Hoddem's DIY Linear Actuator

I put together a BOM and unfortunately all the little things really added up on this. I was hoping to keep the cost under $400 for just the actuator and under $500 for the actuator with sabertooth/kangaroo and power supply. Im sitting at $500 for just the actuator so I'm $100 off the mark.


https://www.dropbox.com/s/f8klubri7993mnh/DIY Linear Actuator R2 Assembly.xlsx?dl=0

The items in yellow are opportunities for improvement. Example, I am using clear PVC pipe at about $70 for 2ft, it goes for less then $20 at the hardware store for 10ft. I also purchased a lot from mcmaster carr to make life easier, I'm sure I could knock a few buck off by shopping around. 3d printed parts are based on Solutech PLA filament at $17.99/kg and 50% fill on all parts. No shipping is included in any pricing.

Maybe @SeatTime, @wannabeaflyer2, @SilentChill and others that have built linear actuators can weigh in on how it compares price wise

216 total parts, seems like it got a little away from me

Brilliant explanation as to your design thought train. and the reasoning behind certain decisions I for one thinks this helps a great deal for people experimenting , Thnaks for the Info @Hoddem

we must have posted at the same time so I missed the BOM got admit I lost tarck of what each actuator cost so somewhere down the line i'll have to revisit that , the consolation for me was that this was something we made and not off the shelf ( paying crazy Prices ) These were never going to be cheap as chips as we say in the UK but even now im still happy with what they cost me and more than happy with the amount I have learnt here see other designs being developed Loads of ways to skin a cat and there all on this Great forum ..Amen to that LOL

I follow with interest, really nice project!

@Hoddem
after longer time of thinking i decided to make both flange of the U-joint assembly with my CNC machine with 7075 aluminum.
this is definitely strong enough. OK this takes more time compared using the 3D printer.

The long actuator shaft is made of polished stainless steel in my build. i believe this will be strong anough for any movements incl. side-force-impact.

also will use contactless position-sensors inside the actuator. 500mm magneto pot in my case.
https://www.digikey.de/products/de?keywords=905-1037-ND


thanks again for the good actuator design.

Best,
-Kermit

Have you had first-hand experience with these?
What are they like for jitter & linearity?

I looked into these and it looks as though there's a small internal magnet *inside* the pot which carries/is the wiper and rides up & down contacting the resistive strip and completing the circuit ...this follows your external magnet.

My worries were:

* Jitter caused by the internal magnet not moving completely smoothly and not following the external one as quick as I'd like
* That friction of this internal magnet would eventually begin to wear out the resistive element causing inaccurate readings, especially where the tracks get most used
* That fast sudden movements could cause the pot's internal magnet to lose track of the magnet mounted to the actuator.
* They're advertised as 'linear' as in move linearly instead of rotationally, they *don't actually advertise themselves as being 'linear' in terms of electrical characteristics, so if that's the case I'd need to correct for that in software.

...So yeah, when these are advertised as "contactless" it didn't seem to be in the same way as a hall effect sensor is. There are still internal parts which contact each other and will wear out (most likely unevenly).

Bearing all this in mind if you're going down the linear pot route you may as well just get a regular one and mount the wiper to the actuator directly.

Awesome, I love CNC parts. What CNC do you have and how do you like it?

I recently picked up a Cheapo Chinese CNC to play around with. I wont use it for anything on this build, but I am hoping to work it into future projects. I don't have a lot of confidence that it will do aluminum, but it should do plastic and hopefully carbon fiber (I am starting to dive into FPV Quad Racing).

OMG, I have workshop envy!
How do you keep your workspace so tidy? I have to pre-warn the fire department every time I set foot inside mine just incase I need rescuing

Haha, I used to be like that.
Last year I convinced my wife that the garage needed some attention so I got to fix it up just the way I wanted it. Be careful what you wish for though, I seem to spend almost as much time keeping it clean as using it now. I even "accidentally" leave stuff where my wife parks to persuade here to park outside.

I had a little time this afternoon to work on the actuator, something I have been meaning to do for a while was address the shaft on my dc motor.

The shaft is about 1.5" long and .75" are threaded, that doesn't work for my design so I had to cut the threaded part off.




I used my angle grinder with a cutoff disk to cut it off and then cleaned it up with a hand file. I was careful not to overheat shaft.



Here is the motor with the gear and couple installed.



I installed the mounting plate and put in the 3 zip tie mounts that will hold the encoder cable.



I ran into a problem that I kind of knew would happen. On the bottom of my motor is a small protrusion that interferes with the threaded rods in my design.



I marked the location of the rods and then filed them down with a hand file. because the part is aluminum it didn't take very long. A Dremel would make quick work of this problem, but a hand file works just fine.

