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So, this might be a somewhat strange need, as I don't seem to see many resources on this. I'm trying to create a device where I can set an amount of force for it to generate, and when it would behave as such:

  1. If there is no or only a small opposing force, it would drive forward in the direction of the force.
  2. If there is a constant force being applied that is equal and opposite to the force being generated, it would stall indefinitely without damage.
  3. If there is an opposing force larger than the generated force, it would be pushed back, while still providing the constant force as a resistance, therefore reducing the effective backward force; and it should be able to handle all this without damage.
  4. All this only need to occur in the range of no more than 5 cm, and the simpler and smaller the system is, the better.

I was wondering if a linear motor, considering that they are also called a force motor, can handle such a demand, and if so, what type? There's also the concern that such a small linear motor can't be found anywhere (or might be prohibitively expensive).

Another thought that I had was to use a torque motor (with some gears to translate torque into linear force, of course), but I couldn't find a definitive source saying that those can indeed provide a constant torque even when being pushed back by the load, I just see that they provide high torque at low speed. Also, on the topic of torque motors, do DC torque motors exist, or are they AC only?

Of course, if you have a better idea for achieving this need of a constant force no matter what's actually happening in terms of movement and outside load, please let me know!

Finally, please do tell me if you think a different community would be a better place for this question.

Thank you all for your time!

Jason Long
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If the changes are slow enough, a simple pulley with counterweight might do the job. Constant force hangers are used very commonly for piping, where you can find interesting designs using combinations of springs and lever arms. One of the simplest designs is here. enter image description here

Similar effect is also achieved in compound bows, that are optimised to resist the middle part of the draw with the maximum force in order to store maximum energy (the force also drops at the end of the draw, so you can hold the fully drawn bow with a lots of energy with smaller effort than traditional bow).

Tomáš Létal
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