Rotation angle measurement of pedal with ball and socket joint

[Mousa saleh]

TL;DR Summary

Hi all,

I have a pedal with a ball and socket joint in its center.
the pedal is allowed to rotate in 3D.
I need to figure a way to measure the three angle rotations.

please help!

the device that I have is the same as the mirror of this truck.

 

[berkeman]

Welcome to PhysicsForums.

What precision do you need in this measurement? Can you just mark graduations on the ball, and look to see what graduations are uncovered?

Also, can you add other structure to this type of joint? For example, if you run 3 rods from 3 of the corners of the pedal to a spot on the brace, and allow the 3 rods to pass through 3 rings there, then graduations on the 3 rods where they pass through the 3 rings will give you the angular position of the pedal.

 

[Mousa saleh]

Welcome to PhysicsForums.

What precision do you need in this measurement? Can you just mark graduations on the ball, and look to see what graduations are uncovered?

Also, can you add other structure to this type of joint? For example, if you run 3 rods from 3 of the corners of the pedal to a spot on the brace, and allow the 3 rods to pass through 3 rings there, then graduations on the 3 rods where they pass through the 3 rings will give you the position of the pedal.

Hi, Berkeman,

I need a high precision for the angles, maximum 0.25 degree, so I think graduation won't help.
If you have a link for such a device with the three rods and three rings please provide it to me, it might help.

Thanks,

 

[Baluncore]

What is the pedal used for? Does it control a vehicle?
What is the environment, inside, outside, clean or wet?
Is the pedal always operated by a person's foot?

Over what range do the angles vary?
Can you define the angles needed?
1. Left-right = Azimuth.
2. Forward-backward = Elevation.
3. Rotation of plate on Az-El surface.

 

[Mousa saleh]

What is the pedal used for? Does it control a vehicle?
What is the environment, inside, outside, clean or wet?
Is the pedal always operated by a person's foot?

Over what range do the angles vary?
Can you define the angles needed?
1. Left-right = Azimuth.
2. Forward-backward = Elevation.
3. Rotation of plate on Az-El surface.

Hi Baluncore,
The Pedal is used to be attached to a sedated cat foot.
the experiment will be inside and clean.
the angles will vary over a maximum +-60 degrees.
I need to find the angle of Az-El surface along with the rotation around the the brace axis.

Thanks,

 

[berkeman]

If you have a link for such a device with the three rods and three rings please provide it to me, it might help.

The best I can do is show a simple 2-D example with 2 rods attached to an object that can move in a plane. The rods are fixed to the object (with swivel joints) and pass through micrometers (that can swivel) located along 2 orthogonal edges of the plane.

https://electronics.stackexchange.c...osition-of-an-object-constrained-to-x-y-plane

Also paging @Ranger Mike since he works a lot with mechanical measurements.

 

[Mousa saleh]

What is the pedal used for? Does it control a vehicle?
What is the environment, inside, outside, clean or wet?
Is the pedal always operated by a person's foot?

Over what range do the angles vary?
Can you define the angles needed?
1. Left-right = Azimuth.
2. Forward-backward = Elevation.
3. Rotation of plate on Az-El surface.

It might be ok to measure the angle of plate on Az-El surface only and neglecting the third angle.
Thanks,

 

[Tom.G]

For 2 degrees of freedom, perhaps the simplest and least expensive is hinted at by the example you gave, the truck mirror!

Glue or otherwise attach a small mirror then shine a Laser beam on it. The movement of the reflection to a wall or screen at a measured distance gives enough information to find the angles.

Here is a link that lists some suppliers:
https://www.rp-photonics.com/bg/buy_helium_neon_lasers.html

When I bought a low-cost one several decades ago, it cost USD $150. Inflation since then would put current starting price around USD $800.

Or you could just use a slide projector for a light source.

Cheers,
Tom

 

[Ranger Mike]

being involved in dimensional measurement since1980, i have seen this before. You are asking for what the manufacturers of coordinate measurement machines (CMM) have sought since 1959. Instead of a gas pedal pivot ball orientation, the makers of the CMM seek the XY and Z location of a ball stylus in the cartisean coordinate system. This is done with mechanical structures that move in xyz axis and have digital scales and read heads.
All measurement is calculated from the center point of this ball stylus probe.
Other times they use photo optic grids located in an xyz location and use a laser projector(emitter) fixed , in your case, to the pedal and monitor the laser beam location on the xyz location. In some cases they may attach a second laser emmiter to the pedal at 90 degrees and even a 3rd laser emitter at another 90 degrees to " map" the xyz movement.
look up CMM

 

[Mousa saleh]

For 2 degrees of freedom, perhaps the simplest and least expensive is hinted at by the example you gave, the truck mirror!

Glue or otherwise attach a small mirror then shine a Laser beam on it. The movement of the reflection to a wall or screen at a measured distance gives enough information to find the angles.

Here is a link that lists some suppliers:
https://www.rp-photonics.com/bg/buy_helium_neon_lasers.html

When I bought a low-cost one several decades ago, it cost USD $150. Inflation since then would put current starting price around USD $800.

Or you could just use a slide projector for a light source.

Cheers,
Tom

Thanks Tom,
But the pedal will be attached to a foot to measure its rotation, so using a mirror won't help,

cheers,
Mousa

 

[Mousa saleh]

being involved in dimensional measurement since1980, i have seen this before. You are asking for what the manufacturers of coordinate measurement machines (CMM) have sought since 1959. Instead of a gas pedal pivot ball orientation, the makers of the CMM seek the XY and Z location of a ball stylus in the cartisean coordinate system. This is done with mechanical structures that move in xyz axis and have digital scales and read heads.
All measurement is calculated from the center point of this ball stylus probe.
Other times they use photo optic grids located in an xyz location and use a laser projector(emitter) fixed , in your case, to the pedal and monitor the laser beam location on the xyz location. In some cases they may attach a second laser emmiter to the pedal at 90 degrees and even a 3rd laser emitter at another 90 degrees to " map" the xyz movement.
look up CMMView attachment 275361

Thanks Mike,

The pedal will be attached to a small animal foot ,so I am afraid that this huge device will hinder the foot rotation.

Is there small CMM devices that can fit my application?

Thanks,

 

[Ranger Mike]

anything is possible ifin you got the $$$$$$$

https://www.creaform3d.com/en?aw_ca...8vJXxwmxDt-QFSgj3vOUpYxan0z1xFSBoCigwQAvD_BwE

 

[Mousa saleh]

anything is possible ifin you got the $$$$$$$

https://www.creaform3d.com/en?aw_ca...8vJXxwmxDt-QFSgj3vOUpYxan0z1xFSBoCigwQAvD_BwE

My budget is somehow good, so please help me with one!

 

[Mousa saleh]

My budget is somehow good, so please help me with one!

Thank you very much,
I didn't see the link

 

[Ranger Mike]

call these guys

they already have 3 axis encoders and all you need do is mount the gas pedal to the end ofthe probe in place of the screw in ball stylus.

https://apimetrology.com/vprobe-tra...7by4tCzphjtMyZowZqstDGFTG-Ry9QcxoCh6sQAvD_BwE

 

[Ranger Mike]

had to go get beer from local drive thru.

https://tech.faro.com/faroarm/?C_Le...MrL6oYC8gJhdLyKhz25eoxgp9sCGVHThoC9OQQAvD_BwE

what this is for you new people is a manual CMM arm. The CMM is operated by a human being ( not cnc controlled) so you have a manual CMM. The cmm operator places the ball stylus on the part to be measured. He pushes a button when the ball is resting on the intended feature and a data point is recorded. The arm is constructed with 3 rotary encoders so the XYZ location in space is known ( once calibrated).
What you are doing is wanting to track the ball stylus center point realative to the xyz axis. Instead of the cmm operator moving the ball stylus probe to touch the part, you are anchoring the cmm arm and permitting the probe to articulate via the gas pedal. May take some fixturing but the basics are here.

 

[Baluncore]

This is an interesting angular magnetic encoder, 360 degree, high resolution.
https://docs.broadcom.com/doc/AV02-2792EN

 

[berkeman]

This is an interesting angular magnetic encoder, 360 degree, high resolution.
https://docs.broadcom.com/doc/AV02-2792EN

Interesting IC. The +/- 2 degree INL isn't too bad either.

