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Topic: How to attach a potentiometer to a servo motor shaft (Read 2321 times) previous topic - next topic

birddseedd

Why does it matter to a servo whether the command is relayed over a remote control system?

Unfortunately OP hasn't provided info on the actual servo in use, nor on the actual application, and only little information on why he would want to do this.
Automating the control valve of a hydraulic driven lawn mower.

Have not picked out a serval yet, trying to find out what I need to look for in a servo. Which I believe is going to be a Servo where the motor is powered on a different wire then the power for the internal potentiometer. That way when power is lost in the motor the potentiometer still works

raschemmel

#16
Jan 11, 2019, 07:00 pm Last Edit: Jan 11, 2019, 07:14 pm by raschemmel
Quote
Why does it matter to a servo whether the command is relayed over a remote control system?
Reread the previous post. Nobody said anything about remote control.
The wording used was "Radio Control"
If you have never used radio control then perhaps you should Google "Radio control servo"

If you are an experienced radio control hobbyist then you already know that the arduino uses
the Servo Library to talk to RC servos and also that RC servos are a specific form factor
that uses RC servo "Arms" that plug onto the servo shaft. If, however the servo is NOT
RADIO CONTROLLED (at this point it is irrelevant that radio control is in fact a form of remote control since the discussion is about form factor and programming) then the term "servo
motor" means something completely different, which I might add, your typical RC hobbyist
would have no experience with , since a typical industrial servo motor costs hundreds if
not thousands of dollars, especially if equipped with absolute encoders. Even the ones
with incremental encoders are expensive.

RC SERVO

AC BRUSHLESS (NON-RC) SERVO

So, in conclusion, the difference between "RC" (which stands for RADIO Controlled, NOT REMOTE controlled) and "NON-RC" is the difference between $16 USD and $622 USD.

So yeah, it does make a difference. It's not about whether it is REMOTE controlled or
NOT REMOTE controlled, it is about WHAT KIND of SERVO we are talking about.
If we were talking about RC servos, (which we are not) then we would ALSO be talking about the SERVO library which , (as already pointed out) takes a position argument in the command so you know WHERE (what position) you are commanding it to .
If , on the other hand we are talking about industrial servos, then knowing WHERE the shaft is requires a whole other approach, hence the OP's request for a way to couple the motor shaft with the pot shaft


So if you have this:

INDUSTRIAL AC SERVO MOTOR

you can couple it to this:

POTENTIOMETER


using this:
SHAFT COUPLER

There is of course the caveat that you must write you software to NOT allow the motor
to attempt to drive the pot PAST the END-STOP.

And just for the record, we have not yet discussed AC vs DC regarding servo motor type.

It is unknown at this time whether an adaptor will be necessary since the pot shaft diameter and the motor shaft diameter remain unknown.

Quote
hat just doesn't make much sense as you always know where a servo is: at the position you tell it to go  
Clearly this is a reference to an RC servo since nothing has been said about absolute encoders or incremental encoders and the OP's first post is clearly a statement of intent to build a closed loop system which he obviously wouldn't need to do if he had an absolute or incremental encoder, so no
he doesn't yet know where the servo is because he doesn't even know what kind of servo he is going to use, let alone how he is going to get feedback. (although he has a theory about that)
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birddseedd

Reread the previous post. Nobody said anything about remote control.
The wording used was "Radio Control"
If you have never used radio control then perhaps you should Google "Radio control servo"

If you are an experienced radio control hobbyist then you already know that the arduino uses
the Servo Library to talk to RC servos and also that RC servos are a specific form factor
that uses RC servo "Arms" that plug onto the servo shaft. If, however the servo is NOT
RADIO CONTROLLED (at this point it is irrelevant that radio control is in fact a form of remote control since the discussion is about form factor and programming) then the term "servo
motor" means something completely different, which I might add, your typical RC hobbyist
would have no experience with , since a typical industrial servo motor costs hundreds if
not thousands of dollars, especially if equipped with absolute encoders. Even the ones
with incremental encoders are expensive.

RC SERVO

AC BRUSHLESS (NON-RC) SERVO

So, in conclusion, the difference between "RC" (which stands for RADIO Controlled, NOT REMOTE controlled) and "NON-RC" is the difference between $16 USD and $622 USD.

So yeah, it does make a difference. It's not about whether it is REMOTE controlled or
NOT REMOTE controlled, it is about WHAT KIND of SERVO we are talking about.
If we were talking about RC servos, (which we are not) then we would ALSO be talking about the SERVO library which , (as already pointed out) takes a position argument in the command so you know WHERE (what position) you are commanding it to .
If , on the other hand we are talking about industrial servos, then knowing WHERE the shaft is requires a whole other approach, hence the OP's request for a way to couple the motor shaft with the pot shaft


So if you have this:

INDUSTRIAL AC SERVO MOTOR

you can couple it to this:

POTENTIOMETER


using this:
SHAFT COUPLER

There is of course the caveat that you must write you software to NOT allow the motor
to attempt to drive the pot PAST the END-STOP.

And just for the record, we have not yet discussed AC vs DC regarding servo motor type.

It is unknown at this time whether an adaptor will be necessary since the pot shaft diameter and the motor shaft diameter remain unknown.
Must be dc. 12v

In this project I can probably get away with less than one revolution in order to open and close the valve. But for the sake of knoledge i am hoping to find one with an internal encoder that is independantly powered so i can turn off the motor but still get a position reading.

raschemmel

Quote
Must be dc. 12v
That covers everything from 1 cm to who knows how large.
Can you narrow it down by adding the current rating ? (or motor size in mm ?)

