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

November 26th, 2008
Robot

Robot

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

Robot

Robot

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:

echo “I am a robot”|espeak

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.
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Using distcc for distributed compiling on an alix 3c2

November 26th, 2008

Since I’ve been working on the alix board for the robot it’s become increasingly useful to just compile software on the board itself rather than on a host machine – with an AMD Geode 500MHz processor, it’s certainly capable.

I generally work on a USB hard drive attached to one of the spare ports whilst I’m testing stuff live, and then I back up the hard drive every so often.

I made some modifications to the cp2102.c kernel module and I wanted to recompile the kernel on the board directly as I had some other modules I needed, such as for the wifi card. 2.6.18 compiled eventually over about 7 hours but after wanting to make further kernel changes, I decided that I didn’t have another 7 hours to wait. I decided to use distcc to compile ‘locally’ but use the processing power of any number of other servers.
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The Robot: Independant, moving, talking, and controlled via WiFi

November 22nd, 2008

Robot

Robot

I’ve made some excellent progress over the last week! The Robot is now independant, and it moves freely. I’ve written a simple shell script to take the following characters as control:
a – left
s – stop
d – right
w – forward
x – back
q – hard stop
k – turn anticlockwise
l – turn clockwise

This sends a single byte to the serial port. I am using 2xUSB to TTL converters which show up as

Robot

Robot

/dev/ttyUSB0 and /dev/ttyUSB. Each serial port controls two motors through the sabertooth controller. As we control two motors with only a byte, each motor has a 7 bit resolution from full reverse to full forward. For motor 1, 0 is stop, 1 is full forward, 64 is stop, 127 is full reverse. Motor 2 starts at 128 for full forward, 192 for stop, and 255 as full reverse. Although 7 bits of accuracy, speed changes only seem to occur at roughly 4 intervals, so we technically have about 32 different speeds, 14 forward, 2 stop, 14 reverse. We’re only using 3 speeds though as I can’t see the benefit in programming for any more right now.

The movement now seems to be working well. Smooth, controlled and straight which is something of a miracle 😉

Robot

Robot

The battery is a 12V/7.2Ah sealed lead acid battery. With USB devices active, the board running and the processor 100% active, as well as peripheral fancy LEDs, digital outputs high, wifi active, etc, it uses 12v/800mA.

With all four motors moving at full speed, it uses 12v/6A. Seeing as the motors will be in action for short periods only, I would expect 6h+ battery life.

I have tested the sensors, and they are all working and reporting data except for the top back one which I’m going to have to investigate. Here are some more pictures:

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Linux: AVIT Research USB to TTL Cable

November 20th, 2008

I ordered a USB to TTL Cable to control two Sabertooth 2×25 motor controllers as part of the Robot project.

I plugged it into a Windows PC, and used ‘RoboRealm’ to control the motors via the COM port that appeared. Worked perfectly. Motors, controller, USB to TTL and virtual COM port – excellent.

I then plug the cable into my Linux board and guess what, no driver claims it and I have every standard USB Serial module compiled. AVIT Research’s website also gives no help on Linux support.

The device shows up under lsusb as:
Bus 002 Device 002: ID 10c4:818b Cygnal Integrated Products, Inc.

The solution was luckily simple. After prising open the cable and doing some research, the ‘cp2101’ driver is the one that we want. I’m using 2.6.27.6 but this should work for any cp2101 version.

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The Robot: Base, Wheels, Motors, and Sabertooth Motor Controllers

November 16th, 2008


After attaching the 4 motors and brackets to the acrylic square, I found that it started to dip slightly due to the weight, and as I’d planned to put a 1.5kg lead acid battery in the center and I realised that this needed to be addressed. Rather than another visit to Homebase for some steel reinforcement, I just stuck (melted) two pieces firmly together with polycarbonate acid glue and then trimmed the edges with an electric saw.

Base

Base

Here is the base, the insulation tape all over the place is to hold down the connectors that I won’t be needing. The motors all contain encoders which I didn’t just want to rip out, so I’ve preserved the connectors for future usage, and just cut the – and + cables in a way that they can easily be reconnected to the connector if I ever want to. They were expensive motors so I didn’t want to ruin them!

If anyone is wondering why I didn’t attach standoff cylinders to the controller’s super large heat sink rather than attaching it directly to the acrylic base [which would normally be a bad idea], it’s because I didn’t have any standoff’s left, and the controllers are capable of 25A per channel. I will never drive them at higher than 4A, and the motors running on 4A for 30m or 2A for 2 hours solidly as a test didn’t generate any noticeable heat on the heat sink at all. At first I had also predicted the use of a fan to suck air in from the base, but I’m not sure it will be necessary, as nothing seems to get remotely hot so far..

I’ve also slightly indented the 4 points where the acrylic cylinders will be glued, just for extra stability. The motors are all wired to the two motor controllers, which has a junction box waiting for 12v now. The picoPSU should arrive some time this week, so hopefully I can get on with it.