Tough to see in the picture, But the threaded rods ride right on the motor housing now.




I Built up the encoder with mounting bracket and gear.



For whatever reason I didn't get a picture with the encoder mounted, but it seems to fit nice and the gears mesh very well.

For the heck of it I threw the whole thing together and set it vertical to get a feel for how big it is. Keep in mid the middle section is not the correct length as I have to cut the PVC down yet, but wow this thing is tall.



I believe I have everything printed and ready to go so now it is just a matter of assembly. I will have to cut the threaded rods, but I will probably do that while they are installed to get the correct length.
I can already tell this thing will be a bit of a chore to assembly, I may have to print up some jigs to help with assembly.

Hi,

i have the proxxon FF500CNC type of machine with an additional 4th axis and a 5- axis rotary table for smaller parts


i also made all the stuff for my current 6DOF motion seat with it, e.g. the steel servo arm or the sensor chassis with POM material.

yes they sell this as contactless
but you are right it is a magnet inside which follow the movment-magnet. so it is not really contactless.

the data sheet said , is specially made for linear position sensing of actuators, so i hope this will be fine.
the only think which makes me wonder is that theres a small hysteresis. this should not be a problem, because i have programmed
a hysteresis already to prevent noise movements. I've already bought 6pcs, so lets see. hopfully it can be used.

this is btw. my DIY 6DOF motion seat controller. it's an ATMEL1280 CPU with an USB interface internally.
The device is taken from my project which i made for my radio controlled model helicopters and delivery everthing what is needed to control the 6DOF motion seat and deliver an adequate interface to the computer.

Wow, that is just awesome. Blows my setup out of the water, but everyone has to start somewhere. Congrats, you should do a time lapse video of a part using all axis's.

I was doing a little thinking and I think I need to change my connectors for the motor. I was planning on using 3 audio twist lock connectors for my panel (4 circuits per connector).



I need a total of 12 wires to run everything
Motor - 2
Encoder - 4
Limit Switch - 4
Fans - 2

By the looks of the Audio connectors they will work great for the limit switched, fans and encoder because they are all low current applications. however the motor is going to be drawing 65+ amps at full load and probably even more. Looking at the wires coming off the motor (10g) and then the terminals on the audio connectors(.187") it just doesn't look like a good idea. right now I am thinking about throwing an XT90 connector at the problem, It looks like I can design a panel mount that would be a direct replacement for the audio connector.

The problem is I will be 2 wires short so I would have to either add another connector into my already small space or come up with another solution.

It looks like the Kangaroo board is using ground for the limit switches (I need to investigate) so I should be able to share the ground between each limit switch and free up 1 connection. and possibly share the ground for the fans with the limit switches.




If it works out, I would have the following wiring.

XT90 - Motor
1 - M+
2 - M-
Audio Connector 1 - Encoder
1 - 5V
2 - G
3 - A
4 - B
Audio Connector 2 - Limit and Fans
1 - Limit switches & Fans ground
2 - Limit 1
3 - Limit 2
4 - Fan 12V

This would open up the option to still use the audio connector but use two circuits for M+ and two circuits for M-. If anyone else can weigh in on how they connected their motors Id be glad to hear it.

FYI, I updated the 3d model on grabcad

https://grabcad.com/library/hoddems-diy-linear-actuator-r2-1

For whatever reason the 3d preview doesn't work so you have to be able to import .step files which fusion 360 does.

Link to all the pictures I have taken so far of the design/build

https://www.dropbox.com/sh/ctzopvevrqbyady/AAAne3_lItC_UxgIZxVJoV5Wa?dl=0

Have you considered an industrial connector such as Han Harrington... http://www.harting.co.uk/new-han/
With this style of connector you can configure the pins to your own requirements. Where I work we even mix pneumatic and electrical connections into the same connector.
They won't be the cheapest of solutions but they sure are a good quality product.

PS, loving the attention to detail on your actuator. Hope it works as great as it looks!!!

I looked at similar solutions on McMaster Carr and Automation Direct. I have used those types of modular connectors before and they are really nice, but a little out of my price range for this build. I was thinking about it more and I might go with 2 standard PC power cords for the motor and an Ethernet cable for the limit switches, fans and encoder.


it would look like this





I forgot to check the kangaroo for common grounds so I still have to do that tonight.

I also ordered some XT90 Connectors and I will see how those look when I get them. I like the Idea of using off the shelf cables though.

Boom!

Just WOW, awesome work dude ! can't wait for tests

What is the material of the tube OD20xID12 you put between rod end and carbon shaft ?

will the collar be strong enought ?

edit : just a stupid question : why did you buy the 25mm shaft in carbon nor in steel ? because of the weight or the rugosity in bearing ?

Thanks

wow very nice!!! need some led light inside