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Topic: modding an RC car (Read 15 times) previous topic - next topic

cr0sh


okay I have my new car, except things aren't looking so good now I opened it up (by the way it is a new bright).

the IC is new bright 2007 R209-2 0228


This looks real similar to the board posted on that link I originally posted (waay back on page one) - I'll post it here again:

http://www.et.byu.edu/~bmazzeo/LTR/tech.phtml

Not identical - but close...

Main issue is the back of the board is completely sealed, so no points to solder too on back. I can see they have soldered on the front, but the points are so small I don't think I have the skill to solder on points that tiny or how i would get the IC out.


This is a SMT (surface mount technology) based board - more difficult to work with, but not impossible. All the traces are on the front. Once again, though, trace the points to the resistors (which will be SMT too); the pads on the resistors may be "fatter" and easier to solder to. You'll probably want to use 24 gauge or similar wire (wire-wrap wire is perfect for this). Just be sure to tin the end of the wire; use a soldering iron with a fine point to allow you to heat up the small area. Take your time, and you should be able to get just the wires you need put on.

You'll want to re-measure the voltages, too; my only "fear" here, with the SMT parts, is that it could be using 3.3 volt levels for some of the parts (transistors/fets); if this is the case, then some kind of level conversion would be needed (a few diodes to drop the voltage of the Arduino outputs by 2.1 volts could be used). If the output voltage of the Arduino is higher than what you measure, you'll need to do something to drop it.


I am unsure how to proceed.


Slowly and carefully, taking your time, and documenting everything...


Note: i realise my numbering is wrong and 1-8 should be on the top not the bottom.


No - it looks ok to me...?
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Destined

oopps i was comparing to my incorrect one previously. I deleted that so i don't do it again. I did get it correct!


Can i use the VCC in the top right corner as a probe? That is nice and big and easy to solder too.


Can't I just use the 3.3 volts instead of the 5 volts from the arduino then?

cr0sh


oopps i was comparing to my incorrect one previously. I deleted that so i don't do it again. I did get it correct!

Can i use the VCC in the top right corner as a probe? That is nice and big and easy to solder too.


You could...just be real careful in positioning the probe - the pins are much smaller!


Can't I just use the 3.3 volts instead of the 5 volts from the arduino then?


If you can run your Arduino off 3.3 volts, then sure (the key is the digital outputs of the Arduino should match what the current chip is outputing)...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Destined

#48
Jan 20, 2012, 06:40 am Last Edit: Jan 21, 2012, 05:10 am by Destined Reason: 1
I mean the VCC labeled which is a giant blob in the top right of my picture. It is connected directly to the power source from what i can tell.

Is there an easy way to follow the trace out of the IC?

Destined

I am a bit stuck. I got my probe out of VCC and tested forward and back okay.

However I probed the left and right which was initally okay, but now it is stuck on right. Even when i switch it off take batteries out, or use the control it automatically goes right. The controller does allow me to go left but then it flicks back right. I didn't really want to do this much cause i figured it was doing something bad.

I figure i must of done something wrong but can't figure what(i don't want to make a mistake again!). Is there anyway i can find the problem/fix this? Should one of the other pins set it back to straight?

cr0sh


I am a bit stuck. I got my probe out of VCC and tested forward and back okay.

However I probed the left and right which was initally okay, but now it is stuck on right. Even when i switch it off take batteries out, or use the control it automatically goes right. The controller does allow me to go left but then it flicks back right. I didn't really want to do this much cause i figured it was doing something bad.

I figure i must of done something wrong but can't figure what(i don't want to make a mistake again!). Is there anyway i can find the problem/fix this? Should one of the other pins set it back to straight?


Are you sure it isn't a mechanical issue?

Also - did you measure the output voltage of the pins on the RX2 that feed the motor drivers, and compare that to VCC? If the voltage from the pins is lower than what VCC is - then you probably don't want to exceed that voltage by using VCC.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Destined



I am a bit stuck. I got my probe out of VCC and tested forward and back okay.

However I probed the left and right which was initally okay, but now it is stuck on right. Even when i switch it off take batteries out, or use the control it automatically goes right. The controller does allow me to go left but then it flicks back right. I didn't really want to do this much cause i figured it was doing something bad.

I figure i must of done something wrong but can't figure what(i don't want to make a mistake again!). Is there anyway i can find the problem/fix this? Should one of the other pins set it back to straight?


Are you sure it isn't a mechanical issue?

Also - did you measure the output voltage of the pins on the RX2 that feed the motor drivers, and compare that to VCC? If the voltage from the pins is lower than what VCC is - then you probably don't want to exceed that voltage by using VCC.


I am not sure! :)


However I have gather a number of cheap R/C cars to work on in my attempts to learn (i got this one damaged floor stock for free with another damaged one I got. Both the damage was too the shell but the car still ran).