What about this ? (you also haven't mentioned speed criteria (degrees per second etc)
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

birddseedd

That covers everything from 1 cm to who knows how large.
Can you narrow it down by adding the current rating ? (or motor size in mm ?)

What about this ? (you also haven't mentioned speed criteria (degrees per second etc)
Fogive me for being a noob. Im not fully sure exactly how to figure that out.

Here is the application.

Im automating a lawn mower. There are handle bars that pivot at the bottom. Partway uo their attached to a rod. This gives lonear motion. The end of the rod attaches to the hydro controls. I havent measured the throw distance, but somewhere around an inch at the connecting rod. The valve itself takes virtually no effort but there is a shock absorber. It may take a bit of strength to overcome the shock absorber. Im not sure how to measure it. For testing i can use my old mower without shock absorbers on.

I will need to convert the motion from the servo to linear. Putting an arm on it would work. But threat still take quite a bit of strength from the motor. The longer the lever the more torque is needed. Im just not sure how to measure it.

Rotations per minute probably depends. The higher up on the handle bars the longer the throw. The less Needed toque and slightly needed rpms per minute. But in general. Slower rotation higher torque iss needed.

I can take some pics and measurmnts when i get home. Just let me know what you need to see

Thanks

wvmarle

I will need to convert the motion from the servo to linear. Putting an arm on it would work.
Consider a linear actuator in that case, may be the better tool for the job. There are linear actuators with location feedback. Some can even be addressed in a manner similar to servos.

To measure the force needed attach a spring scale and start pulling, see how much force you have to apply to get it moving.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

birddseedd

Consider a linear actuator in that case, may be the better tool for the job. There are linear actuators with location feedback. Some can even be addressed in a manner similar to servos.

To measure the force needed attach a spring scale and start pulling, see how much force you have to apply to get it moving.
The issue with a linear actuator is that you cannot move them manually.i would not be able to use the handle bars. I woukd have to use joysticks to control the machine in a record mode. Which would give me less control over the machine.

birddseedd

Side question. Will an arduino actually hold this much information?

raschemmel

The motor size is related to the required torque, but not directly related to the size of the shaft it is driving because shaft couplers allow two different size shafts to be coupled, but they should be roughly
the same size. the motor I linked has an RPM of 100
MOTOR SPECS

Obviously , there is no way for us to know what size motor you need since you haven't posted a drawing
of your design and you can't tell us.
By the sound of it a geared motor is what you need. The question is how big.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

outsider

How much torque required to turn the valve? How many degrees from full open to closed? Have you thought about proportional flow hydraulic solenoid valves?

birddseedd

How much torque required to turn the valve? How many degrees from full open to closed? Have you thought about proportional flow hydraulic solenoid valves?
The valves are built in mechanical.
The other queations i just havent had a chance to figure out. Im juat now starting to get things together

raschemmel

To a certain extent, some of the information can be obtain by simple manual testing.
Example, you have a valve that has a shaft. You clamp a pair of vise grips on the shaft and open and
close the valve by hand. Then you remove the visegrips from the valve and clamp on the motor shaft and turn on the motor and tell it to turn (slowly) one way or the other , then you try to stop that motor from turning by holding onto the vise grips and mentally compare the force needed to turn the valve with the force needed to stop the motor.

Additionally there are other more accurate ways to measure the torque, like attaching a pully to the shaft
and having the motor lift a weight, (like a bucket you add or remove water from and then weigh the bucket. ) The converse of this is attach a pulley  to the shaft of the valve and measure the weight of the amount of water needed to open and close the valve and then see if the motor can lift that amount of water (or sand, or rocks, or diamonds, or coins etc)
At the end of the day, you don't need to know the torque spec in Nm. All you need to do is find a motor that is capable of performing the required task and then look at the spec sheet for that motor and whatever it is , it exceeds the torque spec for you task.

Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

birddseedd

To a certain extent, some of the information can be obtain by simple manual testing.
Example, you have a valve that has a shaft. You clamp a pair of vise grips on the shaft and open and
close the valve by hand. Then you remove the visegrips from the valve and clamp on the motor shaft and turn on the motor and tell it to turn (slowly) one way or the other , then you try to stop that motor from turning by holding onto the vise grips and mentally compare the force needed to turn the valve with the force needed to stop the motor.

Additionally there are other more accurate ways to measure the torque, like attaching a pully to the shaft
and having the motor lift a weight, (like a bucket you add or remove water from and then weigh the bucket. ) The converse of this is attach a pulley  to the shaft of the valve and measure the weight of the amount of water needed to open and close the valve and then see if the motor can lift that amount of water (or sand, or rocks, or diamonds, or coins etc)
At the end of the day, you don't need to know the torque spec in Nm. All you need to do is find a motor that is capable of performing the required task and then look at the spec sheet for that motor and whatever it is , it exceeds the torque spec for you task.


Fish scale?

couka

birddseedd, when will you stop opening threads in the forum before you have figured out what you want?

You want to control a valve both by hand and by a motor, right?

You didn't even use the word "valve" before your FIFTH post and another TEN answers from users that spent their time trying to help you.
youtube.com/DieBastler1234
Don't send me technical questions via PM. They will be deleted unanswered.

birddseedd

birddseedd, when will you stop opening threads in the forum before you have figured out what you want?

You want to control a valve both by hand and by a motor, right?

You didn't even use the word "valve" before your FIFTH post and another TEN answers from users that spent their time trying to help you.
Thats because im not controlling the valve itaelf but the handle bars their attached to.


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