Ok I think I might have found a solution for running a pwm signal to control a ac motor but I am not sure. I have read up and seen a few videos on how folks are making wiper motor servos using H bridge units. So my question is can the dc voltage be inverted to run an ac motor like a servo??

The signal is pwm into the H bridge, and using a pot on the center shaft as a position sensor, with a scavenged servo allows the wiper motor to be used as a giant servo on dc, following the same principal but my idea is to take the voltage dc out and invert it to ac. Would this work?? the ac motor is geared already and rotates at 6 degrees per second so it is not super fast, nor do I need it to be.

Let me know, your thoughts. Or is there a simpler way to get a pwm to control an ac motor like a servo???

 

What type of AC motor, there are several!
1ph induction, not worth it, BLDC or AC sysnchronous require a 3ph signal, or 3 drive signals, not the same as DC brushed.
Max..

 

As far a the load is concerned, an H-bridge inherently puts out AC.

If the drive to the switches in the bridge is such that the "upper" switch of the "left" side is ON at the same time as the "lower" switch on the "right" side is, current flows through the load with the left side positive relative to the right. When the drive is changed so that the lower switch on the left side is ON at the same time as the upper switch on the right side, current flows in the opposite direction through the load. Everything is always positive with respect to the circuit common, but the load gets true alternating current. Even the DC servo motor gets alternating current, just without the notion of definite frequency that usually goes with the idea of AC.

The output can be as simple as single "pulse" of one polarity representing one half-cycle and the opposite polarity for the other half cycle, or each half-cycle can be a series of varying-width pulses intended to more closely approximate a sinusoidal half wave.

It might be worth looking at how "class D" audio amplifiers work in "bridge tied load" mode.

As Max say, how it will work depends very much on the type of motor.

 

Hello guys basically I am trying to get 24vac, motor type unknown, to work.
The motors are in a pan and tilt camera housing, for security cameras, I can not change out the motors nor can I change the PWM source signal to operate it. the pan and tilt is down below, the pan and tilt needs to move up to 35lbs antenna

As far a the load is concerned, an H-bridge inherently puts out AC.

If the drive to the switches in the bridge is such that the "upper" switch of the "left" side is ON at the same time as the "lower" switch on the "right" side is, current flows through the load with the left side positive relative to the right. When the drive is changed so that the lower switch on the left side is ON at the same time as the upper switch on the right side, current flows in the opposite direction through the load. Everything is always positive with respect to the circuit common, but the load gets true alternating current. Even the DC servo motor gets alternating current, just without the notion of definite frequency that usually goes with the idea of AC.

The output can be as simple as single "pulse" of one polarity representing one half-cycle and the opposite polarity for the other half cycle, or each half-cycle can be a series of varying-width pulses intended to more closely approximate a sinusoidal half wave.

It might be worth looking at how "class D" audio amplifiers work in "bridge tied load" mode.

As Max say, how it will work depends very much on the type of motor.

 

Pan and tilt motors that I have seen are either stepper motors or split-phase induction motors with a capacitor between two similar windings. Power is applied to one side or the other of the capacitor to select the direction, the other side of the line goes to the common junction of both windings. You might be able to use an H-bridge set up to sine wave, but if you have AC power available it is a lot less effort needed. If the motors are stepper motors you will need two H-bridge circuits to drive them, plus PWM control to reduce the power when they are stopped. Stepper motors take a special sequence to drive them so you will need to do a bit of research to learn how to deliver the sequence.
Where is this PWM signal that you are unable to change coming from, and is it related to the original motor control arrangement.
You really need to have more information before anybody can give definite advice.

 

Hello Misterbill2
The PWM signal is coming from a manufactured antenna tracker software/ brain, used to drive servos up to 1/4 scale for pan and tilt, with antennas up to say 3 lbs. The problem is I need this unit to drive a 28dbi parabolic antenna that weighs up to 35lbs, something that 1/4scale servos nor wiper motor servos can do.

I have access to several cheap government surplus pan and tilt security camera heads cheap that will do the job I need, BUT I can not figure out how to get the 5vdc PWM signal to drive a 24ac motor that are inside the surplus pan and tilt heads.

