Low-Cost Linear Actuator Based on the Sarrus Linkage

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Intro: Low-Cost Linear Actuator Based on the Sarrus Linkage

Linear actuators are used in all sorts of cool machines such as 3D printers, laser cutters, and CNC routers. One of the main contributors to the total cost of these devices is the linear guideway, which consists of components that maintain the straight-line path of the actuated portion of the device (e.g. a set of precision rods and linear bearings). Prices for guideway components can range from tens to thousands of dollars depending on their size and accuracy. One way to get around the high cost of these components is to replace them with a mechanism that converts rotary motion into straight-line motion. The Sarrus linkage, invented in 1853 by Pierre Frédéric Sarrus, is one such mechanism that can produce perfect straight-line linear motion without the use of any reference guideways. This project utilizes simple 3D printed or laser cut linkage plates and plastic "living" hinges to construct a low-cost Sarrus mechanism. A NEMA 17 stepper motor and threaded rod are then added to get it moving. The travel length of the actuator in this project is approximately 10 inches (254 mm) but larger or smaller version can be made by simply changing the length of the linkage plates. Enjoy!

Step 1: Materials and Tools

Materials

A. Linkage plate (4 each, 3D printed or laser cut in Step 2)

B. Motor plate (1 each, 3D printed or laser cut in Step 2)

C. Actuator plate (1 each, 3D printed or laser cut in Step 2)

D. Plastic hinge (6 each, McMaster-Carr part no. 1637A713)

E. Flat head screw, 6-32 thread x 3/8 in. long (24 each)

F. Press-in nut, 6-32 thread (1 pack of 25, McMaster-Carr part no. 94674A515)

G. Socket head cap screw, M3x0.5 x 12 mm long (2 each)

H. Hex nut, M3x0.5 (2 each)

I. Socket head cap screw, M3x0.5 x 10 mm long (4 each)

J. Shaft coupling, 5 mm to 8 mm (1 each)

K. NEMA 17 stepper motor with M3x0.5 threaded mounting holes (1 each)

L. M8 Acme threaded nut (1 each)

M. M8 Acme threaded rod, 300 mm long (1 each)

Tools

N. Metric hex key set

O. #2 Phillips head screwdriver

P. Needle nose pliers

Step 2: 3D Print or Laser Cut the Sarrus Linkage Plates

Using the attached STL or DXF files, 3D print or laser cut the following parts:

  • Linkage plate (4 each)
  • Motor plate (1 each)
  • Actuator plate (1 each)

The parts used for these instructions were 3D printed in gray ABS plastic. If you laser cut your parts, the thickness of the material should be around 0.25 in. (6.35 mm) thick. Wood, acrylic, MDF, or any other rigid material should work fine.

STEP files have also been attached for anyone who wants to make modifications prior to printing or cutting. If you're planning on using this actuator in an actual machine, you will probably need to add some custom mounting holes and/or increase/decrease the length of the linkage plates to fit your application.

Step 3: Insert Press-Fit Nuts

Insert press-fit nuts into the linkage plates, motor plate, and actuator plate as shown. Pay careful attention to the orientation of the motor plate and actuator plate.

Step 4: Install Linkage Plate Hinges

Position a plastic hinge between two linkage plates as shown and secure it using four flat head screws. Be careful not to over tighten the screws.

Repeat this step and connect the two remaining linkage plates with a hinge. You should have two sets of hinged linkage plates at the end of this step.

Step 5: Install Motor Plate Hinges

Position the motor plate and the two sets of linkage plates as shown. Install two plastic hinges between the motor plate and linkage plates using eight flat head screws.

Step 6: Install Actuator Plate Hinges

Position the actuator plate and linkage plate assembly as shown. Install two plastic hinges between the actuator plate and the linkage plates using eight flat head screws.

Step 7: Install Acme Nut

Insert two M3 x 12 mm socket head cap screws through the actuator plate as shown. Slide the Acme nut down onto the screws. Thread two M3 hex nuts onto the ends of the screws. Flip the actuator plate over. Tighten the two screws by holding the nuts with the needle nose pliers (or a wrench if you have one) and turning the screw with the appropriate size hex key.

Step 8: Attach Stepper Motor

Attach the stepper motor to the motor plate using four M3 x 10 mm socket head screws.