 

[Lnewqban]

...The pedal will be attached to a small animal foot ,so I am afraid that this huge device will hinder the foot rotation.
...

Should the device have a self-centered position, offering some resistance to the movement of the foot of the small animal?
Will the animal be stepping on the pedal, like when walking?

 

[Mousa saleh]

Should the device have a self-centered position, offering some resistance to the movement of the foot of the small animal?
Will the animal be stepping on the pedal, like when walking?

the animal will be sedated and its will be strapped to the pedal as in following picture.

So, instead of the pivoting armature, the pedal will have a ball and socket joint with little resistance to rotation.

 

[berkeman]

Um, may I ask what the purpose of this procedure/experiment is?

 

[Mousa saleh]

The purpose is to stimulate the nerve of the cat and see how the foot will rotate.
giving different stimulation forms will give different rotation movements in 3D.

I do not want heavy device to be attached to the pedal because that will hinder the movement of the foot.

 

[Mousa saleh]

This is an interesting angular magnetic encoder, 360 degree, high resolution.
https://docs.broadcom.com/doc/AV02-2792EN

Does it measure 3D angle rotations??

 

[berkeman]

The purpose is to stimulate the nerve of the cat and see how the foot will rotate.
giving different stimulation forms will give different rotation movements in 3D.

Are you the Principal Investigator (PI) on this project, or do you and others report to the PI?

I don't think you are in the US, but do you have similar regulations governing animal research compared to the US? There are federal regulations here in terms of protocols and accountability for conducting animal research that the PI is ultimately responsible for:

https://www.nature.com/articles/s41684-018-0089-5

https://www.aalas.org/iacuc

(Full disclosure -- my ex-wife worked in animal research for many years, and always complied with these federal regulations and AALAS standards)

I do not want heavy device to be attached to the pedal because that will hinder the movement of the foot.

Why do you want to constrain the cat's foot at all? Why not just put a light-weight position-sensing bootie on the animal for the experiment? You can probably adapt an input device like the gloves, etc., that are used for input devices in immersive AI games...

 

[Baluncore]

Does it measure 3D angle rotations??

No. Each unit measures only one axis. For azimuth and elevation you will need two, with a third if you also require foot pad rotation.

The problem with measuring an angle is that there needs to be a reference. You are using a knee clamp as the reference, with the table closing the reference loop.
You could place reflective dots on the leg and foot, then use three fixed cameras to gather the required 3D orientation information without any constraint, though it might not be sufficiently accurate in this case.

I don't believe that a ball joint need be present, you are simply using the ball as an example of 3 degrees of angular freedom.

It is very difficult to measure the orientation of a ball without establishing more linkages across the joint. The mass of the linkage and transducer system can increases until the mechanism becomes too heavy a load at the speed of the cat's response. We must keep the weight down, hence my interest in the magnetic rotary sensor.

The foot attachment mechanism establishes the degree of freedom. As an example, a ball joint with two degrees of freedom would be equivalent to a gimbal mount. The angle encoders need to be linked to the individual axis bearings of the gimbal. But that does not allow for the 3D linear translation of the ball centre.

 

[Mousa saleh]

Are you the Principal Investigator (PI) on this project, or do you and others report to the PI?

No, I am not the PI, but we have done all the regulations required.

Why do you want to constrain the cat's foot at all? Why not just put a light-weight position-sensing bootie

The bootie idea is great, do you Know how to get one??

 

[Mousa saleh]

I have a camera that

No. Each unit measures only one axis. For azimuth and elevation you will need two, with a third if you also require foot pad rotation.

The problem with measuring an angle is that there needs to be a reference. You are using a knee clamp as the reference, with the table closing the reference loop.
You could place reflective dots on the leg and foot, then use three fixed cameras to gather the required 3D orientation information without any constraint, though it might not be sufficiently accurate in this case.

I don't believe that a ball joint need be present, you are simply using the ball as an example of 3 degrees of angular freedom.

It is very difficult to measure the orientation of a ball without establishing more linkages across the joint. The mass of the linkage and transducer system can increases until the mechanism becomes too heavy a load at the speed of the cat's response. We must keep the weight down, hence my interest in the magnetic rotary sensor.

