Servo Issue Hello Margret.....it's me again.

smithdavidp · 2012-04-01 14:18

I'm baaaaaccccckkkk LOL

Okay. I was told that there needed to be a 3.3 ohm resistor placed on the signal wire for the Ping sensor. This was to protect the signal circuit to the Processor. I read the servo schmetic, for the Prop board, which showed a 3.9k resistor in the signal wire of the servo. I am currently going through the servo test in the new Prop BOE BOT section. Ran through the "Wheels Example.Spin" test. The Bot lurched forward for 1 second and stoped, forward another second and stoped. (Of course this test is in the Propeller Boe-Bot Navigation section). The only way that the operation worked is when the 4 AA cells and the USB cable were both connected to the board. I show 5.4 volts at the adapter end and all the jumpers are in the 5 volt position. The assembly portion, of the Prop Boe-Bot, does not show any resistor in the signal line for any of the servos. The servos will also run if connected individually. 2 servos connected and the system is dead. Could the Brown Out circuit be kicking in? I am using P14, P15, and P16 for servo controll. The Ping))) sensor is connected at P17.

Come on guys........ I realize it's April 1st but this is a bit much. It's my guess that the resistors, in the signal line, are drawing too much power 3.9k X 3 (Left, Right, and Ping Servos). But I can't see how that could be possible since the servos are only activated across the SG pins. I should also add that I have the XBee installed.

al1970 · 2012-04-01 14:43

Hi:

I don't use the "Prop board"; I just used my own boards with PICs. to control servos so you have to take what I say with a grain of salt. AA cells don't give much power so you need to use a higher voltage than 6 volts for the main power; this voltage will come down as soon as you start turning on servos. I use a 5 volt regulator to feed the chips.

I never seen a 3.9k resistor used in the signal wire of the servo before. That seems very high. I use a 220 ohm resistor. You may be picking up noise by using a 3.9k resistor.

Al

Duane Degn · 2012-04-01 15:16

You want a 3.3K ohm resistor on the Ping line. I'm hoping you just left out the "K" and you are using a 3.3K resistor.

Regarding resistors on the servo line, I personally don't use resistors on the signal line with servos. I've had some servos not work with a resistor that would work without the resistor.

I'm not sure what examples you're using with the PropBot-Bot. I don't recall any Parallax material on using servos with the PropBOE. I'll need to look around a bit.

You say you're using four AA batteries to power your PropBOE-Bot. This might be a problem. I'm personally using two Li Ion batteries with mine. I think six AA batteries would be a better choice (than four AAs) with using the PropBOE-Bot, but I'm not sure about this. Four AAs might be enough if they are freshly charged.

I'll look for the material you're using. If you find a link to it before I do, I hope you post it here.

smithdavidp · 2012-04-01 15:42

http://learn.parallax.com/PropellerBoeBot#overlay-context=

There ya go :-)

smithdavidp · 2012-04-01 15:48

http://learn.parallax.com/node/284 this one assures you that they are giving instructions for the Prop BOE

Duane Degn · 2012-04-01 16:15

Thanks for the link. I wonder why the "learn" pages are linked to from the PropBOE's product page or download page? I don't think those tutorials should be so hard to find.

I don't know if you've seen my PropBOE project or not (I can't remember if I've asked you this before)?

I think Parallax's examples are easier to follow than my servo use examples. My basic servo examples were written with plans of being able to record the pulse commands to a SD card so they're a little more complicated.

I'm going to need to read though the tutorials you linked to. I'm still amazed I didn't know about them.

Since your servo will run individually but not at the same time, then I think you need a better power source.

Beau Schwabe · 2012-04-01 18:58

The series resistor is there to attenuate electrical noise that could be created from the servo itself or if the distance between your servo and driver are great. In the latter case, the long wire can act as an antenna that can make it's way into a micro controller and potentially cause damage and/or unwanted behavior. If however your leads are short and your servo is electrically quiet ( <- Not all servo's are created equal) , then a series resistor may not be necessary. I typically use a 4.7k resistor if I'm running lengths that are greater than 1 foot.

smithdavidp · 2012-04-02 07:38

Okay. I have run through quite a few tests and the only thing I can come up with is that I am drawing too many amps. I breadboarded the servo circuits and used pins 7 and 8 for the servos. Same issue. I monitored the 5 volt circuit with the servos engaged and the circuit held at 5 volts. The only thing I am adding, with the USB cable connected, is more amperage. I say this because the voltage regulator holds at a steady 5 volts with, or without, the USB being pluged in. I double checked the jumpers and they are all jumpered to the 5 volt side and not to VIN. The Prop BOE specs say that it requires 4-16 VDC. Will the Li-ion batteries fit the standard AA cell holder? If so would it be possible to mount 4 of them in the stock holder? This would give me 14.8 volts which is under the 16 VDC rating. The more robust Li-ions would probably handle the extra amperage. It is, however, baffeling to me that the BS2 BOE handled the same servos along with the Ping))) sensor and servo. Is it possible that the Propeller BOE I received is defective? I just don't understand how a 3.3 volt device can draw more amperage than a 5 volt device......then again......the circuits used to generate a clean 3.3 supply could do some damage. I am at wits end here. I have opened a Tech support ticket on this issue.

