# Precision moving candlestick. Need servo controller help.



## GOT (Apr 17, 2007)

I want to move a candlestick remotely (I will explain later) and I want to do it with a simple 555 servo controller circuit I found and has worked just fine for me with a Hitec HS-425BB. I need something bigger so I bought a mega quarter scale HS-805BB which requires 1.2 amps. The idea is to have two identical arms. One arm is attached to a potentiometer that controls the servo. The other arm is attached to the candlestick. As I rotate arm 1, I want arm 2 to move at the same angle. Two questions. Can I use the circuit as drawn and not fry the 555 chip with 1.2 amps moving around and how do I modify the circuit so that I can calibrate the motion of arm 1 with arm 2?


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## Otaku (Dec 3, 2004)

The servo control (PWM) signal is different from the power the motor uses to move. As long as that PWM signal remains under 200mA (~100mA if using the CMOS version of the 555) you should be OK. I would think that the PWM current would be quite low; I can't think of a good reason for it to be a power hog.


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## hpropman (Jul 27, 2008)

Do you want to manually control the servo but moving the arm attached to the pot. If so then yes that will work. You may have to add manual stops on the arm to avoid damaging the pot (moving past the stops in the pot). I should just be a matter of lining up both arms.


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## GOT (Apr 17, 2007)

Yes, I will move the arm attached to the pot, and this will move the servo. What I need is a method to calibrate the two arms so that they move together at the same angle. As written, the servo moves at a slightly greater angle than the pot.


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## GOT (Apr 17, 2007)

OK, I was playing with a bread board and came to my amateur conclusion... You can add capacitors in parallel. Is this true? Do two 0.1 uf and one 0.01 uf capacitors hooked up in parallel function just like one 0.21 uf capacitor? Any issues doing this?


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## hpropman (Jul 27, 2008)

yes that is correct. Here is a link if you want the full details. There should be no issues doing that it will just look like one larger capacitor.

http://www.tpub.com/neets/book2/3e.htm


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## fritz42_male (May 5, 2009)

Could always do it on a PicAxe 08M - component count would be similar and any calibration issues could be taken care of in the programming!


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## GOT (Apr 17, 2007)

Ahhh! I built it as the schematic above and my servo is vibrating as it moves and sits at rest. I think the 2 amps is flooding the 555. What should I insert between the power source and pin 8 to reduce the amperage?


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## spinman1949 (Jun 29, 2009)

*Isolate power to servos.*

I would think the first thing to do would make sure the power to the servos is isolated from the 5 volt logic to the 555 circuit. You should be able to provide power to the board with a small regulated wart. 1.2 amps is a healthy draw for a servo, so likely a hefty wart or even a 6 volt sealed battery for the servos.


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## GOT (Apr 17, 2007)

OK, I tried this and nothing happens. Sorry, I am a novice. How should I go about isolating the power suppies? I am assuming the grounds are all tied together.


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## pshort (May 6, 2008)

If you're not doing it already, use a separate battery to provide power for the 555 chip and the stuff around it, while continuing to use the beefy wall-wart for the servo itself. The grounds of the battery and the wall-wart should be tied together, of course, while the positive output leads of the battery and the wall-wart are kept separate.

Also, try re-connecting your low-power servo into the circuit just to make sure that nothing else has gone wrong in the meantime.


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## hpropman (Jul 27, 2008)

Yes that is correct all grounds need to be connected together. Remember ground is ground the world around (one of my professors kept drilling this into our heads). Can you show us a picture of the circuit and how you constructed it? You are getting noise in the circuit that is causing the servo to jitter. Noise can come from long component leads like those used on a breadboard or poor connections also the pot may be noisy. The best way to deal with noise is to add capacitors to the circuit. I would start with a .01uf cap on the 555 chip between pins 1 and 8 and another on the red and black wires at the servo connector. BTW the picaxe has a new servo command that is supposed to greatly reduce or eliminate this issue. If you want to go that route I can help you get started. If you have the skills to build a 555 circuit then you can build the picaxe it is a simpler circuit. Some websites call the picaxe 08M the new age 555 chip.


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## GOT (Apr 17, 2007)

OK, I think the issue is coming from the wall wart. Both my high-torque and low-torque servos run smoothly on the board run by 4 AA batteries. If I connect the wall wart (servos only, the batteries are still powering the 555) both servos have a case of the jitters. I added the 0.1 uf capacitors but they were no help. I need the big servo because I will be moving a heavy candlestick. So, what is this picaxe thingy?


