modding an RC car

Hi,
As you will know if you have looked at my blog, I am a huge fan of the Tamiya M03 radio controlled car, it also has a large following in your part of the world, check http://www.rc-mini.net/joomla/index.php

Its not the fastest, it definitley won't go far off road, but its a great fun little car.

You might be better off with a scale truck for projects though, they are slower and will take you on and off road. If I didn't already have so many cars I would get one of these - http://www.rcmart.com/rc-axial-scx10-trail-honcho-w24ghz-p-34715.html look up 'trail honcho' on your favorite video site to see if this type of truck is for you, check out the 'Tamiya M03' while your there.

Duane B

ajofscott:
A simple bridge rectifier module with the AC terminals on the motor legs and the DC outputs tied to the motor DC supply is in effect the same thing.

My BS meter is pegging on that, but I am always open to learning something new; would you care to supply a schematic or a link to one detailing what you are talking about...?

:slight_smile:

Okay well disaster has struck :slight_smile:

I went to bed with it working and my ardunio program working. Took the battery out to recharge cause the front wheels weren't responding that well and i assumed it was the battery.

Today the car is pretty much dead. If i move the probe around the right a bit it will eventually go right other than that dead. The remote doesn't work.

I am guessing i need to go buy another to start again! :frowning:

I am wondering if maybe my right and left wires accidentally touched at some point because they are very close on the board.

edit:the probe wire doesn't work

Destined:
Okay well disaster has struck :slight_smile:

I went to bed with it working and my ardunio program working. Took the battery out to recharge cause the front wheels weren't responding that well and i assumed it was the battery.

Today the car is pretty much dead. If i move the probe around the right a bit it will eventually go right other than that dead. The remote doesn't work.

Well that stinks... :frowning:

Destined:
I am guessing i need to go buy another to start again! :frowning:

I am wondering if maybe my right and left wires accidentally touched at some point because they are very close on the board.

Could be anything. I would verify a number of things first:

1: Verify that your Arduino is still working ok (I know it probably has nothing to do with anything - but it is an expensive part of the project)
2: Verify all of the connections - use your meter to do some continuity tests on the wires; keep the car turned off, set the meter to measure resistance, then touch the probes to the ends of the wire and where you soldered it. You might also try one probe on the first part lead on the board and the end of the wire. The resistance should measure 0 ohms if continuity is good; "infinite" ohms if it is bad.

Although you do say the remote no longer works...so it could be that the h-bridges are dead. Keep the chassis anyhow, if you are sure this is the case; cut the PCB away from the car - likely the on-board motor and steering motor/actuator work OK; you might be able to use the chassis with a separate h-bridges (measure the current needs for the motor(s) first, though - likely you will need to use L298 h-bridges or better, because of the amperage needs).

Finally - next time - never have a bunch of dangling wires with bare ends flopping around while any source of power is connected; before connecting power, you want to secure and make certain that nothing is touching anything that you haven't decided to let touch. Anything that has to dangle, put a piece of electrical tape over (or, if the wire is thick enough - a small wire nut) - so that it is insulated and can't short out anything.

Consider it a cheap lesson learned, and move on with another vehicle (or purchase h-bridges/drivers for this one) and try again. You were real close with chassis; I think the next one will end up being a success (btw - what brand was the vehicle you used? New Bright is a brand that typically uses the RX2/TX2 chipset, so keep an eye out for those).

I think the motors are fine by the fact i can occasionally get the front motor to go right and stay right until i switch it off.

I have learnt a lot, i have certainly made some mistakes I won't do again. Like when i cut the wires i left way too much exposed at the bottom when welding.

I think the truck was emetec. I will probably try to get the same one although it was on sale in the new year. I think im not ready to buy the $400 one yet, so i might buy another el cheapo one in case i destroy it again.

That said it has been a lot of fun, and for the short period i was controlling it from my ipad was very exciting. For now I am going to work on getting the sensors to show up on my ipad and go buy another one tomorrow.

Destined:
I think the motors are fine by the fact i can occasionally get the front motor to go right and stay right until i switch it off.

I'm sure the motors are fine; like I said - you can keep the chassis, and maybe in the future use it for something else (with separate h-bridges - like a motor shield or two).

Destined:
I have learnt a lot, i have certainly made some mistakes I won't do again. Like when i cut the wires i left way too much exposed at the bottom when welding.

Yeah - you only want to expose the wire needed and no more; the insulation should be right next to the solder point when you are done (also note: welding is a different process from soldering, and forms of welding - most spot welding - are used in the electronics industry; mainly for making battery packs).

Destined:
I think the truck was emetec. I will probably try to get the same one although it was on sale in the new year. I think im not ready to buy the $400 one yet, so i might buy another el cheapo one in case i destroy it again.

You've never said where you are located at (country) - but if you live in the States, or have a good selection of thrift stores nearby - check there first. Nearly every weekend I go to Goodwill stores and scrounge for junk; I almost always walk away with 2 or 3 "junk" R/C cars (I think I even have a few emetec's - but mostly New Bright) that have no transmitter; I only pay a max of $5.00 USD for most of them (some of the larger ones I might pay $10.00 for - I did once find an MGA Tarantula (look it up) for $25.00 - that was more than worth it).

Why do I buy them? Well - I have a plan that I am veeeery slooowly executing...

Destined:
That said it has been a lot of fun, and for the short period i was controlling it from my ipad was very exciting. For now I am going to work on getting the sensors to show up on my ipad and go buy another one tomorrow.

Well, you learned a lot and had some fun! Good for you! Making mistakes is how we learn; sometimes those mistakes can be very expensive (sometimes, they can be fatal - but I doubt this will be the case with a small robot). In this instance though, you lost a minor bit of kit (and I still urge you to check over the Arduino - just to be sure; hook up an LED with a resistor, and check the digital I/O pins for operation - particularly the ones you used for the experiment; the main reason to test this is because if there is damage, you want to fix that too - because otherwise, you'll be trying to build something with a bad system, and you won't know whether the bug is the Arduino, the wiring, or the program - you need "known goods").

Good luck with your next attempt!

:slight_smile:

I actually did say where I was from but probably missed in the more important stuff, I am from Sydney Australia. This somewhat limits my choices and initial costs are higher.

I checked over the arduino and did a similar thing to what you suggested. I can't find anything wrong with it. That was the first thing i did in case I needed to order another one because it would take a week to get here.

The one I got was from an aussie chain called Dick Smith Electronics (don't let the name fool you, by electronics it means phones/computers/navagators/TV's etc).

Quick question is I get one operated by AA batteries is it easy to convert to using a rechargeable power source?

Conversion to rechargable is easy, you have to account for the .25V lesser cell voltage in the recharchable cell types, ie 1.25V vs the 1.5V of carbon-zink and alkaline.

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

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.

I am unsure how to proceed.

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

Chip removal is easy. thread a piece of magnet wire behind the legs and pull outward on the wire gently while heating the pins. Once the leads are free the ic can be popped off with an exacto knife if it was glued down.

Destined:
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...

Destined:
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.

Destined:
I am unsure how to proceed.

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

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

No - it looks ok to me...?

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?

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.

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

Destined:
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 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?

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?

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.

cr0sh:

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! :slight_smile:

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.

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.

Destined:
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...

Destined:
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.

Destined:
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...

Destined:
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).

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