Building a Lower-power Linear Actuator with Arduino | James Bruton

Building a Lower-power Linear Actuator with Arduino: quite a few people have asked me about scaling down openDog to make it lighter and cheaper, so I thought I'd discuss the options in this video. I'm using a motor with an encoder and an Arduino Uno to control position and velocity.
You can get the CAD and code from: github.com/XRo...
My open source robot dog project. It includes everything from 3D printing to coding, including a lot of CNC cutting and installing all the electronics myself.
If you want your very own four-legged friend to play fetch with and go on long walks then this is the perfect project for you. This way a dog can literally just be for Christmas. The full CAD is available at the link below for anyone that’s keen to build their own.
github.com/XRo...
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Former toy designer, current KZbin maker and general robotics, electrical and mechanical engineer, I’m a fan of doing it yourself and innovation by trial and error. My channel is where I share some of my useful and not-so-useful inventions, designs and maker advice. Iron Man is my go-to cosplay, and 3D printing can solve most issues - broken bolts, missing parts, world hunger, you name it.
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[@Diamonddrake]

James knows this, but for anyone that was interested in how to tune the pid controller for not quite reaching the set point. That’s the integral value being zero. The i in pid will gradually increase the power if it’s not strong enough to reach the set point, so having it zero means that it won’t be able to speed back up after its started slowing down. James awesome video as usual.

[@daedalusspacegames]

I propose we call the scaled-down version of the Open Dog project Open Pup.

[@averagejoe9040]

I second this

[@MouseGoat]

LOL yes! I 3rd this!

[@dummypg6129]

im gonna leave this dot(.) in case this gets many likes...

[@toop4538]

Opup

[@Scott_C]

I 4th this.

[@michaelangeloonassis2427]

What a great series of videos. I've been working on building a smaller quadroped, and am planning on making my mk2 version roughly 1/2 the size of OpenDog using a combination lead screws and custom planetary gears as well as pancake brushless motors like the ones I use on my drones. Thank you for the great vid!

[@Will_Huff]

Awesome example of making a smart cheap linear actuator...useful for many projects..Thanks James.

[@douglasmaclean5836]

This is the greatest channel ever ! hands down... James is the Elon Musk of "just do it" robotics technology education. This guy needs a Knighthood. Seriously. In fact, i bet Elon Musk watches this channel with his kids.

[@jamesbruton]

thanks!

[@douglasmaclean5836]

Your welcome James ! ... I love all of it !

[@bruceneely4859]

looks like a good start on a way to do this on a tighter budget, for a half scale project. my experments with planetry gears have not been a lot of success so I may look at going this way, though I may want to gear down some, since the current motors I have a re much to fast.

[@jdphotograph]

You also need a dead zone. Most actuator drivers have a dead zone. If you don't have a dead zone your motor could end up riding the edge all the time and kill the motor or the battery power.

[@jamesbruton]

Yep - you could set a condition that if the output of the PID is less than some amount, then just make it zero.

[@oisiaa]

Twelve 2kW motors means this robot has a max power of 24kW...that's a 32 horsepower robot!

[@jamesbruton]

yes that's the peak, but they are limited to 30A at 24V at the moment and it looks powerful and fast enough

[@computerjantje]

I work with horses. The power of 32 horses? I really cannot imagine this touches any reality.

[@MrFlyingSquirl]

@@computerjantje rather hilariously one horse is actually equivalent to 15 horsepower. So it's about the same as two horses(?) which is still pretty scary

[@KuraIthys]

Lol. Just shows you the flaws that can arise in measurement techniques. Still, it worked at the time to establish a point of reference...

[@Scott_C]

@@jamesbruton James, It seems, then like you could make a saddle for Open Dog. You know you want to ride it. (whispering) Doooooo iiit Ask Colin to help with the seat design, or ask him to ride it if you want a crash test dummy. :D Also this makes me want to expect galloping not just walking from the OD.

[@joeldday]

Great video James, really useful to go through, and I learned some stuff that I didn't pick up from your other open dog videos, very interesting! I would love to see someone build a mini open dog!

[@jamesbruton]

thanks!

[@Scott_C]

"Open Pup"

[@bgrant1512]

Its great to see you doing more hobbyist level content. thinks like open dog are great but I enjoy the projects that I can build on a hobby budget.

[@nickjs5773]

Boston dynamics has just upped the game. We want to see it dance!!! You have got a good range of motion, and once you are able to lift the legs, I am sure you will be able to choreograph something.

