Dish motor less wear and tear

Lasseparabol

Lasseparabol

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86
My Satellite Setup
3 m Prodelin
C band 25K Chaparall Sidekick
Ku band SMW X-line lnb
Chapparal Corrotor 2 Wide band
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Sweden south part
I have noticed that at the end positions, the actuator gets the biggest stresses and probably the biggest wear and tear.

The actuator should have 36V but if I lower it to 24V the speed should be smaller and the loadings will be smaller and the actuator should last longer.

Comments on this thought ?, someone who tried?



Used Google translate, as evidenced by the language!
 
jeallen01

jeallen01

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FWIW, the motor is designed to run best at its rated voltage (36V) and at 66% it will have far less torque because the current will be proportionately lower. Therefore it will run slower and it might struggle to start the actuator moving, especially if the actuator mechanism is a bit dirty/rusty, and so might actually run hotter, or even stall (which will do it no good!), because of that. Also, because of the lower motor torque, it might not actually be able to drive the actuator to the ends of its travel = reduced scanning arc.

However, you could also trying running it at around 30V.

Also remember that you will need some form of voltage reduction circuit - could be a simple resistor network (large wire-wound resistors) but a semiconductor regulator would probably be better, especially if that has a voltage control which can be altered so that you can experiment to find the lowest voltage at which the actuator moves smoothly.

Final thought, it might even be worth running the actuator at a little more than 36V as that would give it more torque and so it would struggle less at the extremes of the scan arc (especially if the supply cables are long and so there is an appreciable voltage drop along them - but that means that you would need a voltage step-up circuit instead of a reduction circuit.
 
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S

s-band

Contributor
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844
My Satellite Setup
1.5m IRTE PF, Octagon OSLO external Ref., TBS6983,
Various L, S, C, X & Ka bits. 1.2m S/X/Ku/Ka Prodelin on Az-El
My Location
SE UK
A counter-balance makes a huge difference, although it can look silly. If fully balanced, the torque should be similar across the arc.
Channel Master 1.8 Restoration
Satellites Community - My Prodelin 2,4m
However, it increases the inertia so stopping and starting movement can be shaky if not controlled.
An offset dish is easier to balance if mounted upside-down.
 
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Terryl

Terryl

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2,507
My Satellite Setup
OpenBox X5 on a 1 meter motorized dish.
And now a 10 foot "C" band dish.

Custom built PC
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Deep in the Boonies in the central Sierra Nevada mountains of California.
I would not do this, a DC motor rated at 36 volts DC has a starting load maximum rating, (starting torque) this is called a locked rotor condition, the motor at a dead stop has a very high torque load on it when starting up, (rotor is not moving, load is at a dead stop) if the DC starting voltage is too low the resulting DC current draw may be too high for the DC supply circuit, this may also cause overheating in the motor.

The internal DC resistance of the motor does not change, this is just a big resistor under a locked rotor state, the design of the motor calls for 36 volts DC at X amps to overcome this state, reduce the DC voltage and the current requirement to over come the locked state (starting torque) may do some damage to something.
 
jeallen01

jeallen01

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Following something I mentioned earlier, it might be worth measuring the actual voltage received by the actuator motor to see if there is a substantial voltage drop between the Rx and that point - if so, then I would look to reduce that (thicker cable cores => less resistance => less voltage drop at a given current).

I like s-band's counterbalance approach, but it might be difficult on a big dish if there is not much space around it - and that's a lot of work in itself!
BTW: the pics of those dishes show very long actuators - do the long ones tend to bend or flex, because, if they do, then that would also cause more strain on the motor at one end, and possibly the other end as well, due to misalignment ?
 
Channel Hopper

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An actuator is an inductive load, not unlike a large loudspeaker.

During operation, at the point of initialising the load has two draws from the supply, the actual drive load, and the energising load.

The latter does not require a specific voltage to get things moving, but the energising should be fast enough to stop this drain from causing loss in the drive. If the voltage is too high this can cause breakdown of the winding insulation, if too low then the windings heat up before the actuator turns and could become distorted.

A large supply is necessary on a large actuator , elsewhere on the forum there is a thread on an actuator controller that has to be modified with an updated transformer to work on bigger dish systems.

Additionally the ideal supply for an inductive load is also inductive, ithe the impedance of the windings closely matching that of the actuator at the other end, taking into account the resistance of the cable between them, which could be in the region of a few ohms over a long distance.

Lastly the relay system for reversing and dumping of the back emf should be 'clean' in terms of the contacts to prevent arcing, with a capacitor system that neutralises the inductive pulse that travels back to the supply.
 
S

s-band

Contributor
Messages
844
My Satellite Setup
1.5m IRTE PF, Octagon OSLO external Ref., TBS6983,
Various L, S, C, X & Ka bits. 1.2m S/X/Ku/Ka Prodelin on Az-El
My Location
SE UK
The RC2000 uses PWM in a closed loop.
See extract from manual & attached pdf.
"The Adapti-Drive slow speed control system allows the user to specify a desired slow speed. When the antenna is moving at slow speed the controller will vary the voltage to the drive to maintain the actual antenna slow speed at the value specified by the user. Other slow speed drive systems in use reduce the voltage to the drive to a constant value whenever slow speed movements occur. This results in poor speed regulation as the load on the motor varies or as friction in the drive system changes with temperature."
Screen Shot.jpg
 

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Terryl

Terryl

Specialist Contributor
Messages
2,507
My Satellite Setup
OpenBox X5 on a 1 meter motorized dish.
And now a 10 foot "C" band dish.

