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Simple R/C Car Controls made usable
 Moderated by: W C Greene Page:    1  2  3  4  Next Page Last Page  
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 Posted: Mon Jul 3rd, 2017 10:39 pm
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Helmut
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Guys, the desire to use that cheap crappy on-off R/C car controls in trains seems to be unextinguishable.

Well, those contented with a jerk-on jerk-off operation may skip my ramblings altogether, there certainly are more interesting topics on board.

For the scroogy ones ( like Si ;)), being halfway educated in electronics, and not afraid of tackling chinese pcb's, I've come up with a modification applicable to all the R/C car receivers, provided you intend to use the original motor and batteries.



First, when buying one of the toy cars, what are the features you get ?
There are two channels that can be operated simultaneously, i. e.  forward/backward and left/right.
These are simple on/off affairs not capable of any in-between states.

Second, what are the minimum requirements when operating a loco ?
It must be able to go forward and backwards, and the speed must be adjustable.

These requirements are not fully met when using  R/C car electronics- you get the forward/backward feature, but no adjustable speed.



The applications described in this forum so far have only used the on/off f/b feature compensated by high gearing ( to make those jackrabbit starts and stops a bit tolerable ), leaving the second channel unused.

If one were employing the second channel for speed setting, a much more satisfying behaviour could be achieved.



A solution has to meet the requirement that only the receiver's output signals may be modified in order not to hamper its working and to remain independent of whatever Chinaman has implemented to produce the output to the motors.

This can be achieved by inserting a PWM control into the f/b H-bridge, controlled by the 2nd channel.
It serves as an acc/dec control by sort of joystick operation.


 

That's the way it is done, some in-depth explanations will follow.
IMPORTANT!
To avoid confusion by the not-yet used relay, I've changed the picture


Last edited on Wed Jul 5th, 2017 12:07 pm by Helmut



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 Posted: Mon Jul 3rd, 2017 11:13 pm
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Si.
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" For the scroogy ones like Si. "


" halfway educated in electronics "



Hi Helmut :brill:



How do you think I got to retire so early as a millionaire ? ! ;)



I did attend various educational establishments in my late teens & early twenties.

I studied 8-ball Pool, girls & pop music mainly.


I did manage to fit in a few technical classes a couple of times a month as well.

London University even thought it appropriate to award me an Honours Degree ! :shocked:


Bet you didn't know it was possible to graduate in pub games, girls & pop !! ;)



I am going for a N.A.S.A grade E.S.C, as you know Helmut. :P


But the temptation to hack a 'push & squirt' R.C. controller, keeps me awake at night ...

... and my Bank Manager reassured that I can afford his usual case of bubbly at Christmas.



It looks like a cunning plan !

How much does it cost ? ;)



:moose: :moose: :moose: :moose: :moose:



Si.



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 Posted: Mon Jul 3rd, 2017 11:52 pm
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Lee B
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That diagram is like trying to make sense out of the computer screens in the movie, "The Matrix."
I'm a bright person with a pretty high IQ, but I've long ago given up on trying to make sense of any electrical schematic.

And for those this comes easy to, FOR THE LOVER OF GOD, do not simply declare that it's easy. For you? Yeah. But I think plenty of things are 'easy' that are downright impossible for most other people.

Flying airplanes (in a simulator, anyway, as I can't afford a pilot's license), calling in artillery onto moving objects (the Army paid me to do that, which I took to right away) and drawing cartoons. Many people can't do these things, but I took to each right away.

I don't assume others have my same skill set. I only bring this up as that's ALWAYS the response when I post somewhere that I just don't 'get' electronic stuff. Sheet music either. I tried several times to get the hang of each, and it just didn't take.

Man, how I wish someone would come out with a good RC chasis in 1/48 or 1/43 scale, so I could drive some 1930s vehicles around my layout!



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 Posted: Tue Jul 4th, 2017 12:49 am
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Si.
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" That diagram is like trying to make sense out of the computer screens in the movie, 'The Matrix'."



While I was looking at Helmuts diagram, the SAME cat walked past TWICE !

Does that mean there is an error somewhere ? ;)


- - - - - - -


I can read literally any kind of map you care to think of.

I have met some who recognize the green bits as forests & that is about it ...

... other than the blue bits being water of course. :P



Diagrams of many types can often be somewhat overwhelming, when looked at as a whole.

My simple strategy is to often draw 'red hoops' around the components that are functionally associated together ...

... as the diagrams are normally drawn for topological clarity, rather than functional clarity.

GEE ... Bet that helps & makes a lot of sense. :shocked:



I was surrounded by sheet music from an early age & played several instruments, badly.

Never really could get my head around the crotchets, quavers & staves ...

... it didn't stop The Beatles though ! ;)



:moose:



Si.



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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Tue Jul 4th, 2017 07:34 am
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Helmut
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Yep, some electronic trickery is needed to work one's way around the idiosyncrasies of the cheap stuff. This trickery results in sometimes hard-to-understand schematics. I assure you - no errors in the drawing!
Got to go now for more sensible things ( like digging up a grassy patch in the garden, as wifey wants another flower bed ). 'til later



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 Posted: Tue Jul 4th, 2017 04:29 pm
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W C Greene
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You get what you pay for! Buy a cheap r/c car rig and you get... Spend maybe $80 for a nice car/transmitter and you get operation comparable to any DC/DCC setup. At least that's what I have done.

