Servo PWM input speeds with NAZA

Ok, did some reading the other day and found this:

Here:

http://pcbheaven.com/wikipages/How_RC_Servos_Works


"As mentioned before, servos are controlled with a PWM signal driven to their signal wire. A PWM signal has three parameters that characterizes it: The first is the amplitude (or peak to peak voltage) of the signal. You should use from 3 to 5 volts for your signal, according to it's specifications. The second is the frequency. In PWM, the frequency is usually fixed to a value. For analog servos the frequency is 30-50 Hz, and for digital servos it is 300 to 400 Hz."

But I also see reference to where a digital servo has an amplifier on it's control board to speed up the Hz.

My question is this, does a digital servo take a 50 Hz input signal and then increase this signal to 300 Hz at the motor output for fine precise fast movements? Or is that all wrong and it just means that a digital servo can take a 300 Hz input from whatever is hooked to it (Rx or Gyro or control board)?

Reason for asking is that I see the NAZA can put out a 300 Hz signal into the ESC of the quad copter. But can a digital servo take the same 300 Hz input and move like it is suppose to without catching on fire? This would allow the NAZA to control a collective pitch servo on a quad.

So it seems there must be servos out there that can take a 300+ Hz input because Beastx has reference to setting swash lines from 50Hz to 200Hz and tail to anywhre from 50 Hz to 560 Hz with a lot of reference to 330 Hz.

I didn't realize that there was so many Hertz in the world.........

http://www.beastx.com/products_specs.html

Your question: "Or is that all wrong and it just means that a digital servo can take a 300 Hz input from whatever is hooked to it".  Your last assumption is correct.  It just means that the servo is capable of receiving the faster update rate.  As for your reference to something that basically multiplies the rep rate, that makes no sense.  Yes it would be possible to make a device that would output a higher rep rate based on a low rep rate input, but it would have no impact whatsoever on the performance.  You can't get out something that you didn't put in!  

Yes many modern digital servos are capable of faster update rates, but not all  digital servos can!  There are a bunch of "digital" servos that are still limited to the slower (analog type) rep rates (50Hz).  I don't ever recall seeing a servo that required less than 50Hz (you mentioned 30Hz).

As for ESC's that handle faster rep rates, there are many.  The problem is that the specs generally don't reflect that parameter.  The Open Pilot site has a page dedicated to listing ESC's that have been tested for higher update rates.  My recollection is that many of the HobbyWing ESC's are capable so those that you just bought for the tri-copter probably can.  If that's what you want to do, you might search the Open Pilot site.  I have also seen firmware updates (hacks) for the Turnegy and other ESC's to increase the rate.  I question how much real impact it would have on flight, but it would be interesting to play with it.  I think you'd have to be a lot better pilot than I am to see any difference at all.  Note that increasing the update rate might very well require tweaking of the PID parameters for proper operation.

Lastly, most modern gyros can be programmed for faster output if you're looking to do that on your heli.  Keep in mind that it's only the gyro correction that would utilize the faster rep rate, because the "commands" from your transmitter are still going to be slow.  Now that I think about it, the gyro is kinda doing the multiplication you mentioned.  It still has no impact on control, but it would allow the gyro itself to respond faster.  Don't forget that a fast update to a slow servo usually generates smoke.

...Tiger

Yup sure are servos that do 300+Hz, my TRex 450 does 4 such servos running at 333Hz. The MKS DS95 and it's Tail Servo MKS DS95i, both also need 6v for MAX performance, speed and torque


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That is a nice looking servo wood, looks like a machined case even.

Sorry PP but I had a system crash before I had a chance to finish my thoughts ... Just wanted add there are many, many servos out that can do 333Hz. We only need to search em out but teh only issue I have found is that spec is not always listed on the retail site so we have to go to the manufacture to get those numbers

Thanks PP I do believe they are one of the nicest servos going, GPS also does sets on his BEAM and he seems to like them. In fact we bought ours at they same time

This PIC shows em best

http://i823.photobucket.com/albums/zz158/pwoodyp/T-Rex%20450/T-Rex_450_02.png

EDIT: and here's GPS Yoda's BEAM

http://i823.photobucket.com/albums/zz158/pwoodyp/eMote/Beam_E4_Head.png

and a Vid of the DS95's ---->

http://youtu.be/gaDkDwM-yZQ



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Servo Database is a great place to look for servo specifications: http://www.servodatabase.com/

So this discussion leads me to believe what I am scheming up just might work. The other issue is whether a 333Hz servo can take a 300Hz signal and still be happy.

