If you haven’t already discovered this site and your into hobby robotics, go to http://letsmakerobots.com/ right now and set up an account!
There’s a companion Facebook page too: http://www.facebook.com/groups/52847854131/
There is a lot of activity with cool robots and robot makers around the world.
A Facebook friend of mine asked me why I chose the XBee modules for the R1 system. I’ll answer here so others might benefit.
There were basically three classes of wireless link technology in the running: Low cost digital radio, XBee and WiFi. I ruled out WiFi without really testing it because I was afraid the robot communications might get bogged down if someone else in the house was watching Netflix or doing a download. I don’t really have any evidence that there would be such a problem but, I didn’t want to put down the money and find out later. That left the choice between radio and XBee.
Pros for XBee
- No special software is needed on the host computer. The PC “sees” nothing but a standard serial port.
- No special software needed on the Arduino. Just connect the Tx and Rx pins and it’s off and running.
- Two way communication. Many of the cheaper radio modules are one-way. R1 needs to “talk” back to the host as well.
- Error detection and correction. I’ve seen dropped messages but, never an incorrect message.
- XBee “looks” like a standard serial link so, I can download new Arduino firmware through the wireless link – no need to connect a programming cable. I do, however, need to press the reset button on the Aruduino – there are articles on the internet about how to do it without pressing reset.
- More than two nodes can be involved in an XBee network. It would be possible to control multiple robots from one host computer.
Cons against XBee
- Expensive – considering the cost of two XBee modules and two adapter boards, it’s the most expensive “part” of the system.
- The 1mW “regular” XBee modules are unreliable when the robot is in a different room than the host computer. Several retries are often required when doing a sensor scan because of dropped data. The Pro modules may be better in this regard – I’m not sure.
That’s all. Thank You!
Just a quick look at the lower compartment of R1.
As shown in this bottom view, R1 has two drive wheels (the yellow wheels) and a caster wheel (the silver looking thing). The only way the software can drive the robot around is by setting the speed and direction (forward or reverse) of each wheel. The left speed and direction can be different from the right.
Controlling only the speed and direction of each wheel, how would you make R1:
- Go forward in a straight line?
- Turn toward the left?
- Spin clockwise in place without really going anywhere?
My answers will be disclosed in a new video coming soon to ralphsrobots!
I highly recommend Adafruit Industries as a supplier of electronic components.
Her site (I think of the store as a “her” so, that’s the pronoun I’ll use here) promotes education and creativity in the field of electronics especially for women, young people and artists. However, it appeals to me a great deal too and I’m not in any of those categories.
One time, I ordered a bunch of parts from her and after putting them in the robot, I thought one of them was defective. I posted on her “help” page with info about the problem. She handled my case very politely and sent a replacement part free of charge. A couple days later, I found out I WAS WRONG! The part wasn’t broken at all! Maybe I’ll send a couple of customers her way and make up for the money she lost…
Whenever I need a part, I’ll always check Ada first and if it’s on her site, I’ll buy it from her – no doubt.