Can two connected identical motors be run in parallel

[silviasol]

Can two connected motors running on the same shaft be hooked up in parallel like this? http://imgur.com/a/XmLcb
I removed the shaft on my motor and going to add another motor to a longer shaft so both motors share the same shaft. http://imgur.com/a/a1hvC
Both motors will be mounted in a aluminum tube so they both spin the same. https://endless-sphere.com/forums/viewtopic.php?f=1&t=84255
I was going to use two vesc esc's but figured if the motors would work connected in parallel just use one esc.

 

[MrDude_1]

you need to electrically sync them and be sure they dont move. even a half a degree will drastically effect efficiency.
take the first motor and assemble it. put the second motor stator on, as close as possible to the first...
have the 2nd rotor bell loose on the shaft.
then through the same phases, add some current limited power. the loose stator will lock into the same phase as the fixed one. tighten the screws.

then hook it all up to the same esc. as long as you dont mix the phases by accident, it will work. if you cross them it can be very bad. lol.

strangely I tried this when trying to figure out how to hook a 80-85 motor on with my 80-100... same thing you're doing, only bigger.

I ended up skipping it myself because I could just feed more power through one motor by adding a fan.

 

[Chalo]

Brushed DC motors (2 wire) work the way you want, but brushless DC motors (3 wire) don't. If you're using brushless motors, you need separate controllers, but they can run off the same battery and throttle signal.

 

[silviasol]

you need to electrically sync them and be sure they dont move. even a half a degree will drastically effect efficiency.
take the first motor and assemble it. put the second motor stator on, as close as possible to the first...
have the 2nd rotor bell loose on the shaft.
then through the same phases, add some current limited power. the loose stator will lock into the same phase as the fixed one. tighten the screws.

then hook it all up to the same esc. as long as you dont mix the phases by accident, it will work. if you cross them it can be very bad. lol.

strangely I tried this when trying to figure out how to hook a 80-85 motor on with my 80-100... same thing you're doing, only bigger.

I ended up skipping it myself because I could just feed more power through one motor by adding a fan.

Hmm. Seems like it might be best just to use two vesc's. I have 4 working vesc's anyways. The fact that the way the mount will be built will not allow adjustment of the stator unless I do the stator adjustment first then hope I can align the screw mounts for the cnc part to the aluminum tube perfectly. Or possibly have milled slots for the cnc part/aluminum tube connection. Even then if the screws loosen and motor gets out of alignment there would be problems.

 

[MrDude_1]

you need to electrically sync them and be sure they dont move. even a half a degree will drastically effect efficiency.
take the first motor and assemble it. put the second motor stator on, as close as possible to the first...
have the 2nd rotor bell loose on the shaft.
then through the same phases, add some current limited power. the loose stator will lock into the same phase as the fixed one. tighten the screws.

then hook it all up to the same esc. as long as you dont mix the phases by accident, it will work. if you cross them it can be very bad. lol.

strangely I tried this when trying to figure out how to hook a 80-85 motor on with my 80-100... same thing you're doing, only bigger.

I ended up skipping it myself because I could just feed more power through one motor by adding a fan.

Hmm. Seems like it might be best just to use two vesc's. I have 4 working vesc's anyways. The fact that the way the mount will be built will not allow adjustment of the stator unless I do the stator adjustment first then hope I can align the screw mounts for the cnc part to the aluminum tube perfectly. Or possibly have milled slots for the cnc part/aluminum tube connection. Even then if the screws loosen and motor gets out of alignment there would be problems.

The stators dont have to be perfect. the trick is that you're linking the bell with it.
That said, the vesc will be a much simpler, easier build. that way it just shares the shaft and you move on, without another thing to worry about getting just right.

 

[silviasol]

The stators dont have to be perfect. the trick is that you're linking the bell with it.
That said, the vesc will be a much simpler, easier build. that way it just shares the shaft and you move on, without another thing to worry about getting just right.

Maybe I am not understanding. So if I have both motors on the same shaft, hooked up to the matching phase wires(http://imgur.com/a/XmLcb). Then mount just one motor and leave the other unmounted and this same motor leave the bell housing unscrewed from the shaft?

 

[John in CR]

Silviasol,

While what you described will work, it's far better to run 2 on the same shaft using 2 esc's with the stators slightly offset in terms of timing (say 1 stator tooth difference) and the rotors locked in exact parallel. This will result in a quieter smoother starting motor with less pronounced torque ripple compared to running them in perfect parallel. The proof is in the pudding, and for years I've run the highest efficiency quietest outrunners designed exactly in this manner with the only difference being that the 2 electrically separate motors are run on a single stator wound in two 3 phase arrangements. From an ideal perspective , yours could be better since the winding strategy on mine results in some extra copper due to longer non-productive end windings between teeth.

 

[MrDude_1]

The stators dont have to be perfect. the trick is that you're linking the bell with it.
That said, the vesc will be a much simpler, easier build. that way it just shares the shaft and you move on, without another thing to worry about getting just right.

