r/Motors

TL;DR should an unpowered motor with brushed removed spin completely freely?

I'm repairing a DW735 planer. I ordered an aftermarket motor, which arrived damaged in transit--the rotor had been pushed forward and broke the cast aluminum housing cap. So I took the housing from my dead motor and put it on the new motor. When I spin it by hand, with brushes removed, I can feel little bits of resistance. It feels like maybe the armature is slightly contacting the field as it spins. I don't feel this resistance when I hold the rotor by the bearings and spin, so I don't think it's the bearings.

Is this a problem? If so, can I fix it?

Thanks!

https://preview.redd.it/udwyjmojvp0h1.png?width=2816&format=png&auto=webp&s=21a4db529d4e2e35984db5d9e7235e0f7bbda3b4

Hi I have a very nice silent compressor. It's 750w(peak 5a) 60hz 220v. With two pistons. We now moved to a 50hz country. The motor specifically says 60hz and no range. I would really like to try to operate it here. But it's not worth spending a lot of money on it. I also have a 1ph:1ph Chinese AT2 VFD.

What I tried so far with the VFD was playing with torque boost, and slowl/fast ramping to 60hz. The compressor is empty and valves are open. But everything basically leads to the compressor vibrating but not pumping. It pulled roughly 2.5a in that stage.

When I connect to 50hz it works. But I quickly switched it off because I was worried it might overheat.

What other options do I have? Other settings in the VFD? Lower voltage by 20%? But I am afraid it might not work. It would also need a very uncommon transformer. I read you could bypass the starter winding and operate it as a 2 phase motor. But how would that work? And would that be an option?

I suspect that the motor can't handle the output of the cheap VFD.

I'm looking for a motor to generate small pressure pulses. Essentially a heartbeat simulator. I've crossposted this to r/askElectronics because it's for an electronics project and I was not aware of this community beforehand.

I've been looking at stepper motors, since that would allow me to shape the pulses at will, but i also need to generate from 40 to 200 pulses per minute (minimum, more would be ideal), and that is a big ask!

Do any of you know of an small stepper motor capable of that speed? I don't need much power, thankfully. Could maybe use a servo motor, if one is available at that speed.

However, since I suppose such speeds are impossible, or close enough (out of my budget), what are my alternatives?

One paper on the subject I'm studying has a DC motor drive a cam with the profile of a heartbeat pushing a bellows. Speed is not a problem, at worst you need to gear up your motor, but your cam fixes your profile, you cannot have irregular heartbeat, or miss a beat. That is an acceptable compromise.

The obvious choice would be an speaker or a solenoid actuator, but good luck getting a small speaker to reproduce a sub 5Hz waveform, and idk what ranges solenoids work at, but they may be too slow.

Another option I have analysed is gearing up an stepper, but I think that is not helpful. Imagine i move my stepper back and forth; with some gearing the amplitude of those movements is amplified (I could amplify strength too), but the number of back-and-forth oscillations per minute would be the same, would it not? (mechanics is not my main field)

So, I await your opinions!

I have been working on a breakdown of a 1000Kw 750VDC motor in which the non drive end bearing failed. After fitting a replacement, the new bearing only lasted 2 hrs before failing. After replacing again, arcing was seen between the bearing housing and the motor frame, a bad earth brush was found on the shaft, repaired and the arcing has stopped. There is still significant magnetism being produced that is only present when the motor is turning (enough that a m16 x 100mm bolt can be stuck to the frame). My concern is that although arcing is not being seen, there is still current flowing through the bearing and going to again cause premature failure. All electrical testing I have performed on the motor is coming back clear. Looking for any tips/ideas of something potentially overlooked because everyone I’ve been in contact with is at a loss.

Hi, I am an A-level product design student who has to hand in my final piece next week!

My project uses a motor and pulley system to lift and lower a platform. The pulley system works and I have a motor which is a Uxcell Double Shaft Worm Gear Motor DC 24V 120RPM High Torque Speed Reduction Motor with Metal Gearbox.

I also have 6V 12V 24V 28V 3A 80W DC Brushed Motor Speed Controller (PWM) Speed Adjustable Reversible Switch 1203BB DC Motor Driver With Reverse Switch.

