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Author Topic: 12V + RC = ?  (Read 1772 times)

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Offline Mad MIRTopic starter

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12V + RC = ?
« on: August 19, 2011, 03:53:26 AM »
Hey guys, what is the best to way to make my robot RC? It operates on 12V and has high powered motors which i dont think normal servo drivers (gutted from old servos) can handle. Is there any way i can do it with a normal off the shelf hobby receiver/controller?

Offline Soeren

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Re: 12V + RC = ?
« Reply #1 on: August 19, 2011, 06:09:34 AM »
Hey guys, what is the best to way to make my robot RC? It operates on 12V and has high powered motors which i dont think normal servo drivers (gutted from old servos) can handle. Is there any way i can do it with a normal off the shelf hobby receiver/controller?
Just interface the receiver with the microcontroller that controls it in the first place.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #2 on: August 19, 2011, 02:33:04 PM »
I dont have a micro controller controlling it, its literally two heavy duty motors attached to a metal box. This bot is actually the first one I have built, currently im using very basic way to control the motors remotely, I have used a RC receiver to output its signals onto an old servo driver, i actually took the outputs from the driver board and managed to relay its signals through a couple of diodes onto a H bridge made out of relays. This method was tedious and did not allow for any speed control. ( i dont know how to post images otherwise i would have shown you the circuit)

I was afraid this would require use of micro controllers, I dont have any experience programming and dont know how to use micro controllers. ARE micro controllers absolutely necessary for this application?

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #3 on: August 19, 2011, 02:45:04 PM »
Hey i just read the beginners page and realized that i shouldn't really have posted this here, im going to go research my ass off try to find another solution. Your still welcome to help if this post doesn't get deleted by then :P

Offline Soeren

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Re: 12V + RC = ?
« Reply #4 on: August 20, 2011, 09:10:03 PM »
Hi,

I have used a RC receiver to output its signals onto an old servo driver, i actually took the outputs from the driver board and managed to relay its signals through a couple of diodes onto a H bridge made out of relays. This method was tedious and did not allow for any speed control.
Did you use the boards from two servos or what?
A servo board could  be used as driver for some MOSFET's (one for each motor).


( i dont know how to post images otherwise i would have shown you the circuit)
When you write a post, look above the text field. First there's the emoticons and then there's the row of buttons with "insert this or that" - third button is for images, but they have to be somewhere on the net, so you have to upload them to either a web page of your ow, or one of the image storage sites.
If you cannot use that method, click the link "Additional options" under the text field. There's an attachment function that uploads the image from your own computer and transfer it to SoR's server.


I was afraid this would require use of micro controllers, I dont have any experience programming and dont know how to use micro controllers. ARE micro controllers absolutely necessary for this application?
Well no, I made an extremely accurate photo timer from TTL chips back in 1977 and the box was only the size of a phone book  ;)
I just thought that you had it running by a microcontroller already and wanted to add R/C.

As mentioned, servo boards can be used to drive more beefy devices.
Yet an option, if the R/C system you have is a regular one and not just something ripped from a cheap car, would be to get an ESC that can handle the current the motors need.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #5 on: August 21, 2011, 11:56:00 AM »
Yes i did use the boards from the servos, i made a sort of rectifier out of 2 diodes, both facing opp. directions on one pin of the motor out. This effectively sorted the signals CW and CCW so that they could be used to trigger 2 diff relays. The problem was that the servo board was switching outputs so fast that my relays would cease to work after only 5 min of operation.

I believe the same 'rectifier' assembly with the use of a MOSFET Hbridge should work.
 
The servo board output is 6V, give or take, and the motors im running are 24V 250W. Could you suggest some suitable mosfets with which i should make the H bridge? also do you have any tried and tested schematic of an H bridge that may be useful?

THANK VERY MUCH for your time :D

Offline Soeren

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Re: 12V + RC = ?
« Reply #6 on: August 22, 2011, 10:20:25 AM »
Hi,

Yes i did use the boards from the servos, i made a sort of rectifier out of 2 diodes, both facing opp. directions on one pin of the motor out. This effectively sorted the signals CW and CCW so that they could be used to trigger 2 diff relays. The problem was that the servo board was switching outputs so fast that my relays would cease to work after only 5 min of operation.
Yes that's bad for ordinary relays. The problem has probably been the contacts pitting from the inductive kick from the motors (did you use any contact protection?).
Besides, the relays wouldn't be able to follow the frequency of the PWM.


I believe the same 'rectifier' assembly with the use of a MOSFET Hbridge should work.
If you were to use 4 MOSFET's, you shouldn't use the two diodes.

 
The servo board output is 6V, give or take, and the motors im running are 24V 250W. Could you suggest some suitable mosfets with which i should make the H bridge? also do you have any tried and tested schematic of an H bridge that may be useful?
Not tried and tested, but this circuit should work with only one MOSFET each motor.
Do you use Vero board for wiring or can you process PCB's?

Just realized that I didn't annotate the input (left) side:
K1 is the power from your existing servo boards and K2 should go to where the original servo motor was attached to the board.
Just ask if anything puzzles you :)
 
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #7 on: August 22, 2011, 02:53:41 PM »
I see, so this smooths our the signal from the servo board so the relays dont fry

A few questions:
 1) because of the way the relays are wired does it mean there will be no stopping of the motor? Because when there is a low signal on the relays they would go to off position, and in process make motor turn certain direction.

