Digital servo's on USB servocontroller
SkalTura
Posts: 14
Sorry if my English is not correct, but I'm from the Netherlands...
I bought the Propeller USB Servo Controller (no. 28830) recently.
I have a few digital servo's from Graupner (model: DS 8041) that don't seem te work on this controller. The servo's are working on my RC receiver, so I know they are not defective. And when I connect them to a PIC 16F628A micro-controller and use the PIC Basic "servo" command to control them, they also work.
When I try to control the digital servo's with the PSCI software, downloaded from the Parallax website, that don't do anything. My normal servo's do work with this software.
Does anyone here has experience with digital servo's and this USB servo controller ?
Many thanks !!
I bought the Propeller USB Servo Controller (no. 28830) recently.
I have a few digital servo's from Graupner (model: DS 8041) that don't seem te work on this controller. The servo's are working on my RC receiver, so I know they are not defective. And when I connect them to a PIC 16F628A micro-controller and use the PIC Basic "servo" command to control them, they also work.
When I try to control the digital servo's with the PSCI software, downloaded from the Parallax website, that don't do anything. My normal servo's do work with this software.
Does anyone here has experience with digital servo's and this USB servo controller ?
Many thanks !!
Comments
analog servos need a 1-2millisecond pulse every 20 milliseconds.
Digital servos need a much shorter pulse every 400 microseconds
best regards
Stefan
www.futaba-rc.com/servos/digitalservos.pdf
Graham
I programmed a simple test program on a PIC 16F628A micro-controller to test my digital servo's. This uses the same pulse, and on this test setup the digi-servo's also work, so I don't understand why they don't work on the USB controller.
I haven't measured the output of the USB controller on my scope, I'll try this tomorrow. (time difference, I'm going to bed now)
Thanks!
I have used the Prop to drive digital servos, no difference in operation. I use a variation shown below to drive digital servos. You adjust the Time ON to set the position.
You could also just do a crude test of a basic spin loop to see if you can get a motor working:
PUB Rotate dira[noparse][[/noparse]18] := 1 'set your pin here repeat outa[noparse][[/noparse]18] := 1 waitcnt(cnt + 1_362_000) ' TIME ON : vary this to see what works outa[noparse][[/noparse]18] := 0 waitcnt(cnt + 200_000)I have used a few digital servos on the previous USB servo controllers, (28823 - discontinued), without a problem or need to program the servos.
That said, I just did a test, as I am using the Propeller Servo Controller in a new project.
Propeller Servo Board and PSCI (remember it's still Beta)
Standard Hitec HS-55, repsonds normally.
Hitec HSR-5990TG Digital Servo, responds normally.
JR DS8711 Digital Servo, responds very erratically, sometimes not at all, sometimes a 2-3 lag time between moves.
Thinking it might be a problem inthe PSCI program, I made a little repeating loop in 12Blocks.
Standard Hitec HS-55, repsonds normally.
Hitec HSR-5990TG Digital Servo, responds normally.
JR DS8711 Digital Servo, responds very erratically, moves when 5 second pauses are called for (not supposed to move).
I'm going to have to pull out my RC transmitter and test the JR in a regular RC setup to see if it operational. I have 3 more of the JR servos that I will get from work tommorrow to test them also.
Stay tuned,
Jim
@ Todd
http://www.parallax.com/Portals/0/Downloads/docs/prod/motors/28823_Setup%20PSCI.zip
Post Edited (hover1) : 12/5/2009 9:55:50 PM GMT
When I connect a normal servo, there seems to be some noise on the signal. However, this doesn't seem to be a problem for the servo. It works just fine.
But, when I connect a digital servo, there is no signal left. Just random noise on the scope screen.
I made 2 movies and put them on my server since I can't upload WMV files.
Movies of the scope screen with a normal servo connected: www.hacsoftwarecompany.com/test/normal_servo.wmv
Movies of the scope screen with a normal servo connected: www.hacsoftwarecompany.com/test/digital_servo.wmv
Hope it makes sense to you because I don't understand what is going on.
But like "hover1" said, it could be the program... Because when I connect the digital servo to a microcontroller or to mt RC receiver, the servo's work perfectly.
I haven't tested the servo controller by connecting it to a microcontroller, because I only understand PIC Basic (Crownhill) and haven't figured out jet how to do this.
Post Edited (SkalTura) : 12/6/2009 7:11:54 AM GMT
Did you scope the output with the servo DISconnected ?
There is not much to see on both videos
Can you record again with a timebase that 2 or 3 pulses can be ssen on the screen ?
How was the trigger of the O-scope configured ?
adjust the trigger to channel not to auto and adjust the triggerlevel to around 1V
best regards
Stefan
Post Edited (StefanL38) : 12/6/2009 7:44:43 AM GMT
But like "hover1" said, it could be the software because he had problems with the JR servo's *** well.
Made a picture of the scope screen without a servo connected and with the settings you suggested. Same noise, but I'm not sure if this is supposed to be there since my normal servo's work fine.
I'll try to find a digital Futaba or HiTech servo to test with first so I can find out if my controller is defectiv, or that it's my Graupner servo's that cause the problem.
Thanks!
as I still haven't took time myself to explore the possabilities of ViewPort,
is it possible to use ViewPort with the "Propeller Servo Controller USB" Parallax No #28830 ?
I guess yes. Then it should be possible to see how the logic levels of the IO-Pins change over time.
With this it should be possible to analyse if the noise comes from the program or from somewhere else
@SkalTura: can you adjust your scope to a trigger-delay ?
can you take another picture with a timebase that shows one pulse filling almost the screen
and one picture showing the first 1/10th part of a pulse ?
