Pages: 1 [2] 3   Go Down
Author Topic: Geared Stepper Motor  (Read 10775 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 1
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

According to Stolfa the motor requires 64*((22*26*31*32)/(9*9*10*11)) steps for a full revolution. This fraction simplifies to 1650688/405. Therefore 405 turns are needed to get back to the initial starting position.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 1
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Having played around with this stepper for a couple of days, my results show an inconsistent undershoot similar to the previous posts.
Maybe this could be a power supply problem ?
Perhaps any future posters could post the type of supply they are feeding ULN2003.
For my part, I was using 2 paralelled 9V (PP3) batteries.
Logged

0
Offline Offline
Shannon Member
****
Karma: 206
Posts: 12179
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

For high-precision geared motors anti-backlash gears are normally used (where spring-loaded gears remove all
the slack in the mechanism).

Adding a hi-res shaft-encoder after the gearbox would allow accurate positioning without needing to worry about
slack or the precise gear ratios...
Logged

[ I won't respond to messages, use the forum please ]

Offline Offline
Newbie
*
Karma: 0
Posts: 20
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

   I just received a new 10-pk of these 28BYJ-48 5VDC stepper motors and tested one to see if maybe a different manufacturer would use a slightly different gear ratio, some being 4096:1 and some being 4075.7728...   I set the stepper motor sketch up so that it rotates for 4076 steps, pauses for 3 seconds, then repeats; a period of about 15.3 seconds.  Depending on which ratio is in the gear box it either exceeds a revolution by 0.22271 steps or it is short a revolution by 20.2271... steps.  If the gear ratio is 74075.7728.. the paused point of the shaft will precess one revolution in 79 hours.  If the gear ratio is 4096:1 then the pause should precess in the other direction and make one revolution in 51 minutes.  Right now it's on course for about a 79 hour precession.  There may be another source of these motors with a 4096:1 ratio. If you know of one; let me know.

Dave
Logged

Offline Offline
Edison Member
*
Karma: 8
Posts: 1341
If you're not living on the Edge, you're taking up too much space!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I can't believe there are so many motors that are not 4096:1.  Why? 
Does anyone else have the 4096 ratio?
Logged

If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

Offline Offline
Newbie
*
Karma: 0
Posts: 2
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I only just got my Uno a week or so ago, so I'm still somewhat new to this.  I ordered a kit from ebay with a 5v 28BYJ48 stepper included.  It didn't come with a data sheet, but it seemed similar to the others online.

I tested it as accurately as I could with no tools and some arduino codes (mostly the oneRevolution example) and for it to do a full revolution with the standard stepper.h library, I have to use "2046" as my stepsPerRevolution value.  I assume the way I have it wired means it's doing full steps vs half steps or something, but even doubling that would result in 4092 instead of 4096.  Additionally, when I use setSpeed(2), it seems to take about 28 seconds rather than 30 to complete a full circle.

Any help with this would be fantastic, though I know it's not the point of this thread.  But my motor does have an unusual number of steps to go full circle.  I haven't tested to see if it's exactly one circle, nor have I opened it to check the gear ratios, but hopefully it helps.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 20
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

sbright33,

   I popped off the face of a 28BYJ I had and found the following:

 

  I highlighted the gear teeth with a red dot and show the teeth/gear.  My gear ratio is:
(31*32*26*22)/(11*10*9*9) = 283712/4455 = 25792/405 = 63.68395...  If anyone can show 64:1 please similarly pop the face and count teeth.  Can anyone find anything but the above ratio of gear teeth.  The face is replaceable with a little added Vaseline inside.    All motors I've seen pictures of have three intermediate shafts (the shaft ends show through the case) for a total of 4 gear reductions.  It is conceivable that someone may have (40*40*20*20)/(10*10*10*10) = 64 or similar. Yes, there is some slop in the nylon gears but I'm using it for a clock so I'm only driving it in one direction.  I am driving it many revolutions so I do need to know the ratio precisely.  If someone can show me a 64:1 eBay gear source I'd be delighted!  Right now for me the total number of steps are (64 * 25792)/405 =  4075.7728395...  Therefore I step 4075 steps for one revolution and add an additional step every 313 out of 405 revolutions (313/405 = 0.7728395.. the decimal remainder of 4075.772...).  Unfortunately I make an array named correction[404] = {1,0,1,1,1,0,....  0,1,1,1} to decide if a correction step is needed.  It's messy but it keeps the second hand pointing up at 12 o'clock.
Logged

