Need advice motor learning project rotor construction - Page 1
Forum section: electronics / projects

author: fahraynk
author_rank: Newbie
timestamp: October 21, 2016, 02:24:03 am
content: Hi I was wondering if I could get some advice. I am building a motor as a learning project and I am finally past all the electric stuff and onto the actual construction.I have to design the rotor...In this picture... Does the shaft get thicker because the electrical steel is more expensive than a thicker shaft? Also, how is the shaft attached to the steel, is it all just glue or interference fit? And if interference fit, would you have to hammer the shaft in manually or get it manufactured that way by the people who do the electrical steel lamination?In this picture I think there are circles cut out of the rotor because you don't need material there to pass the magnetic flux, so it would just be extra material. Not sure about the half moon cut outs on all 4 sides though. Also my main question about this next picture is.... how would you attach a shaft to this rotor?I was originally thinking get a keyed live shaft roller, attach it to a shaft and then glue a ring of electrical steel followed by a ring magnet.... But its really hard to find a roller with the exact dimensions I need because its really small.Any tips or answers are appreciated. This is the first thing I have ever tried to design.

author: Ian.M
author_rank: Super Contributor
timestamp: October 21, 2016, 02:56:26 am
content: You cant do anything useful with the disks punched out from the center of the laminations other than send them off to recycle for a very small fraction of the value of the same weight of new material so you can start by assuming the larger diameter is required for mechanical reasons. e.g to reduce the shear force at the joint between shaft and lams.For high torque you'd want a shrink fit so heat the lams and chill the shaft and assemble quickly. There are induction heaters commercially available specifically for doing shrink fits of annular parts.

author: fahraynk
author_rank: Newbie
timestamp: October 23, 2016, 01:50:02 am
content: Quote from: Ian.M on October 21, 2016, 02:56:26 amThanks a lot. That shrink fit thing is probably what the electrical steel people were talking about when they said "If you want us to do the rotor also you would need to provide the shaft"... they probably do the shrink fit.Can I ask, in this picture I think the ring magnet is glued to electrical steel, and inside the electrical steel is another circular ring that sits on the shaft. Do you think that ring is keyed on the inside and shrink fitted to the electrical steel on the outside? Also.... do you recommend any design book that could teach me the answers to these questions.

author: JS
author_rank: Frequent Contributor
timestamp: October 23, 2016, 02:30:28 am
content: You need some kind of winding throw the holes, even if the winding goes nowhere, just shorted, called squirrel cage, which would make a asynchronous motor. The alternative is permanent magnets making a synchronous motor or windings throw collectors making whatever motor you want depending on what you do with them. There are synchronous motors with no collectors or permanent magnets but let's not get into them.Sometimes funny holes are punched throw the lams for funny windings or squirrel cages to provide a particular starting mechanism. As the rotor start spinning the slip would be high (high (source) freq over the rotor) and as it speeds up the slip goes down and so does the freq to under 1Hz. While starting a low inductance and high resistance path does the job starting it slow, once up to speed a higher inductance lower resistance path takes the load. (thin conductors close to the edge of the rotor vs thick conductors further in the rotor). That's probably not the case of the picture you uploaded since it looks like a variable reluctance motor, but it might have a similar reason.JS