Any Stronger DC motors than 9v?

mngeow · Dec 8, 2011

I can't just connect the motor in series with a resistor to step down the voltage?

misterT · Dec 8, 2011

mngeow said:
I can't just connect the motor in series with a resistor to step down the voltage?

No. Maybe a resistor and a 5V zener across the servo would work if you calculate the values right, but that also is a poor solution. You would need a 18 ohm 20W resistor and a 6V 6W zener.. And those power ratings are at the lower limit. I assumed the servo takes max. 1A of current.. which it easily takes for a short period of time.

You should use a 7805 or 7806 linear regulator or similar.

mngeow · Dec 8, 2011

Ok sounds good, I think I'll go try it out. But I think I'll do a little research on the connections first , and how do you " check how easily you can generate a proper servo pulse-signal with your PLC " ? I also found out another issue , I took a look at the motor and it's attached to some gear , but I need to somehow connect the motor to my compartment so that it can spin. Is there anyway to extend a shaft or rod out of the motor?

misterT · Dec 8, 2011

mngeow said:
how do you " check how easily you can generate a proper servo pulse-signal with your PLC " ?

The servo is controlled by sending short pulses to it regularly (one pulse every 20 milliseconds).
1.5 millisecond pulse keeps the servo still. Shorter pulses make it rotate in one direction and longer pulses make it rotate to the other direction.

Can you generate this kind of signal with your PLC?

mngeow said:
Is there anyway to extend a shaft or rod out of the motor?

The servos have a very useful "arms" where you can easily attach all kinds of things.
Found some accessories online: **broken link removed**

mngeow · Dec 8, 2011

Yes I believe my PLC can. Would this affect the connection?

misterT · Dec 8, 2011

mngeow said:
Yes I believe my PLC can. Would this affect the connection?

If the PLC output is 24V, you need a resistor divider to dampen the signal to 5V.
18k and 4.7k resistors would work just fine.

mngeow · Dec 8, 2011

misterT said:
If the PLC output is 24V, you need a resistor divider to dampen the signal to 5V.
18k and 4.7k resistors would work just fine.

After the resistor divider would I still need the zener diode?

misterT · Dec 8, 2011

mngeow said:
After the resistor divider would I still need the zener diode?

You need the resistor divider for the control signal.. no zeners.

You need a (linear) voltage regulator for the operating voltage. Use a LM7806 or LM7805 regulators. Forget the zener, it really is a bad solution.

mngeow · Dec 8, 2011

Oh ok,I did a little research on the two components and I found a little diagram for the resistor divider : **broken link removed**

So I just connect the voltage regulator in series with the resistor divider ? (Connect Vout in the diagram to the voltage regulator)
Cause for my voltage regulator to produce a 5V output , I need to have a voltage input that's not too high but still above the voltage dropout , that's what the resistor divider is for right?

misterT · Dec 8, 2011

mngeow said:
Oh ok. I found a little diagram for the resistor divider : **broken link removed**

So I just connect the voltage regulator in series with the resistor divider ? (Connect Vout in the diagram to the voltage regulator)

No. The resistor divider is only for the control signal.

You are confused with two things here: the control signal and operating voltage. They are two different things here. As I said:

1) You need the resistor divider for the control signal.
2) You need a (linear) voltage regulator for the operating voltage.

There are 3 wires going in the servo. Two of them (red and black) is for the operating voltage (5V). And one of them (yellow) is for the signal.

mngeow · Dec 8, 2011

misterT said:
No. The resistor divider is only for the control signal.

You are confused with two things here: the control signal and operating voltage. They are two different things here. As I said:

1) You need the resistor divider for the control signal.
2) You need a (linear) voltage regulator for the operating voltage.

Oh. Yeah it's two totally different circuits , I think I understand now. One is for the control signal , the other is for the voltage input to the motor right?

misterT · Dec 8, 2011

mngeow said:
Oh. Yeah it's two totally different circuits , I think I understand now. One is for the control signal , the other is for the voltage input to the motor right?

Yes. There are 3 wires going in the servo. Two of them (red and black) is for the operating voltage (max 6V). And one of them (yellow) is for the signal.

mngeow · Dec 8, 2011

misterT said:
Yes. There are 3 wires going in the servo. Two of them (red and black) is for the operating voltage (max 6V). And one of them (yellow) is for the signal.

Oh ok I finally get it now! Thank you so much for your help so far! I'll go and give it a shot.If I encounter any more problems I'll probably make a post on this thread.

4pyros · Dec 8, 2011

misterT said:
You don't use servo "like any other motor". You use them like you use any standard servo. Normal servo works with 5 to 6 volts and the signal is 0.75 .. 2.25 ms pulses at 50Hz.

You can't connect a standard servo to a 24V PLC system directly. You need a 5V operating voltage and signal levels. You can dampen the signal with a resistor divider, but for the operating voltage you need a 5V regulator. You also need to check how easily you can generate a proper servo pulse-signal with your PLC.

And you don't have to modify a servo for continuous rotation. You can buy a continuous rotation servo: https://www.acroname.com/robotics/parts/R174-CONT-RO-SERVO.html

MisterT; Maybe you misunderstood me. The continuous rotation conversion would not only remove the stop on the arm but the electronics as well. Leaving you with a motor in a box of gears. At that point you can use it just like any other geared motor. No need for servo pluses. It will have only two wires going to the motor. I think you may have confused the OP now and sent them down a overly complicated route.
Andy

4pyros · Dec 8, 2011

Continuous rotation conversion;
https://www.tedpavlic.com/post_servo.php

mngeow · Dec 8, 2011

4pyros said:
MisterT; Maybe you misunderstood me. The continuous rotation conversion would not only remove the stop on the arm but the electronics as well. Leaving you with a motor in a box of gears. At that point you can use it just like any other geared motor. No need for servo pluses. It will have only two wires going to the motor. I think you may have confused the OP now and sent them down a overly complicated route.
Andy

Wouldn't that be the same as buying a geared motor then? They do sell those kinds of motors connected to a box of gears at the shop that I went to.

4pyros · Dec 8, 2011

mngeow said:
Wouldn't that be the same as buying a geared motor then? They do sell those kinds of motors connected to a box of gears at the shop that I went to.

Yes it is the same as buying a geared motor, but it is easyer to find and cheeper and smaller.
If you want the motor to stop and start at the same place all the time then I would use a servo setup, but you never said that.
Andy

mngeow · Dec 8, 2011

4pyros said:
Yes it is the same as buying a geared motor, but it is easyer to find and cheeper and smaller.
If you want the motor to stop and start at the same place all the time then I would use a servo setup, but you never said that.
Andy

Oh ok. But if I just want it to spin as long as there is current going into it ? Also , those a geared motor have higher torque than a servo motor ? Or is it the same ?

misterT · Dec 8, 2011

4pyros said:
MisterT; Maybe you misunderstood me. The continuous rotation conversion would not only remove the stop on the arm but the electronics as well. Leaving you with a motor in a box of gears. At that point you can use it just like any other geared motor. No need for servo pluses. It will have only two wires going to the motor. I think you may have confused the OP now and sent them down a overly complicated route.
Andy

All the conversions I've seen still use the original electronics and feedback system of the servo. That way you can control the speed of the motor with the standard servo signal. I wouldn't call ripping out the electronics "a conversion".

4pyros · Dec 8, 2011

If you remove the electronics and the stop from a servo motor it will become a geared motor, just like any other geared motor. It will spin slowly with lots of torque.
Andy

Any Stronger DC motors than 9v?

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