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### Topic: modding an RC car (Read 39513 times)previous topic - next topic

#### ajofscott

#30
##### Jan 17, 2012, 05:17 am
@DuaneB There are a number of Open collector buffers which with use of a external pullup resistor can be used as a logic translator.

#### ajofscott

#31
##### Jan 17, 2012, 05:23 am
Just a note on those cheap motor drivers. They are resoundingly sloppy in the linear region and may not tolerate PWM due to high shoot through currents.

#### keeper63@cox.net

#32
##### Jan 17, 2012, 05:34 am
Kinda did this backward - oh well...

I am prepared to spend if i can get it going. Actually i might go down the hobby store and look and ask some questions. I am from sunny Australia so most of the stuff I have to get online or improvise (actually improvise a lot because I want to get this working so I can justify the purchase of more. )

A quality electric R/C truck (no radio or such), such as a Traxxas will run you around \$400.00 USD; just keep that in mind - it isn't a cheap hobby (and combining that with robotics - well, if you have the money - have fun!).

The battery on this car is a 9.6 volt, 750mA NiCd rechargeable. Honestly I am amazed the car came with it at the price. I did measure the voltage, but I can't see it in my notes which probably means I wrote it on a post it note(yeah smart I know)(edit: about 3.5, but it was really hard to measure cause I just had to stick the multimeter in while holding it on which is hard to do without a third hand. I figured holding control in palm still allowed me to hold the probe off multimeter), so I will look it up.

Could you explain what TTL equivlent is? (I would rather understand than just do).

This is from wikipedia (http://en.wikipedia.org/wiki/Transistor%E2%80%93transistor_logic):

"Standard TTL circuits operate with a 5-volt power supply. A TTL input signal is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal, and "high" when between 2.2 V and 5 V[19] (precise logic levels vary slightly between sub-types and by temperature). TTL outputs are typically restricted to narrower limits of between 0 V and 0.4 V for a "low" and between 2.6 V and 5 V for a "high", providing 0.4V of noise immunity."

Currently I am using a 9 volt clip battery for arduino, but I have read the wifi shield I have needs a fair amount of juice and I plan to hook an array of sensors up to it.

A couple things - that battery has enough voltage to run your Arduino via the barrel jack, which is OK for now, but I would do something different about the battery. It has a fairly low "run level" - that is, a battery is measured in amp-hours (AH) - that is, a 1 amp-hour battery can supply 1 amp for one hour (or 500 mA for 2 hours, or 2 amps for .5 hours - see how that works? In practice, you'll never see these numbers in real life, but that's the idea - I won't elaborate here on why). Your's is smaller than 1 amp-hour, though - a larger battery will be better.

Look at hobby shops and the like for 9.6 VDC R/C packs - NiMH are a good option, but LiPo packs are starting to become popular as well (just be aware that such packs, while lightweight, pack a helluva punch - there are videos online of what can happen if they should be accidentally shorted, or overcharged - though I think with a proper charger you should be OK); get something around 2-3 AH (2000-3000 mAH). That way you'll have a longer run-time for the car, with the Arduino and anything else you add.

The next step would be to bypass the 5V regulator on the Arduino (it wastes a lot of power as heat, being a linear device), but I would save that for your real R/C truck; for that, you can use a 5V BEC (Battery Eliminator Circuit) - do some research on these, they are basically switch-mode DC-DC converters, to efficiently take the voltage of the battery down to the level needed by an R/C receiver (but you'll power the Arduino with its output).

Oh - something else to keep in mind: In the R/C world, the battery may have a different connector that what you have on your current R/C truck - so you may have to do some improvisation here, too (and, you'll need to parallel the barrel connector in some manner as well; the best way would be to solder it to the PCB - trace the battery connections on the PCB, and find a convenient solder point for power and ground).

I currently don't have a solder sucker, although i might be able to find one to borrow. Is it possible to do it without the sucker?

You could try solder wick, but really, your toolkit should have a solder sucker -and- solder wick (I actually have a plunger-type solder sucker, a bulb-type solder sucker, and solder wick of various types - but I've been playing with electronics for a couple of decades now). Sometimes one works better than the other in certain cases; generally the solder sucker is good for the bulk of the work, and the wick for final cleanup of any extra.

How do I sever the antenna? It is clearly marked on the board so easy to find.

It's not just the antenna - you have to sever the power to the RF circuit. You'll need to trace the battery positive and/or the ground to the circuit, and this may take making a rough schematic (while comparing it to the datasheet's example schematic for that portion - which was located in the upper-left part of the schematic); it may or may not be easy to do. It may take some time. Ultimately, it might not even be worth it for this stage of the project (it likely doesn't consume very much power, and if you upgrade the battery pack, it won't make that large of a difference anyhow).

I already figured I can't turn back and forward on and will write my if statements so it always switches the other one off before starting as a failsafe.

Well - the thing is, on some h-bridge designs you can; it allows you to set the motor in "brake" vs "freewheel" mode - but it is a good design in your code to do these checks; put them in functions, that way you don't have to worry about them, and can just call the function you need, and you'll know it works (for that matter, put the "set all outputs LOW" in a function as well - call it something like "initOutputs()" - then call that function from setup(), before loop() is entered).

Something I forgot to mention in the last post, in regards to cutting traces: To cut a trace, you can either scrape the copper away with a hobby knife (x-acto or similar), or use a dremel-type tool with a diamond point burr cutter or similar. Just remove enough of the trace so you see the PCB material underneath, leaving about a 1-2 mm gap.

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

#### keeper63@cox.net

#33
##### Jan 17, 2012, 05:36 am

Just a note on those cheap motor drivers. They are resoundingly sloppy in the linear region and may not tolerate PWM due to high shoot through currents.

That is very true, too - I had forgot that those h-bridges may have left off the flyback diodes (you might try looking into adding some in - which may or may not be very easy - four per h-bridge would be needed); even that may not cure things...
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

#34
##### Jan 17, 2012, 01:02 pm
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.

#### DuaneB

#35
##### Jan 17, 2012, 06:10 pm
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

http://rcarduino.blogspot.com/

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

#### keeper63@cox.net

#36
##### Jan 17, 2012, 10:27 pm

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...?

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

#37
##### Jan 18, 2012, 05:32 am
Okay well disaster has struck

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!

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

#### keeper63@cox.net

#38
##### Jan 18, 2012, 06:07 am

Okay well disaster has struck

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...

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

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

#### Destined

#39
##### Jan 18, 2012, 07:19 am
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.

#### keeper63@cox.net

#40
##### Jan 18, 2012, 05:23 pm

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).

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).

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...

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!

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

#41
##### Jan 18, 2012, 11:20 pm
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?

#### ajofscott

#42
##### Jan 19, 2012, 12:17 am
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.

#### Destined

#43
##### Jan 19, 2012, 06:45 amLast Edit: Jan 19, 2012, 08:06 am by Destined Reason: 1
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.

#### ajofscott

#44
##### Jan 19, 2012, 01:27 pm
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.

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