# shaft rotation detection

#### Riv007

Joined Aug 1, 2023
4
Hi, I am trying to understand what sensor I would need to use if I have a plate that is mounted around a shaft where the shaft turns independent of the plate. There is one motor that will rotate the shaft in either direction and another motor that will rotate the plate. When the shaft rotates I need to be able to sense and know the direction and counter that direction with the plate motor to keep the plate in a stationary location.

The plate will be driven by a stepper motor and the only way to secure the stepper motor to allow it to rotate the plate independently is to clamp it to the shaft. So when the shaft motor turns the plate motor will rotate by default but I want to have the plate motor counteract the shaft rotation.

I hope that makes sense and really appreciate any insights you have.

Thank you
Terry

#### Pyrex

Joined Feb 16, 2022
214
Hi,
any DC motor with permanent magnets can be used as a sensor. It will generate DC voltage proportional to RPM. Voltage polarity is positive or negative if rotate CW or CCW

Joined Jul 18, 2013
28,059
Seems a few confusing points, do you have a DWG or something to be more explicit?

#### crutschow

Joined Mar 14, 2008
33,363
When the shaft rotates I need to be able to sense and know the direction and counter that direction with the plate motor to keep the plate in a stationary location.
The plate will have to rotate some so you can detect the direction of rotation, so how much can it rotate for that detection?

Joined Jul 18, 2013
28,059
Why two mechanisms? If the object is to:
" When the shaft rotates I need to be able to sense and know the direction and counter that direction with the plate motor to keep the plate in a stationary location."
Single axis positioning is done all the time?

#### Riv007

Joined Aug 1, 2023
4
The plate will have to rotate some so you can detect the direction of rotation, so how much can it rotate for that detection?
hi I hope this rough diagram helps.

Moderator edit: Photo added to post.

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#### djsfantasi

Joined Apr 11, 2010
9,131
Still don’t understand what you’re trying to do!

Why do you need to rotate the shaft AND keep the positioning fixed? I can’t envision one happening with the other. To me, it appears that a fixed axle is what your trying to create. Which can be done with a pipe or rod without any motors or motion.

#### Riv007

Joined Aug 1, 2023
4
hi I hope this rough diagram helps.
Still don’t understand what you’re trying to do!

Why do you need to rotate the shaft AND keep the positioning fixed? I can’t envision one happening with the other. To me, it appears that a fixed axle is what your trying to create. Which can be done with a pipe or rod without any motors or motion.
sorry For not explaining very well. In my application the shaft is 20 ft in the air. The shaft only rotates 180 degrees in either direction and does not continuously rotate in one direction. I need to mount a sensor at a point where the shaft is and no way to support the sensor so I want to have it in a plate that will rotate around the shaft using M1 to turn it. M1 has to be fixed to the shaft so it can turn the plate. When the shaft turns 30 degrees I need M1 to counteract that 30 degrees to keep the sensor in the starting position. Then if/when the shaft turns 15 degrees the other way M1 will again counter act it.

M1 can also be adjusted to move the sensor via an input independent of the shaft. So my thought is if I know the shaft rotation direction and speed I can send a signal to M1 to counter it.

I just don’t know how on a rotating plate I can measure shaft rotation when the sensor is not on a known fixed spot.

#### LowQCab

Joined Nov 6, 2012
3,589
You are here because You don't have enough experience with mechanical devices.

Sensors come after the working principles and materials to be used are worked-out.

The device You are proposing may not reliably perform the functions that You want.

Start by stating exactly what it is that You expect the device to do,
and an accurate overall description of everything surrounding the device,
that may be involved with producing the functionality that You want.

Is this an Antenna-Mast, or an automated Garden-Sprinkler, or what ???????

The more information that You can provide, the more appropriate the suggestions can be.
.
.
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#### Riv007

Joined Aug 1, 2023
4
You are here because You don't have enough experience with mechanical devices.

Sensors come after the working principles and materials to be used are worked-out.

The device You are proposing may not reliably perform the functions that You want.

Start by stating exactly what it is that You expect the device to do,
and an accurate overall description of everything surrounding the device,
that may be involved with producing the functionality that You want.

Is this an Antenna-Mast, or an automated Garden-Sprinkler, or what ???????

The more information that You can provide, the more appropriate the suggestions can be.
.
.
.
Thanks for the feedback, but not in a position to explain specifics on the product.

#### MrChips

Joined Oct 2, 2009
29,855
Thanks for the feedback, but not in a position to explain specifics on the product.
Sorry to say, but that is a huge stumbling block.

Too often we get requests for a solution to a little problem that the requester is stuck on only to eventually discover that the little problem was totally avoidable when a better solution was offered to solve the bigger problem.

If you are not in a position to disclose the big picture then this is not the place to discuss your problem.
I would suggest that you hire an engineering consultant who would be bound by a NDA.

#### Sensacell

Joined Jun 19, 2012
3,330
I don't quite understand the mechanical portion of your system, but conceptually, something as simple as a potentiometer could provide position feedback.
A servo amplifier and analog control system could be used to move the motor to keep the parts aligned.

#### en_djinn

Joined Jul 29, 2023
49
Why not just mount a tiltable spinning wheel to the side of the plate with accelerometer data as the control input from the plate?

Edit: may not even need control input. Gyroscopes will automatically orient to conserve angular momentum.

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#### GetDeviceInfo

Joined Jun 7, 2009
2,180
The bracket, must it hold a specific position, or will it’s position need to be variable. From what I understand, you want it to hold some position, regardless of shaft movement. If so, the shaft movement is not important, rather the bracket position in relation to some fixed (or variable) reference, that will provide the feedback.
How’s do you power M1?