[@judgenap]

Thanks James . Your leading the way forward

[@Kah7654]

The main problem with brushed motors is that they have a very limited speed range. For robotics it's important to be able to move from very slow to very fast. Otherwise the robot won't be able to react fast enough to compensate failing balance while still be able to move slow enough to do smooth tracking movements. This is very visible in all those cheap servo driven robots: If they are able to move fast, they are also quite jittery. And they are generally open loop systems, so they aren't able to balance and use fixed, precalculated movements. So I don't think that brushed motors are a good replacement for BLDC motors, unless you don't want a real balancing robot.

[@jamesbruton]

That is true, but it's fine for someone who wants to learn on a budget

[@artbyrobot1]

I disagree with this. Just because one uses brushed motors does not mean one cannot set up position feedback systems and make it closed loop in that way. You can also create custom motor controllers that vary the voltage in order to vary the speed for slow movements that are smooth tracking movements and crank the voltage way up for high-speed movements. Or to slow the speed down you could simply pulse width modulate the current flowing to the motor to slow it down that way. I think you are too quick to rule out brushed DC motors which are way cheaper and because they're so cheap custom solutions and accommodation should be made in order to use them as effectively as brushed DC motors. This can and should be done and can give you professional results no less than a brushless DC motor would give you.

[@computerjantje]

I heard the magic words that just made my day: "...a humanoid robot in the future....." YES YES with James on a humanoid robot project, the world will finally get an affordable build-able help around the house (Sonny, I Robot 2004 C3PO, Stars Wars). Or if the autonomi is the bottleneck then at least we can have a remote control robot like in Surrogates (2009). Boston Dynamics are good but they are very very slow considering the size of the team and the money they have. I set my hopes on James :) :) :)

[@Vampyredh]

Have you not looked at his other bi-ped projects?

[@computerjantje]

Ofcourse I did. I just am hoping James will eventually put a lot of knowledge and energy in an new and better humanoid.

[@tibfulv]

A T-800 endoskeleton could be useful, too, lol.

[@danwood1121]

Thanks for the info in this video, I was trying to do something like this to mimic hydraulic functions on an R/C excavator.

[@10p6]

Woof woof. Doggy wants to go walkies.

[@lifefacts.8794]

I APPRECIATES YOU BROTHER,YOU'RE LIVING MY DREAMS.

[@tad2021]

I've done a bit with quadrature encoders with Arduino before and found PJRC's / Paul Stoffregen's "Quadrature Encoder Library for Arduino" to work quite well. There does exist dedicated chips for quadrature encoders, but these are pretty difficult to source in the age of super cheap microcontrollers.

[@yalgret]

You can buy linear actuators which are basically this, and are available with position encoders. Although I think this could be done cheaper.

[@jamesbruton]

Yes you can, but as you say DIY with 3D printing is often cheaper and fits the machine better

[@the_real_foamidable]

Ball Screws! Count me in.

[@calebsherman886]

If I were to make my own Dog I would use variable compliance/stiffness actuators. They seem to act more organically and I like that.

[@AttilaAsztalos]

Yup. Anyone taking a go at this needs to stop thinking in terms of commanding absolute positions and start thinking in terms of applying force to soft joints. All your stiff maths goes up in a puff of smoke in the real world the first time you tried "positioning" one of the legs straight trough a pebble you didn't know was there.

[@calebsherman886]

@@AttilaAsztalos Exactly.

[@johnbeck6996]

You have a point, but walking in an controlled environment is hard enough. Get THAT working, and then enhance it for less predictable ground.

[@Paint2D_]

I wonder if the big robot is powerful enough to carry a person and make it the most insane way to get around the city.

[@jamesbruton]

Probably with some metal upgrades, although balancing and waling would be a lot harder

[@tibfulv]

I'm sure the levitated platform I've got planned would rival it in insanity, lol.

[@thecrazylooser7]

You again at top of my searches... ok ok subscribing 😒 Good stuff

[@user-zj2mb3sp3x]

I recommend you look at the electric skateboard motors, that are based on the 6374 and 6354 motors. For a little bit more money ~$20 more, you can get a higher quality, better wound, better wire motor, that will put out 3.2kw in the same package, and also stay cooler. DIYelectricskateboard, and enertion both have motors like this. They started with the same motors as you, and have had a nicer version made for skateboard use.

[@yalgret]

Where can I get those rotary encoders? I mean the ones in use on the large Open Dog. Would be really grateful if you could let me know.

[@jamesbruton]

The ODrive Robotics web shop

[@yalgret]

Thank you, I will have a look

[@SianaGearz]

I wonder, how did mechanics in 28cm toy robot dogs like SONY Aibo and Silverlit i-Cybie work? It must have been pretty damn cheap and simple at least in the latter.