Woodie



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 Posted: Wed Jul 5th, 2017 11:54 am
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Helmut
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Why did I come up with that modification of a cheap R/C set?
Admittedly, I prefer some solid standard versatile equipment
and do not fancy the limited-use stuff that is brought up every once in a while by someone thinking he'd found a way of having almost the same for less money. The drawbacks were so obvious: Two simple on/off outputs for drive and steering, and no
way to operate more than one car at a time. The frequencies were fixed, and there was no way to change them. Also, due to the use of 27.12 or 40.68MHz transmission, the receiver/driver footprint was not small enough to fit into tight spaces.
Until recently, 2.4GHz FHSS wasn't heard of in that field. Two weeks ago, a cheap set was offered by one of Germany's leading discounters, being advertised as using 2.4GHz technology. Taking a look at the features, I found that it used 'binding', so one could operate several of them simultaneously without interference.
Now that spurred up my imagination - was there a way to have the minimum
requirements for loco operation fulfilled by using a bit of trickery?
The price tag was 15€. If one would spend say another 5€ for additional
hardware, a real alternative for the not-so-demanding could be found.
As an added bonus, the footprint is really small.
The receiver chips are mostly from AMtek-semi, a chinese company. The
data sheets provide sparse info, the text is mainly in Chinese,
but usually a diagram is provided where you can learn that there are two
H-bridges with MOSFETs. One bridge is for the drive, and the other for the steering.
Operation is as follows: When there's no contact closed on the transmitter,
the units idle. Both receiver outputs are switched either low or off.
As soon as a contact is closed, e.g. you pull the trigger for 'forward',
the transmitter wakes up and emits a signal. The 'F' output of the receiver is switched on 'high'(+4.5V), and the 'B' output is switched on 'low'(0V return), making the motor turn at full speed. When you push the trigger for 'backward', 'F' and 'B' will change. The same happens with the steering outputs 'L' and 'R'.
Replacing the trigger by a center-off SPDT switch would allow for direction change and
full stop. When you put the lever in the neutral position, no signal will be sent
and the receiver shuts the outputs down. You must have a speed control now, because when choosing either direction, the motor would run at full speed.
For speed control,I inserted two MOSFETs between the 'F' and 'B' outputs and the respective motor terminals. They are so oriented that when the output is low
( = Ground ) their source will be grounded, too. The intrinsic body diode is used to bypass the current when the output is 'high'.
The gates are connected in parallel, so that the PWM chopping is always in effect
regardless of direction.
The 'left over' steering channel is used to achieve that speed control. The easiest way
to have a continuous adjustment is to charge/discharge a capacitor as long as there is a signal, and the capacitor keeping its charge when there is none. You have to find switching elements that provide an almost infinite resistance when open. The easiest switch for charging is a diode: If the respective output is high, it will pass current to the capacitor, and block its return when the output goes low. Alas, all those diodes you can buy have a reverse leakage current orders of magnitude higher than one can tolerate here.
But you can use a transistor for this purpose if you short base and collector. This 'diode' ( depending on the transistor type! ) has a reverse leakage current small enough for  the purpose here. The drawback is, it will only tolerate a maximum voltage of 5V. Furthermore, not every NPN transistor is usable, that being the reason for my choosing those rather dated transistor types. This feature is nothing you find spec'd in the data sheets, you have to find out by yourself. Similarly, you have to find a suitable MOSFET for the discharge.
The remainder is straightforward -a simple RC-sawtooth oscillator. I've chosen some 150Hz, because the stock motors seem to response best at low frequencies.
On the transmitter side, you employ a SPDT center-off spring loaded toggle. It is operated just like a joystick, up for acceleration, down for braking, and neutral for coasting.






Last edited on Wed Jul 5th, 2017 12:10 pm by Helmut



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 Posted: Wed Jul 5th, 2017 02:19 pm
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Si.
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Before my 1/2 a Euros worth ... ;)

... thanks for posting Helmut. :brill:

New approaches are always a good thing. :bg:



- - - - - - -



My short blurb about having BOTH affordability AND quality, is simple.

Transmitter aside, which is up to you how 'flashy' you wanna be ...

... the HIGH QUALITY parts for an R.C. loco installation, cost me the following :-



£ 1.36p - Battery

£ 3.84p - Receiver 'FlySky' 3 Chanel 2.4 GHz

£ 2.54p - E.S.C. 20-Amp electronic speed controller

£ 0.56p - Voltage regulator board

-------------------

£ 8.30p - TOTAL inc. all tax & shipping charges



This is a totally modern 2.4GHz 'FlySky' 3 Chanel system.

Which would be just as at home in a plane as in a car or a train.



There is simply NO NEED to spend BIG MONEY on quality R.C. components !



I looked at 'cheap' R.C. cars to pull apart ...

... but why do it ? when I could buy top quality R.C. parts for my loco at only £ 8.30p inc. P&P ?



:moose:



Si.



Which is no reason NOT to experiment, which I'm all in favour of ...

... but it is important, especially for 'newcomers' to understand ...

... that HIGH QUALITY installations of R.C. gear, need NOT be expensive or complex !




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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Wed Jul 5th, 2017 03:25 pm
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Helmut
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@Si
as I said, I really do not fancy those cheap sets.
But - you may have an advantage when you use the motor and drive train that come with the car, too. Sometimes even the batteries are included. So, if you don't consider your time and effort....
I just checked -
Flysky FS GT3B LCD 2.4G 3CHset with LCD screen gun transmitter, receiver, and LiPo direct from China  for 24.00€ incl. p/p. ESC + 3.52€. So it totals ~28.00€. BTW-does your listing include the gun, too?

So, is it worth the effort to tinker around with that cheap stuff? Definitely not for me!

Last edited on Wed Jul 5th, 2017 03:28 pm by Helmut



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 Posted: Wed Jul 5th, 2017 03:38 pm
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Lee B
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I really think there'd be a good market for a good RC system that you could place a diecast car shell on top of. I'd for sure but at least a couple of them.



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