servo motor Servo motor with syncro and speed reducer

[dikman]

The needle positioner that I bought with my servo worked fine - until I fitted a speed reducer pulley setup. It did not like it one bit! So I removed the positioner.

Fitting a small motor pulley and a (very) large pulley in place of the handwheel works great for slower speed and extra torque without messing around with pulleys and bearings and shafts.

[Gregg From Keystone Sewing]

On 2/11/2018 at 9:45 PM, Uwe said:

 The needle positioning problem with speed reducers usually stems from the fact that most controllers have an internal programming rule that limits how many motor revolutions it will attempt to reach the desired needle position before it gives up. If the needle position sensor does not give the "we have arrived" signal before the maximum number of allowed motor revolutions is reached, an error condition will trigger. It's a safety feature to keep the motor from spinning uncontrolled forever when you let go of the pedal and the position sensor has failed. The motor controller basically thinks there is something wrong with the needle position sensor because it's not reporting back in time.  Exactly what that limit is depends on the controller software.

Uwe, great explanation.  This is my understanding as well.  When the sync takes too long to cycle we get an error message.  

[Reacher10]

Uwe, it looks like you are correct. The needle positioning did not work above a 5:1 ratio on either direct drive or with the speed reducer. I didn't check it at 5:1 exactly but it's safe to say that below 5:1, it works.

The REX is setup at 4.8:1 direct drive and the JUKI is setup at 4.85:1 with the reducer and the NPS works perfectly on both.

It looks like 5:1 is the cutoff point for the NPS.

Hopefully this information will help others in the future.

Thanks

Rick

[backyardcnc]

Glad I read this post as I was just about to build and add a 3:1 reduction to one of my Sewquiet 6000 equipped machines and was not aware there might be issues with my needle positioner which I cant live without!

Great forum and love reading the various posts!

Gerald

 

Edited February 16, 2018 by backyardcnc
fix typoos

[Dragoblaztr]

On 11/2/2018 at 8:20 PM, Reacher10 said:

I have a REX 607Z setup in a custom table (had my friend CNC the top) so I could hook it up to a servo motor with a Syncronizer. The servo motor is brushless and has four buttons on the control unit, Consew CSM-1001. The machine is working absolutely great with the servo motor and syncro...it took the machine to a higher plane.

 

Now this machine is very good for what it is however it will struggle power wise with the 550 watt motor, nothing major for the work I'm doing and nothing that bothers me...it is still light years better than the little motor it comes with.

I picked up a JUKI 55 with the table and a clutch motor in good condition for $125. With how well the REX responded with the servo motor it was a no brainer to use the same brushless setup on the JUKI.

Knowing that the 550 watt motor wouldn't have the same power as the clutch motor I bought pillow blocks and a shaft to make a speed reducer, I had a 2" and 6" pulley. My initial thinking was to use the 3:1 reducer with the clutch motor just to see if perhaps I could stick with the clutch motor if I indeed had better control.

Well trying to deal with that giant motor just flat out got on my nerves so I said screw this, I'll just get the brushless/syncro setup for it as it would be much easier to deal with and in the mean time put the reducer on the REX. It would give me some extra torque and I could get the reducer up and running and get any kinks worked out.

I did have to make a timing pulley for the brushless motor since the REX uses a timing belt. This was simple enough to do, I modeled up 30 tooth pulley for the motor and an adapter to increase the fly wheel to 5 inches...same deal as the power wheel sailrite sells.  I made these on my 3D printer and away I went. Since I had the 30 tooth modeled for the motor shaft I just had to change the model to fit  the 3/4" shaft for the reducer. Printed it out and boom, had me a nice reducer. It turns out I got it up and running in no time.

Here is where the problem came in. The syncro was no longer working as it should. I have read reports of the syncro not working when a speed reducer was installed as well as reports of the syncro setup working fine. My initial thinking was that it SHOULD work correctly, thinking that the needle would go where it's supposed to based on the syncro. The total reduction ended up to be 6:1 and the servo setup doesn't know or care how this is achieved, like a 1" pulley on the motor and a 6" flywheel pulley. ...right?...wrong!

I was perplexed by this. Well lets take a look at the numbers and I admit they are kind of all over the place. I put the original 70mm v-belt pulley back on the servo motor because the 6" pulley going on the reducer shaft was for a V-belt. The 30 tooth timing pulley I made for the reducer is 1 1/4" dia.