Step 9: Attach Shaft Coupling

Insert the 5 mm diameter end of the shaft coupling onto the stepper motor shaft. Tighten the set screws using a hex key (key size may vary depending on where you purchase the coupling from).

Step 10: Install Acme Threaded Rod

Thread the rod through the Acme nut about half way. Flex the Sarrus linkage so that you are able to insert the threaded rod into the shaft coupling. Tighten the set screws on the shaft coupling using the appropriate size hex key.

Step 11: Make Things Move... in a Straight Line

You're done building! Now you'll need to hook up your stepper motor to a controller to make it move. There are lots of great Instructables on how to do this, for example: https://www.instructables.com/id/Controlling-a-Step.... As always, I welcome your comments and feedback (good or bad).

If you like this Instructable, please vote for me in the Epilog VII and Robotics contests. Thanks!

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    47 Discussions

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    ponad1

    2 years ago

    Cool, you do a great job, it is like a hydrolic car jack

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    kooth

    2 years ago

    This is really cool! I ran into a sarrus linkage definition on Wikipedia a few years ago and thought they are very interesting -- now you have given me a reason to try to build one! Thanks so much for sharing!

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    steve000

    2 years ago

    What application would something like this have? The benefit of a linear actuator is that the overall height when wound down is just the length of the actuator, wound up its actuator length and extended bit.

    This on the other hand the length never shrinks as you still have the 300mm shaft sticking out. I can imagine sideways movements could work but up and down like a jacking action would be pointless due to having to run the 300mm shaft through the hole

    1 reply
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    mrandlesteve000

    Reply 2 years ago

    And you could replace the side hinged arms with sliding stabilization arms if width is an issue I would think, seeing as you have the big acme screw anyways.

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    Gilius

    2 years ago

    Beautiful design!

    How exactly does this handle loads? Aren't they transferred right into the motor shaft? Maybe I'm missing something.

    2 replies
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    MakerStrongGilius

    Reply 2 years ago

    Yes, you are right. It is definitely not designed for heavy loads in its current configuration. For a heavy vertical lifting application the motor plate would need to be redesigned to incorporate a thrust bearing to take the load off of the motor shaft.

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    GiliusMakerStrong

    Reply 2 years ago

    It still looks great. I love the large scale of the movement.

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    qamarsk

    2 years ago

    GR8 IDEA

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    RoyA10

    2 years ago

    There is a Bosch miter saw that uses this principle: http://m.youtube.com/watch?v=I10K3N-UCnY

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    OffBeatSocker

    2 years ago

    Is that all done to make sure that the motor base is to move relatively linear going up and down?

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    AndrzejR

    2 years ago

    nice. now if i could just scale this up to safely hold 500 pounds, (in weight, not currency) i'd have a good application for it.

    6 replies
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    dssokheyAndrzejR

    Reply 2 years ago

    Your best bet is a hydraulic jack for that kind of weight. The nut can slip under weight with not so happy results

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    AndrzejRdssokhey

    Reply 2 years ago

    Kind of what I was thinking as well.

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    AndrzejRbruce.desertrat

    Reply 2 years ago

    Neat, thanks, didn't know these even existed :) I'm looking for something 120v though. I'll dig around.

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    bruce.desertratAndrzejR

    Reply 2 years ago

    Surplus Center http://www.surpluscenter.com might have what you're looking for. The RV industry uses a wide variety of linear actuators that will support a bunch of weight; they're used for moving the pop-out sections in and out. They do tend to be 12 or 28 v though.

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    travlinjohn

    2 years ago

    Very interesting? As far as strength for the actuator Acme Nut is concerned you could raid the standard auto screw jack for the nut and the Acme screw. I'm not to sure if the shaft and screw are standardized sizes but would think so. Then getting a longer screw would be a snap. Why use plastic hinges? The joint is prone to fatigue failure and premature wear.

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    fozzy13

    2 years ago

    This is awesome! I never would've though of doing it that way. It would be interesting to actually build a 3D printer entirely using these mechanisms, and compare it to a more traditionally built one with rods and bushings. Thanks for sharing!

    1 reply
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    MakerStrongfozzy13

    Reply 2 years ago

    Thanks! I am actually working on a 3 axis design right now. I've seen at least one prior design that used Sarrus linkages for all 3 axes: http://www.thingiverse.com/thing:1425. It's a cool design but only has a 105 x 105 mm build area. I'm working towards a larger design that has less parts.