Arduino Forum

Using Arduino => General Electronics => Topic started by: birddseedd on Jan 11, 2019, 04:44 am

Title: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 04:44 am
I searched google but it was all about controlling a servo with a potentiometer. Thats not what i want to do. I want to have the servo motor turn the potentiometer so i can read the position of the servo motor. I know they often come with POs built in, but i will be turning the motor off and setting the position by hand. I looked at pics of them but i dont see how i would attach it to a shaft.

Thanks
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 05:02 am
Quote
I want to have the servo motor turn the potentiometer so i can read the position of the servo motor.

I know they often come with POs built in, but i will be turning the motor off and setting the position by hand.

 I looked at pics of them but i dont see how i would attach them to a shaft.  
"they" ?
"them" ?



Get a shaft coupler. Done. If you have heard of motors, (which, BTW, have SHAFTS)
then you must have heard of shaft couplers, since that's what everyone uses with their motors.

What exactly is your electronics background ?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: Willpatel_Kendmirez on Jan 11, 2019, 05:13 am
Nice save on the edit of the rude, condescending post there raschemmel; I was responding but it's a pity I didn't grab a quote in time.

Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 05:17 am
I may need to pick out a Servo motor first. I found a couple of hours, they look simple enough to build. But all of the servo Motors on Amazon seem to be for little plastic robots. I need something big
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: Willpatel_Kendmirez on Jan 11, 2019, 05:23 am
But all of the servo Motors on Amazon seem to be for little plastic robots. I need something big
So just to clarify, you are talking of the ones that look more like steppers in those big nema style casings, not the normal Arduino world rc servo?

(fwiw, adafruit do have the latter with 4 wires (https://www.adafruit.com/product/1404), the extra one being a take-off from the internal pot to bring the position out.)



Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 05:32 am
So what's wrong with these (https://www.google.com/search?client=firefox-b-1&q=shaft+couplers) ?


Quote
I may need to pick out a Servo motor first. I found a couple of hours, they look simple enough to build. But all of the servo Motors on Amazon seem to be for little plastic robots. I need something big
I worked with the kind of servo motors you are talking about with wafer lifters and they are hella
expensive.

Servo motors (https://www.google.com/search?client=firefox-b-1&ei=nxw4XMHFMM28tgWA9YyYBA&q=servo+motors&oq=serv&gs_l=psy-ab.1.0.35i39j0i67l4j0i20i263j0i67j0i131l2j0.239995.241173..243419...0.0..0.154.575.0j4......0....1..gws-wiz.......0i71.ioHPRMfj_AU)


What are the specs for the motor in question ?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: Willpatel_Kendmirez on Jan 11, 2019, 05:41 am
I'll repeat it for your benefit ...
(how rude is that ? Am I not allowed to say that ?)

Well obviously even you had second thoughts about having said it, else you wouldn't have removed it.

Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 05:50 am


Quote
I may need to pick out a Servo motor first. I found a couple of hours, they look simple enough to build. But all of the servo Motors on Amazon seem to be for little plastic robots. I need something big  
Have you considered posting a description of you project with enough details for someone to pick out a servo motor or do want to do that yourself ?


Quote
I know they often come with POs built in
POs ?

What is that ?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 11, 2019, 02:48 pm
I want to have the servo motor turn the potentiometer so i can read the position of the servo motor.
That just doesn't make much sense as you always know where a servo is: at the position you tell it to go.

If it's not there, then there's a malfunction of the motor, or it's not strong enough. Either way that's a design error, and should never happen. Therefore having a pot to read back the position of a servo is unnecessary.

That, or your description of the problem is flawed.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: Willpatel_Kendmirez on Jan 11, 2019, 02:59 pm
.... you always know where a servo is: at the position you tell it to go.

If it's not there, then there's a malfunction of the motor, or it's not strong enough. Either way that's a design error, and should never happen. Therefore having a pot to read back the position of a servo is unnecessary.

That's very simplistic, and neglects the fact that it takes time for a commanded movement to happen, even when things are all nominal. The next step in a process might rely on this process completing, and only closed loop control (which is what this is) will tell you that.

And then, when things do go wrong, which is not necessarily a design or manufacturing flaw, but perhaps unusual untoward and unforeseen circumstances preventing completion of a commanded movement, it's imperative that the system as a whole, knows that. It would need to prevent that next step happening, or perhaps reverse the incomplete movement back to a checkpoint.

