RAMPS for 5V Stepper Motors? (MOD)

Hello,

I am interested in driving 5V stepper motors scavenged from old DVD and FLOPPY drives with a stock Arduino + RAMPS 1.4 board.

To prevent burning out the motors, I would like to step down the voltage from 12V to 5V without messing up the control information.

Any suggestions?

Graham Leach

Stepper motor ratings are determined by current, not voltage. The "rated" voltage is calculated by the resistance and current rating of the stepper, which should be listed on the spec sheet for the stepper if you can find it and normally can be exceeded for better performance.

Hello,

Thank you for your quick response. The motors are getting too hot to touch. Is this normal? Should I be worried about burning out these little motors?

Graham Leach

Hello,

We have been using the pololu trim pots to limit the current going to the motors to help keep the heat down, I was just wondering if there wasn't another way...

[help.printrbot.com].

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GrahamLeach
We have been using the pololu trim pots to limit the current going to the motors to help keep the heat down.

That is exactly the right thing to do.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I have disassambled a few CD-Roms and 5.25 floppy drives myself, but never found stepper motors?
These usually are brushless DC motors that need a 3 phase ESC. Or am I on the wrong path?

I found many steppers in old copymachines and laserprinters, but they usually can´t do microstepping.

Do you have pictures of the motors?
-Olaf

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o_lampe
I have disassambled a few CD-Roms and 5.25 floppy drives myself, but never found stepper motors?

Most CD/DVD-ROMs I've torn apart have used 4-wire bipolar stepper motors for positioning of the read heads, not the spinning of the discs.

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I found many steppers in old copymachines and laserprinters, but they usually can´t do microstepping.

I'd be curious to know why. Both bipolar and unipolar steppers can be microstepped, although unipolar is a bit more difficult.

A stepper controller specifically for 5V stepper motors (DRV8834) will get you a lot better results than using the standard ones (eg: A4988, DRV8825) at 12V.

Issues: Pinout is different, so would be incompatible with the RAMPS board as-is.

Note: If you want to continue using DRV8825's or A4988's, recommended to use a lower voltage (eg: 8-9V) rather than 12V. This will reduce the max voltage the motors may ever see, which will definitely help on the heat side of things. You can't use 5V because the drivers have issues with voltages below 8V on the driver side (their minimum drive voltage, according to the specs).

I run DRV8825 at 24V without any issues.

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@Wurstnase: That is fine with normal motors, but the motors in CD/DVD Roms and the like get VERY hot if you put too much voltage into them. They have very little thermal mass to absorb that heat, and they also have very little surface area to dissipate it. They're also designed specifically for running off a 5V source, so the coil voltage is even lower than you might be used to with standard size motors.

We're talking about a motor that is typically about 2cm long and about 1cm in diameter (though there tends to be little to no standards used, since size is a concern). It's not even NEMA14 size (the main size down from NEMA17) so overheating is a real concern. The higher the voltage, the more power for a given (typical) resistance, so keeping the voltage low seriously reduces the power output.

And yes, while stepper controllers do reduce the max current, in such a small device there is absolutely no margin for overshooting the power they have to dissipate. To get the most out of the device you want to match the current and voltage as best as possible to the device to avoid excess power dissipation.

With larger motors, you have much more margin for error without it becoming a problem. In many ways, this is part of why they're so commonly used in designs like RepRaps. They're quite forgiving, which is quite useful for DIY machines and small production runs alike.

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Cefiar
@Wurstnase: That is fine with normal motors, but the motors in CD/DVD Roms and the like get VERY hot if you put too much voltage into them. They have very little thermal mass to absorb that heat, and they also have very little surface area to dissipate it. They're also designed specifically for running off a 5V source, so the coil voltage is even lower than you might be used to with standard size motors.

You don't seem to understand the concept of constant current drivers. Driven from a constant-current driver, those motors will get too hot if you put too much CURRENT into them. Standard stepstick-type drivers should be just fine provided you can turn the current down low enough. Preferably, the OP should increase the value of the sense resistors on them to get more accurate current setting and regulation at low currents. This wouldn't be hard to do with a fine-tipped soldering iron.

Edited 2 time(s). Last edit at 06/20/2015 06:11AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

dc42: Have you run these motors on these drivers yourself? I've done it and burned my fingers on the motors with the absolute lowest current setting using as low as 9V into the driver motor side. I didn't have access to a variable supply at the time to take it down to about 8.5V. This is the lowest I'd run the drivers VMOT at, even though they should go down to 8v.

You can't turn the current down low enough, which basically my point. Sure you can modify the drivers to do it, but when other purpose built drivers exist, it seems a bit pointless to me.

I understand very well the concept of constant current, but when the current is still in excess of the maximum the motors should be driven at (and are therefore giving them too much voltage per coil), you need to look at another solution.

I think that that the point being missed is that power dissipated in this case is I^2R, where R is the resistance of the motor windings. Thus, with a constant current driver, a given current will produce the same amount of hest regardless of the input voltage to the driver. The key issue here is the inability to set the driver low enough, for which solutions have been offered, not to reduce the input voltage to the driver.

- Tim