Picaxe 08M AXE024 Servo Control and Digital Servos

[heli_madken]

Hi Everyone,

Havent posted here for some time, previously I had been messing about with an 08m AXE024 Servo control board to drive a couple of analogue servos, I have a simple question having replaced the old analogue servos with a couple of digitals the program does not work, can digital servos be controlled with this board?

Any help would be appreciated

Ken

 

[srnet]

I guess digital servos can be purchased or configured in such a way that they wont emulate standard analogue servo operation.

Why are you replacing the analogue servos ?

Any chance of details of the servos or the program you are using ?

 

[sniper887]

Most digital servos can be controlled with the standard 50Hz pulse train required for analog servos. I have replaced an analog with a digital servo on an RC plane and it worked fine. In the datasheet for the AXE024 it says more capacitors across the power rails may be necessary if the servo generates a lot of electrical noise (they can sometimes) and causes the Picaxe to reset. Another thing is digital servos specifically use more power than their analog counterparts due to their updating their position much more frequently. That could cause problems as well.

 

[heli_madken]

Thanks for the help.

Yes as I understand it the signal to the servo is just the same as an anlogue servo, I fly planes and helicopters with both types of servo from the same receiver.

I need digital in this instance as I require a lot of torque over 17kg in this instance.

I have tried powering the servos seperately but get the same result they move erractically from one extreme to the other even when the switch is in rest position, also happens with a few other digital servos I have, could this be a symptom of the 08m resetting?

The program is very simple -

Do_loop:
pulsin 3,1,b0

if b0 < 120 then goto servowait

servo 1, 100

servopos 1, 200
pause 500
servopos 1, 100
pause 500

servo 2, 100

servopos 2, 200
pause 500
servopos 2, 100
pause 500


servowait:
goto Do_loop

Except for one thing the servopos command causes a syntax error, the chip I am using dates back to 2007 as does the editor so I am assuming that this command wasnt supported then or isnt supported on the 08m so I modified it to -

Do_loop:
pulsin 3,1,b0

if b0 < 120 then goto servowait

servo 1, 100

servo 1, 200
pause 500
servo 1, 100
pause 500

servo 2, 100

servo 2, 200
pause 500
servo 2, 100
pause 500


servowait:
goto Do_loop

But I have read somewhere that this may cause timing issues could this be the problem?

Thanks

 

[heli_madken]

Apologies everyone I am so dense! solved this by binding the negative of the servo to the negative pin of the AXE024 servo output negative pin. The reason I hadnt done this previously is that I want to power the servos seperately at 7.2v, I am not too good with electronics so one more question please, if I power the servos at 7.2v keeping the live wire seperate from the AXE024 but connecting the negative to the servo output along with the signal wire am I in any danger of applying 7.2v to the AXE024?

Any help woudl be appreciated

Ken

 

[Technical]

Two supplies like this is completely fine, but you must link the 0V connections, as you have found out!

 

[heli_madken]

Many many thanks, Ken

 

[sniper887]

I'm assuming your servo can handle the 7.2 volts. Not all can. Glad you got it working.