Advice on motors for c-bot.

I wish to upgrade my Prusia I3.
I am considering making the C-Bot core-xy printer.

The BOM for this printer states the NEMA17 motors should be 68oz-in (48N-m) or better.

Looking at Ebay I can find these:

Manufacturer Part Number 17HS19-1684S1
Step Angle 1.8°
Step Accuracy 5%
Holding Torque 45Ncm(64oz.in)
Rated Current/phase 1.68A
Phase Resistance 1.65ohms
Voltage 2.8V
Inductance 2.8mH±20%(1KHz)
Weight 400g

.. and these:
Manufacturer Part Number 17HS19-2004S1
Step Angle 1.8°
Step Accuracy 5%
Holding Torque 59Ncm(83.6oz.in)
Rated Current/phase 2.0A
Phase Resistance 1.4ohms
Voltage 2.8V
Inductance 3.0mH±20%(1KHz)
Weight 400g


My questions are:
- Do I really need 68oz-in motors? Would I be better off using the 45N-Is thecm motors?
- If I went for the larger motors, would I encounter problems driving them with a Ramps1.4 and A4988 drivers? Would I gain anything by using DRV8825 drivers instead?
- Are there motors better suited to this application available (preferably in the UK) for a similar price (£9 each).

Thanks.

I have also found these form Stepperonline:

Nema 17 60Ncm(85oz.in) 0.64A Bipolar Stepper Motor 17HS24-0644S

Manufacturer Part Number 17HS24-0644S
Motor Type Bipolar Stepper
Step Angle 1.8°
Holding Torque 60Ncm(85oz.in)
Rated Current/phase 0.64A
Phase Resistance 15ohms
Recommended Voltage 12-24V
Inductance 13.2mH±20%(1KHz)

Much lower current and greater holding torque.

Does the lower current make these more suitable for driving from the ramps/ A4988 drivers?

RAMPS will struggle to drive all of those motors near to their maximum torque, because the plug-in drivers have far too little PCB area to keep the chips cool. The 17HS19-1684S1 motor is a very popular one, but most people using RAMPS run it at 50 to 65% of its rated current, partly to avoid overheating the drivers, and partly because setting the current properly on those drivers is so difficult. OTOH if you use a modern board with on-board drivers and software-settable current, such as Duet or Smoothieboard, the drivers are much better cooled and you can run the motors much closer to their rated current (best to limit them to 85% or so of rated current so they don't get too hot).

So if the 48Ncm torque recommendation is based on using RAMPS with motors rated at 1.7A or greater, then the 17HS19-1684S1 used with more modern electronics with the currents accurately set should be more than adequate. In fact that motor is overkill for most small printer designs. I don't know the C-Bot design, but unless it has a particularly heavy print head (e.g. because you are mounting 3 or 4 extruder drive motors on it), I would have thought it should be adequate. All the same, I suggest you ask the designer why he specifies 48Ncm and what proportion of rated current he runs the motors at.

The 17HS19-2004S1 is even less well suited to RAMPS because of its higher current requirement. The 17HS24-0644S is unsuitable because of its high voltage requirement.

DRV8825 drivers can take a little more current than the A4988, but they have some well-documented problems with some types of motor.

One area where high motor torque really is needed is if you insist on using non-geared extruder drives. OTOH an extruder with gearing of 3:1 or 5:1 needs only about 20Ncm of motor torque.

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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].

Thanks dc42.
That will be very helpful.
I will try to contact the designer and ask the question.

Hello!

I´m looking to use this same model 17HS24-0644S with POLOLU DRV8825 driver. The guys on POLOLU said me that´s all right with using this two together. After one year from this fisrt post, do you think this ir right?

The 17HS24-0644 requires higher voltages than typical motors used in repraps. With a 12V supply, it will only provide good torque at low speeds. At 24V it will work somewhat better. You would do better to choose motors with a rated current in the range 1.2 to 1.7A.

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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 am running 17HS19-2004S1 stepper motors with the raps128 drivers and they never failed me. and I am running them on ~1.5A on 12v ( was planning to go to 24V but I don't see it necessary any more)

Here on of my first prints

Fast

an another test printing a gear

gear printing

Edited 2 time(s). Last edit at 05/08/2016 06:23AM by amigob.

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P3steel DXL, with Due/RADDS/Raps128 dual Wade's extruder

Quote
amigob
I am running 17HS19-2004S1 stepper motors with the raps128 drivers and they never failed me. and I am running them on ~1.5A on 12v ( was planning to go to 24V but I don't see it necessary any more)

Here on of my first prints

Fast

an another test printing a gear

gear printing

How big is you printer?
Do they get eventually hot?
Iam about to buy motors for my CoreXY(60*60cm) and iam considering this 2Amps motors(X,Y and Z with belt for two ball screws).
I will also use Duet wifi + 24V PSU.