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Offline brian aTopic starter

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controlling a HiTec servo rookie question
« on: June 07, 2009, 01:40:55 PM »
Hello gang-

First off, fishing is my passion. I have a outboard trolling motor that I want to make a speed control for.

Simply put, I want to make one of these

http://www.controllking.com/

I know the servo I need, I just do not how to control it. I have been reading as much as I can locate on the internet about this subject.

Can someone help me with the controller aspect of this? The way the unit works is very simple, the servo turns back and forth with a twist of the knob. There is a switch on the unit in the link for maximum full throttle control but I dont want that, just the ability to turn the knob and control the servo using a 12v power supply. There is also a "idle" switch that returns the servo to the parked position, that would be nice to have but its not really necessary either.

I am pretty handy with the soldering, etc. I just dont know really where to begin with the control unit.


thanks for any help you can provide
« Last Edit: June 07, 2009, 01:44:28 PM by brian a »

Offline Razor Concepts

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Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #2 on: June 07, 2009, 02:21:22 PM »
Hi,

If all you want is a way to moving the servo to any position you choose, you can use any of these:
http://www.uoguelph.ca/~antoon/gadgets/servo2.htm
http://www.uoguelph.ca/~antoon/gadgets/servo3.htm
http://www.uoguelph.ca/~antoon/gadgets/servo4.htm
Personally, I find the last one the "cleanest" looking.

If you want to learn more about the 555 (the chip used), here's a pagefull:
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

The 555 can work on 12V, but your servo cannot, so you need a voltage regulator to get down to 5V to 6V!

The idle switch could be incorporated but isn't right away of course.

Are you planning on programming the servo for new endpoints?
Usually, a servo returns to it's midpoint (i.e. half open gas in your app.) when not powered, so either you reprogram it, use only half it's travel or you dispense with the servo alltogether and build a circuit to control a small DC-motor (could be 12V, removing the need for a voltage regulator) from scratch (just tell me if you want a complete circuit for that) - then you can have whatever extra options you like - but that depends on your mechanical skills and dexterity.

If you have access to a scrap yard, an idle control motor from a car with fuel injection might be a likely candidate for modification (it's a stepper motor, so needs a special circuitry however).

How far is the travel of the throttle in degrees (and/or in mm) and what are your means to interface it?
How much force is needed to turn the throttle axle? (easy/hard/impossible to do with two fingers directly on the axle?)
Got any photos of the area around the throttle axle you could post?
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #3 on: June 07, 2009, 02:33:10 PM »

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #4 on: June 07, 2009, 02:37:20 PM »
Is it your motor with the servo mounted allready?
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #5 on: June 07, 2009, 02:47:14 PM »
sorry all of my text was omitted in the last post.

I dont need any help with the mechanical installation. I can do that. This is pic off the site of the company that sells them. Its very close to what I am doing.

this is the servo used.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDEM3&P=7

It is a very low torque application. I can move the throttle easily with one finger.

In operation, I start the motor normally and let it idle. Then I adjust the throttle with this unit. When trolling we are going very slow so this is used only at low idle speeds as a fine adjustment. The servo travel is not more that about 45 degrees I would guess.

So I would not need to program a max travel into it, but probably would be good as a failsafe so something does not break if its accidently moved past its maximum travel

man you guys are great! Very helpful replies already! Really apprecaite it

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #6 on: June 07, 2009, 03:04:48 PM »
Ah, OK, but if you allready have the controller, then why do you want another?

I don't think you'll ever see it going past it's end positions. I was merely thinking of the situations where the power disappears and the servo returns to its off position (the middle if it isn't changed allready).

What happens when you turn the power off on your setup?
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #7 on: June 07, 2009, 03:14:48 PM »
No, I dont have any of this stuff yet. I apoligize if I was not clear on this. I know what servo to buy, but thats it. I had one of these units on my old boat but I have a different boat now and would like to build the controller, etc. From the schematics you linked me to it looks pretty simple.

