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Author Topic: modding an RC car  (Read 12473 times)
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Dubai, UAE
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Hi,
   Assuming you are looking at hobby grade cars, most 4WD Cars use a gearbox/transfer case to mechanically link the four wheels. There are a few exceptions with rock crawlers and monster trucks which use a front and rear motor, but with more recent dedicated crawler motors your really don't need this.

   All of my trucks use a single motor for four wheel drive, the torque from a rock crawling motor is enough to twist and break axles so you really do not need more than one.

   For toy quality cars, there is no reason why you could not use a motor for each wheel, there would be a real benefit here as the wheels are often oversized for the torque available from toy motors.

   As for the resistors, I would advise always using a current limiting resistor when connecting your Arduino to the outside world. In my own projects I found the RC Components pulled too much current from my Arduino leading to odd results but thankfully no immediate damage.

Duane B

rcarduino.blogspot.com







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Making good progress smiley Have all my wires out and working off the probe in 2 cars.

But have a couple of questions.

1.Should i stick a resistor between the arduino and the R/C board just to make sure I am not running too much current(even if the voltages match)? (wanted to check before hooking it up in case this is why i blew the first one up).

If you are concerned, then go for it (it can't do anything but not work - in that there won't be enough current to activate the transistor) - but if you traced your lines right, you should find a resistor before the base of the transistor involved for the action; note the schematic on the datasheet. Something similar should be on the board. The only difference might be if the chip on board is being run at a lower voltage than the Arduino, then on-board resistor might be sized for that voltage for the current needed (measure the resistor, measure the voltage - then work out the current; once you know that, then knowing the HIGH voltage of the Arduino is 5 volts, you can figure out the needed resistor size for the Arduino at the current needed (don't exceed about 20 ma!) - so if currently there is a 400 ohm resistor on-board for the RX2, but you figure the Arduino needs a 500 ohm resistor, then you just need to add a 100 ohm resistor in front of the first - note that all of those figures are pulled from my rear - you need to measure it all yourself!).


2. Sometimes my solder doesn't seem to stick to the board very until dry. Is there a reason for this?

What do you mean by "until dry"? The only possible reason why the solder might be an issue (I think) is if you are using a different solder from what the board was soldered with (ie, you are using lead-free and the board was done with leaded solder, or vice-versa; note also that lead-free solders have a higher melting point than leaded solders, so it could be technique or your iron; likely technique though, if this is the case).

3. Any tips on how to get a third hand. Wire + solder + iron = 3 and i only have 2 smiley-sad. I have tried a number of ways including sticking the wire down in place before soldering but I keep thinking there must be an easier way.

Well, here in the States I use leaded solder, so I have an extra arm growing out of the side of my torso...

smiley-wink

Seriously - get some electrical wire like used for house wiring (large guage, single solid core wire) - cut a few lengths of about 10 cm or so (gauge for yourself what you need); on one end, crimp a largish alligator clip; nail or screw the other end to a board. Voila - el-cheapo "third hand". Not quite as good as a PCB vice, but serviceable for many jobs!

4. With a 4WD car am I going to need more than 4 arduino ports(not sure if that is what to call them) than you need for the standard car?

What kind of 4WD car? If it is a hobbyist 4WD car (like a Traxxas), then no - you will only need two pins: one for the speed controller, the other for steering; unless you have extra accessories and such; basically you need one pin for each servo or ESC (electronic speed controller).
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Don't drive against the original chip's outputs! That is what fried the first one and i was just lucky you didn't fry your ATMega. Those 680 ohm SMD resistors will pop right off with a blade tip on your iron, load it up with a puddle and heat the whole resistor at once.

Are you saying I should remove the resistor? Should i be using a resister between the arduino and the car?


Thanks for the link on the truck, i will try find an aussie dealer. Yes I want more of a crawler.

I don't think you should remove the resistors, but without having a real (or even a guessed) schematic of the PCB, you can't know for sure; the resistor is there on the base of the transistor to prevent too much current flow from the controlling chip; now - with the RX2 still in the loop (ie - power not cut), it might be possible that it's output (if HIGH) could backfeed into the Arduino; or the Arduino could be shorted to ground via the RX2's pin while it is LOW (more likely). This is why when you know what your inputs and outputs are, you need to remove the RX2 (and I might not have explained this well or forgotten it entirely - my apologies if that is the case; I'll make sure to clarify it when I write the article).

If what you are wanting to do (ultimately) is crawl around on rocks, then 4WD (or more - a few years ago there was a guy at a university who made a small R/C 6WD vehicle with wireless video from traxxas parts; seems like there are a bunch of people doing it now) is pretty much mandatory. You'll also want a nice articulated suspension system. Controlling such a vehicle with an Arduino is fairly painless; steering is handled with regular servos, and the control of the drive motors via ESC (electronic speed controllers) for the brushless motors; power to the Arduino could be done via a BEC (battery eliminator circuit - basically a small device, meant to power the receiver, that converts the battery pack power to 5 volts or so).

