Introduction: 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!

Comments

author
ponad1 (author)2016-06-29

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

author
kooth (author)2015-12-13

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!

author
steve000 (author)2015-11-24

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

author
mrandle (author)steve0002015-11-25

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.

author
Gilius (author)2015-11-24

Beautiful design!

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

author
MakerStrong (author)Gilius2015-11-24

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.

author
Gilius (author)MakerStrong2015-11-25

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

author
qamarsk (author)2015-11-25

GR8 IDEA

author
RoyA10 (author)2015-11-24

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

author
OffBeatSocker (author)2015-11-24

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

author
AndrzejR (author)2015-11-24

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.

author
RedBinary (author)AndrzejR2015-11-24

I recently had a positioning project in which I used a 1000 LB screw jack from McMaster: http://www.mcmaster.com/#miniature-acme-screw-jack...

We use acme thread to support far more than this. I wouldn't shy away from screw actuation - just use the right size thread and nut.

author
dssokhey (author)AndrzejR2015-11-24

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

author
AndrzejR (author)dssokhey2015-11-24

Kind of what I was thinking as well.

author
bruce.desertrat (author)AndrzejR2015-11-24

There are numerous electric car jacks that will do this, hers' just one example: http://www.amazon.com/Black-Bull-EJ212-Automatic-...

There is a Make magazine article about modding one of these for Arduino control; sorry, I don't remember which issue.

author
AndrzejR (author)bruce.desertrat2015-11-24

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

author
bruce.desertrat (author)AndrzejR2015-11-24

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.

author
travlinjohn (author)2015-11-24

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.

author
fozzy13 (author)2015-11-18

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!

author
MakerStrong (author)fozzy132015-11-18

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.

author
zielger (author)MakerStrong2015-11-24

I really like this project and where you want to take it.

I found this design, that could (maybe) help you.
http://s3images.coroflot.com/user_files/individual...
http://www.coroflot.com/sulabhgupta/Wally-3D-print...

I hope you can use it somehow.

author
fozzy13 (author)MakerStrong2015-11-18

That looks awesome! I can't wait to see it when it's done!

author
Phil_S (author)2015-11-24

Nicely presented and engineered.

My old scissor jack will be called Mr Sarrus from now on.

I am planning to do an arduino controlled greenhouse window opener soon and was just going to use M8 stainless studding running in tapped nylon bushes instead of Acme. A 1-metre length of studding has a lot of possibilities.

Aren't steppers wonderful?

author
clazman (author)2015-11-24

Very
nice attention to detail, nice craftsmanship.

Utilizing the Sarrus mechanism is wonderful. There is much to be learned
from the ages.

I have but one concern and that is with the use of nuts.
Yes, nuts are okay for low precision.

I would like to suggest to the reader, that threaded bushings
be incorporated. They are meant expressly for this situation. The result is higher
precision. The extreme deformation necessary for nut installation can result in
poor alignment. Also, I might add, proper pressing procedures should be
followed.

On another note, I would suggest the inventor and/or readers, also
consider “four bar linkages”. I was introduced to them with the early
automobiles. That linkage system was used to guide the hood travel.

In my mechanical
engineering studies I took a class in four bar linkages. It was quite exciting
to create a linkage whereby the output would create a rather nice straight
line, albeit for a limited distance.

Again, kudos to you, my friend. You are a designer to be reckoned
with.

Best to you.

author
kriemer (author)2015-11-24

Very clever. I would not hesitate to go so far as to say "Very very clever".

One question; while I really like to look of the Press-Fit Nut (in step 3), I have to wonder if the construction would not be a but more robust if the nuts were located behind each of their respective plates. I do not see anywhere that this would cause any kind of limitation to the actuator movement. Not a criticism, just a question.

Great ible.

k

author
MakerStrong (author)kriemer2015-11-24

Hi kriemer, thanks for the question. I should have added a better photo of the nuts. The hex part of the nut doesn't press into the plate. I've added an image of the part drawing from the McMaster-Carr website to help clarify. There is a cylindrical section on the nut that actually presses into the plate. The hex portion sits on the surface of the plate. I used these instead of regular hex nuts because they center the nut in the hole much more accurately. If I had designed this to be strictly 3D printed, I would have added a recessed hex-shaped hole so that a regular hex nut could be pressed it. But because it is designed to be made by either laser cutting or 3D printing, I chose to use these nuts instead.

94674a515l.gif
author
kriemer (author)MakerStrong2015-11-24

Again, very very clever. I now have a 2nd question (sorry).

Thinking about X-Y axis stability I and wondering why you chose 2 sets of linkage plates rather than 4, or perhaps making a triangular plate and use 3 sets?

Thanks again

k

author
MakerStrong (author)kriemer2015-11-24

No problem, thanks for the questions. The three main reasons for using only two sets of linkages were:

1. Reduce part count and cost. You could definitely go with a tri or quad arrangement for improved stability but the cost will increase.

2. Allow for easier use in horizontal applications. If you use 4 linkage sets, the assembly can no longer be laid flat on a horizontal surface. It can still be used horizontally but you would need to raise it up so that there is clearance for the lower linkage set.

3. Reduce potential interference with adjacent parts and assemblies. With only two linkages sets, you only have to worry about clearance on two sides of the actuator.

author
_soapy_ (author)2015-11-24

You could make one of these better by adding a bearing to take the load that would otherwise be transferred to the motor.

