Platform + Motor Control + Power

Weekly Report 6.20.05

The major problem I have run into this week involves my motor controller. It turns out that the TNX0 screw header on the Maveric-II board does not actually drive TTL values as the documentation implies. Instead, even with the appropriate switch flipped you still have to get the TTL values from PORTE. As a result, I am fairly certain that I ran -6 volts (still far too low, I am starting to wonder about the level shifter) across my controller. If it did ever work properly, it doesn't now. Fortunately, when I saw that something was wrong I put out an order for a few H-Bridges. While these don't provide as much functionality as the motor controller they should be perfectly appropriate for the application. A secondary problem is finding a place to mount an LCD, I need to wait until I see how much room my H-Bridge leaves me before trying to place the LCD.

Since my robot doesn't have mobility now that the motor controller is dead, I was unable to add software control to my IR triggers. However, I did finish the circuit and I wrote test code so I know that I can read values from the IR and respond to those values in programming. When the H-Bridges come in (which should be on Thursday) it should be a simply matter of getting collision avoidance coded, I expect to have it done by this weekend. After that, I have to mount the photovoltaic cells (used for light/dark detection) and then the only thing that remains to be done is finish my software and get my RF sensor circuit built. Despite this set back, I think that I should be on track, most of the legwork is complete and now it is just a matter of putting things together.

Life Lesson -- Datasheets

Since this site is supposed to detail all of my progress while building Tracker I'm taking a little time out to point out something important that I've learned thusfar.

Always read datasheets!

I don't mean skim, scan and then put away. When you are new to a part take the time, sit down and read the sheet. That little lesson cost me 3 hours today.

I was building a test circuit for my Infrared Sensor [http://www.active-robots.com/products/sensors/sharp/gp2y0d340k.pdf]. Everything seemed easy enough, it took me about 5 minutes to hook the five pins to my breadboard plus a LED to make sure it was actually working. I hit the power, ready to celebrate my newly interfaced circuit and I was greeted by a green and glowing LED. When I tried passing my hand in front of the IR sensor I was surprised, the light didn't turn off as I expected.

2 hours later and about ten thousand different minor adjustments to the circuit, and I was about to give up. Exasperated I sat down and looked at the datasheet one last time, hoping that I would see something that I hadn't already seen two dozen times. This time, I did.

Apparantly, there is a rather substantial difference between a 1k Ohm resistor (the one I had been using) and a 1 Ohm resistor.

Food for thought.

Weekly Report 6.13.06

This wednesday the rest of my parts (IR Sesnors / Perf Board / Photoelectric cells / Cables / Wires and Headers) came in. I finished writing the test version of my motor controller code. The an updated version will be completed once I mount the sensor suite.

The most difficult problem I'm running into at the moment is space. I have a relatively small chassis that I am trying to mount quite a few sesors on. I have spent a lot of time trying various mounting arrangements. It seems that I have found one that should allow me to put all of the sensors on with minimum interferance.

I also recieved the Arduino ATMega8 microcontroller board in the mail. This second controller will be used in the RF beacon. For the remainder of the week I am going to finish getting my motor controller functioning and work on mounting my IR sensors.

A Few Pictures of Tracker

Isn't it beautiful? This is without the Maveric board or the second level of perf board. For a first design I think it is making a decent use of the available space. Who would have thought 5" would really be that small.

Weekly Report 6/6/06

This week I have completed assembling Tracker's chassis. I also finished the gearbox (203:1 gear ratio) and have put on wheels and a caster wheel for steering. In the same shipment of supplies I received the motor controller that I will interface with the Maveric in order to drive the motors (rated for 1A).

I am still waiting for the RF transmitter and receivers to come in, as well as the new USB Atmel programmer. Today I also put in an order for the rest of my sensors and an Atmel based Arduino board in order to drive my RF beacon. Once the programmer arrives I plan on interfacing the obstacle avoidance IR sensors, until then I will continue to research solutions to the RF tracking problem.