To have a better solution how the noise looks like ?
and if you have a trigger-delay showing 1/10th of the pulse in the middle of the pulse ?
Can you take two(three) pictures like descibed above but with the signal applied to a 10kOhm-resistor
Servosignal
and Probe >
10kOhm
Ground-of board---Ground of O-Scope
best regards
Stefan
best regards
Stefan
It seems to me that the noise should no be there and this is a possible problem, perhaps related to your PSU or perhaps the firmware.
Graham
I do have an idea worth testing... what if the servo's control input needs more current, or a higher voltage, than prop servo circuits normally provide?
I usually use a 1k current limiting resistor in-line to the servo input, so maybe it needs more than ~3mA at 3.3V?
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www.mikronauts.com Please use mikronauts _at_ gmail _dot_ com to contact me off-forum, my PM is almost totally full
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Do you mean the voltage/current provided by the USB port that runs the servo controller, or the voltage/current that is used to power the servo's ? Because I have the hardware connected to the PC via USB, and a powersupply (stablized) of 5V 2.5A for servo power.
that one wire where the 1-2 millisecond-pulses comes into the servo
maybe the servo needs REALLY 5V to work properly.
What voltage does your RF-receiver deliver ?
What voltage does your pic-testcircuit deliver ?
I guess 5V. A propeller-io-pin DIRECTLY delivers just 3.3V.
But I'm not sure what the servo-controller-board delivers.
put a shunt-resistor in serial between prop-board and servo and measure the voltage-drop across a the shunt-resistor
with your O-scope adjusted to the lowest voltage-scaling 5-20 millivolt / div
then you can measure the current that flows while the signal-pulse is applied to the servo
servo-board----shunt (0,1-10 Ohm)----servo
can you measure a difference between your RF-receiver, PIC-tester and Prop-servo-board ?
best regards
Stefan
The new Propeller servo controller has voltage translators (TXB0108) at·each output. The servos should be getting a 5 Volt Signal. But this is based on the USB port providing enough current. I am in the consulting mode right now and have speced the new servo controllers in a new project. The same servo worked fine on the old USB servo controller. I am doing some more testing now.
Jim
I tried Hanno's 12Blocks which uses Servo32V6 and overwrote the firmware, same outcome. I going to try Servo32V7 to see if there is a difference.
Gosh..I wish my PropScope would get here. My 20 year old Phillips scope died this year.
Jim
Update:
Here's what I found with (3) JRDS8711 servos. None of them work with the Propeller USB Servo Board. The HiTec HSR-5990TG Digital Servo works just fine. I did a project about two months ago that used the JR DS8711 servo on the old USB Servo Controller (Parallax 28823) and it worked just fine. I still have one 28823 left, and I tested all the JR's and HiTec on it with PSCI software, and they all work fine.
The following pics show P0 pin in 12Blocks, (pretty much ViewPort output).
The JR Servo almost seems like it is injecting signals onto P0 during the time at which the Propeller is not outputting any. And during a normal 1.0ms or 2.0ms command, the trace shows trash. This may be the noise that was seen on the Grauptner servo?
I have to drop this right now as I have another deadline for Monday, but will revisit this soon, as I have a project·based on this product.
Chris, Josh, Dave. Have you got any Digital Servos to test this out on?
Jim
Post Edited (hover1) : 12/6/2009 9:19:47 PM GMT
The vast majority of digital servos will work fine on a 1 -2 mS pulse every 20 mS. There are some specialty servos, like for use with a gyro that use shorter pulses and higher frame rates but that is not the norm.
Rich H
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The Simple Servo Tester, a kit from Gadget Gangster.
And JR·sells this as a "drop in" replacement servo. I can't even find a JR programmer, but HiTec seems to think you need one.
Jim
@Stefan·(I THINK the 400 microseconds is done internally in the servo)
I wonder what would happen if you put a small cap across signal and ground?
Rich H
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The Simple Servo Tester, a kit from Gadget Gangster.
I have over 17 years of experience with flying model airplanes and helicopters, and what I can remember from the early days is that Graupner used another signal than Robbe/Futaba and Multiplex. I'm not sure if this is still the case, because the servo's work on my Futaba RC receiver.
So to make sure, I borrowed a digital Multiplex servo from a friend, and this one works fine with the USB servo controller using the beta software.
Guess I'll sell the JR servo's on eBay and buy Futaba or HiTech instead ?
Post Edited (SkalTura) : 12/7/2009 7:14:23 PM GMT
Jim
Just reading again, this looks like the problem, it would seem as if the servo is pulling too much from the propeller pin. There should otherwise be no difference between having the servo connected and not.
A series resistor on the signal line might be a good start.
Graham
The controller that we have outputs the standard 1 to 2ms pulse that servos will operate at. There are some digital servos that will operate properly with those signal; however you would need to verify with the manual of the servo to verify or deny that. If the digital servos do not support the standard 1 to 2 ms pulse for operation; you can use the firmware we release for the PSC to support the new syntax to support the digital servos. We keep the firmware open as the PSC could be used in a number of ways other than a servo controller.
I hope this helps,
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Respectfully,
Joshua Donelson
www.parallax.com
Not sure if you caught this information in one of my·last posts. The servo is not connected directly to the Prop,·it goes through a TI Voltage Level Translator:
http://focus.ti.com/docs/prod/folders/print/txb0108.html
Schematic of PSCU:
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PSCUsb_A%20Schematic.pdf
I'm still stumped. The JR servo I am using is supposed to meet all standard servo specs.
.....Waiting on PropScope.......
Jim
Graham