Custom built PC
My Location
Deep in the Boonies in the central Sierra Nevada mountains of California.
An actuator is an inductive load, not unlike a large loudspeaker.

During operation, at the point of initialising the load has two draws from the supply, the actual drive load, and the energising load.

The latter does not require a specific voltage to get things moving, but the energising should be fast enough to stop this drain from causing loss in the drive. If the voltage is too high this can cause breakdown of the winding insulation, if too low then the windings heat up before the actuator turns and could become distorted.

A large supply is necessary on a large actuator , elsewhere on the forum there is a thread on an actuator controller that has to be modified with an updated transformer to work on bigger dish systems.

Additionally the ideal supply for an inductive load is also inductive, ithe the impedance of the windings closely matching that of the actuator at the other end, taking into account the resistance of the cable between them, which could be in the region of a few ohms over a long distance.

Lastly the relay system for reversing and dumping of the back emf should be 'clean' in terms of the contacts to prevent arcing, with a capacitor system that neutralises the inductive pulse that travels back to the supply.
Sorry to disagree good buddy......but a DC motor is a resistive load, an AC motor is an inductive load. (an AC motor is commonly called an AC induction motor)
 
Channel Hopper

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Sorry to disagree good buddy......but a DC motor is a resistive load, an AC motor is an inductive load. (an AC motor is commonly called an AC induction motor)
That is true when a DC motor is running at a constant velocity, but definitely not during the ramp up, nor (especially) when the supply is disconnected.

Whilst there is some foundation for doubt, an inefficient commutator design, such as those used in satellite linear actuator, create induced current through motion change, the resultant losses requiring supression (rarely full cancellation ) of the excess energy using a capacitive dump.
 
3virgul14

3virgul14

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Messages
31
My Satellite Setup
2.4m Famaval motorised+Tbs6903+Prof8000+ TM 5502HD

Now has a working Prodellin 3.7m! 30W to 62E ! 20db average signal.

Next : 100.5 E asiasat
My Location
Dodecanese
Hi all, I have a current problem with this matter.

As @Channel Hopper knows , my power cables( although quite thick') run a good 90m from the actuator to the house and at the end of each ark ( 30w to 62E) I have trouble getting back the dish( giant 3.7m prodelin) to the center, after 5-6 degrees the counter starts counting normally but till then its a pain in the arse.

They are 36` QARL Heavy Duty Superjacks with a lot of wear, almost crying now under the load.

Any McGyver ideas to modulate the voltage at the end of the cable ?


Happy feedhunting all,

Regards.


Alpi


FWIW, the motor is designed to run best at its rated voltage (36V) and at 66% it will have far less torque because the current will be proportionately lower. Therefore it will run slower and it might struggle to start the actuator moving, especially if the actuator mechanism is a bit dirty/rusty, and so might actually run hotter, or even stall (which will do it no good!), because of that. Also, because of the lower motor torque, it might not actually be able to drive the actuator to the ends of its travel = reduced scanning arc.

However, you could also trying running it at around 30V.

Also remember that you will need some form of voltage reduction circuit - could be a simple resistor network (large wire-wound resistors) but a semiconductor regulator would probably be better, especially if that has a voltage control which can be altered so that you can experiment to find the lowest voltage at which the actuator moves smoothly.

Final thought, it might even be worth running the actuator at a little more than 36V as that would give it more torque and so it would struggle less at the extremes of the scan arc (especially if the supply cables are long and so there is an appreciable voltage drop along them - but that means that you would need a voltage step-up circuit instead of a reduction circuit.
 
Terryl

Terryl

Specialist Contributor
Messages
2,507
My Satellite Setup
OpenBox X5 on a 1 meter motorized dish.
And now a 10 foot "C" band dish.

Custom built PC
My Location
Deep in the Boonies in the central Sierra Nevada mountains of California.
I have a long run out to my "C" band dish, (135 feet) this would have been a long run for the motor voltage cables and the voltage drop would have been excessive, so I moved the satellite "V" box out closer to the dish, (10 feet) this is mounted in a water tight box with an AC power source in it, works great.
 
Channel Hopper

Channel Hopper

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A little less analogue, and a lot more crap.
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I have a long run out to my "C" band dish, (135 feet) this would have been a long run for the motor voltage cables and the voltage drop would have been excessive, so I moved the satellite "V" box out closer to the dish, (10 feet) this is mounted in a water tight box with an AC power source in it, works great.


That might assist, though the solution is to counterweight the dish.

Hi Alpi :Y

If you have an - analogue - ammeter then try looking at the peak current at motor start (along with the associated drop in voltage, which will be down to the ASC circuit falling down when it is needed most)

Adapting the 3.7m with standard polarmount will consist of three spars - top/left/right - running back from near the ends of the existing supports (ribs), and careful addition of a cage where they meet behind the mount, with weights to compensate until you get reasonable motor engagement at the extremes. Unless you have the brace brackets installed, constructing three triangular braces across two of the rib bolt-holes will reduce potential distortion of the panels.

Ideally the weight should be as far as possible behind the polarmount to keep the counterweight mass down, though practically it will be about double the distance from the reflector front to the motor gearbox, approximately 2.5 -3m.


Prodelin always did guarantee only limited movement on their motorised dishes, I recall us trying well outside the recommended parameters when I was with you.
 
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