CloudSkipper

Hi,
Can an older generation RX like the one that came with my Hitec Prism 7X get power from the BEC on an ESC? The RX has a separate "BAT" connection, but I would need to plug the power into the throttle channel obviously through which it will feed 5.2v of power.

Should I not even try that? Wouldn't want to fry the RX because it still works great. Plus I suppose the ESC could be damaged if the RX is not compatible with getting power that way.

edit: Just realized... could I just get an adapter that separates the signal wire from the power wires? Then power into "BAT" and signal wire on its own into the throttle channel. That would work right?

Thanks

Campgems

Just plug in the BEC to your throttle channel. To the receiver, a BEC is two things, a throttle servo and a battery. A receiver doesn't care which slot the battery is plugged into. The Red and black wire are common throught out your system. The B slot on the Receiver is usually one that doesn't provide a signal out, but not always, and this is usually on a 8 ro 9 channel receiver. If there is any compatability issues, it is wiht your BEC, not your receiver.

Don

CloudSkipper

Ok thanks. I just thought since this RX is from the days when electrics were nothing much (and things like BEC's probably didn't exist), that it might not be wired such that power could also flow-in through a channel slot. That was just my reasoning; I could be wrong. I don't think anyone in the days when this RX was new ever connected power through a channel... it was not the design intent at least with the RX in those days to have that option (even though it might still work). Or am I wrong on that bit of RC history?

But if I wanted to play it extra safe, would it not work to make an adapter that splits the signal wire from the BEC-out? Then connect pos/neg wires from BEC separately to BAT slot and signal wire from BEC by itself to throttle channel. I guess the only theoretical risk there is that ESC does not respond right?

My ESC has the BEC built-in as is usually the case.

Thanks for help

CloudSkipper

I was just thinking that that makes sense when you consider that there is the signal wire between RX's and servos. IF it were the case that RX's themselves varied the volts and polarity of the servo power wires, then there would be no need for a third signal wire. So the pos/neg wires are a constant throughout the RX and the signal wire causes the servo to vary volts/polarity for control.

I still have a tiny bit of apprehension over connecting power to this old style RX (Prism 7X era) via a channel since it has a "BAT" slot, but I guess they add the "BAT" slot merely as a convenience eliminating the need for a Y-harness.

Cheers

JohnBuckner

My Feedback: (1)

If you have selected FM(PPM) modulation type on your Prism 7X then your Rx is likely a supreme which by the way is still current and your Prism 7X is not all that old.

All Rx have a common power buss and rx power can be provide in any of the Rx ports either through any avaliable port or shared with a servo using a Y cord.

Campgems

There is no polarity reversal in the system. There quite often seems to be a misunderstanding the my reversing the polarity of a servo power leads, will reverse the rotation. This is a sure way to destroy a servo and possibly the receiver.

The way the servo works is that it created a square wave pluse internally and then compairs it to the receivers signal square wave for that channel. When the receiver and servo pulses are equal in duration, there is no movement. If the pulses don't match, the servo determines whether it's internal pulse is longer or shorter than the receiver signal and moves accordingly. As the gear train is moving, it is also turning a poteniometer to vary the width of the internal pulse and when the receiver and servo pulsed are equal, movement stops again. The greater the difference, the faster the servo moves.

The ESC doesn't have any moving parts, so it generates pulses in a series of steps, not a linerar move like a servo. When the steps are close, no change in output is given from it present amount. Some of the cheaper ESC only have a limited number of steps, so you motor increases speed in steps verse ineral. THe BEC output is simply a voltage regulated output to your receiver and has no interaction to your ESC. They could be standalone circuits or built one the same board, but all the share is the voltage from the battery.

Don

CloudSkipper

Yep it's a supreme. It's not ancient, but looking more and more antiquated I've seen one other guy still using a Prism.

Yeah I was just sort of postulating that IF there were no third signal wire, then that's what the RX would have to do to get the servo to do different things. And if that were the case, then you could not have a common +/- bus and it would probably not be possible to feed power via a channel unless the RX could sense that condition and switch. But since there of course is the 3rd wire, then the existence of just a common +/- bus makes perfect sense in any and every RX...

Thanks for the information. Your replies convinced me that I won't harm anything. I tried feeding power through a channel and it worked fine. That's good because I want to use this RX with a ESC/BEC.... so I don't need to buy yet another component.

Cheers