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I designed this mechanical actuator to enter into Pinshape’s “Mechanical Design” Challenge. A mechanical actuator is utilized to turn a rotary motion into a linear motion. It has a built in gearbox to reduce the speed of the motor and increase the output force of the actuator. All the components for this actuator are 3d printable and its constructed similar to an actual mechanical actuator used in industry. It utilizes three stages of gear reduction, a dual roller bearings and a acme screw.
The actuator has three stages of reduction utilizing spur gears to achieve a total ratio of a 10.39:1. (Sorry for the odd ratio, I had an even reduction all figured out but my printer was just a little too small to utilize it so I had to reduce the number of teeth on a couple of gears to make it fit.) You will notice that the teeth on the gears are larger on the last stage as the torque increases thru the gears.
Stage #1: .577:1 (15 to 26 tooth, module 1)
Stage #2: .417:1 (15 to 36 tooth, module 1)
Stage #3: .4:1 (12 to 30 tooth, module 1.5)
Total Reduction: 10.39:1
I utilized a twin lead 5/8” diameter X .375” acme screw. A twin lead screw means that there are actually two threads revolving around the screw to give it more strength. This is a result of how coarse the thread pitch is in ratio to its diameter. A coarse thread was chosen because I wanted the actuator to travel more quickly. I could have chosen a motor with a higher RPM to get the same result but then you run the risk of the spur gears overheating and failing. I found it’s better to run a lower RPM on the gears but utilize a more aggressive thread pitch on the screw.
I utilized twelve 1/8” diameter x 3/8” long dowel pins for the roller bearing on the drive shaft. There are bearing cages to keep the rollers at the proper spacing. Set screws allow you to set the bearings preload to remove any slop in the bearing so a tight tolerances fit is not an issue making it an easy print.
I choose a 1000 rpm DC gear motor to drive the actuator, the max linear speed is calculated as shown:
1000 rpm/ 10.39 ratio x .375 = 36 in/min
Max payload: With the 1000rpm gear motor it starts to bog down at around 80-100lbs.
The files are loaded in the correct orientations for printing. Supports are not required for any of the parts. The max bed size you will need is 120mm x 120mm x 120mm. There are plenty of clearances built into all of the components and they are all pretty easy to print. The only one with any difficulty is the screw since it is so tall and narrow. I printed it directly on the bed but you may choose to use a raft to help hold it vertical. It also helps to print it slow for better print quality.
This is very easy to assemble, it takes less than ten minutes. Find the PDF that shows the assembly view of the actuator. I have outlined the order of assembly below.
1. Print out all the required components.
2. Install heat-set inserts into bearing housing. (If you are not sure how to install these there are some very good resources online.)
3. Put the roller cages into the bearing housing and cap and install the rollers into the cages.
4. Insert the drive screw into the bearing cap and then install the cap onto the housing.
5. Once you achieve the proper amount of preload on the bearings tighten the four screws that set the preload.
6. Bolt the bearing assembling onto the main plate.
7. Bolt the gear motor on the main plate.
8. Bolt the drive gear onto the motors shaft.
9. Install stage 2 & 3 gears.
10. Bolt the gear on the screw.
11. Bolt the back cover onto the main plate.
12. Screw the actuator rod onto the drive screw.
13. Slide the guide housing onto the drive screw lining up the anti-rotation keyway and bolt it on.
Note: it would be recommended for longer life and more capacity to utilize lithium grease on the gears, bearings, and screw.
- 1/8” Diameter Dowel Pins X 3/8” lg. - 12X
- M3x.5 Socket Head Cap Screw X 6mm lg. -21X
- M3x.5 Socket Head Cap Screw X 10mm lg. -8X
Voltage: 24vdc/ 1amp
RPM: 1000 (20-1000 available same gearmotor)
You can find it on Uxcells site or I got mine on amazon for $14:
M3x.5mm thread, 5.6mm od x 3.8mm lg. brass
You can find the threaded inserts on Mcmaster:
If you are looking for means to control the motor you can find the motor controller and a housing I designed for it here under a previous project: https://pinshape.com/items/36399-3d-printed-115th-ton-jack-screw
Gears in action: