Geared stepper motor

[drinu]

Hi,

I am building a Cartesian robot  (X,Y,Z) and will be using two stepper motors for the X and Y axis to rotate the ballscrew. If I go for a geared stepper motor will it be a good idea? I was thinking of something similar to this one:

http://www.robotshop.com/en/geared-bipolar-stepper-motor-3v-233-oz-in.html

Also, will this driver work with this stepper:

http://proto-pic.co.uk/drv8825-stepper-motor-driver-carrier-high-current/

Any kind of help will be appreciated.

Thanks.

[waltr]

Gear reducing a stepper increases the output torque and decreases the maximum speed (RPM).
Is this what you need?

The driver is just barely enough (look at the Max current rating of the motor and driver) for that motor.
It might require forced air cooling as per the instructions.
It also depends on how hard to work the motor (mechanical loading), how fast you try the run the motor and at what Voltage you feed the driver.

[jwatte]

Gearing on a stepper motor will give you more torque, slower speed, higher losses, and higher play/backlash.
If it's worth it to you depends on your requirements. It may be better to use a larger stepper motor, or a finer-pitch screw, or both, instead of a gearbox.

The stepper motor you link to is rated 12V and 1.6A; the driver you link to is rated 8-45V and 1.5A (up to 2.2A peak if you add heatsinks.)
So if you add heatsinks, and don't exceed 12V (so the stepper doesn't draw more,) then that driver may work.

[drinu]

Thanks for the replies. Are there any other drivers which are similar to this one (small and easy to use) but with higher current rating?

[bdeuell]

The first question I would ask yourself is what the operating speed, torque, and resolution you need from the motor is. Then do theses specs align better with a geared motor or a un-geared motor.

Some things to keep in mind when designing the optimal solution for your application and may determine if this gearbox will meet your needs/objectives:
 
- all gears some loss of energy, so they will affect the efficiency of your system

- stepper motors have an optimal efficiency towards the lower end of there operating speed range , every motor is different but you could look up some graphs to get an idea

- planetary gearboxes have backlash, ball screws are often used because they have very low backlash which would be negated by the use of a planetary gearbox.

- a gearbox adds cost even using a slightly larger motor could be cheaper it all depends on your design requirements, for many applications a gearbox is the best solution.

Edit: I see a few others responded while I was writing this response, I apologize if I repeat the same things.

[drinu]

Thanks for the reply bdeuell. Are there any other drivers which are similar to this one (small and easy to use) but with higher current rating?

[drinu]

Hi,

I decided to go for the 12V, 1.6A, 233 oz-in Geared Bipolar Stepper Motor ( http://www.robotshop.com/eu/en/geared-bipolar-stepper-motor-3v-233-oz-in.html ) since torque is required for my project.

Regarding the driver, which one from these three will be best to choose with this stepper motor:

http://proto-pic.co.uk/drv8825-stepper-motor-driver-carrier-high-current/
http://www.robotshop.com/eu/en/pololu-single-bipolar-stepper-motor-driver.html
http://www.robotshop.com/eu/en/big-easy-driver-bipolar-motor-controller.html

Your help will be appreciated. Thanks.

[jwatte]

Neither of them is great for what you want -- specifically, all of them will only actually deliver the rated currents with additional cooling (adding a heat sink.)
If I had to choose between those, I would probably get the 8825 and add an aluminum heat sink to the chip with some thermal glue.
If I wanted something robust, I would go with a bigger driver.

[drinu]

If I wanted something robust, I would go with a bigger driver.

Are you referring to something similar to this one:

http://www.ebay.co.uk/itm/CNC-Mill-Router-DIY-CNC-Stepper-Driver-Board-Controller-M335-0-5A-3-5A-12V-30VDC-/350947200478?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item51b6154dde

Why you would not choose those drivers please?

[jwatte]

That device does have the heat sinking, but it doesn't say whether 3.5A is "per coil" or "in total."
However, it does look more robust than the Pololu bare boards, given that it has the heat sinking already integrated.