Four DC motors in synch or close too.

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Thread Starter

Mr. Kelly Johnson

I am a newbie with a question. Please understand that I do not understand a lot of the terms used in this type of thing. But I could really use some direction as my searches for such technology have been unfruitful.

I made a four actuator lifting system that works great in its field, and many people have asked me to build them one. So commercial application is my goal.
However, the products weakest part is something I can deal with as the person that designed the system. But wouldn’t expect the average user to deal with. That problem will happen, does happen, and causes devastating damage. Unless I can find a motor controller smart enough to realize it’s happening and adjust to compensate.

Think of it this way. I have four custom designed acme thread linear actuators (without feedback at this time). They are actuated up and down via 30 Amp RF remote control and momentary toggle switch outdoors where 12VDC is the only power available. One is in each corner of a large box to lift the box straight up roughly 16 inches. At times, there will be a heavier load shifted to one corner of the box or another. Therefore, causing one or more motor to run slower than the others. This causes a strain/ twist on the box being lifted that I am trying to avoid.

I need to find a way for the circuit to realize that one of the four actuator is running slower (Or drawing more current) than the others. Then make adjustments to the voltage of the remaining motors to slow them all down to roughly the speed of the slowest actuator. I think the adjustment is normally done by increasing the off time of the volts going to the motor?

It doesn’t have to be perfectly synchronized as the box does have some flex. But I would like to see them all run within 20% of each other. Or not power at all if one of the motors is completely over loaded. I would prefer to stay away from encoders if possible, but if that is the only way to do it?

Basically, I want something that monitors current draw on four motors. And reduces voltage to all the motors with lower current as they relate to the motor with the highest current until they are all within range of each other.

I have all the motor specs, and more details. I thought I’d ask if anyone has seen something like this before that I can research? Or ideas on what the next step would be in obtaining such a circuit that I could potentially have produced as the rest of the components are in production now.

Thank you for your time.
 
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curt wuollet

You should be able to do that with servos, and whether you call them encoders or not, you have to measure the speed of the screws to synchronize them. This type of thing is called electronic gearing and done all the time. That way when one is loaded more, the slowdown is sensed and more power is applied to bring it up to speed up to the limits of the system. To do it the way you mention you would need a supervisor that makes the slowest screw the master. The cheap method would be to run a chaim between the screws and use a single motor. You could also do this on displacement, but rotary encoders are cheaper than linear encoders and if all you need is rate, can be something simple.

Regards
cww
 
Kelly Johnson... if it has anything to do with lifting boats or ships out of the water evenly, I suggest you look into a company called "Synchro-Lift!"

Regards, Phil Corso
 
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William Sturm

If you do not use encoders, you will probably need to sync the four motors periodically to a home switch.  The encoder will give you position data, which can be used to keep the axes synchronized over time.  Some companies have used a single pulse per revolution signal to control the velocity and provide position syncronization, but it would be better to use encoders, IMHO.

 Bill Sturm
 
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Gerald Beaudoin

I would guess that the cost of installing DC motors and setting up all the controls and safeguards to make it all work properly would come pretty close to the cost of simply installing servo-motors. Sounds to me like a good application for servo-motors and would certainly be a lot easier to do than the DC route. That kind of synchronization is already built into most of today's servo controllers.

Gerald Beaudoin
 
J
Did you ever receive a satisfactory answer to your question or come up with a solution. I have a similar problem with a load that will bind if the motors don't. The motors operate screw type linear actuators. The present solution is mechanically complex. The screws are connected together with a chain. I'm looking for a mechanically simpler solution. Please contact me directly [email protected] Thanks - Jim

> I made a four actuator lifting system that works great in its field, and many
>people have asked me to build them one. So commercial application is my goal.
>However, the products weakest part is something I can deal with as the person
>that designed the system. But wouldn’t expect the average user to deal with.
>That problem will happen, does happen, and causes devastating damage. Unless I
>can find a motor controller smart enough to realize it’s happening and adjust to
>compensate.

>Think of it this way. I have four custom designed acme thread linear
>actuators (without feedback at this time). They are actuated up and down
>via 30 Amp RF remote control and momentary toggle switch outdoors where
>12VDC is the only power available. One is in each corner of a large box to lift
>the box straight up roughly 16 inches. At times, there will be a heavier load
>shifted to one corner of the box or another. Therefore, causing one or more
>motor to run slower than the others. This causes a strain/ twist on the box
>being lifted that I am trying to avoid.

>I need to find a way for the circuit to realize that one of the four actuator is
>running slower (Or drawing more current) than the others. Then make adjustments
>to the voltage of the remaining motors to slow them all down to roughly the
>speed of the slowest actuator. I think the adjustment is normally done by
>increasing the off time of the volts going to the motor?

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