Let's Make Robots!

Build 1 - Please Review!

Hi all, I'm an 18 year old from South Africa interested in all aspects of technology! I hope to enter a Bsc in Computer Science next year at UCT in Cape Town. I am even thinking of going further and doing more afterwards for some crazy reason but thats later.. anyways!

Right so this will basically be my first build from scratch, my own design etc. Being my first build I want to keep it as simple as possible so please comment on anything, I don't mind.

Skills:

  • Have experience in RC not vast amounts, but I know the basics I'd say. 
  • Able to program in Java and know basic logic and arithmetics etc.
  • Willing to put in effort to learn, and put it to practice!
What I have:
  • Charger: Swallow AC/DC2 Digital Peak Charger.
  • JR Spektrum DX6 (not sure if I will need it at all).
  • Batteries: (7.4V 800 mAh 2-cell Li-Po) x 2, (7.4V 300/340 mAh Li-Po) x 2, (11.1V 800 mAh Li-Po) x 1 
  • Servos: JR Servo (ES 539) x2 (not sure if I can use these).
The Idea:
 
Basically I want to make a robot that just avoids walls, obstacles etc. I have this in mind. Two wheels and a little guide wheel with the IR Range finder on a servo. 
Questions:
 
  • I have no experience with microcontrollers, does the Arduino Duemilanove have all the features I would need for controlling the motor, servos, IR range finder etc?
  • When looking for motors is there anything to be aware of? Should I use geared motors or not?
  • What connectors and wires will I need? Heat shrink? 
  • Have I left anything out?
  • Suggestions?
Please review this list and add information that maybe I have left out or am not aware of, comment, etc on anything. I'd like to get a lot of input if possible! In terms of motors, wheels, wires etc am I looking in the right direction, or do i need guidance? 
 
Many thanks
Sync. 

 

 

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

I just made my own motor shield as you can see here.

And so far it works fine with NO caps. Perhaps cause the motors I'm using are very small. I dunno. I did however solder a cap directly on the motors between the terminals as suggested in the link I posted earlier.

Just though you should know that making your own shield isn't as hard as you may think :)

The only thing that is giving me a major major headache at the moment is: (Please excuse me if I am being stupid) Do I need capacitors & voltage regulators as shown here: http://farm4.static.flickr.com/3524/3235658022_7f505922e3_o.jpg

If I do need them how come most other L293D guides don't show it or is it not needed thats why I'm confused. Am I supposed to like sort of know there must be a capacitor there? 

Also the grounds, do they just go into nothing (blank hole) I know what ground means and all but I'm not sure how it works on a PCB etc.

Sorry to trouble you guys but I need to understand this : < 

 

The Arduino allready has a voltage regulator so don't worry about that. And atleast 2 of the caps in the circuit you linked to are there to support the voltage regulator. The L293D will work without caps, however it is recommended to use caps to smoothen out the current flow. Here is a good article about why caps should be used in various circuits:

www.thebox.myzen.co.uk/Tutorial/De-coupling.html

Unfortunately there are no rules to how many, which kind or even where to put them. Everybody seems to have their own way of using caps. The circuit you mentioned is one way. But here for instance they recommend soldering the caps directly between the motor terminals OR from a terminal to the motor casing (?).

www.pololu.com/docs/0J15/9

I have the same doubts as you..being an IT nerd who's new to electronics. I bought an L293D a few days ago and seemingly it works fine without any caps. It also depends on which motors or power supply you're using and how many other things you're powering from the same source. I bought a batch of 0.1uF ceramic caps that I'll try to put in different places if my setup starts acting unstable at some point.

And about the grounds..They don't exactly just go into a black hole. The ground is the negative pole of a dc power source. The current flows from the positive pole to the negative pole. If it's not connected to the ground there is no circuit. In this case there are 2 grounds. The Arduino ground AND the external power supply's ground. BTW it's important that these 2 grounds are connected since they form a circuit together...

That's my 5 cents :)

Ready for a loop? Technically the electrons flow out of the negative pole into the negative pole ;) That's neither here nor there for this discussion though, just an interesting tidbit.