Offline Offline
Edison Member
*
Karma: 8
Posts: 1341
If you're not living on the Edge, you're taking up too much space!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I have bought a number of these motors from different vendors.  All of them are 4096.  I would notice if it was 4076, a 20 step difference.  My code does 4096 steps quickly then pauses for 5 seconds.  It stops in the same place even after hours of running.  I don't doubt your picture or you counting Stolfa.  My question is this:

Why would someone design it with 4075.772 steps???
Logged

If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

0
Offline Offline
Shannon Member
****
Karma: 206
Posts: 12179
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Because they were just used to designing gear trains, not gear trains for open-loop motion control?

AFAIK these motors are made specifically to steer airflow in air conditioning systems, which is the
reason they are so cheap and why exact gear ratios aren't part of the original specifications I suspect.

4096 steps sounds great but the gear train backlash means a standard stepper motor with microstepping
controller probably outperforms this motor - except in price!
Logged

[ I won't respond to messages, use the forum please ]

Malaga
Offline Offline
Sr. Member
****
Karma: 6
Posts: 319
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I totally agree with MarkT.
For me, the main problem of this motor is its backslash: it make "vibrate" anything you attach to the shaft even if you rotate only in one direction (anyway, any stepper motor has some backslash, but in this motor it is exagerated by the great play of the gears).

But its advantage is so high: a really reduced price ...
Logged

Vinciduino rocks!

Offline Offline
Newbie
*
Karma: 0
Posts: 20
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

   If anyone knows of one, please post an eBay vendor name that sells a 5V 28BYJ stepper motor  with a 4096 steps/revolution rather than the 4075.722...  that all mine show.  I would love to find a 4096 step source. The three different orders I've made all exhibit 4075+.
Logged

Offline Offline
Edison Member
*
Karma: 8
Posts: 1341
If you're not living on the Edge, you're taking up too much space!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I understand.  Ask Terry his email is at the bottom.

http://yourduino.com/LearnArduino1.htm

Other than this design, is there another cheap source with gears?  I have some with 16:1 that look the same from the outside.  How can you get 4096 steps without gears?  If speed is not a concern, even with backlash, how can you beat it?  Most cheap steppers are about 1 deg/step?
Logged

If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

Pottstown, PA
Offline Offline
Sr. Member
****
Karma: 5
Posts: 318
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Ah! Finally an explanation as to why some users of this stepper cound not attain the hoped for results as sbright33 and others got in getting it to do a precise full revolution in 4096 steps. I too would like to know of a source for these steppers that for sure have 4096 steps per revolution. - Scotty
Logged

Offline Offline
Edison Member
*
Karma: 8
Posts: 1341
If you're not living on the Edge, you're taking up too much space!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I can fix my code to work with 4075+.  All I'd need is a motor to test it.  Already the code is able to rotate by 0.36 x 1000 to make a full revolution.  Notice the step size is not even close to a multiple of 0.36 degrees.  The only disadvantage is the need for floats the way it is written.  Who wants it?
Logged

If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

Offline Offline
Edison Member
*
Karma: 8
Posts: 1341
If you're not living on the Edge, you're taking up too much space!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I guess nobody wants to rotate exactly 1 revolution...
Logged

If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

Pages: 1 [2] 3   Go Up
Jump to: