Ideas of subject concerning stepper/DC motors ?

Hello everyone,

I've been searching for a while, as an engineering student, a system for which I could study the motorisation, something that is not simply comparing different solutions of motors but actually implying quite a big issue about the motorisation. The problem would maybe be around the precision/speed of the system or problems due to the lack of precision of the engine.

Is there any system where a stepper motor in the center of the problematic ? I'd like to make a theoric analysis and then an experimental comparison to check if the theory is acceptable. If not, explain the differences.

I am not asking for something that would be too common, just a good idea of problematic.

I already have several things like steppers, DC motors, an arduino of course, an incremental encoder, a H bridge motor driver and sensors.

Thank you already !

Is there any system where a stepper motor in the center of the problematic ?

In production systems, stepper motors are chosen because they work for that application, such as CNC machines, printers, hard disk head positioners, etc.

I had in mind the 3d printers. Indeed, the precision needed to make models is quite important but i don't really see in this case where there is a problem. Indeed, the stepper is clearly the answer and there is not particular things to study or improve.

I may be looking for something quite specific. I'm looking for problems :P

You’re asking people to suggest a known problem relating to the use of electric motors which is significant and hasn’t been resolved yet?

I don’t know of one and I think it’s not a promising area to look for one. Electric motors and actuators have been in widespread use for many decades and there is a huge variety covering a huge range of applications. What you’re looking for is an area that is so unusual that none of the well known options are suitable, or a project which has been implemented by somebody who doesn’t know enough to choose the appropriate solution. Unless you already know of one, I think your chances of finding one are slim.

The closest I can think of would be a window/wave/solar generator which has been designed by a novice using inappropriate parts e.g. an alternator as a generator with the wrong speed/torque characteristics or using it in the wrong orientation so that the bearings don’t work as intended, that sort of thing. There are some very sophisticated and cleverly designed DIY solutions, but there are also some which seem far less sophisticated. Maybe you could look in that area for somebody who needs your help? It would surely be an amateur project, because a professional tackling this problem ought to be able to deal with the issues correctly in the first place.

Yes you are right. Finding an error made by a novice should be hard indeed. I was asking myself : Do the stepper motors generate vibrations due to the rotor passing through stable and instable positions ? I know this can be resolved by choosing a micro step mode but i've heard of a firm developing a stepper than can receive a distorsion of sinusoidal signals : the signal has a specific shape made to avoid the vibrations, even better than the micro step. I have never find anything about this whereas this seems impressive.

There is another thread running at th moment about somebody who is trying to use a stepper motor to turn a telescope mount. Apparently it is an issue that the speed of the stepper is not uniform as it steps at a nominally constant speed, due to the nature of it moving in discrete steps. This causes vibration in the moving assembly which is bad news for long term exposures. One solution is to use a massive reduction ratio between the motor and the assembly to reduce the effects of the steps.

Maybe you could try to develop a smart driver that uses some sort of feedback mechanism to track the speed of the motor during the step, and actively control it (i.e. by PWM) rather than just letting the rotor fall from one equilibrium position to the next. I suspect that this might involve the sort of sensing methods used in brushless motor controllers. I don't know whether anyone else already does this, or how hard it would be to do, but it sounds like the sort of challenge you're looking for.

Actually, there is a problem in CNC machines where at specific speeds, the vibration of the stepper reaches a resonance with the structure of the CNC machine and so it vibrates.

Not an unsolved problem, however. Flexible connectors, such as chunks of automotive hose with hose clamps, dampen vibrations. Others have put hollow cylinders with a free moving weight inside it between the motor and the threaded rod.