Maybe I am not understanding. So if I have both motors on the same shaft, hooked up to the matching phase wires(http://imgur.com/a/XmLcb). Then mount just one motor and leave the other unmounted and this same motor leave the bell housing unscrewed from the shaft?

Electrically that picture is correct.
Both stators (centers) have to be mounted, but not perfectly.
one motor needs to be completely mounted like normal.
the other one has the bell (outside) loose.

Have your motor wires connected as your pic shows.

Pick any two phase wires and put power through them. This makes them an electromagnet. and it will yank BOTH bells into a specific alignment on the shaft.
With the power still going through it (to hold it still) Tighten the shaft grub screws on the bell. That will make them in sync

You can then use one big controller for both.


However John has a good point... if you run two ESCs and clock the motors out of sync a half tooth, you will have constant even torque, as one motor will always be driving... this might make ringing disappear too.

 

[silviasol]

Silviasol,

While what you described will work, it's far better to run 2 on the same shaft using 2 esc's with the stators slightly offset in terms of timing (say 1 stator tooth difference) and the rotors locked in exact parallel. This will result in a quieter smoother starting motor with less pronounced torque ripple compared to running them in perfect parallel. The proof is in the pudding, and for years I've run the highest efficiency quietest outrunners designed exactly in this manner with the only difference being that the 2 electrically separate motors are run on a single stator wound in two 3 phase arrangements. From an ideal perspective , yours could be better since the winding strategy on mine results in some extra copper due to longer non-productive end windings between teeth.

Interesting. Do you have threads showing your builds with the motors, or how you built them? 1 stator tooth would be 120 degree's difference correct? Is there a way like mr-dude mentioned adding power to a single phase wire on each motor lock the stators in the exact position or does it not need to be perfect? Does it matter which way the stator is adjusted(clockwise or counter clockwise from the way the motor will spin).

Electrically that picture is correct.
Both stators (centers) have to be mounted, but not perfectly.
one motor needs to be completely mounted like normal.
the other one has the bell (outside) loose.

Have your motor wires connected as your pic shows.

Pick any two phase wires and put power through them. This makes them an electromagnet. and it will yank BOTH bells into a specific alignment on the shaft.
With the power still going through it (to hold it still) Tighten the shaft grub screws on the bell. That will make them in sync

You can then use one big controller for both.


However John has a good point... if you run two ESCs and clock the motors out of sync a half tooth, you will have constant even torque, as one motor will always be driving... this might make ringing disappear too.

Ok. When you did yours how did you make the flat spot aligned for the bell screw on the second motor after aligning the bells? If both your and johns idea require perfect alignment it will be tough to make sure the flat spots are perfect. Or with your idea is it have power on the two phase wires then mount/unmount the motor adjusting the stator until the bell aligns up with the flat spot? My 2nd motor is on the way from hong kong, hopefully will be here this week so I can test all this.

 

[MrDude_1]

Ok. When you did yours how did you make the flat spot aligned for the bell screw on the second motor after aligning the bells? If both your and johns idea require perfect alignment it will be tough to make sure the flat spots are perfect. Or with your idea is it have power on the two phase wires then mount/unmount the motor adjusting the stator until the bell aligns up with the flat spot? My 2nd motor is on the way from hong kong, hopefully will be here this week so I can test all this.

What I did was tighten the screw down, to "mark" the area, and used a sharpie on the shaft and bell to tell where they go. then used my drill press to drill a hole right on the witness mark from the set screws.
If you put a long set screw in a drill, and run it at an angle on the belt sander, you can make a "marking" set screw.... but a normal one makes a ring that works just fine.

Johns idea of running two controllers does NOT require perfect alignment (a plus) but does require two controllers... In his case, if you get the magnets not in parallel, it will be extra smooth... but even 100% off as much as possible wont matter because there are two controllers.

 

[silviasol]

What I did was tighten the screw down, to "mark" the area, and used a sharpie on the shaft and bell to tell where they go. then used my drill press to drill a hole right on the witness mark from the set screws.
If you put a long set screw in a drill, and run it at an angle on the belt sander, you can make a "marking" set screw.... but a normal one makes a ring that works just fine.

Johns idea of running two controllers does NOT require perfect alignment (a plus) but does require two controllers... In his case, if you get the magnets not in parallel, it will be extra smooth... but even 100% off as much as possible wont matter because there are two controllers.

Ok I see now. A hole would be best to make sure it doesn't get out of alignment at all also. Luckily I haven't done anything to my shaft yet and can have the machine shop make a perfect sized hole to fit the grub screw. I will test yours and john's way to see what is best. I am curious if anything can even be done to improve the low end of these 245kv motors, all the power with one motor is when I am over 10mph, under 10mph won't even make it thru grass. Even with two motors I won't worry about smooth acceleration, however I did notice the "jumpyness" when in the more powerful rpm range which I assume would be torque ripple. Vesc's now have FOC which I will set up at a later date, haven't tested that yet but vedder says it runs silent. So if yours works out it might be the best route. I still will need to find a way to mount both motors when I mark the shaft since the aluminum tube will of course keep me from doing that.