2) i dont have access to pcb facilities so i will have to vero board it. Is there any more pictures of this circuit so i can plan my board better? {i will research PCB facilities and if i can manage to do it, is there a link to a PCB layout?}

3) The freq. of my servo boards is 50Hz , what should c2 and c3 be? also C6 and C7 should be according to my peak current requirements yes?

4) IC2A, B, C, D are transistors NPN, and 4001N is quad NOR gate DIP ? i want to make sure i get the right parts, it will save frustration later



 

Offline Soeren

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Re: 12V + RC = ?
« Reply #8 on: August 22, 2011, 03:40:12 PM »
Hi,

I see, so this smooths our the signal from the servo board so the relays dont fry
Yes, the R1/C3 and R2/C2 circuits integrates the pulses to the relay logic, that in turn only toggles the relay on for one direction.


1) because of the way the relays are wired does it mean there will be no stopping of the motor? Because when there is a low signal on the relays they would go to off position, and in process make motor turn certain direction.
At stick in resting position, there will be no output from the servo boards and so, assuming that the bridge signals are both low (a pull down on each may be needed), the MOSFET doesn't conduct, so the motor doesn't get power. At least that's the plan ;)


2) i dont have access to pcb facilities so i will have to vero board it. Is there any more pictures of this circuit so i can plan my board better? {i will research PCB facilities and if i can manage to do it, is there a link to a PCB layout?}
Nah, I just made this one and if you aren't positive you're going to make a PCB, I don't wanna spend time making it.
Vero should work just fine.


3) The freq. of my servo boards is 50Hz , what should c2 and c3 be? also C6 and C7 should be according to my peak current requirements yes?
C6/C7 yes.
The servo signal (update frequency) is 50Hz, but the PWM frequency of the board is much higher - do you have any means to measure it?


4) IC2A, B, C, D are transistors NPN, and 4001N is quad NOR gate DIP ? i want to make sure i get the right parts, it will save frustration later
IC2 is (as stated) a 4093 quad NAND gate with Schmitt trigger inputs (pin numbers are on the schemmy). Don't let someone talk you into replacing it with a 4011, which, although being functionally alike, doesn't have Schmitt trigger inputs.
Yes, 4011 is a quad NOR gate.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #9 on: August 22, 2011, 06:52:36 PM »
488.28 Hz to about 1 428Hz is probably the PWM freq. i get this figure using the pulse widths, 0.7ms and 2ms (aprrox.)

Anyways i will start to gather parts and build this day after tmmw. Thank you so much for your circuit design, it has not only helped me solve the problem making my bot efficiently RC, but also enabled me to gain a wider understanding of logic gates and how they are used. I really appreciate you taking your time out to help me :D


Offline The Headacher

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Re: 12V + RC = ?
« Reply #10 on: August 23, 2011, 06:23:02 AM »
If you're already using R/C gear, perhaps you could use R/C motorcontrollers as well? Would make things a whole lot easier..
Information about my first robot: https://sites.google.com/site/theheadacher/robot (work in progress)

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #11 on: August 23, 2011, 10:28:01 AM »
Motor controllers for my kind of applications ( 250 W ) are expensive, also i will have to order them from the US or china. LOL infact any motor controller would have worked, most accept servo serial input.



Offline The Headacher

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Re: 12V + RC = ?
« Reply #12 on: August 23, 2011, 12:34:54 PM »
I guess that depends on your definition of expensive. 250W/12V means you need a controller capable of delivering about 20 A. Anyway, that was just my thought. Since I'm not good with electronics and my robot will be based on an old R/C car, a motor controller was the obvious choice for me.

That's the beauty I guess; no 2 bots are the same ;D.
Information about my first robot: https://sites.google.com/site/theheadacher/robot (work in progress)

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #13 on: August 23, 2011, 02:34:43 PM »
haha i guess  8)

Offline Soeren

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Re: 12V + RC = ?
« Reply #14 on: August 24, 2011, 10:34:24 PM »
Hi,

488.28 Hz to about 1 428Hz is probably the PWM freq. i get this figure using the pulse widths, 0.7ms and 2ms (aprrox.)
Sorry, but no cigar.
The Servo signal is nominally 50Hz, so one period is 20ms.
The PPM (or more correct PDM) signal is this 50Hz signal, no matter the duration of the pulse, it's measured by the period (i.e. one pulse and one pause).
The PWM signal (output) probably have a stable frequency (depending on design), and will be much higher than the 50Hz - 2kHz to 4kHz is likely, but it may be even higher.
Without an oscilloscope, a frequency counter or similar you won't be able to tell (a crystal earplug and a "perfect pitch ear" could be used as well).
It shouldn't be that much of a problem however, as you just start with some ballpark figures and perhaps a trimming resistor to find the point where it get hickups and then select a resistor that gets it within a safe area.


Anyways i will start to gather parts and build this day after tmmw.
I'd recommend taking a bit at a time. After each of the IC's you will be able to test if that works ad if not, don't move forward until it is - and inthat case, just post what doesn't work and what you measure.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Mad MIRTopic starter

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Re: 12V + RC = ?
« Reply #15 on: August 25, 2011, 03:10:27 AM »
okay will do :D

 


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