I'm designing a double pendulum with initial motor driven motion. I'd like the pendulum to be jolted into motion from an initial short burst of rotation and then experience no resistance or holding torque from the motor thereafter, behaving naturally.
I've been researching motors and I think what I am looking for is a variable reluctance stepper motor, however, I have been unable to find any that fit my requirements on RS Robotics and other UK delivering websites.
Am I correct in my motor choice or would something else be better? And if so, does anyone know where I could find such a thing from a European retailer?
It sounds like you might be better off by initialising the swing of the pendulum using a coil to generate a magnetic field to attract the pendulum. With the magnetic field turned off it will not interfere with the subsequent free operation of the pendulum
Sorry for the lack of clarity. By a double pendulum, I mean a pendulum with a pendulum attached at the bottom. Below is an image of the current prototype I am planning to engineer.
There are two bearing at each connection between the pendulums and a wooden shaft to hold them together whilst maintaining free motion. I need to be able to move the pendulum from the foundation (shaft on the left) using apparatus solely located in the foundation, would this be possible with the magnet solution you are proposing?
It looks like you would need to rearrange the bearings of the top pendulum such that it has a shaft connected directly to the pendulum, but with that done the answer is yes.
Put a magnet on the shaft of the pendulum and position the magnet in a coil. To start the pendulum energise the coil. Effectively you have created a motor that cannot turn
However, as has been pointed out by @Railroader the bearings, which you already appear to be using, will introduce drag and there is the problem of the magnet creating back EMF in the coil when moving which if not dealt with will cause the pendulum to lose its momentum
How rigid is the requirement that the pendulum is only moved
What will the pendulum movement be used for and how ill it be measured ?
I hadn't noticed the fault in the bearing placement, thank you for pointing it out.
Could the magnet simply be inserted into the shaft or would it be wrapped around it? Do you know what the parts needed for creating this energised coil may be known as on commercial retailers?
In regards to the bearings, how great will this drag be? I'm aware that a purely kinetic version of the system I've proposed with no motors would still have drag, are you referring to another source of drag outside the material limitations at hand?
The backwards emf, if not too much of an inconvenience, will actually be ideal as it can be used to digitally translate the motion and velocity. If this emf is too much, however, how would I go about reducing it?
The design is for an art installation in which you can only see the pendulum and a backdrop wall. The pendulum will be moved through the input of a pressure sensor mat as people walk through a path with pendulums on either side. To capture the 'magic' of the installation it would be ideal not to have any visual identifiers of how the system works besides the pressure sensor and pendulum.
Sorry for having so many questions, I'm an architecture student and only started learning about Arduino last week and so my knowledge isn't the most comprehensive. Thank you so much for the advice.
Given your description I would simply cheat and drive the pendulum with a stepper motor under control of the Arduino to give the impression of a pendulum motion
That is an option, but it does feel a bit disingenuous as the purpose of the installation is to exhibit the chaotic nature of a double pendulum's trajectory.
Are you sure a stepper motor with holding torque and resistance low enough to maintain said exhibitable trajectories does not exist? The motor would cause an initial kick and then 'disengage' and let the pendulum swing commence and I was under the impression that this may be possible with a reluctance motor as mentioned prior.
Is an encoder a script of code for the Arduino or another physical component that I would have to buy?
Also, when looking through RS components and some other sites I've struggled to find a VR motor, are they commercially known as something else or just particularly difficult to come across?
It looks like a rather light weight pendulum.
Low friction bearings like needle bearings...
Also, take a look at an old clock and its quick CW/CCW swinging wheel.
