Bioloid (20 DOF) with N900 head

[sascha]

The contrustction of my bioloid with N900 head and control unit has been almost completed. I will post some photos of my work.

Robot features:
- Bioloid Premium, Type A
- 20 DOF (2 additional servos for the head)
- Head and control unit using Nokia N900 (running Maemo)
- Second LiPo
- External power adapter plug
- Button to switch between battery and power adapter mode

[sascha]

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[sascha]

[bluecat]

Awesome,

what are the n900 capabilities ?
have you implemented object recognition ? or anything else interesting ?

[sascha]

The N900 is a very potent development platform. It runs Linux and there is a SDK to access certain parts of the hardware like the 3 axis accelerator.

Here are some of the specs:
- TI OMAP 3430: ARM Cortex-A8 600 MHz
- Up to 1GB of application memory (256 MB RAM, 768 MB virtual memory
- 3-axis accelerometer
- 5.0MP (2,584×1,938), f/2.8 Carl Zeiss Tessar lens (rear camera)
- Micro USB connector for charging or host mode
- WLAN 802.11 b/g
- Bluetooth 2.1
- Proximity Sensor

So far I installed ROS on it and can access the camera. I wrote a library to access the Robotis servos in C++ in will port them to ROS. That development was done for an insect type robot, which I build previously using the Bioloid kit and Phoenix Spider base. Finally I didn't like the result much (to heavy and bulky).
I did mount a pico mainboard on my bioloid humanoid before and an additional battery, webcam and voltage converter, but I also found the design to heavy, so I finally switched to the N900.

BTW: The N900 is connected to the USB to Dynanixel adapter, but I removed the Serial portion, since I don't need it.

[billyzelsnack]

Very nice. How much does the N900 weigh?

[sascha]

N900 weights 181 g

Additional specs can be found here:
http://en.wikipedia.org/wiki/Nokia_N900
and here
http://maemo.nokia.com/n900/specifications/

[Fraser]

Nice work, do you have any idea on the serial data latency that you get through the USB with ROS on your N900? It should be pretty realtime yes?

[sascha]

I'm using a C++ library, which I will port to ROS soon. I don't know how much overhead ROS will generate, but I don't think it will have a huge impact.

I wrote a small C program to ping a servo (5000 times), which runs on my PC and N900:
PC = 250 ping per second
N900 = 62.5 ping per second

This was done using 1MBit and ftdi default settings. So I didn't adjust any of the ftdi parameters (especially latency).

[Fraser]

I wrote a small C program to ping a servo (5000 times), which runs on my PC and N900:
PC = 250 ping per second
N900 = 62.5 ping per second

PC: 250 ping per second = 4ms
N900: 62.5 ping per second = 16ms

Were the results the other way round? I'm interested because I'm looking at options for an autonomous controller sometime later this year.

It's a nice controller you've got yourself, plenty of space and power for development. Look forward to seeing more.

edit:
@Billy, I'm just catching up on some of the work you've done and it's all pretty cool, really like the realtime YUV colorspace manipulation stuff.

[sascha]

Hi Fraser,

I was working on the FTDI latency issue yesterday and integrated some libftdi code in my PC (Ubuntu) code to change the latency setting. I couldn't find the libftdi package for the N900 pre-build and looked for an easy alternative. And I didn't like the idea of having this FTDI low level code in my library.
I read that the FTDI driver parameters in Windows can be easily changed using the device manager. I was wondering if a similar possibility would be available in Linux?
Finally I found out, that some of the FTDI parameters in Linux are available in the sys filesystem, including the latency timer.
/sys/devices/platform/musb_hdrc/usb1/1-1/1-1:1.0/ttyUSB0/latency_timer

I could easily retrieve and set the latency timer in this file, without having to include FTDI low level coding in my program:
Nokia-N900-51-1:~# cat /sys/devices/platform/musb_hdrc/usb1/1-1/1-1:1.0/ttyUSB0/latency_timer
16

Nokia-N900-51-1:~# echo 4 >> /sys/devices/platform/musb_hdrc/usb1/1-1/1-1:1.0/ttyUSB0/latency_timer

The lowest value, which improved the communication speed was 2ms.

N900 = 500 ping per second

[billyzelsnack]

Nokia-N900-51-1:~# echo 4 >> /sys/devices/platform/musb_hdrc/usb1/1-1/1-1:1.0/ttyUSB0/latency_timer

The lowest value, which improved the communication speed was 2ms.

N900 = 500 ping per second

Very nice! Thanks for looking into this and posting it. It should be useful for my Linux based controller too.

[Fraser]

Yup, thanks for the info, 2ms, that's a nice quick ping, compared to that I'm wading through treacle with my 15ms ping on windoze.

[MOHIT JINDAL]

Hi Sacha,
Can you please share your pc code with me. I want to control all AX12+ with Usb2Dynamixel.
Please Help.
Thanks Cheers.

[sascha]

Hi Mohit,

Version 0.1 can be found here.
http://robosavvy.com/Builders/sascha/DynaBot.zip