If what you say is correct, there would be no need for closed loop control and everything would work on open loop, dead-reckoning.



Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 03:05 pm
That just doesn't make much sense as you always know where a servo is: at the position you tell it to go.

If it's not there, then there's a malfunction of the motor, or it's not strong enough. Either way that's a design error, and should never happen. Therefore having a pot to read back the position of a servo is unnecessary.

That, or your description of the problem is flawed.
I will be turning the servo off to move it by hand
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 03:07 pm
The OPhas not specified Radio Control servo.
He simply stated "serbo motor".
If he means RC servo , it should be explicitly stated as such .
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 03:21 pm
The OPhas not specified Radio Control servo.
He simply stated "serbo motor".
If he means RC servo , it should be explicitly stated as such .
Not radio controlled
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 04:07 pm
Then the previous comment about knowing the position because the Servo command takes a position argument does not apply.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 11, 2019, 06:27 pm
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.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 06:30 pm
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
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 07:00 pm
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 (https://www.horizonhobby.com/category/radios/aircraft-radio-systems/aircraft-servos)

AC BRUSHLESS (NON-RC) SERVO (https://www.automationdirect.com/adc/shopping/catalog/motion_control/servo_systems/drives_-a-_motors_components/svl-210?gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwjGyQNQ3yWX5AKPONMeH3EmPxnKt7NJ94c7kupvYo__MFaWU_oWNLoaAtcTEALw_wcB)

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 (https://www.automationdirect.com/adc/shopping/catalog/motion_control/servo_systems/drives_-a-_motors_components/svm-210b?gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwhSB_FPoXIAY7PTwv_M2FOwt0tg-svy9YWwnPP5JTeMKj2qfHlAOksaAkd_EALw_wcB)

you can couple it to this:

POTENTIOMETER (https://www.mouser.com/ProductDetail/Honeywell/53C3100K?qs=VJkZAnU6DY2GVpH%2F0VKOBg%3D%3D&gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwgtROJe3DCYQzh1_DumoGb7Wx9UfRMHY7TJQ-8O8042qNDbEH0GlzYaAq3KEALw_wcB)


using this:
SHAFT COUPLER (https://www.google.com/search?source=hp&ei=Mtk4XKDhCcisswXXvJTYAw&q=shaft+couplers&oq=shaf&gs_l=psy-ab.1.0.35i39j0i67l7j0i131j0.1904.3972..6674...0.0..0.599.1680.0j2j1j5-2......0....1..gws-wiz.....0.RHeGzeNZ6Yg)

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)
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 07:10 pm
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 (https://www.horizonhobby.com/category/radios/aircraft-radio-systems/aircraft-servos)

AC BRUSHLESS (NON-RC) SERVO (https://www.automationdirect.com/adc/shopping/catalog/motion_control/servo_systems/drives_-a-_motors_components/svl-210?gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwjGyQNQ3yWX5AKPONMeH3EmPxnKt7NJ94c7kupvYo__MFaWU_oWNLoaAtcTEALw_wcB)

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 (https://www.automationdirect.com/adc/shopping/catalog/motion_control/servo_systems/drives_-a-_motors_components/svm-210b?gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwhSB_FPoXIAY7PTwv_M2FOwt0tg-svy9YWwnPP5JTeMKj2qfHlAOksaAkd_EALw_wcB)

you can couple it to this:

POTENTIOMETER (https://www.mouser.com/ProductDetail/Honeywell/53C3100K?qs=VJkZAnU6DY2GVpH%2F0VKOBg%3D%3D&gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwgtROJe3DCYQzh1_DumoGb7Wx9UfRMHY7TJQ-8O8042qNDbEH0GlzYaAq3KEALw_wcB)


using this:
SHAFT COUPLER (https://www.google.com/search?source=hp&ei=Mtk4XKDhCcisswXXvJTYAw&q=shaft+couplers&oq=shaf&gs_l=psy-ab.1.0.35i39j0i67l7j0i131j0.1904.3972..6674...0.0..0.599.1680.0j2j1j5-2......0....1..gws-wiz.....0.RHeGzeNZ6Yg)

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.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 07:28 pm
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 (https://www.amazon.com/Torque-Reduction-Encoder-Self-locking-Output/dp/B073S6DCRQ?ref_=fsclp_pl_dp_3) ? (you also haven't mentioned speed criteria (degrees per second etc)
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 08:17 pm
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 (https://www.amazon.com/Torque-Reduction-Encoder-Self-locking-Output/dp/B073S6DCRQ?ref_=fsclp_pl_dp_3) ? (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
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 11, 2019, 08:25 pm
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.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 08:33 pm
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.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 11, 2019, 08:33 pm
Side question. Will an arduino actually hold this much information?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 11, 2019, 09:29 pm
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 (https://www.amazon.com/dp/B01N990WOU?ref_=ams_ad_dp_ttl)

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.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: outsider on Jan 11, 2019, 11:48 pm
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?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 12, 2019, 12:23 am
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
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 12, 2019, 12:41 am
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.

Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 12, 2019, 12:43 am
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?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: couka on Jan 12, 2019, 12:59 am
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.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 12, 2019, 01:25 am
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.

Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 12, 2019, 01:43 am
I am inclined to request/demand a drawing but I  fear that probably doesn't exist either.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 12, 2019, 02:17 am
I am inclined to request/demand a drawing but I  fear that probably doesn't exist either.

I could just take pictures of it.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 12, 2019, 02:27 am
It' your dime.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 12, 2019, 06:15 am
I could just take pictures of it.
33 replies in I'd say it's about time you start doing those things. Or do you really have the feeling you're getting anywhere with this thread? I for one don't.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 13, 2019, 11:21 pm
33 replies in I'd say it's about time you start doing those things. Or do you really have the feeling you're getting anywhere with this thread? I for one don't.
I'm learning. that's the point. I've also been dealing with an emergency c section. But i do have a grasp on what type of servo will allow me to read position with it being powered down. Of course, now that i'm starting to put all this together, i'm starting to question everything. pro's and con's to everything
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 13, 2019, 11:25 pm
I am inclined to request/demand a drawing but I  fear that probably doesn't exist either.

(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50411500_2243980575877138_6262661637304483840_n.jpg?_nc_cat=103&_nc_ht=scontent-ort2-2.xx&oh=f93e851a509a07f4a3557203602f3ee7&oe=5CC46438)
(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50240829_2243980579210471_797512458351673344_n.jpg?_nc_cat=109&_nc_ht=scontent-ort2-2.xx&oh=cddfa03295f71ce881c99d943b889c12&oe=5CBFCE29)
(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50107959_2243980585877137_8677183193306103808_n.jpg?_nc_cat=102&_nc_ht=scontent-ort2-2.xx&oh=5bec504a621a5b0e6dfe63ee5a1bc020&oe=5CBEBE2E)
(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50177633_2243980629210466_7743526245970739200_n.jpg?_nc_cat=110&_nc_ht=scontent-ort2-2.xx&oh=cbb6964cfe452e6131c3b49b170566ed&oe=5CCBB080)
(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50272022_2243980642543798_2683264428580798464_n.jpg?_nc_cat=102&_nc_ht=scontent-ort2-2.xx&oh=8c636c72b75f197cd6a6d1a49dba3bec&oe=5CB7A14E)
(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50474539_2243980672543795_936017585915297792_n.jpg?_nc_cat=108&_nc_ht=scontent-ort2-2.xx&oh=4b7143c526f18974029cccf466743076&oe=5CCE16E4)
(https://scontent-ort2-2.xx.fbcdn.net/v/t1.0-9/50411500_2243980575877138_6262661637304483840_n.jpg?_nc_cat=103&_nc_ht=scontent-ort2-2.xx&oh=f93e851a509a07f4a3557203602f3ee7&oe=5CC46438)
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 13, 2019, 11:37 pm
so. if i build a bracket allowing me to attach at one of the two bolts, i measured 10 lbs of force to go forward 3.5 inches over about 4 seconds and 15 lbs backward about 2.5 inches over about 2 seconds.