I have 2 of the three pieces of the puzzle, I just need to get the last piece to fall in place.
Please help

Pan and tilt motors that I have seen are either stepper motors or split-phase induction motors with a capacitor between two similar windings. Power is applied to one side or the other of the capacitor to select the direction, the other side of the line goes to the common junction of both windings. You might be able to use an H-bridge set up to sine wave, but if you have AC power available it is a lot less effort needed. If the motors are stepper motors you will need two H-bridge circuits to drive them, plus PWM control to reduce the power when they are stopped. Stepper motors take a special sequence to drive them so you will need to do a bit of research to learn how to deliver the sequence.
Where is this PWM signal that you are unable to change coming from, and is it related to the original motor control arrangement.
You really need to have more information before anybody can give definite advice.

 

BUT I can not figure out how to get the 5vdc PWM signal to drive a 24ac motor that are inside the surplus pan and tilt heads.

You need to state exactly what type of AC motors they are.!!
Max.

 

According to the pinout on the pan and tilt head, there is one pin for left movement, one pin for right movement, and one common. same for the tilt, one pin for the up movement, one pin for the down movement, and one common. I don't know if this helps in any way. Below is a pinout of the connection from the manual I can find online.

Pan and tilt motors that I have seen are either stepper motors or split-phase induction motors with a capacitor between two similar windings. Power is applied to one side or the other of the capacitor to select the direction, the other side of the line goes to the common junction of both windings. You might be able to use an H-bridge set up to sine wave, but if you have AC power available it is a lot less effort needed. If the motors are stepper motors you will need two H-bridge circuits to drive them, plus PWM control to reduce the power when they are stopped. Stepper motors take a special sequence to drive them so you will need to do a bit of research to learn how to deliver the sequence.
Where is this PWM signal that you are unable to change coming from, and is it related to the original motor control arrangement.
You really need to have more information before anybody can give definite advice.

 

I will have to call the MFG, but it is unlikely that they will have much information, as these were commonly built in the 1980's

You need to state exactly what type of AC motors they are.!!
Max.

 

Would a wire schematic help to determine them? If I was to guess it would be a stepper motor. this is a similar model, page 14 has a schematic

You need to state exactly what type of AC motors they are.!!
Max.

 

Hello Max

This guy built an manual antenna tracker using the aforementioned pan tilt head, he states that they are synchronous motor. https://github.com/bgelb/sat_rotor/blob/master/README.md

he is using a 4 channel relay controller https://web.archive.org/web/2015062...om/usb-four-channel-relay-controller-pcb.html programmed to windows.

I will still call the mfg to see about the exact motor type.

But this software does not help me with the pwm problem Ideas?

You need to state exactly what type of AC motors they are.!!
Max.

 

The motors in the pan tilt head are 24vac synchronous motors in the V330APT, as they drive at a constant speed based on the 60Hz rate of the AC power supply.

So how do I go about getting the 5v pwm signal to move a 24vac synchronous motor in the v330apt??

Ideas?

What type of AC motor, there are several!
1ph induction, not worth it, BLDC or AC sysnchronous require a 3ph signal, or 3 drive signals, not the same as DC brushed.
Max..

Pan and tilt motors that I have seen are either stepper motors or split-phase induction motors with a capacitor between two similar windings. Power is applied to one side or the other of the capacitor to select the direction, the other side of the line goes to the common junction of both windings. You might be able to use an H-bridge set up to sine wave, but if you have AC power available it is a lot less effort needed. If the motors are stepper motors you will need two H-bridge circuits to drive them, plus PWM control to reduce the power when they are stopped. Stepper motors take a special sequence to drive them so you will need to do a bit of research to learn how to deliver the sequence.
Where is this PWM signal that you are unable to change coming from, and is it related to the original motor control arrangement.
You really need to have more information before anybody can give definite advice.

As far a the load is concerned, an H-bridge inherently puts out AC.