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## spinman1949 (Jun 29, 2009)

*Noisy power from the Wart*

Sounds llike the wart is poorly regulated and noisy. Getting clean and stable DC from AC requires some work. Quite a few Warts supply devices that have voltage regulators and filters built in. Your Servos need clean power. One reason it is always safer to power servos with batteries. Is your wart rated as regulated ?


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## GOT (Apr 17, 2007)

Yes. It is a Mean Well model number GS12U05-P1I. The rated ripple & noise is 75mVp-p (max) and the line regulation is +- 1% and the load regulation is +- 5%. These numbers mean little to me. I looked around for a battery pack first but the only 5V, 2 amp packs I could find were really expensive.


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## pshort (May 6, 2008)

The specs for that power supply seem quite reasonable for this application, so I'm not sure why it isn't working. I think that it would be a good idea to double-check your setup for other problems, such as bad/missing connections.


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## spinman1949 (Jun 29, 2009)

*Batteries.*



GOT said:


> Yes. It is a Mean Well model number GS12U05-P1I. The rated ripple & noise is 75mVp-p (max) and the line regulation is +- 1% and the load regulation is +- 5%. These numbers mean little to me. I looked around for a battery pack first but the only 5V, 2 amp packs I could find were really expensive.


4 D cells will provide the current you need. You might want to visit Frys if you have one near. They have new rechargeable Rayovac's AA NIMH that are very reasonable. Plus they have battery trays that hold up to 8 batteries. I run 6 batteries in mine and the servos have no problem. I modified the tray with a jumper to eliminate 2 batteries.

Another place to check for batteries are surplus stores. I can get a sealed motorcycle 6 volt battery for about $12 That would be perfect for your servos's. I would check with the electronic guru's re if 6 volts is too much for your 555. If not then you could run the entire prop off one battery. Probably could put a resistor to drop the voltage to the circuit. Again a question for the electronic guys.


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## spinman1949 (Jun 29, 2009)

*Follow up*

How about a lantern battery. Not rechargeable but I found a site that sells a 6 volt for $1.85. One thing to remember re batteries. They are rated in amp hours. This relates to how many amps the battery is capable of providing on a constant basis per hour. For instance. My electric racing trucks used 1200 Mah and 1400 Mah NiCad's. A race generally lasted about 5 minutes. In that 5 minutes the battery was nearly fully discharged. So the truck electric motor and steering servo utilized an average of 12 to 14 amps during the race. Most of that was drawn by the motor of course. My point here is that you do not need a 2000 mah rated battery to run your servos's. Your servo's will not be using a constant 2 amps. That is peak amp draw under load. So if your prop has periods of non-movement, then your average amp draw will reduce and your battery life will increase. These lantern batteries are pretty cheap. You could wire a few in parallel and I bet you will have plenty of battery life to cover Halloween night.


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## hpropman (Jul 27, 2008)

GOT said:


> OK, I think the issue is coming from the wall wart. Both my high-torque and low-torque servos run smoothly on the board run by 4 AA batteries. If I connect the wall wart (servos only, the batteries are still powering the 555) both servos have a case of the jitters. I added the 0.1 uf capacitors but they were no help. I need the big servo because I will be moving a heavy candlestick. So, what is this picaxe thingy?
> View attachment 1014


The picaxe is a microcontroller like a prop 1 or a prop 2 - but it is just the chip. The smallest version of these chips are an 8 pin version called 08M. If you go to my website and read Microcontrollers 101 and visit the links it should help you clarify things. The software and books are free and the chips start at about $3.50. add a few resistors and a homemade (or purchased) programming cable and you are off and running. I have been using them for about 5 years now and I love them. They can do anything that the more expensive controllers can do once you build the board. Please ask me if you have any more questions. Also 4 D cell batteries is 6 volts which will work fine for the servos and the 555 but the picaxe maximum voltage is 5.5 volts so you would have to use 3 D cells if you use a picaxe. Otherwise you can build you own 5 volt regulator circuit (again very easy). There is also a free electronics course in the links section of my website.


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## GOT (Apr 17, 2007)

I changed out the pot. No improvement. Everything else looks good. Again, things run fine if I run the smaller servo (and larger one) off the 4 AA batteries. Are there any cheap 5-6V battery packs that can deliver 2 amps?


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## GOT (Apr 17, 2007)

Or maybe my circuit just can't handle this one?


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## JacksonManor (Jun 27, 2007)

you don't necessarily need servos to do this, two motors wired together can acheive this effect. assuming Arm1 controls Arm2, The arm1 motor will act as a generator to power Arm2. I have seen this work with larger motors, no experience with anything on a smaller scale, and it produced 1:1 movements.


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