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Old 10-22-2019, 10:25 AM
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Servo power/expander box question

Hey all, what are these boxes for? Is this a unit to plug one receiver channel into and then you can power multiple servos from that one channel input?


Jim
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Old 10-22-2019, 10:37 AM
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In a nut shell, yes. But you can get varying options, like regulated, servo matching.
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Old 10-22-2019, 01:43 PM
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One of their main purposes is to ensure that all of your servos get full power. They do this by using properly sized connectors and wires to the battery and distributing that to each servo.
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Old 10-22-2019, 04:13 PM
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Or, if yoy run Spektrum or JR DMSS, just buy the powersafe Rx's. Then balance everything out in the Tx.
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Old 10-22-2019, 05:21 PM
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There's some cases for having one, and there's many cases where its nothing but overkill and adds weight, expense, and needless complexity.

If you have an example of a particular setup in mind we could be more helpful.
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Old 10-23-2019, 06:07 PM
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This is the very basics of power expansion devices, and why they exist.

Servos draw power. In the old days, not a lot of power. These days, servos can be HUNGRY for power. Some models can draw 10 amps for very short periods of time. Imagine having a 35% airplane with 7 servos, then having them all spiking to a combined 70 amps in some aggressive maneuvers.

That is why power expansion devices exist. Receivers may be able to handle the current themselves, but the servo connector powering the receiver from your battery(ies) cannot. Servo plugs are rated to 5 amps continuous for 30 seconds, and 10 amp bursts- quality ones that is. Imagine trying to put 70 amps of current through that connector in a split second. Not possible in our applications, what ends up happening is the system bottlenecks and voltage is reduced. In some instances, you may brown out the receiver (where the receiver loses sufficient enough voltage to continue operating) and lose your airplane entirely.

The power expansion devices solve this problem by allowing you to plug your power source directly into the device using heavy duty connections (like EC3 or Deans connectors) that can handle this current. The power is them spread over the entire positive and negative sides of the servo bus, so when a servo needs to draw 10 amps to hold its position, the power is available.

These power expansion devices also typically isolate a specific voltage for the receiver, and give the receiver priority so that it does not shut down, nor is it subject to voltage sag from batteries or other issues.

You can think of it like this.
  • Imagine you have a field of cows, and they all need to drink water simultaneously, least they perish. You can give them water with your 1" diameter garden hose (or two), dumping into a bucket, but each cow will not get the water it needs to survive. This is powering your system with servo plugs.
  • Now imagine each cow has its own water trough, supplied with a huge irrigation system. Each cow is able to drink plenty of water and lives to fly another day. This is powering your system with a power expander.

Some manufacturers have taken this a step further and have built a power expander with an integrated receiver (Spektrum PowerSafe, Multiplex WingStabi, JR/DeeForce XBUS, etc.) to further simplify your airplane.

On 35% and larger, I would say this is nearly a mandate. On something smaller, it's not as critical.
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Old 10-24-2019, 07:41 AM
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@ XPRES: Now this is a great and understandable explanation! Thanks so much for taking the time to provide it.


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