Author Topic: Another $50 robot help thread  (Read 1782 times)

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Offline krichTopic starter

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Another $50 robot help thread
« on: October 29, 2007, 11:58:46 AM »
First of all, great website.  It's very concise and to the point on a topic that can get down in the weeds really quick.

For the last year or two, my 10-year-old daughter has been bugging me to help her build a robot.  And not just a robot, but a robot alligator with whipping tail action.  Fun!  Recently, she's changed her mind and wants a robot turtle with a wiggling mustache.  I've since advised her that we'd be doing real good to get something that moves, much less something that wiggles (by design).

At first, when doing my research, I got caught up in the "RC Robot" train of thought.  I ended up not wanting to do that because its really simple to buy a $15 RC car, throw on a paper mache' turtle shell with a mustache on a spring and call it good.

After reading the content on this site, it became clear to me (and appealed to the programmer side of my brain) that "real" robots are those that control the large amount of their movement/activities themselves.  When I explained this to my daughter along with the various simple types of robot intelegence, she promptly change her mind, yet again, and has decided she wants to build a "Carrot-ovore" as depicted on the main SoR web page, but with a "bunny ear mod".  Her words. 

So, after spending a few weeks doing bench experiments to reinforce how the various electronic components work (resistors, capacitors, switches, LEDs, etc), we are both educated enough to try to tackle soldering all these components together into a robot, hopefully without failing the "smoke test" at the end.

This is where I have some feedback on the $50 robot tutorial and some questions (read, a lot of questions).

Feedback:
1)  There is definitely a method to your madness when placing the components on the PC board, especially the headers.  I think it would add a lot to the understanding of the tutorial to explain why things are placed where they are.  During my analysis of the circuit designs, I kept thinking that the placement was ingenious, so why not give yourself a little credit.  It may be second nature or NBD for the robot gurus, but this is the kind of things us newbies should start learning early.
2)  When in the soldering section, you explain that you need to solder in the resistor, but you don't say which one.  It took me about 10 minutes to figure it out by reading the LED tutorial, but if you could be more specific and say "solder in the 340 Ohm resistor", that would be better.
3)  Recommend some basic testing and QC procedures.  When I started soldering things onto the board, I found that my hands were just a little too shaky to get everything right the first time.  I used my multimeter to check all adjacent soldering points to be sure that they hadn't shorted to their neighbors unintentionally.
4)  In Section 2,  you talk about modifying the servos, but the modification procedure requires the fully built circuit board in Section 3.  So, I've skipped that part of the tutorial and will have to come back to it later.

Okay, enough constructive feedback.  Let's get to where I show my ignorance.  I only have one question right now, mainly because its something that is stumping me and I've applied logic and reasoning to the problem with little success.

In Section 3B, you show the connections for the Voltage Regulator.  The battery header is connected to the VR which is then connected to the capacitor, which are then connected to the power and ground rails.  I understand that part.  What I don't understand is why the "regulated voltage" pin on the VR goes unused.  Shouldn't the battery + terminal be connected to the unregulated side of the VR and then power taken from the regulated side of the VR to power the capacitor the power rail?  From what I can tell, the VR is being bypassed and its sole purpose in life squandered.  Poor little guy.   :'(

The picture I'm referring to:  http://www.societyofrobots.com/images/sbs_connect5_large.JPG

I'm sure I'll have many more questions.  I'll keep them to this thread so as to not clutter the boards with my newbish rantings.   ;D

Keep up the good work, Admin and other primary contributors.  The day I understand even 10% of what's going on here will be a major milestone for me.

Ken.

« Last Edit: October 29, 2007, 12:41:06 PM by krich »

Offline krichTopic starter

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Re: Another $50 robot help thread
« Reply #1 on: October 29, 2007, 02:43:34 PM »
Okay, moving on through the tutorial, I see now where the regulated output comes into play.  I feel like a doofus.

Now, playing to my retentive personality, and given that I'm using the two battery option, it seems logical to me to move the regulator and the cap over to the servo side of the PCB.  The only common connection is ground and I'm assuming that, for my simplistic purposes, ground is ground no matter where you get it.


Offline krichTopic starter

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Re: Another $50 robot help thread
« Reply #2 on: October 29, 2007, 03:56:01 PM »
Alright, I'm continuing my one man conversation.   So many questions, so little time...  ;D

I don't exactly get what's going on with the LED circuit.  I understand the concept of placing a resistor in series with the LED.  I guess I don't exactly understand the connection to PD4.  Does this provide a ground to th e LED circuit when the MCU is operating so that the LED only shines when the MCU is active?  Guessing that's it, but not 100% sure, or if I'm right for the wrong reason.

Also, reading the AVR docs, PD4 is used for USART functionality.  If I eventually want to put a serial port on this thing, would that LED interfere or stop working correctly?  Can I put the LED on a different port?

As a minor enhancement, should I go ahead and wire a LED circuit in parallel with the BIG capacitor on the servo side of things to help drain the cap when power is removed?


Offline krichTopic starter

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Re: Another $50 robot help thread
« Reply #3 on: October 29, 2007, 04:08:18 PM »
Found the answer to my LED question.  Excellent explanation, proving that I was right, but for the wrong reason.

http://www.societyofrobots.com/robotforum/index.php?topic=1243.0

Cheers.

 


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