Author Topic: Using an RC car instead for the $50 robot (Read 13367 times)

Lefteris · « **on:** March 27, 2008, 01:06:24 PM »

Hello,

I just read the 50$ robot tutorial and to be honest I liked it a lot. I am almost finished with my BSC in computer science but completing this tutorial just for fun will give me the good start in diving in the electrical and mechanical stuff I need.
So I was wondering the possibility of using a hacked RC car as a chassis instead of making my own as mentioned in the tutorial. Will I need to buy the servos too from a hardware store or, will the RC car have them? I am asking this stupid question since I have never bought a RC car before and I don't know if it mentions in its package if it is using DC motors or servos. Any more complications I should know of since I will be choosing this approach. Thanks in advance!

Rebelgium · « **Reply #1 on:** March 27, 2008, 01:08:59 PM »

rc cars use dc motors,
search the forum for using dc motors instead of servo's.

Lefteris · « **Reply #2 on:** March 27, 2008, 07:35:34 PM »

I might actually try it with a servo after all, since I will need the experience. But I got another question ... I feel like a total noob asking questions like this but as far as mechanics is concerned I guess this is what I am. I am really excited to have found this site though, to help give me a nice push

So ... many times I see the word drilling being mentioned. How do you drill? What kind of driller is most commonly used? Drill a hole there to connect that. Reading it is one thing .... how will I do it is what actually concerns me. I am going to go to a hardware store in like 4 hours at dawn to get the equipment needed. I hope I can get an answer by then so I can start feeling comfortable working with all these materials.

I really feel embarassed, I almost got my BSC in CS and I am asking so noobish questions

AndrewM · « **Reply #3 on:** March 27, 2008, 09:42:19 PM »

I will try not to razz you about not knowing how to use a drill, but seeing as you asked... You said you were going to a hardware store, so if you have the money for it, the space needed (look at one in the hardware store), and the intention of continuing to build robots from scratch then you should think about getting a drill press. A cheap one will do nicely, but they making drilling holes straight and true much easier, plus you can adapt most into a sudo mill if the need arises. Aside from that, depending on what you will need to be drilling, a simple electric drill will most likely suffice, or even a hand drill if you are only going into plastics or wood on a rare basis.

Whatever you go with at the hardware store, make sure you get a small drill bit set, and then ask the person at the hardware store how to use what you are planning to buy including safety information.

Webbot · « **Reply #4 on:** March 27, 2008, 10:00:13 PM »

Dremmel make a neat hand held high speed drill that comes with a set of bits. But their range includes bits for everything from polishing to engraving to everything you can think of. So if you want an all round drill but with hand-held precision then they aren't too expensive.

Lefteris · « **Reply #5 on:** March 28, 2008, 11:04:19 AM »

Hello all again. I came back from the electronics store and found literally everything apart from the Servos. I am afraid I will have to order those from the net or do the RC car thingy and use its DC motors.

Thanks for all the answers so far but I have 2 more questions that have arisen just from buying the parts. From what I had understood by reading the tutorial before buying the parts was that the programmer was soldered onto the board. But I found this which was also suggested in the tutorial. Please tell me that such a programmer can be used to program any microcontroller of the AVR family as many times as I need, because in the electronics store that I went to buy it at least it was quite expensive

Also for capacitors putting the wrong kind of voltage capacitors into the circuit can ruin it all? Because now that I am doing a sum up of what I did today I realise I failed to check the voltage of the capacitors I bought. All in all , it was a fun day at the store buying stuff I hope I don't get to destroy

Webbot · « **Reply #6 on:** March 28, 2008, 11:33:23 AM »

Quote

But I found this which was also suggested in the tutorial. Please tell me that such a programmer can be used to program any microcontroller of the AVR family as many times as I need

Yes. One end plugs into your USB port on the computer, and the other end plugs onto the header on your board. You can download AVR Studio to use it to program the Atmel suite of microprocessors as many times as you need. Although the chip may give up if you manage to do it about 10,000 times.

Quote

Also for capacitors putting the wrong kind of voltage capacitors into the circuit can ruin it all?

Yep - you're best getting capacitors with at least twice the voltage level that you are using so that they survive any power spikes. Since you're probably using low volatges ie 5v or 6v then you should be ok as its difficult to get capacitors with a rating less than about 16v.

Lefteris · « **Reply #7 on:** March 29, 2008, 03:40:11 AM »

Thanks for the reply

I will go out again to stock up on some stuff I seem to have forgotten or bought uncorrectly yesterday. Like the 28 dip pin socket for the microcontroller. I got a 28 dip pin but it is bigger than the one I required >_<

I will also go get an RC car to hack it ... I guess that this will be the hardest part since I really don't know much about electronics and I am afraid I might not give the correct voltage to the DC motors.

