Older blog entries for ROB.T. (starting at number 18)

11 Jan 2003 (updated 11 Jan 2003 at 14:56 UTC) »

I got my boards back from Olimex the other day, they look nice, real professional. I'll be hard pressed to go back to etching my own PCBs. The only real problem I had was it took almost 3 weeks to get them. Olimex had them done and shipped in two days, but it took a few weeks to get to me. Shipping was probably delayed because of Christmas.

As expected I'm finding errors in my schematics and PCB layouts, so I'm documenting them with the intent of fixing before I order the next set. I'm also having a slight problem getting some of the connectors, they won't be available until 1/22/03. I haven't tested the boards yet, but most are at least partially populated and they look good and fit together great.

I've also been working on a leg axis design that includes a mounted motor and a potentiometer for position sensing. While welding two separate pieces of aluminum, I've been having problems due to one piece being made of a different grade of aluminum than the other and melts faster. Another problem is getting all the pieces to lined up properly. I'm thinking up some tools and methods to get me past these difficulties and speed up development time.

Design wise, I have finally gotten the number of robot- size options to two, the difference being the us of 8 batteries or 4 batteries. I'll probably build for 8.

I promised my robot club that I would submit the UML diagrams I'm using during the design phase of my robot, so today I'm working on that.

10 Dec 2002 (updated 10 Dec 2002 at 00:45 UTC) »

Finished the first set of 11 boards! I'll be sending them into Olimex this Tuesday (12/10/02) - I have to check them against my materials list first. These are all the different types of modular boards I will need to get my robot moving (I'm sure I've said that).

I just got a tank of Argon for my MIG welder. I need to get a couple more parts and then I can teach myself how to weld Aluminum.

The platform is mostly designed, I should be testing circuits by January - I feel it's important to establish time lines so you can blow them ;-)

Well, gotta go study, I've got a final I need to pass.

23 Nov 2002 (updated 23 Nov 2002 at 10:50 UTC) »

Naturally my University extended my degree program to include 1 more semester, they tell me if I pass this class and the next I'll be done by summer. So I've had to deal with more class time and homework, but that doesn't mean I've stopped working on Predecessor...

Since I couldn't find the motors I need anymore, I upgraded to a car window motor, in fact I bought 50 of them. I also bought (8) 12V-17Ah batteries to power this beast, and I upgraded the drawer slides I'll be using to extend the legs.

I've determined that this robot has gotten to a size that requires some welds, so I'm collecting MIG welding equipment as well.

But wait there's more -

The following proto-boards have been completed and are waiting to be sent out for a test run - Controller Board AT90S8535 (Atmel), L298 Driver Board, Sensor Board - Strain Gauge Amplifier, Analog Board, Test Board - Switch, Test Board - LED, Emulator Board, Expansion Board, and a Motor interface Board. I still need to make the RF modem Board, Communication Board - SPI, and the Remote control Interface Board. Hopefully all these boards will be sent to Olimex by December. Fellow TCRG member Alan Kilian had these boards made there.

The cool thing about these boards is they are very modular so I can use them to make other robots. Part of the Core Technologies concept the Twin Cities Robotics Group has been developing.

The president of TCRG, Jeff Sampson, has working on a robot-qualifying concept called the ``Science Museum Challenge'' or SMC. The basic idea is that your robot maneuvers from the parking lot of the Science Museum of Minnesota, up a couple levels and through the lobby, up a couple more levels and to the room where the robot meeting is held. The current rough draft has the SMC divided into different degrees of achievement, the first being to guide your robot remotely, and higher SMC levels can be reached by the addition of various layers of AI to your robot (Jeff is still working on this part). Jeff has been working on his own robot for SMC.

I want to have the Predecessor platform ready to take on the SMC - Remote by summer. Well, that's my intent. As my wife continues to say - "Show me the Robot".

Steve I lost my login password.

School has started, it's going to be hard, but hey by December it will all be over.

I'm going to try and finish all the boards in that period of time and when I get out of class in August I'll be able to assemble the platform and test it.

It's going to be a long time before my next entry.

9 May 2002 (updated 11 May 2002 at 12:35 UTC) »

I laid out the board I call the controller. This board simply has an AT90S8535, support components, and 8 connectors one for each port on each side of the board. I'm going to give it a once over and send it off to a board house and see how it goes. Since I have to build 8 of these 3'' boards, It's going to cost me $327 just for the controller boards and I still have many boards left to lay out. Here is a list of the boards I need to assemble just to get the platform to walk -

8 controller boards

8 motor boards

8 leg-stack test boards

8 strain gauge amplifying boards

1 SPI communication board

1 communication controller (probably the same as the leg

controller boards)

1 RF modem board

1 communication test board

1 power board

1 Emulator board

I haven't worked out the single boards yet, and I still need to lay out the motor boards and the stack-test boards - they're next.

