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### Topic: Motor for very slow rotation (Read 9788 times)previous topic - next topic

#### Sievers

##### May 27, 2014, 08:06 pm
Hi there

I am new to the world of Arduino and very excited about what I have learned so far. I am looking for a stepper/motor which can rotate very slowly. Essentially I would like to be able to vary the speed between e.g. one rotation a minute down to one rotation per day. My first thought was somewhere along the lines of combining gears of various size to slow things down a bit but I thought I'd just throw the question into the pit among more experienced users and see what came out of it.

Cheers

#1
##### May 27, 2014, 09:48 pm
You can create a pulse to make a stepper "step" whenever you'd like. If little discrete steps won't do it for you, then gearing would be the next step.
1/minute = 60/hr = 1440/day
Down to 1/day. Quite a range.

Hmm - did you intend one/period as one rotation at the end of a period (minute or hr or day), or a slow, continuous rotation?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Sievers

#2
##### May 27, 2014, 10:36 pmLast Edit: May 27, 2014, 10:38 pm by Sievers Reason: 1
Sorry for being unclear
I meant slow continuous rotation.
The reason for the wide range is because I would like to make a camera mount for rotating timelapse videos and those require slow rotation, yet I also need to rotate it quickly around to a given location during each initiation. If a solution to the "goto angle X now" problem could be solved, the range could probably be narrowed to, say 1/hour-1/day. So in general a "slow" gear.

#### MarkT

#3
##### May 28, 2014, 09:55 am
Stepper motors have a fixed number of steps per resolution (200 commonly) which
may not be enough angular resolution for you.  Microstepping can help increase the
resolution but if you need a lot more then gearing or toothed belt reduction drive would help.

Steppers consume power continuously which may be an issue - the alternative would be
a closed loop system with encoder and DC motor.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### RoBoTs9999

#4
##### May 28, 2014, 12:17 pm
If you type 5v stepper motor on ebay, sorted by best match, there is a very slow moving stepper motor. 2048steps = 1 rotation.

#include <Stepper.h>

const int steps = 1;

Stepper myStepper(8,9,10,11);  //type in which pins the stepper is connected to

void setup(){
myStepper.setSpeed(200);    // type in how fast you want it to turn. max speed 200
}

void loop(){
myStepper.step(2048);  //type in how many steps it should take. write HIGH if you want it to never stop turning
delay(1200);                       //you don't need the delay if you don't want it
}

#### scottyjr

#5
##### May 28, 2014, 01:49 pm
This may be a solution. - Scotty

#### MarkT

#6
##### May 28, 2014, 07:31 pm

If you type 5v stepper motor on ebay, sorted by best match, there is a very slow moving stepper motor. 2048steps = 1 rotation.

Yes and its pretty useless for this task - it has a lot of backlash(*) and doesn't have
the torque to turn a camera.  Its designed to rotate small air vanes in car air-conditioning
systems.  Something like a NEMA17 format stepper might be more appropriate - I've some
Astrosyn ETS535's I got a while ago that are 10 ohm windings and 400 steps per revolution
which would be pretty handy for this (esp with microstepping).

(*) My 28BYJ-48 has 5 degrees or so of backlash, about 30 steps worth.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### michinyon

#7
##### May 29, 2014, 04:05 am
If he is rotating his camera very slowly to follow the sunflowers or something,   then backlash is not necessarily going to be a problem.

#### justone

#8
##### May 29, 2014, 05:00 am
Also if only going in one direction for image capture then a simple anti backlash (a rubber band) could be used.

#### dave-in-nj

#9
##### May 29, 2014, 01:20 pm
the guys who do telescopes have the technology you are looking for.  one rotation per day on a large diameter worm gear.
1 roation per 24 hours, with a 10 inch circumference driven disk (about 3-1/4 inches dia)
and a worm with 10 threads per inch will need 100 rotations of the driven gear too spin 360°.  a stepper has 200 steps per rotation or about 20,000 steps per day or 833 steps per hour or about 13.9 steps per minute.   you can get different threads, but the speed is between that of watching  grass growing and watching paint dry.

use a stepper and a threaded rod.  if your rotation is only a few degrees, then look up barn door stepper.  this is used to mount a camera on a board and follow the earths rotation for a few minutes to take photos of stars.   trigonometry will tell you that the further from the axis, the more steps are needed to move the door.

if you need more rotation and have the budget, buy a telescope worm gear assembly.
for about \$100 you can buy a telescope, tri-pod and two worm gear assemblies.  then add a stepper to one or both.

if you have a lathe, you can make a nice worm gear at home.   if you want to try before investing too much time,
http://www.geocities.ws/kindellism/Nylon_Worm_Gears.html

you can get everything mechanical in the US from McMaster Carr.

stepper motor drivers and programming is available here.

the difference between the home brew and the telescope mount is that gears on the telescope mount are very fine.  the ones you make at home are coarse unless you have the tools and lots of time.

another possibility is to use a worm gear motor.   there are quite a few different types available.  depending on your desire to mechanical things, you have lots of options.

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