Also how do you connect wires together? You solder them too? (Asking since this will be my first time soldering and don't know if we do the wires with the same solder as the circuit).

Lastly ... I guess I will need to study the RC car I buy really carefully since I must see if I need any additional capacitors/resistances added to the circuit, right?

cooldog · « **Reply #8 on:** March 29, 2008, 05:32:29 AM »

Quote from: Lefteris on March 29, 2008, 03:40:11 AM

I will also go get an RC car to hack it ... I guess that this will be the hardest part since I really don't know much about electronics and I am afraid I might not give the correct voltage to the DC motors.

it's accually quite easy lets say the car runs from 2 AA batteries thats 3v (1.5v each) then that is most likely your voltage. or sometimes it's written in the instructions or on the motors

Webbot · « **Reply #9 on:** March 29, 2008, 02:11:03 PM »

Quote

Also how do you connect wires together? You solder them too?

You can do or you can also get connectors that look like a bar of chocolate with screws through the top. This lets you shove the two wires in and tighten the screw to make the connection. Difference is that this is temporary ie you can unscrew it later on - so its useful for prototyping - rather than soldering which, if you keep undoing and redoing will result in the lead getting shorter and shorter.

Also back on the AVR ISP - if you buy it - then you will need to load the device driver (so that your PC recognises the programmer gadget that comes with it and plugs into the USB port). The CD also contains a copy of AVR Studio. If you do install this then make sure that you go their website and upgrade to the latest version. Depending on how long the box has been on the shelves then the CD may be quite out of date. I'm assuming you have a Windows PC rather than a Mac/Unix computer - as I dont have any experience with those.

Lefteris · « **Reply #10 on:** March 29, 2008, 04:10:14 PM »

Hello again and thanks for the replies. Webbot I already bought the AVR ISP programmer and I will be sure to update the AVR studio to its latest version.

As for the RC car itself it uses 4 AA batteries just like it says in the shematic. I will link 3 pictures so you can see it too.

This is an overview picture of the dissasembled RC car
This is a closeup of what I assume is the DC motor and the mechanism it uses to move the 2 small wheels on the back of the car.
This is a picture of what seems to be another DC motor moving the 2 front wheels I guess

The front motor is connected with 2 wires with the circuit board and the back one is connected with 2 other wires in the same way. They both got a small ceramic capacitor there at the connection. I guess all I got to do is scrap the circuit board and after I have made the tutorial circuit board at my bread board, move it to the real one, solder it and connect it to the 2 DC motors like the tutorial?

Any tips would be more than welcome

Thanks in advance.

DC-Electronics · « **Reply #11 on:** March 30, 2008, 02:51:56 PM »

May I ask how much you spent on the RC car? If this is an attempt to save money you might be doing it wrong lol. Should you decide to use some purpose built motors I have a pretty decent selection of 150-400 dollar motors in lots of 2 or 4 for about 30 dollars per lot give or take. Having said that, it sort of defeats the purpose of killing that car does it not?

Lefteris · « **Reply #12 on:** March 30, 2008, 04:18:08 PM »

Hey, hello!

I kind of stole it from my parent's house. Used to belong to my little brother but he killed its cover(car lookalike plastic cover), so I "borrowed" it.

Why ask? Is it too cheap for some experimenting? I just want to remind you I am new at this. I am in computer science and have very little knowledge about electronics in general. My area is programming :p , but I see this as a chance to experiment and learn (aka destroy stuff)

DC-Electronics · « **Reply #13 on:** March 30, 2008, 08:49:48 PM »

Nothing is too cheap to experiment with, (My last gf for example

haha, Sorry had to) However I find its easier to start with something that isnt already assembled into things, that way you know your not breaking anything that shouldn't be broken, or what wires are part of the thing your playing with, and what are just connectors to other things.

pomprocker · « **Reply #14 on:** March 31, 2008, 01:07:54 AM »

Left...I am also working on my computer science degree so I know you know how to study.

just remember keep it simple.

one thing at a time.

i'm sure you know how to study for things, so go read up in some textbooks.

Also if you google for "free robot books" or "free robot e-books" you will be surprised at what you find.