If the drive to the switches in the bridge is such that the "upper" switch of the "left" side is ON at the same time as the "lower" switch on the "right" side is, current flows through the load with the left side positive relative to the right. When the drive is changed so that the lower switch on the left side is ON at the same time as the upper switch on the right side, current flows in the opposite direction through the load. Everything is always positive with respect to the circuit common, but the load gets true alternating current. Even the DC servo motor gets alternating current, just without the notion of definite frequency that usually goes with the idea of AC.

The output can be as simple as single "pulse" of one polarity representing one half-cycle and the opposite polarity for the other half cycle, or each half-cycle can be a series of varying-width pulses intended to more closely approximate a sinusoidal half wave.

It might be worth looking at how "class D" audio amplifiers work in "bridge tied load" mode.

As Max say, how it will work depends very much on the type of motor.

 

Is the intent to use a control signal as for a hobby type servo where the width of a repetitive pulse sets position e.g. 1 ms pulse is centre, 0.5 ms pulse is one limit and 1.5 ms pulse is the other limit (I don't remember the actual widths used for hobby servos, but it is the general idea)?

Do you have / can you have AC power for the motor available?

Is the intent to use the position signal from the drive to close the positioning loop?

What sort of positional overshoot do you get after the AC power is removed?

Depending on the answers, this is almost as simple as taking the controller for a hobby servo, connecting a pair of optoisolated triac drivers & triacs in place of the original motor, and connecting the position signal from the pan-tilt in place of the potentiometer driven by the output shaft of the original servo. The triacs would drive the AC motor. The position feedback is possibly a bit tricky. I have never looked closely at the so-called "digital" servos, but I think they operate in essentially the same way except behavior is programmable to some extent, which could be beneficial. I don't know if the ICs for the older analog servo controls are still available. The job could be done with a low-cost microcontroller with an analog to digital converter used for the position feedback signal but of course that requires firmware. I presume there are Arduino variants that would be suitable.

 

Hello EBP
Yes the intent is to have the servo pwm control the rotational position of the Pan and tilt head. i.e. if the pwm commands 28 degrees, the head will tilt 28 degrees, if the pwm says rotate 359 degrees to X position the head will rotate to that position.

I have an external ac power supply if needed.

I do not understand to close the positioning loop???

Overshoot, it says on the docs +-1 degree which is based on the joystick triggering an on off switch.

I have never screwed with triacs nor this type setup you described. if you can please send me a circuit diagram, I have a vague conseptual idea of what you are talking about, as per programming a ADC that should not be too hard I have friends that can help me with this.

Is the intent to use a control signal as for a hobby type servo where the width of a repetitive pulse sets position e.g. 1 ms pulse is centre, 0.5 ms pulse is one limit and 1.5 ms pulse is the other limit (I don't remember the actual widths used for hobby servos, but it is the general idea)?

Do you have / can you have AC power for the motor available?

Is the intent to use the position signal from the drive to close the positioning loop?

What sort of positional overshoot do you get after the AC power is removed?

Depending on the answers, this is almost as simple as taking the controller for a hobby servo, connecting a pair of optoisolated triac drivers & triacs in place of the original motor, and connecting the position signal from the pan-tilt in place of the potentiometer driven by the output shaft of the original servo. The triacs would drive the AC motor. The position feedback is possibly a bit tricky. I have never looked closely at the so-called "digital" servos, but I think they operate in essentially the same way except behavior is programmable to some extent, which could be beneficial. I don't know if the ICs for the older analog servo controls are still available. The job could be done with a low-cost microcontroller with an analog to digital converter used for the position feedback signal but of course that requires firmware. I presume there are Arduino variants that would be suitable.

 

Ok I called Vicon and they told me that they are not sure the type of motor used, they opened one up and they think it is a slo-syn motor.
another resource I found says they are probally correct. this guy built a computer controlled satalite tracker, https://www.albemarleradio.org/2013...imuthelevation-rotator-and-satellite-tracker/ he states that (his was a 115vac system, mine is a 24vac but the same principals apply.