I need to wire these to a power supply. My teacher has suggested to either a 12v or 24v 2000m a battery. I don't have one and looking on line they are quite costly for a single use as well as it looks like I will struggle to get one delivered in time.

My dad has asked if it would be possible to wire it to the mains supply using an old computer charger that he has. The charge is a 12V 2000mA Power Supply ICP30-120-2000 Laptop Charger. Can anyone confirm whether this is feasible... it looks as though it might work.

Any constructive advice would be GREATLY appreciated as my product won't work otherwise!

Sorry for the rant, but IME they are complete crap compared to brushless. I will give you my experience with both and you can chime in with any comments or suggestions.

My first e-bike was a brushless geared front-hub drive, 500W nominal, 1000W peak. It worked fine, it's just that I mountain bike and an extra 10 lbs on the front is not great for descending hills. It's also difficult to take the front tire off due to the torque arms, etc. It's still sitting in my garage and after this brushed fiasco that I'll explain below, I may throw in the towel and revive this brushless hub motor. I think it has 7000-8000 miles on it. Some controller wires have been partially melted but otherwise there have been ZERO problems with a brushless motor.

A few years ago I bought a brushless mid-drive that was a dual chain system. It was far more finicky to setup but it worked (a similar 450W nominal 1000W peak system as the hub drive). Climbed hills great, blah blah blah. 3500 miles on it. Then this February I took off in a high gear from a stop, heard a snap inside the motor, and then a loud thunk thunk thunk roughly every pedal revolution. The motor still works but the noise is horrible and the gearing will fail at any moment, I can tell. So it's on the shelf now (I can't take it apart, they glued it super tight). And they are not selling it now. I have a carbon frame that is too thick for a run of the mill Bafang mid-drive so I need a dual chain setup (CNC would be fine for $1000, but replacement motors for brushed are between $50 and $115).

So I got what I 'thought' was the 450W replacement motor. The tip-off should have been from the 24/36V setup instead of 48V. Chinese GNG mid-drive, they of course never told me it was brushed. I look at the power wires, there are only two, I'm like WTF. The controller doesn't even have a display option. So after about 15 hours of playing around with the wiring and the 2nd dual chain setup, I finally get it to work. Now this is where I have to admit I'm at fault: I used a 48V battery for a 36V motor. And ran it full throttle up a modest incline. However, I was shocked at how fast the motor overheated, literally in under 30 seconds. It was so hot that black semisolid plastic insulation was leaking out of it. It was toast after 5 miles. A grand total of 5 miles. Brushed motors have a heating problem...I've run full throttle up a hill with a brushless motor and never had it fail. You can blame 48V but the controller is rated at 35A, and so even with a 36V battery if I would have used that, the controller can take over 1000W. The motor CANNOT. Because it's brushed.

So I get a replacement motor. This one lasted 25 miles. And then? I even have a fan underneath it and a temperature sensor to make sure it doesn't overheat. So last Tuesday I'm offroading very modestly, really just coasting down a short section to a flat location, and heard a weird click underneath me. I at first thought it was the drivetrain slipping a gear into one higher, sometimes that happens when you coast or start pedaling again if the chain is between two cogs on a cassette. It then falls into the next higher gear and everything is fine. Keep in mind I was NOT under any e-power at all. Suddenly the brushed motor ramps up power to max. Without me touching the throttle. Somehow one of the 3 pin throttle wires touched one of the two power wires and bypassed the throttle. Now you can blame the cheap throttle I bought (which is in the trash now) but something like this never, ever happened with a brushless setup. Brushed setups are so delicate, one thing goes wrong and the wiring or motor is fried. So I had to immediately turn off the battery. But now I have no power. When I turn on the battery, the the power shoots up again to max. After the 3rd time I turn on the battery (only for 3-8 seconds), the motor cannot work properly and is only putting out like 30W, not even enough to carry its own weight. So now I get a 2nd replacement motor, coming in the mail. I have separated the wires as much as possible in a cramped space in the frame's triangle. I also now have a fuse cutoff and will experiment with 15A and 20A fuses to see how much power I can get before either the fuse blows or the motor gets over 60-70C. If this 3rd brushed motor fails for whatever reason (if I can't get at least 1000 miles out of it), I'm going back to brushless, this is ridiculous. I got over 10,000 miles from 2 brushless motors and can't even get 30 miles from a brushed one.