What I discovered is that even though from the motor to the flywheel is a 6:1 ratio there seems to be a direct correlation between the revolutions that the motor turns and where the revolution on the syncro is. So the motor is spinning a 2.75" (70mm) pulley and turning a 6" pulley, that is a 2.18:1 ratio. Then on top of that I'm going from a 1.25" pulley on the reducer shaft to a 5" flywheel pulley which is a 4:1 ratio.

So as I was about looking the positions of the drive pulley and the flywheel I realized the servo motor was turning a certain amount of degrees compared to how many degrees the syncro was reporting and they didn't add up! 

So if the needle position was simply based on the syncro postion then Bobs your uncle but because what the syncro reports and what motor reports don't jive, it ain't gonna work.

So I'm not sure it will work even if I get the drive pulley diameters in line. A 2" on the motor to a 6" on the reducer and then from a 2" on the reducer to a 6" on the flywheel. The motor would be reporting 2 times the amount of rpm's than the syncro is reporting it should have....who the hell knows? I think I'll model and print the pulleys and flywheel adapter to those diameters and see what happens. Lets face it with the hodge podge of diameters I'm using now, yeah, that would throw anything out of sync...lol. As a test I made an adapter for the syncro to go right on the 3/4" reducer shaft and it worked perfectly.

If anyone has any thoughts on this please feel free to chime in.

For those that report no problems, my guess is that relationship between motor and flywheel rpm's does not apply on there control units.

I'll post some pics of my reducer but right now it looks like 3 kids and dog had a wrestling match in there.

Here's an FYI. On my unit, if I set it up for needle down I can additionally press the back of the treadle and the needle will raise. However if I set it for needle up, when I release the treadle. that's it, needle up, no needle down option. So what I do is set the control unit for needle down but the needle is up and the syncro is set to report that it's in the needle down postion. When I release the treadle the needle goes to the up position but then if I want the needle down i just press on the back of the treadle....it works great.

Stay tuned...

BTW...first post...I've learned A LOT form this forum...THANKS!

Great work, can you share the files for 3D printing?

 

[Reacher10]

Whoa... didn't see your post..... What format, dwg, stl, dxf or all 3. It will be the flywheel and the drive pully for 1/5 pitch timing belt and needle positioner hub.

Edited November 13, 2018 by Reacher10

[Reacher10]

Here are the files in STL, DWG (Autocad 2000) and DXF formats

30 tooth.dxf

30 tooth.stl

flywheel.zip

30 tooth washer.dxf

30 tooth washer.stl

rex flywheel dxf.zip

sycro hub.dwg

sycro hub.dxf

sycro hub stl.zip

rex flywhee stll.zip

Edited November 15, 2018 by Reacher10

[eturk]

Thanks a ton @Reacher10    I was thinking about making an adapter like this to slow down the flywheel, rather than invest in a monster wheel.

Looks like it's the "rex_flywheel.stl" for the 5" cog upgrade? 

What belt would we buy to use this adapter on the Rex, w/o changing the smaller cog?

P.S. I'm wanting to try my hand at recovering a bunch leather parts in my old car. A just few places for contrast stitching so I'd get the Rex pass it on, so keeping the investment low on Rex vs. finding a used leather machine for short use.

 

[hansknec]

Another grateful Rex owner.  This saved me a bunch of time!  I have a 3D printer, but even if someone doesn't own one, there are a ton of online places (Shapeways, Protolabs, Rapidmade, etc) where you can send the stl files for printing and your parts will come in the mail.  At some of these online places, you can even have them 3D printed out of metal, but that is unnecessary for this application.  If others are reading this, I discovered that you can't download the files unless you join the forum.  Thanks @Reacher10

[DonInReno]

On 5/1/2020 at 7:19 AM, hansknec said:

Another grateful Rex owner.  This saved me a bunch of time!  I have a 3D printer, but even if someone doesn't own one, there are a ton of online places (Shapeways, Protolabs, Rapidmade, etc) where you can send the stl files for printing and your parts will come in the mail.  At some of these online places, you can even have them 3D printed out of metal, but that is unnecessary for this application.  If others are reading this, I discovered that you can't download the files unless you join the forum.  Thanks @Reacher10

Great information!  
 

The Rex and sailrite machines definitely benefit from extra reduction - I have a monster wheel, but it was expensive for what it is.

For those new to the cogged belts that these machines use - they are called XL timing belts and are not anything unique to sailrite, Rex or any of the other clones.