[@ashaygoli3014]

In this case we will be requiring two external interrupts per encoder(motor actuator), Since uno has only 2 external interrupts we would need that many controllers for each actuators. Mega has 6 interrupts would still be less in case we need to build more actuators. Next option would be to use pin change interrupt as in Due so as to use all pins as interrupts.But I am not sure about its reliability. Another bit expensive option would be use external counter circuit and send data to Arduino via SPI or I2C. This solution would reduce the load on Arduino for counting the pulses. What would be your preference in such scenario?

[@pawelaco]

Beautiful machine

[@tinker7722]

Great Job! that's nearly an infinite pinion :=)

[@AureliusAurelius]

Great video. I initially thought the encoder difference was a partial derivative dx but since the loop is running at a constant time interval it’s actually dx/dt with dt being a constant 20ms. BTW James, do you have a dev server running on a raspberry pi? If not, that would be a cool and easy project :)

[@noisevector]

I'm wondering how Boston Dynamics did their legs for SpotMini. They are very fast, slim and dynamic.

[@jamesbruton]

I think that is an entirely different setup with complaint joints - some discussion is coming up in the openDog series

[@cheesypufs]

They're using compliant actuation. Could probably do something similar with OpenDog by adding some springs in the leg joints to create Series Elastic Actuators. In fact James did a video on this a few years ago.

[@hectoraraujo1822]

I like it is there going to be an other episode or part 2

[@jamesbruton]

nope, this one is a one-off

[@FlyWithSergio]

Hello ! How can I put a switch that tells the actuator to finish the movement and then go to the other direction? Thanks so much!

[@Edwin-dh2oc]

beautiful design

[@CristiNeagu]

This video made me realise how cheap all of these things are. I never expected you can buy a linear ball bearing for anything under 250 pounds, let alone for 25 quid.

[@code-grammardude5974]

Yeah, Awesome, Cool! (first edited)

[@ashleyobrien7514]

is there anyway of modifying the code to use digitalinput signals to position the rail rather then using the identifier a ?

[@solarsynapse]

Couldn't you use a standard pot at a hinge joint or a linear pot on the actuator as feedback and it would work as a standard servo with proportional speed each direction?

[@jamesbruton]

long linear pots are hard to find

[@bendevereux7696]

Downloaded the Arduino code and I'm having an error with PID_v1.h not being recognized as a file or directory. Any ideas/solution as to why?

[@asas12337]

can you do something with hydraulic motor like boston dynamics atlas

[@kryptocat4240]

How to interface linear actuator with load sensor or with strain gauge ??

[@jamesbruton]

Check out my Sonic the Hedgehog series for info on that

[@kryptocat4240]

@@jamesbruton thanks for the replay

[@kryptocat4240]

@@jamesbruton sir which encoder is best among AS5047P and AS5048B Sir please answer thise question

[@bbogdanmircea]

Wow, a practical lesson about cheap Arduino linear actuator AND cascaded PID control ! That's amazing ! Would a Mabuchi RS-540 work for the same purpose ? They are so cheap and powerfull ! And also a technical question, I cloned you repo from GitHub, what Arduino version is needed to compile the files ? Keep up the fantastic work, I am amazed by your projects every day ! Do you have also an actual job ?

[@jamesbruton]

yep - you could use any motor with an encoder on

[@bbogdanmircea]

@@jamesbruton I would think about a combination, for the top motors a screw like you did, but for the knee and hip 10kg servos, would they work for a smaller dog ?

[@statorworksrobotics9838]

From what I've been able to research, linear actuators are not the way, because of space and the inefficiency of lead screws. I think boston dynamics and the ishikawa lab just use geared motors with 90 bevel gears right at the joints. There are worm geared motors on ebay that are ugly and cant be back driven but offer a huge bang for your buck. I'm about to order some of those. Some smart programming can make up for the lack of compliance.

[@simondevantier3983]

Any way to control the motor not by typing in the serial monitor. Fx a button with a fixed position?

[@jamesbruton]

yes - just by updating the setpoint variable from your own code...

[@mouhidin26]

Hello, I have a small project for my car spoiler and I wanted to customise the spoiler. Like when I reach to 120km the spoiler will rais up and when I slow down the spoiler goes down to its zero position, so I got my 3d printer for my first time and I designed an linier actuator that works either steper motor or servo and I got arduino uno, the quastion is how can I control the actuator to rias up at 3600 turns to rias 15cm hight and to be signaled by reaching the speed 120km and when u slow down it gives a signal ( order) to the actuator to go down? Please if you could help me

[@Traderhood]

Awesome!

[@MrQhuin]

You should work with Boston Dynamics. You just build an amazing robot by yourself.

[@crayzeape2230]

I'm not sure powering the encoder from 5v is the best idea here, the Arduino appears to be configured for 3.3v, and you can't be sure the encoder outputs won't go above the Arduino's 3.3v supply rail. Edit: I might have been looking at it wrong, can you clarify on the Arduino supply voltage?

[@jamesbruton]

It's a 5v Arduino

[@crayzeape2230]

@@jamesbruton All is good in that case, thanks for the clarification James.

[@lionwangsinovoip]

BPI:bit arudino IDE support: github.com/BPI-STEAM/BPI-BIT-Arduino-IDE/wiki

[@neodymium2557]

Would a tail theoretically work on a model like this?

[@makewhat8908]

Well， it's really a nice project！However I wanna to know how to make the opendog walk and rotation? how to do the gait planning?

[@jamesbruton]

some of it is coming up next week, but it's a lot of development

[@makewhat8908]

Sorry to bother you again. But Thanks a lot! It is worthy of waiting indeed.

[@One-real-human]

Make like a Big Dog sized robot

[@jacktheripper2746]

Is that Optimus Prime on the right and Megatron on the left?

[@paxon57]

I have a challenge for you, look up newest Boston Dynamics video "UpTown Spot" xD

[@MR-id6fz]

Nice 😍😍😍😍😍😍

[@tiagotiagot]

What about using drone motors?

[@jamesbruton]

yes those are brushless outrunners, so you'd need the Odrive

[@tiagotiagot]

You can't just use an encoder and a regular reversible ESC?

[@jamesbruton]

An encoder linked to what?

[@tiagotiagot]

Either the motor shaft itself, or the long screw rod thingy

[@jamesbruton]

connected electronically to what?

[@Jkauppa]

brushless dc motors

[@TomsBackyardWorkshop]

Why not just use a linear actuator? Ive seen them as cheap as $10 on ebay.

[@jamesbruton]

With an encoder? Links?

[@MrNlce30]

Isn't it cheaper and easier to just buy a dog?

[@sdqf]

Wow! Like! c;

[@JuraganLED]

18:03 don't do that, you can get splinter or cut

[@Br1ckInTh3W4LL]

Perhaps an even cheaper method to get large gear reduction would be a differential cable drive. Do a google search for "act5020017"

[@takismail]

James, did send you a PM on your FB page, has something that will help your future project, feel free to contact me anytime.

[@anthonybolston8982]

Can we see it walk and try to jump

[@jamesbruton]

eventually, but there's quite a bit of development to go.

[@SpaghettiEnterprises]

If(currentMillis % interval == 0)

[@ashuklplays4624]

Watching in 2018?

[@Dust599]

Robotics is expensive.... Sounds to me that some viewers just want a toy.

[@DebzLife]

Second

[@R1T24mnt]

Omg why are you dragging this project sooo much just make the dog walk please! 😭😩

[@jamesbruton]

These types of projects take time - making it walk isn't that easy, so some weeks I need a different/shorter/easier video.

[@CaptainNuki]

yes. Go budget builds

[@sourdonkeyjuice]

You're just procrastinating programming the walking gait.. ;)

[@MsSomeonenew]

Well that stuff is a ball buster, essentially still the final frontier of robotics.

[@KlaasDeSmedt]

To remove the final position error of the motor, increase the Ik factor of the PID by just a little bit. If Ik is 0, you only have a PD controller, not a PID controller.

[@adriancarreno3661]

Exactly. Integral gain is what controls the accuracy of the final setpoint, derivative gain controls the responsiveness to quick changes and proportional gain controls the overall speed. James (I hope he reads this) your should also tune your PIDs using some method like Ziegler-Nichols instead of manually

[@anoirbentanfous]

Thank you James

[@Nathaniel_Belles]

Once you get it walking you should work on using ROS for object recognition, SLAM, and path planning with like the Xbox Kinect or something similar.

[@jamesbruton]

That's the vague plan!

[@Nathaniel_Belles]

James Bruton Can’t wait!

[@dummypg6129]

i had a project when i was in college that i made a bi directional dc motor using astable multivibrator circuit driven by 555 ic for pwm, if i could get a gear, belt, linear actuator guide, i could theoretically make a small OpenPup (as name suggested by fellow commentators). I wanted to make one using the small drone motors.

[@DanSayers]

But can it dance tho?

[@jamesbruton]

One day

[@ZillionPrey]

Would be awesome if you could do the same as the recent one from Boston dynamics :D

I also work on a belt driven linear actuator if you interested we could discuss it in detail.

