28BYJ-48 Mechanical Actuator #5
I thought it would be cool to see what kind of Mechanical Actuators we could make using the 28BYJ-48 stepper motor and mostly 3D printed parts. The 28BYJ-48 is the motor that comes with most Arduino kits. It's a 5v dc motor with a max rpm of 15 and is capable of around 4 oz force/in of torque. You can get these motors with the driver for around $2 each.
Linear Ball Bearing Stepper Slide
This is a remix of the first Liner Bearing Stepper Slide I made. The bearing carriage on the first slide is slit down the center of the bearing groove but on this version I thought that I would design the bearing more similar to an actual linear bearing so it has a solid carriage and end caps for the bearing return. Since the print orientation is different on this version I was able to utilize Gothic bearing grooves typical to the type on an actual linear bearing instead of a “V” groove like I used on the first version.
I was hoping for a little smother transition of the balls to reduce the noise and vibration but I think both designs preform very similar. The first design is actually a little easier to assemble.
This is a linear bearing slide driven by a 28BYJ-48 stepper motor. The linear bearing utilizes standard .177 (4.5mm) caliber steel BB’s and has adjustment screws for setting the preload. The trapezoidal drive screw utilizes an integral ball bearing also made with BB’s to handle the thrust loads of the slide.
I included two different lead screws; a twin lead screw with a 1/2” pitch and a quadruple lead screw with a 1” pitch. Given the max rpm of the stepper motor is 15 rpm the twin lead screw will result in the carriage traveling at 7-1/2 in per/min and the quadruple lead screw will travel at 15 in per/min.
The linear bearing actually works very well and the BB’s recirculate just as they are supposed to! There is some noise and vibration as the BB’s are not caged and I think they meet a little resistance as they recirculate back into the bearing. On the next version I’m going to split the housing like an actual linear bearing to see if it improves on the vibrations.
This slide will actually move over 25 lbs with the twin lead screw! If you have seen the previous Dovetail Stepper Slide it could move around 7lbs so this version has a 4x’s the load capacity do to its reduced friction. However the load is not as stable as it is on the dovetail slide. I believe the dovetail slide can handle more load it’s just the stepper motor is not strong enough to push it.
The mounting holes on the base, carriage, and the endplate all match up so multiple slide assemblies can be bolted together to make a two or three axis cartesian system.
- M3 Nut (14x)
- M3 SHCS x 10mm lg. (12x)
- M3 SHCS x 20mm lg. (2x)
- .177 BB’s (8x) for Thrust Bearing
- .177 BB’s (8x) for Linear Bearing
- 28BYJ-48 Stepper Motor
Here is my amazon affiliate link to a set of five of these stepper motors and drivers. They are a little more expensive from amazon but you will get them a lot quicker.
To start assembly the first thing you need to do is install the two M3 x 20mm screws and nuts into the carriage for the preload adjustment. Don’t tighten the screws up at this point. Then use the M3 x 10mm screws to install one endcap and slide the bearing onto the rail. Next fill the bearing up with BB’s, it should take 34. Next put the remaining 6 BB’s in the other end cap. Here is the hard part, you have to move the carriage to the end of the rail and carefully tip the end cap with the 6 BB’s onto the carriage without dropping any of them. It may take one or two tries. Once the bearing is packed with BB's adjust the screws to get the desired preload. Once you have the linear bearing properly set you can build the thrust bearing flange.
Note: Using grease on the thrust bearing, drive screw, and nut is going to improve the load capacity and the lifecycle greatly as well as reduce noise and vibration. I would not put any lube on the ball bearings, it could cause issues with the balls recycling. If you are having trouble with the BB’s recycling you can also try taking out one of the BB’s on each side.