"Note that the AC motors inside, separate from the gearboxes, look like they may be NEMA 23 frame size – the same size used by many stepper motors and indeed, they may be the 115VAC equivalent two phase motors, similar to a Slo-Syn motor. These motors would be run with one phase directly on 115VAC and the other phase connected to 115VAC through a capacitor. With one wire of each phase connected to common (neutral) and the capacitor connected between the other connections on each phase, then depending on which phase you connect AC to, the other phase is fed through the cap and the motor direction changes.

Note that since these are apparently synchronous motors, you can more or less run them open loop and compute the position based on time, though you will have to recalibrate periodically by driving into the limit switches. This is the approach used by most cheap TV antenna rotators today. You can also make indicators using the shadow motor technique used in some TV antenna rotators, though in this case you can use a meter movement and have absolute accuracy.

Although stepper motors date back to the 19th century, it wasn’t until the 1957 that the permanet magnet version was developed by GE and entered production. But it is the 1960s stepper version of the slo-syn motor (1958) that seems to have largely popularized their use. The slow syn motor was a 2 phase AC motor with an unusually high number of poles with 24 to 200 poles such that it takes 6 to 50 electrical revolutions to make one mechanical shaft rotation. Rewind these motors for lower voltage use and you have a stepper motor. Many of the old stepper motors I have encountered slow-syn steppers. Stepper motors are widely used in applications such as computer printers, floppy disk drives, early consumer hard drives, robotics, pan/tilt IP cameras, and CNC machine tools. Slo-syn museum."

What type of AC motor, there are several!
1ph induction, not worth it, BLDC or AC sysnchronous require a 3ph signal, or 3 drive signals, not the same as DC brushed.
Max..

As far a the load is concerned, an H-bridge inherently puts out AC.

If the drive to the switches in the bridge is such that the "upper" switch of the "left" side is ON at the same time as the "lower" switch on the "right" side is, current flows through the load with the left side positive relative to the right. When the drive is changed so that the lower switch on the left side is ON at the same time as the upper switch on the right side, current flows in the opposite direction through the load. Everything is always positive with respect to the circuit common, but the load gets true alternating current. Even the DC servo motor gets alternating current, just without the notion of definite frequency that usually goes with the idea of AC.

The output can be as simple as single "pulse" of one polarity representing one half-cycle and the opposite polarity for the other half cycle, or each half-cycle can be a series of varying-width pulses intended to more closely approximate a sinusoidal half wave.

It might be worth looking at how "class D" audio amplifiers work in "bridge tied load" mode.

As Max say, how it will work depends very much on the type of motor.

Pan and tilt motors that I have seen are either stepper motors or split-phase induction motors with a capacitor between two similar windings. Power is applied to one side or the other of the capacitor to select the direction, the other side of the line goes to the common junction of both windings. You might be able to use an H-bridge set up to sine wave, but if you have AC power available it is a lot less effort needed. If the motors are stepper motors you will need two H-bridge circuits to drive them, plus PWM control to reduce the power when they are stopped. Stepper motors take a special sequence to drive them so you will need to do a bit of research to learn how to deliver the sequence.
Where is this PWM signal that you are unable to change coming from, and is it related to the original motor control arrangement.
You really need to have more information before anybody can give definite advice.

 

The motors are a slo syn synchronous stepper type motor , (possibly SS241LE 120vac) .4a, what is uncertain is the rpm and the torque, if they are stock 72rpm, 240oz torque.

 

Closing the loop:

Pulse width control of position relies on local feedback to make the motor move to the position commanded by the width of the pulse. In hobby type servos this is done by comparing the width of the command pulse to a locally-generated pulse whose width is set by the time constant of a capacitor and a variable resistor connected mechanically to the output shaft of servo. If the local pulse is too short, the servo is driven in the direction that makes the pulse longer and vice versa. Because of mechanical overshoot, some "deadband" is deliberately introduced so that if the difference in widths between the command and local pulses is small, no motion is commanded. This prevents the servo from constantly "hunting" for position.