The foot attachment mechanism establishes the degree of freedom. As an example, a ball joint with two degrees of freedom would be equivalent to a gimbal mount. The angle encoders need to be linked to the individual axis bearings of the gimbal. But that does not allow for the 3D linear translation of the ball centre.

I have a camera that can calculate the x,y and z points of each marker,
I have suggested to my advisor using three of these markers attached to the back of the pedal.

I think I can calculate the now rotated plane using these three points.

The problem is that I need to calculate the angles in real time, so I can modify the nerve stimulation to get the desired position.

 

[Lnewqban]

the animal will be sedated and its will be strapped to the pedal as in following picture.
View attachment 275426
So, instead of the pivoting armature, the pedal will have a ball and socket joint with little resistance to rotation.

Thank you for posting that picture.
If I understand correctly, the measuring device should have its axis of rotation more or less acurately aligned with the joint of the cat's foot.

Perhaps something light and soft as a gimbal and two potenciometers, just like used in radio control transmitters, or even and old style ball computer mouse, could be connected to a computer for registering continuos 2-D movement.

Please, see:
https://www.thefscreations.info/2019/12/making-professional-rc-transmitter-with.html

 

[Mousa saleh]

Thank you for posting that picture.
If I understand correctly, the measuring device should have its axis of rotation more or less acurately aligned with the joint of the cat's foot.

Perhaps something light and soft as a gimbal and two potenciometers, just like used in radio control transmitters, or even and old style ball computer mouse, could be connected to a computer for registering continuos 2-D movement.

Please, see:
https://www.thefscreations.info/2019/12/making-professional-rc-transmitter-with.html
View attachment 275455

I hope I can find such device, I can not build one my self.
can you provide me with the name of the device in the picture.

Thanks,

 

[hutchphd]

Three ideas:

Bounce a laser off a plastic mirror on the subject foot bottom. Video the reflected spot on a calibrated screen with timestamp.

Use joystick potentiometer (try https://www.digikey.com/en/products/detail/adafruit-industries-llc/3102/6152821?utm_adgroup=Navigation%20Switches%2C%20Joystick&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Switches_NEW&utm_term=&utm_content=Navigation%20Switches%2C%20Joystick&gclid=CjwKCAiArbv_BRA8EiwAYGs23CgXVUYH7JC0ganxecYkCdGHS8jOXWCOepLtHJGwoqoq-3xNF4VRNhoCR4AQAvD_BwE) and read it using A to D dongle

Use flight controller for radio controlled airplane/Helicopter which has MMS gyro. Lightweight an cheap.

 

[Lnewqban]

I hope I can find such device, I can not build one my self.
can you provide me with the name of the device in the picture.

Thanks,

https://hobbyking.com/en_us/turnigy...VPvzjBx1lWwI8EAQYASABEgLaoPD_BwE&gclsrc=aw.ds

 

[Mousa saleh]

Hello guys,

I found three inclinometer sensors with the resolution and accuracy required.
the only problem is the weight, which I think can be solved if using the chip without the housing,

I wonder if you have come across these sensors so I can get your feedback.

https://www.gsglobalresources.com/products/control...

Thanks,

 

[Tom.G]

3-axis accelerometers are used in a range of things from aircraft navigation equipment to cell phones.

Sensitivity is often shown as resolution in mG where your ±0.25° translates to 4.4mG, where G is the acceleration of Gravity at the Earths surface.

Here is a link to one source of low cost ones. The drawback is they are just the packaged sensor itself, you have to supply all the electronics to use them. Prices range from USD $1.32 to $178.55 at this distributor, there are others.
https://www.mouser.com/Sensors/Motion-Position-Sensors/Accelerometers/_/N-axgd7?P=1ynyo5tZ1y9irx0Z1ykfg8jZ1yu25cjZ1y9k2dtZ1y9gw93Z1y96oa1Z1yoi99nZ1y8pyzaZ1yyfbu4Z1yoi9b7Z1yq2rrdZ1yq2rrbZ1yzuq36Z1yvt0viZ1yzv7ytZ1yyg66sZ1y9geabZ1yrhbd5Z1yzvsot

(above found with:
https://www.google.com/search?&q=tri+axis+accelerometer+sensor)

Cheers,
Tom