[@beakz]

I take it you've seen the new Boston Dynamics UpTown Spot video, James? Am really enjoying the progress you are making. This has to be my favourite project to date.

[@jamesbruton]

yep - looks good!

[@lightvsdark21]

SAME!

[@brainmind4070]

I was a little disappointed with that video. It was impressive, but I feel like Spot could do a backflip or at least a handstand using its gripper to balance.

[@mikekudritski557]

I don't understand why you need two interruptions? It is possible to have only one rising/falling interrupt and check the status of another pin.

[@jamesbruton]

It is, but two is more accurate

[@thommashich41]

Thanks for sharing this. It was good to see a cheaper alternative to ball screws on the Open-Dog.

[@richardbloemenkamp8532]

Yes, this is nice. Especially, I think that most people like to make such a robot more to learn, as a hobby and to show to friends. With these components it becomes much more affordable and it still allows to learn about mechanics, electronics, try all the algorithms and future machine learning to make it walk, automatically follow a path, recognize the environment etc.

[@TheWreckingYard]

Cool idea this makes it much more realistic for the amateur, I think I figured that there was several thousand in motors and controllers in open dog, this should significantly reduce the cost.

[@scienceteam9254]

so... uh... boston dynamics made a dancing spot video... *THEY'RE ONTO YOU!!!*

[@mastermattie]

Next level: kzbin.info/www/bejne/oXmllImiptWpkJo

[@statorworksrobotics9838]

This is fantastic 👏 as always, I'm amazed you did this for breakfast as a small 'break' from the big project lol 👍

[@voidofspaceandtime4684]

Now this is dog

[@vilho4649]

Hope id have those recourses ur the best thank you

[@maatwerkengineering3398]

i'm having accuracy problems with this setup. i ran this exact code on my Arduino Nano connected to an encoder with 32 steps/rev. No motor, just an encoder and the Arduino Serial Plotter. It misses about 20% of the steps. What can i do to improve it?

[@nelsondisalvatore9812]

Ah! Screw that, make it bigger!

[@tetradb_]

Thanks for this breakdown, awesome!

[@cheesyboofs]

Hi James, please take this in the spirit intended but the misses and I tune in every week to see it walk! It's hard enough to maintain her interest through all the coding stuff as it is! Can't you focus on getting this one to walk before its offspring?

[@jamesbruton]

Yes I'm not actually going to make a smaller one - it was more of an educational video. It 'walks' in the next video, but it's not pretty. Part 13 deals with dynamic stability and the discussion about what's needed next to make it work well.

[@agentpx]

I would love to see more tutorial for this where you show different components of a robot, I hope you can create more videos like this (e.g. bending a leg of a Robot, rotate head, tilt, etc. ) More power!

[@jamesbruton]

I would like to do that

[@Scott_C]

Stay subscribed or become a Patreon. I'm not saying he's planning on it, but he has alluded to it.

[@multiplio2924]

Have you seen Boston Dynamic's latest video? I think dancing should be the next priority after walking... :-)

[@jamesbruton]

yes

[@TheMrJuoji]

why not use cable and pulley instead of screw ?

[@jimdunleavypiano]

Is nobody developing or using linear induction motors as actuators in robotics? They would seem to be the ideal solution (at least in my head this morning).

[@jimdunleavypiano]

To answer my own question - ieeexplore.ieee.org/document/5379608 (but you need an account to read all but the first few paras unfortunately, and I haven't got one). Edit: full article here - www.researchgate.net/publication/224099052_Novel_design_of_biped_robot_based_on_Linear_Induction_Motors . It's quite an old article and seems not to have been taken further. An issue was power consumption, but with the latest battery tech maybe less so now?? Fancy having a go James? :)

[@kooky45]

Why is there almost inaudible music in the background?

[@jamesbruton]

Is that your only actual comment - the background music? Is that literally how inspiring this project is to you?

[@ZombieB]

Cool

[@rodstartube]

you mean a robot puppy ??

[@martinwalters1954]

*people on a budget* Vs what Mr, DeepPockets? sheeezusfuckingchrist it never ceases to amaze me what people with unlimited money post on youtube. As if the average working schmuck could afford even one of these motors.

[@jamesbruton]

shall I just not make any videos then or?

[@lukerooney2277]

Hi James, do you think it's conceivable to make a miniature version powered by servo motors, rather than using a brushless motor / ball screw combo? Of course this would come at the cost of performance, but it would be a lot cheaper. Right now I'm doing calculations to figure out the joint torques, but in the meantime I'm just wondering if an expert such as yourself thinks it would be possible? Thanks.