Lefteris · « **Reply #15 on:** April 03, 2008, 12:16:14 AM »

Yes you are right pomp. I just got many other things going on and I am afraid that I might not find the time to study. I am dismissing this kind of thinking though! It's bad karma

So coming back to the topic, since I did not want to make a new one to ask some additional questions. I have thought of the design, combined the 50$ robot tutorial with some other things I checked out and am about to start building. But here are some questions which I would like to have checked out. For some of the questions I guess I already know the answer but it never hurts to ask. So here we go:

Even though I got a 4AA battery holder the RC car already has one. Problem is it was connected to the RC board directly so it did not have the two usual red/black wires. Studying the battery holder I got the red is connected to a + end of any of the 4 AA batteries and the black to a - end. Would soldering two wires as described above to the RC battery holder do the trick?
My cousin gave me a small "kit" which includes a small driller to drill holes into pc boards. Could I use this driller to drill holes in plastic and/or aluminium/metals or would it destroy the driler?
I got an L239 IC since I did not want to implement an H-bridge myself with switches. Controlling the IC with the AVR microcontroller is possible since I studied the L239 schematic right? Even read some tutorials to use it but they were using another microcontroller. It does not matter, correct?
The last question is about the photoresistor sensor building tutorial. One end is gonna be a red wire for power. The other end gets the resistance on it.. and a black wire on it to show it is ground. Okay up to now. But where does the blue wire go? I mean we got all two sides of the photoresistor covered. Unless we are supposed to solder the resistance on in a way so that it gets divided in two. One for the end of the resistance and one for the end of the photoresistor?

That's all. I kind of answer all of the questions myself but I can't be sure if they are correct, and I would not want to make any mistakes so I am taking the safe way of asking. I am really excited since when I go home today I plan to implement all these stuff!

pomprocker · « **Reply #16 on:** April 03, 2008, 10:54:54 AM »

I can answer the photo resister question.

There is a tutorial under "Sensors" for the photo resister.

Here is a schematic from that page.

Notice the resister on the ground wire? That would be the black wire. Admin uses 1.5kohm resister, but I just used the one from the parts list of 1.62Kohm, but I recommend you do your own math.

The resister with the circle is the photo resister and the Vin would be your red wire.

The Vout would be your blue wire or whatever color you want.

Gertlex · « **Reply #17 on:** April 03, 2008, 01:02:16 PM »

I haven't technically done the $50 robot, but I have hacked an RC car before.

You might find this thread of mine useful (with link to my writeup of the project)
http://www.societyofrobots.com/robotforum/index.php?topic=1672.0

Admin · « **Reply #18 on:** April 06, 2008, 12:05:14 PM »

Quote

I got an L239 IC since I did not want to implement an H-bridge myself with switches. Controlling the IC with the AVR microcontroller is possible since I studied the L239 schematic right? Even read some tutorials to use it but they were using another microcontroller. It does not matter, correct?

The microcontroller type doesn't matter, you just need to figure out which pins connect to your microcontroller, and how to mod the code.

Quote

My cousin gave me a small "kit" which includes a small driller to drill holes into pc boards. Could I use this driller to drill holes in plastic and/or aluminium/metals or would it destroy the driler?

look up the part and check the specs/instructions

Lefteris · « **Reply #19 on:** April 11, 2008, 02:47:16 PM »

Hello again,

Sorry for posting here again but since I found some time to put into the RC car bot I wanted to ask some more questions.

I will finish the electronics part and I needed to confirm some things. By looking at this image I think I kind of understand how to connect the L293 HBridge IC to the Microcontroller. Thing is in that schematic it uses another microcontroller, some ARDUINO. So I would like to ask what would the equivalent of D1-D13 pins in ARDUINO would be in the AVR that I have in my possesion. I guess what I need is the I/O pins?

By reading the Atmega8 documentation I am confused. Is what I am looking any of the PC#, PB# , PD# ?

I am asking here since I wanna have a clear idea of how the final circuit will be before adding the Hbridge.
Thanks in advance.

Ro-Bot-X · « **Reply #20 on:** April 11, 2008, 02:59:02 PM »

Take a look at this schematic to see one way to connect the H-bridge to your micro.
One motor uses PB1(OC1A) and PB4 and the other motor uses PB2(OC1B) and PB0. This way, you can use Timer1 to generate hardware PWM signal for both motors. The OC1A or OC1B pin will set the PWM pulse. The other pin will set the direction (the PWM signal must be inverted when the direction pin is set High).

Lefteris · « **Reply #21 on:** April 12, 2008, 01:29:34 AM »

What can I say mate! Thank you is not enough, that schematic even though it has lots of stuff I don't understand with my current electronic skills

it has a pretty detailed connection between Atmega8 and an L293 Hbridge. Thanks a lot, I will soon try to implement it

One more question though:

Looking at the schematic above what should I give to the pins 8,16,1,9 of the L293 ? Just 9V to 8? and 5V to 16,1 and 9?

