Mechanism to hold a servo in place ?

Thread Starter

Externet

Joined Nov 29, 2005
2,236
Hi all. My turn to ask for suggestions.

In need to motorize a clamp adjustment. Cannot see one better way to do it, from dozens of possible ways. How would you do it ?

1698364422737.jpeg

it is a plain 5/16" hexagonal head screw worm. Attaching the driving socket could be by drilling both and putting a pin trough them. The 'socket' to be turned by a motor, forth or back, to move it not faster than 1cm/sec. With or without the socket extension shown.
The cork is just to hold it open for better picture visual.

The intention is to have a motor or gearmotor adjusting the position <------> of the worm screw along the length, from a wired remote location with just direction (polarity) switches.
 

k1ng 1337

Joined Sep 11, 2020
986
What object are you clamping and what is its diameter? You mentioned 1cm/sec but not how much force over area is needed.

My experience is those style clamps have a sweet spot. A bit loose and it slides, too tight and the screw fails. I've had several fail on me because I over tightened it to make up for the wear.
 

MisterBill2

Joined Jan 23, 2018
19,034
For holding the socket on the square driver there are square edged detent pins that install exactly like the removable ball detents. They are often used both for production and some master mechanics.
It seems that the "worm screw head" is not serving as a clamp tightener but rather as alternative to a "rack and pinion scheme. So it is for setting a position of something along the track/band.
Holding the socket to the screw head can easily be done with strong magnetism, the challenge will be in holding the motor from rotating. A "co-bot would work very well but it may be beyond the project budget. Another option is a flexible shaft in a flexible housing, which is a mature and available technology. A great deal depends on both the length of the move and the surrounding area clearance.
Is this a production system?? Or a maker project?? How many and how much human input is the concern.
 

Thread Starter

Externet

Joined Nov 29, 2005
2,236
Thanks.
Some kind of servomotor to be secured somehow to turn the worm. How/which am not sure/decided to prevent countertorque.
It is not for clamping, it is to run <-----> along the 'tape' or, to pull/push the 'tape' As a linear motion converter. :rolleyes: Yes, like a rack/pinion action. One single piece, not for production. That stainless hex is not magnetic.
 
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KeithWalker

Joined Jul 10, 2017
3,146
Thanks.
Some kind of servomotor to be secured somehow to turn the worm. How/which am not sure/decided to prevent countertorque.
It is not for clamping, it is to run <-----> along the 'tape' or, to pull/push the 'tape' As a linear motion converter. :rolleyes: Yes, like a rack/pinion action. One single piece, not for production. That stainless hex is not magnetic.
one way of connecting the drive shaft to a motor would be with worm and pinion gears. That would keep the motor away from interfering with the track and would give the torque needed to turn the shaft.
Will you be sensing the position of the "tape"?
 

k1ng 1337

Joined Sep 11, 2020
986
Thanks.
Some kind of servomotor to be secured somehow to turn the worm. How/which am not sure/decided.
It is not for clamping, it is to run <-----> along the 'tape' or, to pull/push the 'tape' As a linear motion converter. :rolleyes:
The parts in your photo form a rack and pinion. Why not mount the shaft to the servo like a traditional drill? Pinning each end is probably sufficient. I've never seen the coiled material used linearly, what are you building?

gears 31.jpg
 
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Thread Starter

Externet

Joined Nov 29, 2005
2,236
Thanks, gentlemen. The position is not to be sensed. Yes, linear use for the 'tape'
Tempted so far to order this, any other you can suggest, and how to counteract torque ?

1698414189413.png
 

Ya’akov

Joined Jan 27, 2019
9,237
It would help a lot to get an idea of the actual final application, and some idea of torque requirements. There are many options for liner motion and this cobbled rig might not be the best for your application.
 

LowQCab

Joined Nov 6, 2012
4,217
Most Worm-Drive-Clamps are made of Stainless-Steel.
Stainless-Steel tends to "gall" and stop "sliding" after multiple uses.
I think that your plan is doomed to failure from accelerated wear.

I would suggest using 2 Pulleys and braided Fishing-Leader-Wire,
it's readily available in ratings over ~100-pounds.
.
.
.
 

Ya’akov

Joined Jan 27, 2019
9,237
Most Worm-Drive-Clamps are made of Stainless-Steel.
Stainless-Steel tends to "gall" and stop "sliding" after multiple uses.
I think that your plan is doomed to failure from accelerated wear.

I would suggest using 2 Pulleys and braided Fishing-Leader-Wire,
it's readily available in ratings over ~100-pounds.
.
.
.
This is basically the same as the tuning indicator in old radios.

1698441121666.jpeg
The larger pulley was on the tuning capacitor, the line is tied off statically on one end and to a spring which is attached to the pulley to provide tension on the other. If one of the other pulleys was to act as a capstan, one turn was taken around it.
 

MisterBill2

Joined Jan 23, 2018
19,034
The two questions are first, as already stated, the force that is required. The second question is just as important, which is how many operations will be required. As mentioned also, stainless does develop a roughness commonly called "galling". Serious lubrication will slow the process but not stop it.
For applications with a lot of moving and a lot more force required, roller chain between sprockets, or anchored with a driven sprocket rolling on the chain can work rather well. The chain between sprockets is similar to some garage door openers, a fair source of both the chain and the sprockets. Other chain and sprocket types are also available , depending on strength and accuracy requirements.
Another option, a bit cleaner but not as durable, is threaded shaft material, driven at one end by either a gear motor or a lower speed motor. That material is available in six foot lengths and different diameters. The standard material is mild steel and so it will wear after a few hundred operation cycles. So there you have other options that mostly will be easier to implement, and will last longer. The selection certainly depends on the application.
 

Thread Starter

Externet

Joined Nov 29, 2005
2,236
Thanks, gentlemen.
Not meant for extended use; perhaps a dozen times extended and contracted to sense a particular resonant length with no chance for galling and then transfer the optimal dimension to another element. Long term wear is not of concern, There is nothing to tighten, so torque is not appreciable. Guessing, less than 10 ouncesinch. (Not translated to Newton metres)
 
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