Undocumented Feature ...... Radio Reception

[ex-egll]

I had noticed recently that my Y motor was getting hotter than the rest, and that there was a "singing" noise coming from it when idle. I decided to check out the Vref, and reset it if needed.

As I put my volt meter probe on the adjuster a new sound came from the motor..... perfectly clear reception of a local AM radio station! Now to be fair this station is pumping out 50,000 watts less than a kilometre away, even so, I wasn't really expecting to hear it. I continued to adjust Vref between the recommended values of .39 - .5 v, but everywhere in that range the motor still made a sound when idle, the sound would change in tone depending on Vref. I had to go as low as .31v to silence the motor, at this value the bed seems to move OK with no skipping, so I'll probably leave it there and see what happens. As a matter of interest I tried the probe on the other 4 adjustment points and there was no radio reception audible, and all Vref values were in range. I am wondering whether I might have a suspect motot or driver board.

[printbus]

The radio reception is a new one, but I don't know that I'd worry about it. By touching the meter lead to the trimpot, you're adding quite an antenna to a sensitive signal point, and the stepper driver is likely just adjusting the idle current through the motor in tune (pun intended) with the pickup noise. You could try swapping driver boards around and seeing if the radio signal moves with the driver board - if so, maybe there's a decoupling capacitor missing or something on that board.

Others have reported noise coming from idle motors. I hadn't noticed it on mine until I replaced RAMPS with Smoothieboard. Now, with motors enabled but idle, the combined noise sounds almost like a cooling fan is running. Again, not sure I'd worry about it.

All things being equal, the Y-motor will tend to run warmer since it is more boxed in than the rest of the motors. Stepper motors are designed to run pretty hot, so there's a judgement call on how hot is too hot. The "proper" stepper driver current limit setting has been argued a couple of different ways. One approach sets the current to the max the motor can handle (and put up with the heat) in order to ensure as much microstep precision as you can. The other extreme is to adjust the current limit lower and lower until a motor starts to skip, then raising it up a bit from that. While I was on RAMPS I had done the latter, and IIRC all the drivers were set to the 0.15 to 0.25v range. I was quite surprised on how much smoother the printer sounded at those lower current limit values, while still maintaining print quality and speed.

[ex-egll]

Thanks for the response printbus. So far my approach to setting Vref is to back off the pot to .39v OR when the motor stops whining, whichever is the lower. If I use the stop whining method I exercise that motor quite a bit to make sure there is no skipping. I agree with "Stepper motors are designed to run pretty hot" even the hot ones here are relatively cool compared to my CNC milling machine.

[ssayer]

When I was a kid and AM radio was in it's heyday, we used to be able to hear the station "CKLW" at night about 60 miles away from the transmitting tower coming from the electric cow fence at my aunt's farm...

[ex-egll]

When I was a kid and AM radio was in it's heyday, we used to be able to hear the station "CKLW" at night about 60 miles away from the transmitting tower coming from the electric cow fence at my aunt's farm...

Ah, the stories of high power AM! I remember if you got close enough tho the towers you could light up a fluorescent tube just held in your hands, true wireless light!

Thread drift, I know, but I started the thread so that should make it OK!