26 Nov 08 The Robot: Hardware working and ready to go, a few minor glitches

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Progress has as always been good lately. The robot boots up quickly and appears on the wireless LAN, with openssh running. The internal Atheros miniPCI wasn’t doing the trick and wireless performance was shaky at best. I’m using an Alfa Networks USB adapter (r8187) and an 8dBi gain antenna now, so this has some distance now!

I was also getting frustrated with the laggyness of the board while VLC was running for streaming audio and video and so I decided on an IP Camera (Edimax), which is connected directly to the LAN port on the Alix board (I don’t have any reason to use it for anything else).

The motor control script works well and the device is responsive. At this point I can drive the device around

relatively easily and accurately, stream video and audio back to my laptop, which again is connected wirelessly.

Using ‘espeak’ you can easily generate a synthesized voice to provide easy text to voice:

Everything is working great and I’m pleased so far. The only reason why there isn’t a video up yet is because I haven’t had the time! There will be one up shortly.


Glitches are as follows:

1. I’m taking regular backups of the 4Gb USB thumb drive and the 512MB internal CF card. I’m easy on the writes to the CF card but they seem to be causing problems way too often. It doesn’t help that I’ve got a cheap unbranded batch. Errors are failed writes and read timeouts, they seem to degrade noticeably daily. I’m going to try and get a few expensive branded CF cards and see if that helps. If not, it’s either the bus or potentially interference (see next glitch!). I might also try a CF to SD card adapter and see if those work out better.
2. The motor control generally runs smoothly however at times it drops commands. At times, during heavy load although the board is running and power consumption is good throughout, the controllers actually misinterpret the commands. During stall, I have littl hope motor control, the board and all peripherals are all running healthily and the board will still provide all other functions. At first I thought that the USB to TTL cables were too long, but I’ve shortened both cables to about 6cm and still no luck. I’m going to check that everything is grounded correctly, then try and pull up the serial tx to the 5v rail slightly harder. If all else fails, I’ll need to completely isolate the supplies.
3. All 12 phidgets sensors work perfectly except the phidgets distance sensor on the back of the head - annoying! I’m going to check cabling and then replace it.
4. The board is heavy and even with the strengthened base, it dips slightly in the middle which impedes motor and wheel performance. Although it moves well at the moment, I think it could be a lot better. I’m going to homebase to look for some steel reinforcement.

Power consumption with everything but motors running on charge is 15v/1A which is more than acceptable on a 12v/7.2Ah battery. After the following glitches are ironed out, the majority of the hardware is complete.  I can then tidy up all round and take a break before I start working on some software.

I’m first looking for some good voice to text engines, then I’ll start building APIs on the hardware sensors. I’d like to output current battery charge to the picoLCD

Next post is definitely a video - promise

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Tags: 8dbi, alfa networks, alix, antnna, atheros, cf card, distance sensor, edimax, espeak, gain, hardware sensors, ip camera, Linux, motor control, phidgets, picolcd, power consumption, r8187, SD card, serial, usb, usb to ttl, vlc

Reader's Comments

1. Anonymous | 18 Feb 2009 7:38 am

   always been good

2. Nelson Neves | 05 Mar 2009 6:16 pm

   Very interesting approach for your robot. I have been making some tests with my NAS drive, NSLU2 aka SLUG with Linux Debian to work has a robot, but have a lot o work going on … Keep up the good work!

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