RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

Receiver, ESC need isolation?

Reply

Old 12-02-2002, 04:23 PM
  #1  
jdbrownwv
Junior Member
Thread Starter
 
Join Date: Oct 2002
Location: Fairmont, WV
Posts: 10
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Receiver, ESC need isolation?

I'm powering my plane with 4.8V. I am going to be attaching a smoke pump (TME smoke pump) and will be controlling the smoke oil rate via an ESC. I have a Great Planes C-10 ESC w/BEC, trouble is I don't want to power the receiver via the 6V battery for the smoke pump, and I also don't want to risk draining the flight battery. I asked Futaba if I could just cut the (+) wire and leave the signal and ground wire between the receiver and the ESC to pass the signal. Futaba's response is that this would not work. I think an optical isolator might work in this situation. Does any have any plans for one, or an idea of something that might work better?

Thanks
Doug Brown
jdbrownwv is offline  
Reply With Quote
Old 12-02-2002, 05:22 PM
  #2  
flatfour
Senior Member
My Feedback: (8)
 
Join Date: Dec 2001
Location: Midlothian, IL
Posts: 597
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Receiver, ESC need isolation?

I realize they said it would not work, but I don't think it would hurt to try it out. Instead of cutting the red wire, just remove it from the receiver connector.

The pulses from the receiver are referenced to ground, so as long as those 2 are connected (ground and signal), it should work fine.
flatfour is offline  
Reply With Quote
Old 12-02-2002, 06:27 PM
  #3  
jdbrownwv
Junior Member
Thread Starter
 
Join Date: Oct 2002
Location: Fairmont, WV
Posts: 10
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default I'll try, but is this an issue?

I'll take your advice and give it a try. Do you have any thoughts about the differing voltage issue. After pondering Futaba's response, I wonder about a 4.8V signal pulse against the grounded reference voltage, compared to the same signal on a 6V reference voltage... I imagine as the receiver pack starts to dwindle the signal voltage would approach 4V and a Fresh 5 cell pack could run as high as possibly 7V. Would a signal pulse effectively be altered due to the change in reference voltages of the 4V and 7V reference voltages?
jdbrownwv is offline  
Reply With Quote
Old 12-02-2002, 08:50 PM
  #4  
Steve Lewin
Senior Member
 
Join Date: Mar 2002
Location: Reading, UNITED KINGDOM
Posts: 904
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Receiver, ESC need isolation?

ESCs expect the signal to be 4.8V. It's only the power (motor) battery that is normally a higher voltage. The BEC circuit reduces it to 5V, that's its purpose. Removing the red wire should work.

However if your ESC has a low voltage cutoff associated with its BEC circuit you may have problems. Most ESCs are not intended to run on as low as 5 cells (6V nominal) so it may keep switching the "motor" (smoke pump in your case) power off because it thinks the battery is getting too low to run the radio. It has no way of knowing that you've disconnected the BEC so it doesn't matter.

Steve
Steve Lewin is offline  
Reply With Quote
Old 12-02-2002, 11:24 PM
  #5  
flatfour
Senior Member
My Feedback: (8)
 
Join Date: Dec 2001
Location: Midlothian, IL
Posts: 597
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Receiver, ESC need isolation?

I just did an experiment with my Zagi. It's the only thing I have with an ESC. Keep in mind the receiver is a Hitec 555 and the ESC an Aveox.

I pulled the red wire from the ESC connector and plugged a 4.8 pack to the receiver. The ESC worked just fine controlling the motor.

I also have a Fluke ScopeMeter handy, so I did a couple more experiments on the pulses coming from the receiver.
I tested the peak pulse voltage coming from 1 channel output.
On a Fut 133F (3CH ground freq) the pulse had a peak of 2.5V
On a Hitec 3800 (7CH air freq) the peak was 3.2V My only Futaba 127DF is buried in a plane right now.

Steve does bring up a good point about the low voltage cutoff.
I didn't even think of that earlier. The web page lists it as ok with 5 cell input and has a cutoff of 3.7 volts

http://www.electrifly.com/gpmm2000.html
flatfour is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service