Add a washer and a bearing under it to take the downward load. It'll add a few £ to the bill, but then it'll take less torque to step under load & not stall as easily under load.

You could also adapt a 12V car jack, that'd take some load!

author
MichaelV57 (author)2015-11-24

Simple demo of sarrus linkage:

https://www.youtube.com/watch?v=CPYbD1GUS1A

author
epss (author)2015-11-24

Very interesting, thank you for sharing.
Do you have a rough idea of the cost ?

author
MakerStrong (author)epss2015-11-24

There are lots of options for stepper motors and acme screws so the price could vary quite a bit. I paid roughly $67.50 (not including shipping). Here is a rough breakdown:

- 3D printed plates (linkage plate x4, motor plate x1, and actuator plate x1): $5.60 (112 cc of material @ $0.05 per cc)

- hinges: $6.90 (6 each, McMaster-Carr part no. 1637A713)

- press-in nuts: $7.80 (1 pack of 25, McMaster-Carr part no. 94674A515)

- stepper motor: $15 (Lin Engineering, model 4018X-07-04)

- acme screw and nut: $22 (purchased from ebay)

- shaft coupling: $5.20 (purchased from amazon)

- all other hardware: $5

Moving forward to the next design iteration, the cost could be lowered significantly (probably under $40) by making the following changes:

- replace the acme screw and nut with a regular M8x1.0 screw and nut (would require a redesign of the actuator plate). The acme screw that I got from ebay is pretty sloppy and probably not worth the price that I paid.

- replace the press-in nuts with regular hex nuts (would require re-sizing the holes on the linkage plates)

- 3D print the shaft coupling

- 3D print the living hinges

author
epss (author)MakerStrong2015-11-24

Thank you for this precious informations !

author
taylorhayis (author)2015-11-17

Brilliant! Good use of plastic hinges for zero movement.
What did you print the hinges in?

author
MakerStrong (author)taylorhayis2015-11-17

Thanks for your comment. Unfortunately the hinges are not 3D printed. A good living hinge requires the use of polypropylene. The hinges I used for this Instructable were purchased from McMaster-Carr and are made of injection molded polypropylene. The only 3D printer I know of that can create living hinges is the Objet Eden, which I don't have access to. I don't know of anyone making filament for FDM style 3D printers that can be used to produce a working living hinge. If hear of something, let me know... I'd love to try it out.

author
juliadee (author)MakerStrong2015-11-24

You can print good living hinges with Taulman PCTPE flexible nylon.

author
MakerStrong (author)juliadee2015-11-24

Thanks, I will have to give this material a try.

author
Raitis (author)MakerStrong2015-11-17

These guys had a pretty useful test of flexible filaments done. Maybe something will seem like a good shot for hinges. (:

author
rybitski (author)2015-11-24

This is a great idea! It reminds me of the Bosch miter saw mechanism http://www.boschtools.com/Products/Tools/Pages/Bos...

Any videos of this in action? I'm curious about how strong it is without the acme screw rod installed (resistant to lateral motion).

author
MakerStrong (author)rybitski2015-11-24

No videos yet. I will try to post one in the next week. The resistance to lateral motion seems to be pretty good as long as the load is centered. The design would need to be changed for a heavier off-center load... probably something with bearings like the Bosch miter saw design (thanks for posting that by the way, I had no idea that it existed).

author
OttawaMaker (author)2015-11-24

IGUS sells all kinds of interesting bearings and guides.

author
MattiV (author)2015-11-24

but not working cnc router table linear slide ,how slide table if not have rail were moving table ? and linear bearing and rod have wery expensives :(

author
electribe (author)2015-11-20

This is fantastic! I've been trying to think of a way to make a lift mecahnism for my Full Spectrum Laser (40W, 5th Gen) and four of this units linked would be a perfect solution. Is there any info how much load one of these can handle? I'm assuming lateral forces come in to play and that will reduce the life of the nut but I'm thinking four units equally carrying the load might negate some of that? Would be great to her your thoughts on that and if you have any ideas about a linked/calibrated control mechanism?

author
grigsby (author)2015-11-18

Have you found Nylon nut for M8 Acme threaded nut? Brass is not good for bearing material. My up-dn Brass (copper/zinc) Nut got wobbly on my MB-2.Brass is not good for bearing material. Bronze(copper/tin) (Nylon) is a good bearing material. I made new nut from nylon and it took up slop from brass nut. It was tight when I first put it on shaft, but oil and some incouragement (sp) made it work OK. I used the M8 shaft for tap to cut threads in the Nylon. (50 some odd years in machine shop helps with odd jobs).

Thanks for idea

author
MakerStrong (author)grigsby2015-11-18

Hi grgsby, I agree, the brass nuts that I get from places like ebay are typically not very good and tend to be rather loose fitting. I have been working on a threadless ball screw design that can be integrated into the actuator plate and will eliminate the slop and backlash. The actuator is definitely a work in progress and upgrades are planned. Thanks again.

author
padbravo (author)2015-11-17

Brilliant!
and tks for sharing the idea with us!...

I'll found a good use for this simple, economic linear actuator...

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Bio: MakerStrong is a maker-owned small business located in Ayer, MA. We offer affordable professional-grade 3D-printing services to individual makers, small businesses, and large corporations located ... More »
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