USB connection. You could also use a nice little camera fed into the video port, and run some frame grabber utility on Linux that would allow you to send the captured frames over the wifi link.

- Jon

[Goldrake]

Thank you very much

About the squealing servos, i tried the configuration writed on wiki: CW e CCW compliance at 2 and Punch L = 200 Punch H = 0.
But i listen intermitted sound not silence. What could be?

[Goldrake]

I think that board it's great. But what about battery consumption. Differences with arm9?

[JonHylands]

The servos will squeal when you apply too much load on them. If you continue increasing the punch, the squealing will stop, but then they start to chatter.

According to the manual, that board consumes between 0.2 and 2 watts, depending on configuration and speed.

http://www.compulab.co.il/x270/download/x270-cm-man.pdf

I don't know what the power requirements for the ARM9 board are...

- Jon

[Goldrake]

i finally bought that arm9 board. I see that the crystal oscillator is 14.7456Mhz. Can i reach 1mbit on UEXT with that clock freq?

Thank you

[JonHylands]

I doubt it. However, with host USB, you can use a USB chip (from FTDI) to talk directly over the bus with just a simple buffer chip (or a bus switch) in between.

Note that gumstix has finally released their PXA270-based version - my new verdex shipped today, and should arrive tomorrow or Wednesday. It comes with a 600 MHz processor, 128 MB of RAM, and 32 MB of FLASH. It doesn't have wifi, but you can apparently interface to some of the usb wifi modules out there, and they will be offering a wifi board for it soon.

- Jon

[Goldrake]

So i need a Ftdi and the 3 buffer as shown on "Simple PC/USB to Robotis bus interface" thread. I saw that board but i didn't find any xscale with a cheap development board. It's more difficult to add circuit to all connectors (usb,serial,etcc) without a development board that has them built-in. Gumstix provides the chip with all connectors?

[JonHylands]

gumstix provides a number of accessory boards.

You could use a breakout-gs or a tweener, which plugs into the verdex board using the 60 pin header, and gives you either USB client or host through the USB connector on the board.

You still need to connect the FTDI board, but you can buy the raw connectors from Digikey, so you could make up a simple cable.

I plan on creating a PCB that has the FTDI chip and a 2-channel bus switch onboard, and connects easily to the usb port on one of the accessory boards.

- Jon

[billyzelsnack]

Super cool. I've been waiting for USB host to showup in an inexpensivish uC!

Are you saying plug the FTDI board into the gumstix?? Wouldn't that USB port be much better utilized with a wifi dongle plugged into it? ( Could you use a USB switch with it for more ports?? )

The way I (probably naively) would think about using this might be..

Wifi dongle for wireless communication back to the PC.
Make available several GPIO pins for use as AX-12 ports
Make available several GPIO pins for use as RC servo ports
Make available several GPIO pins for use as RC gyro ports
Make available several GPIO pins for use as accelerometer ports

There are a bajillion GPIO on this thing!

Doesn't this thing have enough raw power to do all this busy work including generating boring old PWM for servos?