To control all of these parts with the Arduino, you can use the Servo library (or, if you wanted to off-load this work, using serial comms to a servo controller like Pololu sells would be ideal).
What I meant was remove the 680 ohm smd resistors and insert 680 ohm resistors from the non RX chip side of the removed SMD to the arduino port pins.
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What I meant was remove the 680 ohm smd resistors and insert 680 ohm resistors from the non RX chip side of the removed SMD to the arduino port pins.

I'm not sure what the point would be (as the SMD resistors should work OK - provided the voltages are the same), but if you wanted to do that, I suppose you could.
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It was instructed to keep from having collisions and/or the oportunity to cause a shoot through in the h-bridge from conflicting control.
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Well I had what I thought was going to be my first fully functional car but it doesn't seem to work.

When I attach each of them to my Vcc left/right/forward/back work. It measures 1.88 volts when I switch them.

So I made a crude voltage divider with a 100 ohm and 180 ohm resistor and the voltage coming out is 1.86 (and put an LED in to check of course).

However once i hook it to the arduino and turn the pin on and off nothing happens. Not sure why the probe works and not the arduino.

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You didn't excite any point without a resistor in series did you?
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I am wondering if the problem in the above is the resisters are stopping enough current being drawn.

On my latest I found putting a resistor between the arduino and the car meant I couldn't switch it on, but taking it away and bam I have all the controls.


Anyway main reason for my posting is again thanking everyone for the help and to let you know your help wasn't in vain. I have a car full working and controlled from ipad via wifi (i used the dfrrobot arduino wifi shield).

One thing I have noticed is I can't make the motors run slow enough. When I do it just creates a high pitch. Is there anyway to run the motor super slow?

Now I need to deciede on my larger truck with the independant suspensions. So hard when I haven't seen them in action/know that much about them.
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video proof smiley

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Hi,
    Nice to see that you have something up and running. Can you provide a link to the tool kit you are using for the ipad app ?

    On the trucks - you probably don't want independent suspension, its great for high speed but most traction orientated go anywhere vehicles tend to use solid axles.

Check out this SCX-10 video or any other on youtube -



Also check out the cheaper but much less capable Tamiya CC-01, it has independent suspension at the front and a floating solid axle at the rear -



Duane B

rcarduino.blogspot.com
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For wireless communication with arduino I used

http://littlebirdelectronics.com/products/wifi-shield-v2-1-for-arduino-802-11-g-n  (probably not the cheapest but I have work related reasons for using them)

Then I used processing the OSCP5 lib to send and recieve OSC messages

http://www.sojamo.de/libraries/oscP5/

and I also used the networking abilities of processing to talk to the wifi shield

And finally I used TouchOSC on my ipad

http://hexler.net/software/touchosc


This does mean you need a computer in the middle with processing running. I may try to talk to the wifi directly from the ipad but for the current scope this setup works great for me. It is will be in a restricted museum type enviroment so computer running is no problem plus I plan to attach a tilt/pan wireless webcam.


Those trucks look interesting. For the me the main thing will be, being able to run it really slow. The current car is way too fast and when I try to slow down the engine stalls.

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Hi,
   To go slowly you can change the motor for one with more torque and less revs, this can give you very precise control, it will also give you more run time from the batteries, doesn't cost a lot and is easy to do.

I have a draft post about motors that I will put up on my blog soon.

In the meantime I am going to check out TouchOSC,

Thanks

Duane B

rcarduino.blogspot.com
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For wireless communication with arduino I used

http://littlebirdelectronics.com/products/wifi-shield-v2-1-for-arduino-802-11-g-n  (probably not the cheapest but I have work related reasons for using them)

Then I used processing the OSCP5 lib to send and recieve OSC messages

http://www.sojamo.de/libraries/oscP5/

and I also used the networking abilities of processing to talk to the wifi shield

And finally I used TouchOSC on my ipad

http://hexler.net/software/touchosc


This does mean you need a computer in the middle with processing running. I may try to talk to the wifi directly from the ipad but for the current scope this setup works great for me. It is will be in a restricted museum type enviroment so computer running is no problem plus I plan to attach a tilt/pan wireless webcam.


Those trucks look interesting. For the me the main thing will be, being able to run it really slow. The current car is way too fast and when I try to slow down the engine stalls.



Glad to hear and see you got things working!

smiley-grin
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Hi guys,
     Complete n00b here. I just got my first arduino uno and have been playing around with it, with things like musical floppy drives and the standard LED tutorials. Well now I want to control an RC car with the arduino and I found this forum. Great work and explanations have been given here so I hope I can continue in that regard. Basically, I want to control, the controller for the rc car. I figure this way I don't have to hack the car itself and all my RXTX is built in..  The IC inside the controller is an SCTX2B. I have been able to play with it a bit, using probes, and I know all the pin outs for the IC now. But I need some guidance on how I make this work with the arduino. Any guidance would be immensely appreciated! Thanks in advance and please forgive any inadequate info or my lack of etiquitte.
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I don't have the answers for you. But basically you are trying to mod the radio reciever not the car.

I am looking at a crawler like this

I am still looking for a lost cost solution if someone has one for a truck which can go nice and slow


This is one is perfect!!!!


and less than 200, but it is sold out everywhere. I don't know if it is still being made.
« Last Edit: February 08, 2012, 06:41:44 am by Destined » Logged

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