On what happens when the power is turned off, ideally, the servo would stay at that position. Thats what that "idle" switch does. In operation, say you have the unit on, and have adjusted the speed. If you catch a fish and want to slow the motor to idle, you would flip the switch and the servo return to the minimal or start position. When you flip the ilde switch again, it return the servo to the position that it was on before you flipped the switch, this is so it remembers the speed setting where you caught the fish so you can easliy return to it. Its for convienece only, its not really needed. I could just use the pot to controll the speed as needed

I think all I would need in addition to what you gave me is a voltage regulator to reduce the voltage frm 12 to 5, or maytbe I can use a battery pack to power it if it does not consume too much power.  maybe this would work? http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html
thanks


« Last Edit: June 07, 2009, 04:20:35 PM by brian a »

Offline brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #8 on: June 08, 2009, 06:37:59 AM »

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #9 on: June 08, 2009, 12:11:29 PM »
Hi,

Here is the circuit with a voltage regulator: http://That.Homepage.dk/PDF/Servo Driver.pdf

A few notes I didn't get in the pdf:
D1   polarisation protection
D2   Voltage lift. Raises the output of IC1 to ~5.7V. Can be replaced with a jumper to get 5.0V out.
C1   100F to 470F
C3   22F to 100F
C4   Timing capacitor.
C5   only needed if distance to IC1 is substantial.
C6   Not really needed, can be left out, only included for the comfort of those that believe that a 555 won't work without it.

Be aware that I have not tested the circuit (and I find it a little odd looking, but with 2 hours sleep, I might be imagining things ;))

You could use the one you linked to but if you build it yourself, you can add the idle switch and whatever else you like.
The box in your link does need a voltage regulator as well btw.
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #10 on: June 08, 2009, 12:46:07 PM »
I would like to build the circuit just to learm more about it.

But, I may just buy the tester and build this voltage regulator circuit and see how this works.

http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html

I still have to fabricate the mounting bracket and linkage but that should not be a problem for me.

I can work on the other tester circuit in the meantime

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #11 on: June 08, 2009, 01:07:52 PM »
Hi,

Better use the part values from the pdf I posted, as the one you link to has the 100nF cap on the wrong side and a too small output cap. Whether you raise the voltage with the diode or not don't matter for the function, but it will give a slightly lower loss.

If you're feeling adventurous, http://www.romanblack.com/smps/smps.htm will be very low loss and the net current draw from the battery will be under half of what the 7805 will take.
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #12 on: June 08, 2009, 02:11:33 PM »
I see

this one looks better then, correct?

http://www.eidusa.com/Electronics_Voltage_Regulator.htm
« Last Edit: June 08, 2009, 02:32:54 PM by brian a »

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #13 on: June 08, 2009, 06:11:03 PM »
Hi,

Not really, it has got the same errors.
Apart from a large(ish) cap like the 100F (F=microFarad, not mF=milliFarad or even worse MF=MegaFarad) on the input, you need a 100nF (0.1F) on the input as close to the terminals of the IC as possible to counter oscillations.

On the output side you need at least 20F (preferably a low ESR type like solid tantalum if available, to counter oscillations as well and if you use something large like eg. 100F in that position, you need a diode in reverse over the IC - anode on output and cathode on input, to safely discharge the cap away from the ICs internal circuitry).
For some reason, a lot of backwards circuits exists on the net.

You can keep looking for circuits on the net, but the regulator part of the schematic I gave you is done the right way and very stable - just remember to add a small heat sink. And if possible, choose the 78S05, it's a 1.5A device.
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #14 on: June 08, 2009, 06:29:38 PM »
ok, so you are talking about the left part of the diagram thats in .pdf?

with d1, d2, c1-3, and IC1?

for some reason I had a problem opening that file earlier, but i see it now

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #15 on: June 08, 2009, 06:44:29 PM »
Hi,

Yes, that's the voltage regulator parts. As mentioned, you can replace D2 with a jumper for 5.0V (with the diode it will give around 5.7V).
Regards,
Sren

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 brian aTopic starter

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Re: controlling a HiTec servo rookie question
« Reply #16 on: June 09, 2009, 04:40:25 PM »
great!

I will go buy the parts tomorrow.

Im sure more questions will be coming!!!

thanks!

Offline Soeren

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Re: controlling a HiTec servo rookie question
« Reply #17 on: June 09, 2009, 05:33:20 PM »
Hi,

Just ask, but I'll be in Sweden for the rest of the week on a symposium, so I won't be around here until late Sunday (or Monday).
Regards,
Sren

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

 


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