Paradise Robotics Forum
Build A Robot => Other Robot Building Topics => Topic started by: RobotLady on February 10, 2012, 06:43:39 AM
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A teacher at my son's school has 10 Lego Mindstorms robots. They are the educational type and are already quite a few years old. I decided to volunteer to give her a hand. I did not know too much about Mindstorms, so she let me borrow the robots and the software to get familiar with them.
Each robot came with an RCX, or Lego Mindstorms control module. There is also a communication module (tower) that plugs into the PC and communicates with the RCX via an IR (infra red) link. IR is the same technology that is found in a TV remote control. It requires "line of site", or a straight line, between the transmitter and the receiver. There is also software that must be loaded on the PC. The software is becoming obsolete because it will not work under Windows 7. Fortunately, our PC still has Windows XP.
I read the manual and found out the RCX has to have an operating system (OS) downloaded into it. I suspected that the RCX may lose the operating system when the batteries are taken out. I decided it would be best to check each RCX to make sure they worked and that the OS was downloaded. Otherwise, I could foresee problems arising when we work with the kids.
It was a good thing I checked the RCX's. I found that many of them still had their batteries installed. Unfortunately, the batteries leaked in four of them. The ones that had batteries that did not leak communicated with the tower and did not need code downloaded into them. The ones that did not have batteries had to have the code downloaded, as I suspected. It took four minutes per RCX to download the OS.
I was not able to communicate with the RCX's at first. I found the place in the software to test them; I just had to click the "Administrator" button. When I tested the first RCX, it communicated, but would not download the code. After trying several more and having similar problems, I decided to try again at night when the room was dark (light can interfere with IR communication). No luck. I noticed there were several other communication towers, so I decided to try a different one; it was worse than the first. Now I felt like I was onto something...
There was a note in the software that said to check the 9V battery in the tower. The tower ran on USB and did not seem heavy enough to hold a battery. Rather than unscrew it to check the battery, I assumed it did not have one installed. I decided to try another one. This time it worked fine. I still don't know if there is a battery inside because it could be getting power from the USB interface and not need a battery (i.e. the note in the software could be wrong. It could be referring to an older version that used a 9 pin serial connector rather than USB). When I have time, I will take one of them apart to see if there is a battery or not.
The RCX's that had leaky batteries were troublesome. I scrubbed the battery acid off with a toothbrush, but they did not recover. I did a Google search to find out how to clean acid-corroded battery terminals and learned I should clean them with baking soda and shine the terminals with sandpaper. At this point, I had nothing to lose, so I thought I would give it a try. I cleaned the terminals and sanded them with an emory board. It took several tries but finally I was able to get two more working.
Now I only had two left. I cleaned, sanded and shined them, but they still did not work. I got my voltmeter out and found that the voltage was fine. I speculated the battery acid may have leaked inside. I took one of them apart and was surprised to see that the terminals were not soldered to the circuit board. I thought it was strange and decided maybe for some odd reason the terminals should make contact via pressure (personally I thought that is a dumb way of doing it). So I put it back together. It still did not work.
Then I took the other one apart. What do you know, the terminals that looked strange in the other one were soldered in this one! That means the other one was defective from the start and probably never worked. The second one did have some battery acid leaked onto the PC board, so I scrubbed it off, not really thinking it would solve the problem. I re-assembled it and was pleasantly surprised when it worked! When I have time, I will solder the terminals of the last robot to see if it will recover.
My next step is to play around with the software so I will become familiar enough with it to be able to help the kids.
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The one that was unsoldered **did** recover after soldering! Two friends and I helped the teacher teach robotics to 3rd and 4th grade gifted students. The kids had a lot of fun.
Several observations:
1) Teams were 3 students each. This actually seemed to be too large for the age of the kids because the third child in each team seemed a bit unplugged and distracted. Next time, we'll do it with two-student teams.
2) All of the girls and some of the boys enjoyed decorating their robots. Incorporating an art lesson would be a valuable extension of the experience, especially to keep the girls engaged.
3) Pre-planning the robot's movements and actions, testing out the software first on our own and working closely with the kids made the experience much more valuable and engaging. The kids did plenty on their own, but having the adults available to help them when they were stuck kept them from becoming discouraged. It also showed them how to overcome obstacles.