Anyway this one has the IC covered in black stuff. It appears the surface mounted is the most common and finding that one i destoryed first time was just lucky.

Now this one I have i identified VCC as the lower right circle, the circle around R8 and R9 is left and right, and the remaining circle appears to be forward. However I can't figure where backward is.

The next problem is when I measure it with a multimeter it is running at a little less than 2 volts (1.88) and I don't know how to interface that with the arduino.

PS I have on order, 0.3mm solder and a solder sucker which should arrive tomorrow to make things a bit easier.


ajofscott

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.

cr0sh


Anyway this one has the IC covered in black stuff. It appears the surface mounted is the most common and finding that one i destoryed first time was just lucky.


Yeah - the DIP version is probably only common on older versions, or from manufacturers using up NOS TX2/RX2 stock...


Now this one I have i identified VCC as the lower right circle, the circle around R8 and R9 is left and right, and the remaining circle appears to be forward. However I can't figure where backward is.


Well - if you know where forward is, and you know where the motor leads are, then you can construct a crude schematic of the h-bridge, which should lead you to the other resistor/transistor pair controlling the other "side" of the h-bridge for reverse.


The next problem is when I measure it with a multimeter it is running at a little less than 2 volts (1.88) and I don't know how to interface that with the arduino.


You could try using a small trimmer potentiometer as a voltage divider to reduce the 5 volt TTL signal...


PS I have on order, 0.3mm solder and a solder sucker which should arrive tomorrow to make things a bit easier.


To be honest, at this point it might be easier to go back to your first vehicle, and buy or build h-bridges to control the motors on it. It sounded like that vehicle was a better match for the voltage needs and such of the Arduino. Didn't forward and reverse still work in that one? If so, buy a cheap servo and mount it to control the steering (get rid of all the mechanical/electrical parts for the steering actuator being used currently).
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

ajofscott

R4,R5 are forward/reverse R8/R9 are steering. Remove the resistors and map via similar values to the Arduino output pins

Destined


R4,R5 are forward/reverse R8/R9 are steering. Remove the resistors and map via similar values to the Arduino output pins



correct! I did check it but got no reading. It seems the surface mount parts are very touchy about where you make contact. Is there some sort of spray or something which is preventing good contact for me? Many thanks for pointing that out.


I have opened a few now and it seems they all basically work in the same ways it is just a matter of figuring out where everything is.



I am looking at midrange traxxas like http://www.rcworld.com.au/cars/traxxas-australia/grave-digger-2wd-truck-brushed.html as my base car. However i am a little nervous about how simple it will be to make it work with Arduino. I like the inderpendant suspensions and the stepper motor actually allows more than left/right/centre(center for those americans helping me :D). I looked at the 4WD versions but I thought that might result in extra motors to drive.

Bascially where i am looking to go is have a car which can go over reasonable size rocks slowly with variable turning.

I then plan to load it with sensors, webcam, and control it wirelessly from the ipad (That part i can do :)).


Again thank you for your help, while it make appear my success isn't as great as initially you have helped me a lot to the point I can now figure what is going on. I am confident soon I will be able to share a youtube video of my success.

PS Cr0sh, if you do write the article I would love to read it. I am sure there is plenty I can learn from you.




DuaneB

Hi Destined,

The truck you have linked is not a very good match to the project you have described.

Reading through the truck specs, its good for 30Mph + and is two wheel drive. Unless I have misunderstood your requirements, you want something a lot slower and ideally 4wd. The type of truck I would think you are looking for is generally called a 'scaler' or 'crawler'. The difference between the two is that a scaler is more of a scale model whereas a crawler sacrifices appearance for 'go anywhere' ability.

Check out some of the scale trucks here http://www.scale4x4rc.org/forums/forumdisplay.php?f=15 a lot of them are based on the SCX-10 chassis which I posted previously.

Or the crawlers here http://www.scale4x4rc.org/forums/showthread.php?t=66382

I note that you are in Australia, our club is based in Dubai and we order from these guys in Hong Kong, heres the link again - http://www.rcmart.com/rc-axial-scx10-trail-honcho-w24ghz-p-34715.html

Its up to you, but once you get tired of seeing the grave digger on its roof you will wish you had the Axial or a crawler.

Either way, enjoy.

You can see the two trucks I own, a Tamiya CC01 Mitsubishi Pajero and a Tamiya CR01 Toyota FJ40 at the end of this page - http://rcarduino.blogspot.com/p/cars.html I don't have the SCX-10 but believe its is a much better truck than the two I currently have.

Duane B

http://rcarduino.blogspot.com/
Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Destined


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.

cr0sh



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).
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Destined

#59
Jan 25, 2012, 07:55 am Last Edit: Jan 25, 2012, 09:04 am by Destined Reason: 1
Making good progress :) 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).

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

3. Any tips on how to get a third hand. Wire + solder + iron = 3 and i only have 2 :(. 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.

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?




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