But to further explain I am just trying to determine if a NAZA controller can be plugged into a servo instead of a ESC. I see that the NAZA can run at 300Hz but the limited documentation I read seems to indicate that the output is adjustable. If this is the case then a single motor variable pitch constant RPM quad is possible. I like the idea of 4 450 main rotors with a modified swashplate that does not swash but works like a tail rotor slider instead.

You should be able but don't quote me. When I needed to input for my GYRO I needed to tell it which servo and was told by those that know these things it would work but problems CAN arise in a BAD way for the servo if we go over.

But as I said DO check my FACTS as it's been awhile since I had to think about this, as much as I hate to say it I might be wrong!


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How do you want to deliver the power from the single motor to the four rotors?  I think you will need torque tubes or belt(s).

I still like the idea of variable pitch quads, but to me the added mechanics and points of failure defeats the simplicity of the quad system of having only four moving parts. 

Instead of creating a variable pitch quad I think it would be more beneficial to have a electronic drive system that recognized a motor or propeller failure and could shut down that motor down making the vehicle able to hobble back home.

Here is a link to Hobby King's "Specialized Motors" category.  You will find brushless motors with hollow shafts and variable pitch mechanisms pre-installed:
http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?idCategory=523

Using four of those motors might be a easier way to test a variable pitch vehicle before also worrying about all the drive mechanics needed to make a single motor version.

The ultimate goal would be for a Zenoah gasoline engine driven quad copter  ;D All engine power would go lift, none wasted on tail rotor. The four rotorheads would probably be less complicated than the setup a regular helicopter has, but most of all the NAZA is the best and most affordable high end controller out there. And with GPS coming for it..........  8)

TT or belt, I am kind of a belt guy, been around heavy equipment my whole life and belts run the world, no doubt about that. TT would be good, but really adds complications to the design.

Hobby King offers a very nice aluminum mechanism for their hollow shaft motors.  Check it out:

http://www.hobbyking.com/hobbyking/store/__22682__4D_hollow_Variable_Pitch_Unit_without_motor_3mm_Motor_Shaft.html

That's pretty cool, have not seen a unit like that before......

I think it is a higher quality upgrade for this:

http://www.hobbyking.com/hobbyking/store/__6296__Variable_pitch_prop_motor_set_7_Type_B.html

Do any of you know if the NAZA is 760us centering at 400 Hz or is it 1520us centering at 400 hz and can the hz be changed to 300?

The specifications say 400 Hz refresh frequency for the ESC output.  Nothing about the timing.  My guess would be the slower 760us timing.

You can read the specifications here:
http://www.dji-hobby.com/naza/index_en.html

You can get the manual here:
http://www.dji-innovations.com/files/naza/NAZA_M_User_Manual_en_2_0.pdf

Page 8 says that it is 400 Hz and 1520us centering, 760 is actually the fast rate and 1520 is old school. This is making it tough for me to find servos, seems like when you get above 333Hz they go to 760us 

I wonder if you fed a 333 servo with 400 if it would catch on fire?

A list:

http://www.helixrc.com/technology/frame-rates.html

After 333 they go to NPW (Narrow Pulse Width) at 760us 

Arrgh, no luck so far. Guess I will have to find a sound proof room and tie down a 333Hz servo and "waterboard it" with 400Hz to see how bad it will scream.

400 Hz is only 20% over 333 Hz

I read where a 50Hz servo can take 70Hz max, this is a 40% difference in refresh rate. 20% would be 60Hz and I see where that is ok as well on other sites.  ???

You're right, sorry about that.  I should know as I had to re-program my Futaba GY520 on my Beam E4 to 760us for the MKS tail servo.