AP4 Problems... Anyone using the AP4 ???

[JettPilot]

I have an AP4 for my UAV. The instructions say that the voltage should be 6 volts but I run a 4 cell pack that is at about 5.3 volts when fully charged... Seems close enough. When I try the AP4 on the ground, just connected to the GPS and two servos, it moves the servos and seems to react to direction and GPS :) The NEMA out of the GPS is definately getting to the AP4 :p But its hard to tell exactly what its doing while walking around the yard :rolleyes: ....

I put the AP4 in my UAV with remote on off control of the autopilot. With the AP4 commanded off from my transmitter, it passes the signals through as though it were not there, just like it should... When I turn the AP4 on, it wont do anything, the rudder and elevator control go limp :mad: the AP4 never commands anything... Anyone else had anything like this ? Any ideas :confused: ?

Thanks.

[sesat]

Have you set up Waypoints in your GPS?


Ram.

[kd7ost]

I have an AP4 for my UAV. The instructions say that the voltage should be 6 volts but I run a 4 cell pack that is at about 5.3 volts when fully charged... Any ideas :confused: ?Thanks.

Sounds like a voltage problem. You have to feed a regulator on that board. 4 cells won't do it for long.

Dan

[JettPilot]

Sounds like a voltage problem. You have to feed a regulator on that board. 4 cells won't do it for long.

Dan

You mean the board has a regulator built on ? Do you know what voltage the chip runs at ? Maybe I could change the regulator on the board to one that likes 4.8 volts ???

[kd7ost]

You mean the board has a regulator built on ? Do you know what voltage the chip runs at ? Maybe I could change the regulator on the board to one that likes 4.8 volts ???

It is simply an assumption. I've never worked with the AP4 but everything I use that has PIC chips uses a regulator. Read the numbers off of that little half circle, three pin black device sitting off of pin 16 of your PIC. It's the one right near the servo wires and is in the TO220 case. It looks like a little transistor. Post the numbers here or do a google search and use ", specifications" in the search.

I suspect that is a regulator.

The PIC chip is picky about operational voltage. You can't get reliable operation out of the processor by giving it less than design voltage. Too low and it will just shut down. The larger battery pack meets the input requirements so that it (the regulator) continues to put out a 5 volts to the PIC as the voltage in the pack drops off during flight.

However, the battery voltage coming in to the AP4 in all likelihood also goes out to the servos without going through the regulator and that’s why they want you to only use a 5 cell pack. That way you don't put higher voltage to the servos. The regulator is probably rated from 5.5 vdc (LDO version) up to 30 vdc. If your input drops below the lower input threshold it ceases to put out 5 volts. A 4.8 volt pack under load will do that in a very short time. I surmise that the regulator, (if it is one) only powers the PIC chip. The PIC will not likely operate with any reliability if it's voltage drops down to 4.5 to 4.75 volts or lower.

Dan

[JettPilot]

Hi Dan,

I tried the AP4 again today with no success. It just will not react to heading changes. The elevator locks most of the time and the rudder does nothing at all, its like the servo is not even powered, I can move it with my hand :mad:

I measured the voltage and looked up the specs of the regulator. When the input voltage is 5 volts, the voltage being supplied to the chip on the AP4 is 4.8 volts. The voltage specs listed for the PIC16F876A Microcontroller is 4.0 to 5.5 volts, so I would think that the voltage of 4.8 is well within specs would not be an issue here.

Any other ideas ???

JettPilot

[rjet]

When you say "The elevator locks most of the time and the rudder does nothing at all" is this when the autopilot mode switch is on or off? If the AP4 is in auto mode, but not detecting a waypoint signal from the gps it may not update the servos.

Check that your gps is set to NMEA 4800 baud communication mode and it is set to goto a waypoint or route and the cables are plugged in firmly.

[kd7ost]

When you say "The elevator locks most of the time and the rudder does nothing at all" is this when the autopilot mode switch is on or off?

Yes, this is important. Your first post said both "elevator and rudder go limp". Is this a change in symptoms or was there a typo? It sounds easier to troubleshoot if the first statement remains true. Does the elevator lock up when enabled? This would likely mean it's doing what it's supposed to by keeping it at current altitude.

What are those jumpers for?

Dan

[JettPilot]

The AP4 passes signals to the elevator and rudder servos normally when the AP4 is turned off via the remote channel, so I can fly the plane manually. When I activate the AP4 via the remote channel, the elevator locks and the rudder goes limp most of the time, or sometimes activates and jitters a bit, but never tries to make an obvious turn one way or the other :(

I have set my GPS to NEMA data at 4800 baud, and know its working because I have a GPS on screen video overlay on my video, so I see GPS information while im flying...

The jumpers are servo reversing.. The pots are the gains, which I have tried at thier midpoint and also turned all the way up with no success... Any ideas will be appreciated.

JettPilot

[Hovertime]

How about using 5 cell NiCd/NiMH pack or 4 cell alkaline holder from Radioshack to get 6 volts AS REQUIRED??? ;)

If 5.3 would be "close enough" then maybe it would say "5-6V is ok.."

Or it simply may be a bad unit. I would try 6V and if no go - contact seller.
Good luck!

[kd7ost]

How about using 5 cell NiCd/NiMH pack or 4 cell alkaline holder from Radioshack to get 6 volts AS REQUIRED??? ;)
If 5.3 would be "close enough" then maybe it would say "5-6V is ok.."
Or it simply may be a bad unit. I would try 6V and if no go - contact seller.
Good luck!

Agreed.

Dan

[JettPilot]

I agree, that is an easy test to use 6 volts... Even though the chip is getting its rated voltage, I will try the specified 6 volt input. I am rigging a way to put an extra cell on the pack and will try it in a few minutes :D

[typicalaimster]

I agree, that is an easy test to use 6 volts... Even though the chip is getting its rated voltage, I will try the specified 6 volt input. I am rigging a way to put an extra cell on the pack and will try it in a few minutes :D

Seriously how hard is it just to get a 7.4v Lipo Pack and use that?

[JettPilot]

I finally isolated the problem :) It was not the voltage, the AP4 is working just fine being fed with the 4.8 volt reciever pack. My UAV has a long carbon fiber tailboom with the servo wires going to the elevator and rudder running through them and that caused the problem. For some reason the AP4 does not like to be connected directly to a long servo wire and just stops working and gets very erratic :eek: When I put an opto isolator in line, the AP4 works fine, or if I hook a servo with a short lead directly to the AP4, it also works... Its just the long leads to the tail that the AP4 does not like... The elevator always jitters a little bit no matter what is connected, but it responds to altitude deviations and I think it will work. Has anyone ever seen the elevator jittering before with the AP4 ???

I also changed out the servo leads on the AP4 board... The ones that were included were too short and of low quality and did not always make a good connection.. I put JR gold connectors on it so there will be no more connection issues. The jumpers included were even worse, the first time I took a jumper off the metal inside fell out and almost shorted out the board :mad: . Luckily I had some jumpers left over from my computer I used. Attached is a picture of the "new" AP4 and UAV.

[Hovertime]

Glad to hear you got it working! :)

[Medve]

Jett,
I'm watching this thread to see how it works out for you. Really glad that it looks to be working. What is an opto isolator?
Medve