Omnidirectional Wheel

Omnidirectional Wheel

The wheels are omnidirectional as they contain rollers. It’s a clever design and it seems to work well. Infact, I’m pleased with the way the motors and wheels ended up. Instead of having to work with two wheels and spending time on calculating angles for servo motors and turn radius, I can just attach 4 motors instead in the configuration that I have and using omnidirectional wheels. The motors will pull a lot of weight and I only have to concern myself with backward and forward for each motor, which in any combination will allow it to move in any direction. Hey, I’m not saying that I ‘invented’ this ingenious combination, just taking the credit for a smart move in implementing it! I have connected a power source directly across each of the motors to test. They are straight, and when I turn them all in the same direction, the board rotates around a ‘very almost perfect’ fixed axis which is great. I had in mind when I was positioning these, that I didn’t want to spend a ton of time in the software compensating for wheels that aren’t straight.
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The Robot: A body, Sensors and Good Progress

November 14th, 2008


Progress is going really well and I’m happy so far. Unfortunately I didn’t want to show the body yet as it is so far from finished but as I haven’t posted an update in a while I decided to just go with it.

Front

Front

Head

Head

The body is ever so slightly lop sided by a few mm here and there which is a shame however from a short distance you wouldn’t notice, it stands up straight and weight distribution is equal throughout the base plate so I’m happy with it. Ok, ‘professionally’ the body’s a mess however for my zero experience in that kind of work, I’m reasonably happy.

This is the front of it, top is a mounted webcam, to the left of that is a phidgets temperature sensor and top right is a phidgets light sensor. I am waiting to add 8 colored status LEDs around a small flat panel 5v stereo speaker as a ‘mouth’ (I got it from a Nokia phone bundle).
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The Robot: More good progress

November 10th, 2008

Some more hardware has arrived! Very compact USB hub with external power input, Startech USB sound adapter (line out/mic), 4Gb USB mass storage, USB Trust Webcam.

All plug and play, all works out of the box. I’m using Alsa to drive the USB sound adapter, and v4l for the webcam. Works great and the majority of the hardware works.

Now I haven’t added any pictures to this entry, as I don’t think there’s much point in looking at more pictures of a messy table! I hope that my next post will include pictures of a (reasonably) cool acrylic body. I’m still waiting for the acrylic sheets to arrive though.

The two remaining parts of the hardware to get working are wheel movement and power/battery.

With all board hardware working excluding motors, we’re on 12V/600-700mA which I think is pretty fantastic.

I’m going to go for a NiMH battery pack (12V/10Ah) and not plan to generally discharge more than 12V/2A. The motors will realistically be in use rarely as it’ll be making short slow and unfrequent movements, rather than racing around at full speed!

The battery pack will connect directly to both motor controllers, as well as to a PICOPSU and then to the board.

So.. next stage is to get all the hardware off the table and into some acrylic casing with a 12V DC power source. Once that’s done I can look further into the motors and battery!

The Robot: Phidgets USB Interface Board Kit works

November 7th, 2008

The Phidget interface kit arrived and so did a few of the analog sensors that I ordered. I can’t believe just how simple they are to use and just how friendly and comprehensive their SDK is!

Here are some pictures:

Phidget Interface Kit

Phidget Interface Kit

This is the interface kit itself. It’s a regular USB device and draws minimal power. Along the top of the board are the analog sensor inputs. Each is connected via a simple 3-pin wire, ground, data and +V.  Along the right hand side are 8 simple digital on/off inputs. Along the left hand side are 8 just as simple digital on/off outputs. In this case, I have connected the Phidgets analog light sensor which you can just about see on the left of the picture. Download the Phidgets Linux SDK from their site, compile, and run the examples. The range on the light sensor is fantastic. It advertises 0 to 500 range and does indeed live up to the promise. Pitch black and the sensor reads < 5, and pushed up close against a 400W light, the sensor reads > 480. Normal light conditions and the sensor reads between 30 and 180 – very very useful.

The SDK comes with plenty of examples and is incredibly user friendly! I would recommend these all day long.. it really is plug and play.

IR Distance Sensor

IR Distance Sensor

And here’s a distance sensor. It’s a simple IR mechanism that ranges from about 1m to 10cm. There are also 10cm to 5mm sensors available. Again, works great, really reliable.

So now these work, I’ve ordered some more and they’re on their way. One temperature sensor, two voltage sensors, some sonar sensors and more IR sensors – fantastic products.

In the mean time, I’ve ordered a load of clear acrylic and plan to start putting a body together shortly.

I’m still having a little trouble talking to the motor controller so if anyone has any I2C knowledge, please please let me know. I don’t want to buy a prebuilt base.. I think it’s cheating.

The Robot: Successful installation of Debian onto the Alix 3c2 board

November 2nd, 2008

Some hardware has arrived!

Mess

Mess

So my working space is a little bit of a mess at the moment. There’s no better way of getting started than just getting straight to the point.

The Alix 3c2 main board arrived in good health and works well. On the underside is a 512MB CF card and an Atheros MiniPCI Wifi. I’ve soldered single core wire to the I2C bus pinout. GND, CLK, Data & +3v.

I’ve also soldered bell wire across the power input. It accepts a wide input and so I’ve decided on 12v.

This is my prototype “power distribution board”. Currently it consists of 2 12V/2A regulators, some resistors and a 1000uF/30V smoothing capacitor. It provides 12v to the Alix board, and 12v to the motor controller. If both motors stall, they can use up to 6A, so whilst this is fine for testing the controller board, I’m going to have to replace one of the regulators with a transformer system to provide the necessary power to the motors.
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