The positioner has potentiometers for positional feedback but they are arranged as voltage dividers - the output voltage will be some faction of the applied voltage according to position. This configuration is not directly compatible with standard hobby-type servo controllers but all that is really necessary is a minor wiring change. The question then is whether the resistance change with position can be used effectively in the usual RC circuit of the servo controller. It is fairly likely that it can, but experimentation would be required. The voltage divider scheme may be directly compatible with the "digital" servo control mechanism. I have no experience with them, only the older analog type.

If a microcontroller were used the position output from the pan-tilt would be directly compatible. The micro would measure the width of the incoming pulse and calculate what voltage to expect from the position output of the pan-tilt for that width. It would measure the voltage using an analog to digital converter, then apply power to the motor so as to increase or decrease the voltage to match expectation, again allowing some deadband to prevent hunting. A processor has the advantage that the overshoot after stopping the motor could be quantified and compensated for by stopping the motor slightly before the commanded position. A processor would also allow calibration so that the minimum and maximum pulse widths could be accepted "as is" and made to match the limits of movement by applying correction factors. Typically this would require the processor to have non-volatile read-write memory (a great many have some) and some additional program. Multiplication and/or division would be necessary, which is a bit burdensome to small micros, but not a big deal. I suspect most Arduino or similar modules could do the whole job quite nicely. There are many many microcontrollers that would be suitable and inexpensive for someone wanting to build all the hardware.

 

It was my opinion too that they were Slo-Syn stepper motors used in a synchronous manner, in this way they are connected directly to the AC supply (no stepper controller).
They run in synchronism with the applied AC frequency.
In the way they are used there is no way to change the rpm except change supply frequency.
Max.

 

Ok so how do I set this up to use pwm and having the motors operate like a servo??

Closing the loop:

Pulse width control of position relies on local feedback to make the motor move to the position commanded by the width of the pulse. In hobby type servos this is done by comparing the width of the command pulse to a locally-generated pulse whose width is set by the time constant of a capacitor and a variable resistor connected mechanically to the output shaft of servo. If the local pulse is too short, the servo is driven in the direction that makes the pulse longer and vice versa. Because of mechanical overshoot, some "deadband" is deliberately introduced so that if the difference in widths between the command and local pulses is small, no motion is commanded. This prevents the servo from constantly "hunting" for position.

The positioner has potentiometers for positional feedback but they are arranged as voltage dividers - the output voltage will be some faction of the applied voltage according to position. This configuration is not directly compatible with standard hobby-type servo controllers but all that is really necessary is a minor wiring change. The question then is whether the resistance change with position can be used effectively in the usual RC circuit of the servo controller. It is fairly likely that it can, but experimentation would be required. The voltage divider scheme may be directly compatible with the "digital" servo control mechanism. I have no experience with them, only the older analog type.

If a microcontroller were used the position output from the pan-tilt would be directly compatible. The micro would measure the width of the incoming pulse and calculate what voltage to expect from the position output of the pan-tilt for that width. It would measure the voltage using an analog to digital converter, then apply power to the motor so as to increase or decrease the voltage to match expectation, again allowing some deadband to prevent hunting. A processor has the advantage that the overshoot after stopping the motor could be quantified and compensated for by stopping the motor slightly before the commanded position. A processor would also allow calibration so that the minimum and maximum pulse widths could be accepted "as is" and made to match the limits of movement by applying correction factors. Typically this would require the processor to have non-volatile read-write memory (a great many have some) and some additional program. Multiplication and/or division would be necessary, which is a bit burdensome to small micros, but not a big deal. I suspect most Arduino or similar modules could do the whole job quite nicely. There are many many microcontrollers that would be suitable and inexpensive for someone wanting to build all the hardware.

It was my opinion too that they were Slo-Syn stepper motors used in a synchronous manner, in this way they are connected directly to the AC supply (no stepper controller).
They run in synchronism with the applied AC frequency.
In the way they are used there is no way to change the rpm except change supply frequency.
Max.

 

Slo-Syn synchronous motors are typically bi-polar stepper motors, and you would need to bring all 4 leads out in order to index them by individual pulses.
That would be my estimation.
But the motors would have to be examined to confirm.
Max.