Duane Degn · 2012-04-02 08:04

I don't know of any Li Ion batteries that will fit in a standard AA holder.

I doubt your board is defective. How are you monitoring the 5V line? The dip in voltage caused by servos starting to move would likely be too fast for a multimeter to pick up. You'd probably need a oscilloscope to catch it.

Here's two suggestions.

1) Use two 1000uF caps. One on the 5.V line close to the servos and the other on the 3.3V line.

2) Get a bigger battery pack. I think six AA NiMH batteries (freshly charged) would likely provide enough current to keep the servos happy. I've used 2-cell LiPo batteries as well as the Li-Ion batteries with success.

I'm using the two Li-Ion charger I linked to earlier stacked under the PropBOE.

BTW, fully charged Li-Ion and LiPo batteries have voltages higher than 4.0V. If you use lithium chemistry batteries, two cells would probably be enough.

What kind (chemistry and age) of AA batteries are you using?

smithdavidp · 2012-04-02 08:33

Using Energizer NiMH 1.2V 2100mAh. Got my answer though. I just remembered that I had replaced the batteries in my Wah and Fuzz pedals. Pluged in the 9 volt battery and it took off just the way it is supposed to. So I guess it is a matter of voltage. The tests, I made, were at the 5V headers and also at the 5V pins along the servo headers. I also measured at the positive side of the battery adapter plug (circuit board side). It all came up 5 volts.

Duane Degn · 2012-04-02 08:38

If your 9V battery is one of those little ones used in smoke detectors, it wont last long powering a BOE-Bot.

I have a bunch of Energizer NiMH. I very rarely use them anymore. They go dead way too fast IMO.

smithdavidp · 2012-04-02 09:23

Well......... I bought the top of the line. And two for backup. The only thing I hate about Parallax is that when I buy one thing somthing else always catches my eye. I escaped today spending only $167.00. I have come to realize that my project may be more costly than it is worth. lol But I'm the kind that has to see it through to the end. As far as the 9 volt goes I'm not willing to give up my pedals. My SG sounds good enough by it self but I like to play a little hard rock now and then. Imagine that....58 years old and still hammering the strings. lol

Beau Schwabe · 2012-04-02 09:47

With 9V batteries the voltage is fine but they generally just don't deliver enough current for current demanding applications. With any system using a singular power supply to power a micro controller and a motor this will present a challenge. This is why it is often suggested to use dual power supplies in this circumstance because it can solve a lot of potential problems down the road. If you are in fact limited to a single supply, then there are some things that you can do that can help. If you have the voltage overhead and can accept a diode drop, it's a good idea to use a diode/capacitor filter when supplying power to your micro controller. This allows the micro to maintain a reasonable level during a power surge, often seen when starting up a motor, or changing motor speed or direction. ...Additionally placing an inductor at least 1/10th of the inductive rating of the motor in series with the supply power to the motor can help suppress the initial surge to the power supply, further reducing effects that the micro controller could be sensitive to.

smithdavidp · 2012-04-02 10:29

The device I am trying to build must be trustworthy to a fault. I fully understand that nothing can be counted on completly (probably why I'm divorced). Any, and I do mean any, suggestion will be accepted with a very appericiated demeanor. The current draws are part of the reason I was looking into a larger chassis style. I have noted that some are opting to provide a seperate power source for the motors, or servos, freeing up the extra voltage for the other periphials. If anyone has ever endeavored to see what the Propeller will handle it will be me. Carbon Monoxide sensors, temperature and humidity, speech capabilitis, backdoor applications, and a sense of awareness as to current position, or how to get to that position, are all on my list of things that must be integreated into my project. All are equally important and all will perform a vital function within my system. Others include limited voice command and outside sources that will complete a function from a single command from the microcontroller. I fully expect that a dual source of power will be needed before all the tasks can work together. I am, at this point, considering buying another Prop board to be used solely as an informational platform. My concerns are many but I have to tackle them one at a time so that I fully understand the operation and function right down to the components that make it work. My project may take me years to complete but once I am finished it will be a useful, reliable, device that could be used in any home. I am learning engineering, networking, electronics, and programing as fast as I can. Since I no longer work I have the time to devote to it. This is very important to me and possibly will be to others down the road. I print all of this out and put it into the notes section of my binder of which I have two three inch wide binders full already. The money I spend is really not the issue....a completed project is.

kwinn · 2012-04-02 18:08

Duane Degn wrote: »

I don't know of any Li Ion batteries that will fit in a standard AA holder.

Take a look at http://www.megabatteries.com/item_details2.asp?id=15581&cat_id=513&uid=1783 for AA size LiFePo batteries.

davejames · 2012-04-02 18:29

smithdavidp wrote: »

My SG sounds good enough by it self but I like to play a little hard rock now and then. Imagine that....58 years old and still hammering the strings. lol

Keep playin' man, keep playin'!!! :thumb:

(a bit older than you with a '73 SG Special)

Servo Issue Hello Margret.....it's me again.

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