As far as motor caps go, notice that most R/C cars will have one to three caps soldered to their terminals. Most of mine have one cap between the terminals, some will have one on each terminal to the case (ground). One I used to have had three caps, one between the terminals, and one from each terminal to the case. I imagine that one was just in the name of overkill.

"Technically the electrons flow out of the negative pole into the negative pole"

Actually I do remember having read that some time ago. However the way I make sense of a circuit is starting at the positive pole and following the path(s) until I end up at the negative pole.

But you're right off course. And perhaps I'm too much of a noob to be giving advice about electronics :D In this case I was mainly trying to pass on the (admittedly litle) knowledge I've gained about h-bridge setups within the last few weeks. Just got my 1st H-brigde up and running a few days ago. So I thought I could contribute here, since I just went through the same thoughts and doubts our friend Sync is experiencing now..

Sorry if I unintentionally mislead anyone :)

PS: About the 3rd cap you mention. The Polulu link I posted above also mentioned that one could use 1, 2 or 3 caps depending on the noise supression desired. But yeah 3 seems like kinda overkill. I'd try with less to begin with..

Oh, no, I didn't mean anything by it. Apologies if it came off as nitpicky or smack-talking, that was not my intent. There certainly wasn't anything misleading about your post. I too follow them + to -. Just pointing it out as more silliness in this whole electronics thing.

Around here we seem to follow a procedure similar to medicine; "See one, do one, teach one". You've done all three, and are not as much a noob as you may think ;)

And thanks for the links, I've added the decoupling one to my bookmarks.

Ah..just saw your post now. And don't worry about it. I'll keep giving bad advice no matter what :D

That diagram shows the voltage regulator for powering the microcontroller and sensors as well. Then the regulated supply is piped into the H-Bridge's enable lines, so both halves are full-on by default.

It also supplies battery power to VCC2,this is the power that will be supplied to the motors. VCC1 gets the same voltage as the microcontroller, and this is what the logic circuits of the H-Bridge chip operate on.

So, slightly shorter, the capacitors shown in that diagram also seem to be the caps for the power supply circuit, not just the motor driver.

My robot uses the exact motors (2 of them) you describe there controlled via the adafruit motorshield powered by 4AA batteries (the arduino is powered by a 9v). So you should be fine there if you decide to go the motorshield route.

Great to see input on the H-bridge side of things thank you all for the contributions!

My head needs a little help in catching up to the technical side of things.

I have a few points that maybe you all can elaborate on:

  • I haven't yet made a circuit myself and I hope i won't solder it really bad. So if I do take the L293D route I would need some kind of step by step instruction on first making it, then hooking up to the Arduino. Everything seems a bit foreign to me at the moment I have looked for some guides on the H-bridge but none seem to be really in depth and I'm worried I 1. Forget to order some part that I need. 2. Connect it wrong and blow it. So my option here would be make my own H-bridge to control 2 DC motors. I'm just worried about how I'm going to go about getting the parts and knowing that I have them all for it to work, as well as having some guide or helping hand in the process if I don't know whats going on!

  • The other option would be getting the Motor Shield by Adafruit. Now I have some questions about it. First of all say I wanted to use it later on for 4 DC motors it would probably be the best buy I'm guessing. The real thing I'm worried about is that I saw the shield outputs 0.6A. Will this be enough for a small DC motor such as (http://www.hobbyengineering.com/H1415.html) specifically (or would you suggest something else). It says it uses 670mA at stall and 73.2mA free running @ 5V. So I'm kind of in the dark here! I saw on one H-bridge guide the motor uses 12V or something (11.1V). I can't seem to grasp the concept of the voltages on motors and how the relate to other things like the H-bridge. I need some clarity on the workings of the circuit or maybe a buddy to show me how this works.

  • I was thinking maybe someone who is interested with helping me out could MSN with me or post some guides/info to enlighten this darkened mind here.

    MSN: syncza@live.co.za
If any of you could please compile a list of links to useful information or something to that effect or add me to MSN so we can work this out.. or me actually, I really want to grasp these concepts. I understand how the H-bridge works I just don't know the technical side, the resistors, Voltage regulators, pins etc. that is where I'm falling down.
 
Any help will be appreciated! 
Thanks 
Sync the new dude.