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Electronics => Electronics => Topic started by: Mastermime on November 29, 2012, 08:00:08 PM

Title: Servo Issue With Axon
Post by: Mastermime on November 29, 2012, 08:00:08 PM
Hello everyone,

This post is also in software (Servo Code), but I figure this particular issue deals with electrical. 

So here is my setup: 12v > Axon II > 12v Pins > L7805 linear regulator > servo

My servo draws 350ma max.  I will be operating at half speed though so the current draw will be less.  I just wanted to confirm that this little circuit will solve my problem.  I know I'll be wasting 2.5-3 watts, but that doesn't really matter to me.

Thanks

Jason
Title: Re: Servo Issue With Axon
Post by: Soeren on November 30, 2012, 10:00:24 PM
Hi,

[...] I just wanted to confirm that this little circuit will solve my problem.
What little circuit?
Title: Re: Servo Issue With Axon
Post by: Mastermime on December 01, 2012, 12:18:50 AM
Actually it hardly could be considered a circuit.  Those would be the 3 pins on the Axon II.  All I'm doing is placing a regulator between 12v unregulated pin and the servo to drop it down to a voltage the servo can handle.

12v unregulated pin-----------------------LM7805----------Servo

Servo pin-------------------------------------------------------Servo

GND-------------------------------------------------------------Servo

Hope this makes sense
Thanks
Title: Re: Servo Issue With Axon
Post by: Gertlex on December 01, 2012, 01:08:02 AM
Presumably the regulator has a ground, too. :)
Title: Re: Servo Issue With Axon
Post by: Mastermime on December 01, 2012, 09:52:33 AM
Oh yeah I forgot to add that in there.
Title: Re: Servo Issue With Axon
Post by: Soeren on December 01, 2012, 02:01:31 PM
Hi,

Actually it hardly could be considered a circuit.
Anything with current circulating is a circuit, hence the name :)

I have attached a schematic of the minimum use of an 7805 that you ca get away with.
Mind you, the excess voltage means that you need a heatsink.
A 10 Ohm 2W resistor between the 12V and the input of the 7805 will gobble up some of the excess power.

If you want to raise the voltage a little, a signal diode (1N4148 or 1N914) in the ground lead of the 7805 (but the caps need to go to ground directly) will raise it to ~5.7V.
Title: Re: Servo Issue With Axon
Post by: Mastermime on December 01, 2012, 05:28:39 PM
Thanks a lot for the schematic.  So in American terms I need a 0.22uf non polarized capacitor between input and ground and a polarized capacitor between output and ground?  I'm unfamiliar with that abbreviation 'ut'.  Could you clarify?  Sorry for my ignorance.  Im embarrassed :P
Title: Re: Servo Issue With Axon
Post by: waltr on December 01, 2012, 06:42:53 PM
Thanks a lot for the schematic.  So in American terms I need a 0.22uf non polarized capacitor between input and ground and a polarized capacitor between output and ground?  I'm unfamiliar with that abbreviation 'ut'.  Could you clarify?  Sorry for my ignorance.  Im embarrassed :P
Seems to be a typo. The cap value would be in uF (microFarads).

220nF = 0.22uF. Both are now used in the US.
This would typically be a ceramic cap.

No need to be embarrassed. Asking questions to get a clarified answer is a good thing.
Title: Re: Servo Issue With Axon
Post by: Soeren on December 01, 2012, 07:25:39 PM
Hi,

So in American terms I need a 0.22uf non polarized capacitor between input and ground and a polarized capacitor between output and ground?
Yes.


I'm unfamiliar with that abbreviation 'ut'.  Could you clarify?  Sorry for my ignorance.  Im embarrassed :P
Perhaps it didn't write it properly to the bitmap, but it was supposed to read 22F+ (plus sign) meaning 22µF or larger (up to about 50µF, whatever might be around).
Title: Re: Servo Issue With Axon
Post by: Soeren on December 01, 2012, 07:30:22 PM
Hi,

This would typically be a ceramic cap.
This is the best type, due to the low ESR, but I think it's more common to get polyester caps in that value (from hobbyist shops). That would work fine as well.
Title: Re: Servo Issue With Axon
Post by: Admin on December 02, 2012, 10:59:40 AM
As you may already know, the original Axon can't handle more than 10V because that big blue capacitor is rated at 10V. You can just replace it with a higher rated capacitor (and lower mAh), thereby letting you can use the built-in Axon regulator to do what you wanted. No extra circuit needed.

The Axon II can handle up to 20V because I corrected that "mistake". (I didn't think people would use greater than 7.2V batteries when I designed the original in 2007)

The regulator is the same on both, and can handle up to 1.5A. If it overheats, it will throttle back the current automatically.
Title: Re: Servo Issue With Axon
Post by: Mastermime on December 02, 2012, 02:53:04 PM
Ok thanks everyone for the help