20 Nov 08 Linux: AVIT Research USB to TTL Cable

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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Tags: 10c4:818b, 2.6.27.6, AVIT Research, com port, cp2101, cygnal integrated products, diff, Linux, Linux robot, lsusb, motor controllers, roborealm, Robot, sabertooth, usb to serial, usb to ttl, virtual com port

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

14 Nov 08 The Robot: A body, Sensors and Good Progress

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.

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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Tags: battery pack, distance sensor, IR remotes, irda, LED, light sensor, Linux, Linux robot, MAX232, motor controller, nimh, phidget, phidgets sensor, picolcd, picopsu, polycarbonate glue, sabertooth, serial port, stereo speaker, temperature sensor, the robot, usb phidgets, usb sensor kit, webcam