I made the whole circuit now soldered in the L293 IC socket and am about to make the last connections remaining , namely the ones between the micro and the L293 and the L293 and the motors. So after I get the answer to this last question I will be able to make the work/or not test. I need to take a photo of the pref board ... just to remember my first time :p (it has lots of black spots, burned wires e.t.c. and it screams of the word shortcircuit! )

Since it is my first solder job I give me 80% of smoke arising ^_^

Ro-Bot-X · « **Reply #22 on:** April 13, 2008, 12:19:45 AM »

Quote from: Lefteris on April 12, 2008, 01:29:34 AM

What can I say mate! Thank you is not enough, that schematic even though it has lots of stuff I don't understand with my current electronic skills it has a pretty detailed connection between Atmega8 and an L293 Hbridge. Thanks a lot, I will soon try to implement it

You're wellcome!

Quote

One more question though:

Looking at the schematic above what should I give to the pins 8,16,1,9 of the L293 ? Just 9V to 8? and 5V to 16,1 and 9?

Pin 8 is motor power, so you give it what eveer voltage your motors need. Pin 16 is the IC's power, so you must connect it to +5V. Pin s 1 and 9 are the Enable pins. You may connect them directly to +5V or to a microcontroller pin to enable/disable the power to the motors. I usually connect it directly so I don't waste a pin from the microcontroller.

Quote

I made the whole circuit now soldered in the L293 IC socket and am about to make the last connections remaining , namely the ones between the micro and the L293 and the L293 and the motors. So after I get the answer to this last question I will be able to make the work/or not test. I need to take a photo of the pref board ... just to remember my first time :p (it has lots of black spots, burned wires e.t.c. and it screams of the word shortcircuit! )

Since it is my first solder job I give me 80% of smoke arising ^_^

You better don't burn anything!

Lefteris · « **Reply #23 on:** April 14, 2008, 01:25:08 PM »

Ah well ... finished it ... and the good news is that no smoke came out. Bad news is that I can't yet know if it is working since I will connect the Atmega with the programmer tomorrow. Hey ... no smoke must count for something.

I must be doing something wrong since I found soldering EXTREMELY difficult and a job requiring godlike patience. I envy how admin solders wires. I could not find a thinner solder tip and with all those wires I disconnected wires at least 4 times ... putting them back was hard to say the least. How can someone solder without so many wires which are required to connect stuff? Look ... this is the finished robot circuit and my first solder job :

See? A mess! But it's my mess :p

And a close up of the circuit :

Ro-Bot-X · « **Reply #24 on:** April 14, 2008, 01:31:19 PM »

Look at this board (mine):

Lefteris · « **Reply #25 on:** April 14, 2008, 01:49:20 PM »

Wow

even though there are too many wires they are all pressed down and should be kind of easier to solder them ... but how do you press them down like that? Don't you burn your fingers? See my closeup photo I posted above? I solder as if I am making the circuit in a breadboard,I tried to do it like you showed above but almost got my finger burned

pomprocker · « **Reply #26 on:** April 14, 2008, 03:35:47 PM »

were you using jumper wire?

Lefteris · « **Reply #27 on:** April 14, 2008, 03:49:09 PM »

Well ... I think that yes that's what you call this kind of wire. Unless I am mistaken ofcourse.

airman00 · « **Reply #28 on:** April 14, 2008, 05:22:06 PM »

Quote from: Lefteris on April 14, 2008, 01:49:20 PM

I tried to do it like you showed above but almost got my finger burned

Use needle nose pliers

Ro-Bot-X · « **Reply #29 on:** April 15, 2008, 02:46:33 PM »

I am using what is called "wrapping wire". The wire is stiff, so you can solder it easier than the stranded wire. I hold it down with my nail while soldering (I guess I'm pretty funny holding the board and wire with my left hand, holding my soldering gun with my right hand heating the pin, and with the (long) solder wire in my mouth, trying to touch the pin with the solder wire at the same time!).

In the old days the parts were inserted on some pins that were a long square shaped lead underneath the board and then very thin wire was wrapped around the pin with a special tool. That was a method of prototyping before the breadboard was invented.

Some local electronic shops still have different colors of this wire. I only have white, but I will get other colors soon. Color coding makes debugging much easier. I use thicker wire for the power lines, especially for the servos and motors power lines.

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Author Topic: Using an RC car instead for the $50 robot (Read 13367 times)