I've completed the prototype board that amplifies the output of a strain gauge for A to D processing by the microcontroller. Time to start working on the next version of the boards.

I'm looking at making the boards modular with the microcontroller and it's support hardware being the only thing on one board. Another board will have the motor drivers, and a third smaller board will host the amplifier for the strain gauge located in the ``toe'' of the leg. These boards will stack, I need 8 of each and a controller board.

2 May 2002 (updated 5 May 2002 at 18:07 UTC) »

I have completed a crude motor controller prototype. Tomorrow my Digikey order with parts for a prototype strain gauge amplifier will be arriving and I'll be working on that all weekend. Once I get the amplified signal into the microcontroller A to D, I'll order the real controller boards.

Naturally life is interfering yet again. School starts up for me in less than 2 weeks and I've got 2 hard classes. That will probably push robotics out of my life for at least 8 weeks. At least I can say I'm still on this project and the project is still moving forward.

The motor count for the base module is currently at 46 motors. All the motors are in, and the brackets are 75% done. Both tables are developed and will be fairly easy to assemble. I go on vacation next week so I'm shooting for fully assembled <mechanical> base by the end of April.

A proto-type motor-driver board has been tested and works fairly well. There is, however, some start-up interference between motors that I will have to work on, I'll probably try bigger caps.

For the modules that control the legs, I've decided to modularize them. This is more expensive and more time consuming, but motor modules allow me a lot of configuration flexibility, and if I design part of the circuit incorrectly I minimize how much I have to scrap.

I've had to make a few compromises as far as the parts I want to use, but the project is moving along smoothly.

All right, I've thought about it A3I2 is probably more than I can handle right now, and it's producing stress as a change my building methods to accommodate the March 1st deadline. I really want to go, but I have got to give this robot my best effort - even if that means I don't make A3I2.

I'm sort of in one of those funks that builders get in when they tackle large projects. This project is pretty big and it is not without its share of problems. I've been building the first table (remember I call them tables because that's what they look like - fat tables), and one thing I've noticed is that it's heavy! As in ``try and keep the robot under 80 lbs.'' heavy. In fact this table weights around 40 lbs., but I'm also trying to include all the batteries in this table so the center of gravity stays low. During testing I managed to split one of the nylon gears in my protoleg - NOT a good sign.

I'm having a hard time isolating parts of the project. The right thing to do would be to build a leg, test it, build a table, test it, add legs. Etc. What's really happening is I'm starting to build the entire robot. I've almost completed the first table, and soon I'll be building the second table. But maybe this isn't so bad since the tables are fairly unsophisticated.

At the same time I have yet to get a motor running, and that's bad. Part of this problem is I don't have any experience with strain gages/current sensing. Also instead of testing the different elements I just threw together the main board (minus amplifiers) and now it looks kind of daunting. Another problem is, because my memory is so poor, every time I sit down to program I have to relearn everything, language, how to hook the emulator up, everything. Luckily I keep notes, if only I can remember where I put them...

Yet another item that will make my life difficult in the near future - I haven't figured out how to test the base module in an incremental mode. In other words, the best thing that could happen is I set the beast on the floor, tell it to walk, and it walks. What's really going to happen is a series of balance problems, problems figuring out how to make the robot take steps, etc. At this stage if I mess up too bad, I break gears/motors and there are no replacements because my motor source dried up.

What you are witnessing is a project with the potential to spiral out of control.

So I came up with this plan.

First thing I need to address - I need control over my electronics... I need to get my boards working. But I don't have to get an entire board working, just a subset. So I'll put a motor controller on one and learn to work with it. On another board I'll add a strain gage with amplifiers. Right now it's all about the baby steps to raise my confidence and keep me focused, so I'm going to keep the challenges bite-size.

Because of the way life has allocated my free time, I need to finish this table and start building the next one - without going into detail it's just a lot more efficient. Table bodies are nice modules so I'll just concentrate on that and worry about adding the legs later. This will occur simultaneously with the control board development.

Lastly, in the background, I need to be questioning how I'm going to test the base module adequately without destroying it. This might be the most difficult problem of all.

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