Let's Make Robots!

Linear Positional Servo Actuator

Pushes in excess of 3kgs to any position over 2000 steps

Take one Glue stick and wash the living daylights out of

it in 30 degreeC water, as the glue is water soluble.

Stick the servo horn to the rotational bottom

Cut a groove in the movable insert (this is the bit that the glue is normally attached to)

This will marry to the slider lug of the potentiometer (it needs to be a snug fit - no backlash)

Take one normal servo and convert it to a continuous rotation type .... however don't attach the normal 2 resistor mod..

... instead extend the potentiometer wire outside the casing.. these will be attached to the new feedback linear pot. :-)

This means that the servo is able to turn approx 7 full turns along its length, with works out as 2000 steps in my case.

..... and giving 7 times more Mega Torque

Side Tip :- unused Cat5 ethernet cables contain twisted pair wire - great for recycling (thanks NASA)

Testing with sons car controller - however was unable to test full range ........

First Test tipped the balance scale into "Err"

Second test i backed off the pressure to show that 3kgs can be reached..... certainly more........




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Any hints on where you have the slide potentiometer from, Gareth?

   To tell you the truth NilsB...... the "pots" been hanging around my tronics box for longer than i can remember....... when i squeeze my brain i seem to recall it was  from "Maplins" .... let me find a link....... http://www.maplin.co.uk/miniature-dual-gang-linear-potentiometers-2215 (mine was a 10K)  ..... just make sure its a linear type (ie not logarithmic volume control type)

Hey Gareth,

I'm glad that I wasn't the only noticing that Linear actuators are expensive and we should be re-using the worm gear assemblies that are around us everyday!

Last year I used an empty deodorant stick to do the very same thing and I think I should have shared this on LMR as it wasn't really appreciated so much on the MAKE blog http://blog.makezine.com/2011/01/14/deodorant-stick-linear-actuator/
I think you've inspired me to put up some more info on my design :)

I like that you have positional feedback was added, something mine lacked as I just modified my servo for continuous rotation and that was it. Another cool variant that someone came up with after watching the vid I posted was using a deodorant stick to drive syringes for neumatic control http://www.youtube.com/watch?v=_IMbTb4hmUc&context=C48a2774ADvjVQa1PpcFNnZzueNkHweG5icESVWH4qlkmxB_1jgaQ=

Anyway Congrats on getting Hackaday'd Gareth!


Yes that is a great direction too, all you would need is a "Stretched Limo"  potentiometer :-)

that's really a good idea... i was searching for a linear actuator for my robotic microhandler and yours is very good !!


Excellent!  I love it when junk is repurposed with such elegant results.

I bet some polymorph and maybe a bit of glue could be used to make a mounting bracket for a regular servo straight to the base of a glue stick like that. Won't have the range of your design (probably won't have much range at all actually) but saves modifying servo motors if your short on them.

Yes this is not only limited to servos - you could use GM motors and use the pot. to send analog back to mcu for feedback - this way you would get even better torque specs.

I will be adding PM to it shortly ;-)

Simply brilliant. Well explained and ingenious. I felt guilty imagining where I would actually place it on a humanoid. Also I'm going to Harbor Freight to get a pencil torch today now.

They can be used for lifting ladies eyebrows 8P

I use the butane torch knife a lot -  for cutting plastic/plexiglass its a dream however it has to be used out side (re:- toxic fumes), mine also has heat shink / soldering attachements.