Torque Increase from Speed Reduction

[nejcek74]

of course they have, this is from Efka site:

which shows that torque is more or less flat in the lower part of the rpm. It also shows that they have two different servos, one built for speed and the other built for torque.

The power is function of speed and torque:

P [kW] = (T [Nm] · ω [rad/s]) / 1000

in lower speeds where torque curve is flat the power is increasing constantly with speed. Later it can decrease slightly (depends on the turning curve of torque). Of course when the speed is 0, power is also 0. And because of engineering reasons the motors have minimum speed at which they work.

 

[AlZilla]

Those are very informative charts. I'd really like to see the same data on lower end servos.

[AlZilla]

3 hours ago, friquant said:

Everything I read about digital servos says they have high torque from a standstill

Oddly, most everything I've seen about the cheaper servos is that they lack torque in the low end.  I don't know ...

[friquant]

19 minutes ago, AlZilla said:

Oddly, most everything I've seen about the cheaper servos is that they lack torque in the low end.  I don't know ...

I've started to distinguish between digital servo motors and universal motors with triac speed controllers. Unfortunately, both are marketed as "servo motors".

[nejcek74]

I guess the problem is with the minimum speed to start. Which is I guess an engineering characteristic of the motor, but this is beyond my limited knowledge of electric motors

Regarding torque of different types of motor I found this:

[AlZilla]

2 hours ago, friquant said:

I've started to distinguish between digital servo motors and universal motors with triac speed controllers. Unfortunately, both are marketed as "servo motors".

And maybe there's a distinction between brushed and brushless.

[AlZilla]

1 hour ago, nejcek74 said:

guess the problem is with the minimum speed to start. Which is I guess an engineering characteristic of the motor, but this is beyond my limited knowledge of electric

I'm wondering if the minimum speed issue is to decrease heat. I've read that 300 is where heat dissipation is adequate (maybe for sustained operation?). Possibly 200 is banking on the user not staying at 200 for longer periods?

I've also noticed that some of these cheaper motors have actual cooling fins on the outside of the body, where others just have undulations cast into them. My current motor with a 100 rpm minimum start speed has the cooling fins on the case.

I'll have to start noticing if there's any correlation.

Also, based on my recent disassembly of a cheap servo, the fan built into the end is just flat paddles running next to the closed end of the motor. No circulation at all. I think a small computer type fan blowing on the motor housing would really up the cooling game. It's on my to do list, even though with my low volume of sewing, I don't think heat is going to be an issue.

[friquant]

1 hour ago, AlZilla said:

And maybe there's a distinction between brushed and brushless.

Universal motors are all brushed. My universal motor came with extra brushes even.

About half the digital servo motors I see advertise as being brushless---the others don't say. I took the motor apart today on my "stitchman" digital servo and verified that it has no brushes.  If anybody has a digital servo with actual brushes inside, I'd be interested to hear.

[nejcek74]

11 hours ago, AlZilla said:

I've also noticed that some of these cheaper motors have actual cooling fins on the outside of the body, where others just have undulations cast into them. My current motor with a 100 rpm minimum start speed has the cooling fins on the case.

My moderately priced servo has 100 rpm minimum speed has some shaping on the case, but not exactly cooling fans. Efka DC 1600 that I had to remove because of dead control box is completely different beast, 2 the size and weight, cooling fan etc.

[friquant]

21 hours ago, AlZilla said:

Also, based on my recent disassembly of a cheap servo, the fan built into the end is just flat paddles running next to the closed end of the motor. No circulation at all.

Mine has that too--- paddles running next to the aluminum case, shrouded under some plastic.

I think simply removing the plastic cover would be a boon...