16 Nov 08 The Robot: Base, Wheels, Motors, and Sabertooth Motor Controllers

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.

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.

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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Tags: 2x25A, analog voltage, battery, ground, lead acid, Linux, Linux robot, motor, motor controller, omnidirectional wheels, packetized serial, picopsu, rc input, sabertooth, simple serial, the robot, tx pins, usb to ttl

02 Nov 08 The Robot: Successful installation of Debian onto the Alix 3c2 board

Some hardware has arrived!

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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Tags: 12v, 38400 8n1, 3c2, 512MB CF card, alix, alix 3c2, atheros, atheros 5212, capacitor, card reader, clk, data, debian, debootstrap, gnd, Hardware, i2c, i2c bus, i2cdetect, Linux, minipci, motor, null modem, power distribution board, prototype, pxe boot, regulator, resistor, serial cable, serial console, smoothing capacitor, solder, transformer, wifi, wire

13 Oct 08 Robot: Initial Hardware Order [rev 2]

Follow on from: http://www.adamsinfo.com/the-robot-hardware-list-wheel-plan-more-ideas/

Discuss in the forums

I’ve given up on trying to source separate motors, motor controllers, encoders and brackets. I’m concerned that my knowledge of mechanics and motors is limited, and that I’m going to spend too much time and money trying to build a movement package myself.

I’ve decided to go for a good motor/controller/encoder package here:

http://www.active-robots.com/products/motorsandwheels/rd01-drive.shtml

I’ll need two of these, and will have to replace the wheels with the omni directional wheel things I found and linked to in my last post.

I’ll drill the brackets into a thin metal plate, and start building perspex on top. I don’t seem to have paid enough attention to battery/device weight/motor/power and am concerned that the motor and battery combination will not move the device. I don’t yet have an idea of how much it will weigh, but I’ve realized that the perspex is going to have to be as thin and light as possible, and I’m going to have to bear weight in mind with any unnecessary or redundant extra parts.
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Tags: alix, APNIC, atheros, CF, embedded, i2c, Linux robot, motor, picolcd, Robot

07 Oct 08 Linux Robot – Watch this space

I’ve been struggling to think of a good project to start on. I’m currently writing the APNIC Box series here, and I’m on part 4 of maybe 7 or 8 right now. I like to keep at least one personal project of interest on the go at a time so back to struggling for inspiration.. Feel free to tell me that this is an awful idea and suggest something else, but until I hear otherwise I’m going to roll with it.

Linux Robot – Requirements

Here’s what I’m thinking. Small embedded device, way smaller than the Mikrotik 532a used for the APNIC Box. The board will need USB [as we're going to use the 5v for charging later]. I’d like to start with a powerful enough board that it can be expanded later with relative ease.

The device will initially have few inputs and outputs. It will support miniPCI, USB, Serial Console, CF card, GPIO or some other good method for controlling a relay board and some motors. The device will have 4 small wheels, maybe rubber [old mouse] balls instead and some ultrasonic sensors, 4, 6 or 8.
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Tags: embedded, fm, Hardware, Linux, Linux robot, minipci, motor, oscillator, relay, Robot, sensors, servo, usb