so i need to figure out what strength servo i can use to obtain this. i can put a lever on the shaft to get the throw i need, but that means a stronger servo will be needed at the short end of a lever.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: raschemmel on Jan 13, 2019, 11:37 pm
I don't see that working witha motor.
That looks more like acuator application.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 12:09 am
I don't see that working witha motor.
That looks more like acuator application.
that would make some things a lot easier. but the problem that i run into is that you can not move an actuator manually. I need to be able to run the mower by hand while recording the positions, then i know the positions and times that need to be sent back to the motor. to use an actuator i would have to build controls with joysticks and run the machine that way. which can be done, just isn't a great way of doing it.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: outsider on Jan 14, 2019, 01:36 am
15 lbs of force on the handle that appears to be at least 16 inches from the pivot point? 20 pound feet of torque? Oh my, looks like a big gearmotor with an electromagnetic release clutch for manual operation.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 02:20 am
15 lbs of force on the handle that appears to be at least 16 inches from the pivot point? 20 pound feet of torque? Oh my, looks like a big gearmotor with an electromagnetic release clutch for manual operation.
how do i work with the draw weight i measured? how do i convert it to something that is repeatable to motor specs?
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 14, 2019, 04:28 am
That 20 foot-pound is your motor torque specification.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 04:33 am
That 20 foot-pound is your motor torque specification.
How do i calculate that. i apologize for asking. i just need to know how to do it so next time i do a project like this i won't have to ask.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: Willpatel_Kendmirez on Jan 14, 2019, 04:43 am
Quote
20 foot-pound
How do i calculate that.
It's the product of the force and the distance at which it acts from the pivot.

So 15lbs at 16" is 15 x 1.33' = 20



Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: Willpatel_Kendmirez on Jan 14, 2019, 04:45 am
I've also been dealing with an emergency c section.
Why was it important for the forum to know that?



Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 02:35 pm
It's the product of the force and the distance at which it acts from the pivot.

So 15lbs at 16" is 15 x 1.33' = 20




Im a bit confused by why the distance matters. The pivot in this case doess not effect the force needed. If i were to lengthen the handle bars to 100' and moved the damener and moter to the end if the 100', its still going to need the same 15, of force. But now the forumula would say 1500 ft lbs of force.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 14, 2019, 02:59 pm
It's the distance between the centre of the axle of the motor (the pivot point), and the point at where the force is needed (the point where your motor's arm connects to the thing you want to move).
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 03:13 pm
It's the distance between the centre of the axle of the motor (the pivot point), and the point at where the force is needed (the point where your motor's arm connects to the thing you want to move).
Ok. That makes more sense.

Ive been talking about the arm of the mower. Not the motor. That's why it didn't make any sense to me.

The motor wouldnt be placed at the center of that pivot in the pic. Although, if i did it would solve some linear motion issues. So maybe ill take a look at it and see if i can.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 14, 2019, 03:48 pm
You're mixing up things. To calculate the torque of your motor you need to measure the length of the arm the motor has to move from the centre of the motor's axle (that's your motor's pivot point) to where it's attached to whatever you want to apply the force to.

Have a look at these images (https://www.google.com/search?q=what+is+torque&source=lnms&tbm=isch). Should make it clear.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 03:52 pm
That part I believe I understand. Where I think I'm getting confused is that, correct me if I'm wrong, I'm not measuring "torque" I am measuring "pound Force".
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: couka on Jan 14, 2019, 04:02 pm
...and from pound-force and radius (=length of the arm) you can calculate the torque.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 04:13 pm
Ok. The more im reading i think that im measuring in lbs mass not pounds force. So i have to cinvert the mass to force before i can convert to torque.

I'm going to take a break and eat some breakfast
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: wvmarle on Jan 14, 2019, 04:27 pm
The normal way of measuring weight (what is often called "mass" though they're not the same thing) with a scale is by measuring force: the force at which the earth's gravity pulls at the object.

So attaching a spring scale to your handle and pulling it is basically the same thing.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 04:59 pm
The normal way of measuring weight (what is often called "mass" though they're not the same thing) with a scale is by measuring force: the force at which the earth's gravity pulls at the object.

So attaching a spring scale to your handle and pulling it is basically the same thing.
Ok. So i did measure pound force (lbf). I need to convert that to pound to pound torque (lbf.ft). And then adjust for the length of the lever from the pivot point.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 06:23 pm
I got a chance to go out and measure the control arm. It measures 12 inches.

If i attach the motor at the same point thst will illiminate issues converting it to linear motion. Although it means a bigger motor is needed.

15 lbf * 1' means 15 torque? That would mean just about 20 nm of torque?

If i mount the motor higger and just deal with the uneven motion i can cut that in half. Thats still a good size motor.
Title: Re: How to attach a potentiometer to a servo motor shaft
Post by: birddseedd on Jan 14, 2019, 06:42 pm
15 lbs of force on the handle that appears to be at least 16 inches from the pivot point? 20 pound feet of torque? Oh my, looks like a big gearmotor with an electromagnetic release clutch for manual operation.
So really this is another situation where I'm asking the wrong question. I don't need a motor that I can turn off and still get a reading from it, I need a motor where I can release the clutch, and still get a reading from it