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hv servos mixed with lv receiver

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Old 03-29-2018, 05:26 PM
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flier60103
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Default hv servos mixed with lv receiver

is there going to be a problem if you run your servos on 7.4 volts and the receiver (frsky) on 5 volts? Just thinking of a situation where a separate regulator is used for the receiver that is less than the nominal voltage (2 lipo cells).
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Old 03-30-2018, 05:22 AM
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I don't get the question. But if you are asking "can I run a normal receiver at 7.4 v?" then yes, you will burn out your receiver due to current draw from the servos. If you are asking can I buy a board that powers the receiver at 5V and the servos at 7.4v these are readily available but expensive. Smart-Fly puts these out. PowerExpander Eq10E That's why folks just opt for the HV receiver.
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Old 03-30-2018, 10:00 AM
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Have you checked to see whether the frsky receiver is compatible with HV? Most newer receivers are. If that is the case, run everything on HV.

Looking at a variety of frsky receives, the ones I looked at are all rated for up to 10V even though not specifically saying they are for HV.

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Old 03-30-2018, 10:56 AM
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no issue with rx voltage .. but your 7.4 will not have all the speed toque or power you might want or need ..but a ubec and some moving rx plugs will be needed.as in signal wire stays with rx and ubec powers servos.if you can follow.
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Old 03-30-2018, 11:43 AM
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The FrSky receivers I'm familiar with are rated for up to 10V input, so they're fine on 2S lipo.
And no, you won't burn up the receiver due to the supposed higher current with HV servos. For a given amount of torque, a HV servo will draw a little less current than one rated at the same torque at 6V.
The question as to whether there's a problem with too much current for the receivers power bus is determined by how many, and what torque ratings the servos have and other factors.
Pete
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Old 03-30-2018, 11:49 AM
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Originally Posted by pilotpete2 View Post
The FrSky receivers I'm familiar with are rated for up to 10V input, so they're fine on 2S lipo.
And no, you won't burn up the receiver due to the supposed higher current with HV servos. For a given amount of torque, a HV servo will draw a little less current than one rated at the same torque at 6V.
The question as to whether there's a problem with too much current for the receivers power bus is determined by how many, and what torque ratings the servos have and other factors.
Pete
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Old 03-31-2018, 11:25 AM
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The stall current is what you need to worry about. Here’s a link to an example of stall current at various voltages. https://www.servocity.com/hs-7950th-servo With a non HV receiver you need to make sure that the connectors inside can handle not just the voltage but the current as well. Worse case is stall current. Sorry if I wasn’t clear before.
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Old 04-03-2018, 03:30 PM
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Originally Posted by kdunlap View Post
The stall current is what you need to worry about. Here’s a link to an example of stall current at various voltages. https://www.servocity.com/hs-7950th-servo With a non HV receiver you need to make sure that the connectors inside can handle not just the voltage but the current as well. Worse case is stall current. Sorry if I wasn’t clear before.
While I'm not sure about the Frsky receivers, most receivers these days use multi plane boards with more than (1) power carrying land between the various servo pins. I can't say I've ever heard of a receiver having a board problem with regards to current on the power buss. With regards to HV and servos, for a given amount of torque, with HV there will be less current than an equivalent torque LV servo.
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