Motors and noise suppression

[subshop]

What size cap. would you recommend on 2-12v pittman motors both running on a mcd speed controller. neil

[ramius-ii]

Caps

Hi Neil,
The .1 MFD at 50 volts is normal. The key to noise suppression is the "golden triangle". A cap from + to - of the motor and a cap from the + side of the motor to the motor case and from the - side of the motor to the motor case. Most motor cases require a little filing for solder to stick. From the case of the motor(s) connect a heavier wire directly to the battery -. It is also recommended to take the motor wires (+ and -) and the "noise drain" with you hands or a drill (depend on how far you are going) and twist them together until you get to the speed controller then allow the noise drain (case of the motor wire) to continue to the battery. While the first question that normally arises is "can't I just jumper one case to the other?" The answer is no. The reason is that you would be transfering the noise of one motor to the other and expecting that case connection to protect both motors. In extreem cases of noise, a ferrite beads or small toriods are added to the wires at both ends.

Best, Ed

[subshop]

cap.

ed, when placing cap. on motors, the leads of cap. are marked pos/neg which goes where ? neil

[Wheelerdealer]

I think you should be

I think you should be using ceramic or polyester film capacitors which dont have polarity.

[himszy]

Don't use capacitors which are

Don't use capacitors which are polarity sensitive. You kick the motor in reverse and you'll be going in after your sub. You need to use ceramic capacitors.

Michael

[ramius-ii]

Hi Neil

Hi Neil,
Sorry for the delay in answering you and Michael is correct. Capacitors come in polarized (+ and -) and non-polarized. Typically anything less that 1 mfd is non-polarized for general use. There are also some larger values used in audio work. I think the picture will answer you question. Originally, I was going to finish writing an article for the subcommittee report and there has not been time to finish it.

Just for informational purposes only, the capacitors are usually marked with the number 104. This is actually a value of 100,000 micro-micro farads or "pico farads" also refered to as 10 to the -6. So a .01 mfd would be marked 103 and a .001 would be marked 102. With practice it becomes less confusing.

Best, Ed

[captain nemo12]

Re: Caps

Hi Neil,
The .1 MFD at 50 volts is normal. The key to noise suppression is the "golden triangle". A cap from + to - of the motor and a cap from the + side of the motor to the motor case and from the - side of the motor to the motor case. Most motor cases require a little filing for solder to stick. From the case of the motor(s) connect a heavier wire directly to the battery -. It is also recommended to take the motor wires (+ and -) and the "noise drain" with you hands or a drill (depend on how far you are going) and twist them together until you get to the speed controller then allow the noise drain (case of the motor wire) to continue to the battery. While the first question that normally arises is "can't I just jumper one case to the other?" The answer is no. The reason is that you would be transfering the noise of one motor to the other and expecting that case connection to protect both motors. In extreem cases of noise, a ferrite beads or small toriods are added to the wires at both ends.

Best, Ed

About the wire that goes from th motor case to the battery, which end of the battery do you connect it to? + or -?

[ramius-ii]

Hi Captain

Hi Captain!
Good question! The motor case is connected to the negative side of the battery as is any and all shields or metals the may be in contact with the water, etc.

For example, on my sub there is a metal plate that holds gears, motors and switches to operate the conning tower up/down mechanics. There is also a transmitter for sending picture back from the periscope camera and other items.

The water is, for all intents and purposes, a shield around the sub. Therefore you want to keep all your shields together at the same polarity, in this case negative or minus side of the battery.

Your motor shafts are typically metal and mechanically attached to the motor with metal couplings, and the prop is certainly in the water. So automatically you have provided a connection to the water.

The other advantage, in the case of the transmitter, the metal plate becomes the "reflector" for the antenna sending more energy up to the surface rather than down where it does no good.

The motor "shield" wire should be as heavy a gauge as practical. This, by the way, is the common cure for "nervous" servos or "spritual" electronics (sometimes it works other times it does not and you pray each time that it will work!)

Best, Ed

[subshop]

noise

ed, what do you do when your shafts are connected to the motors with plastic dogbones ?
neil

[ramius-ii]

Hi Neil

Hi Neil,
I probably could have done a better explaination. The primary point was that there are many possible places for an electrical connection to the water. Be it a metal plate that is used on top of the WTC, metal tubes for shaft entry or exits, etc. for example, the bow plane motor. Typically, the tubes have the metal shaft inside and there is a electrical contact from the shaft to the tube. The tube in in the water, thus you have a connection! Another way to think of it is that the drive motor(s) exit the WTC with a metal shaft that is mechanically connected to the plastic dogbone. That part of the shaft, from the WTC to the dogbone, is in contact with the water thus you now have an electrical connection. Hope this makes more sense now. Sometimes I write with not enough coffee.

Best, Ed

[subshop]

noise suppression

ed, a couple more questions ... i want to do this right the first time.
i'm building a 32p gato. i will use 2 - 21 amp. hr. 12v batteries in the wet area. i understand the magic triangle and the twisted power leads. since i am using bolts through the wtc to get power inside, one question is do i need to run the noise lead back to the neg. battery post by means of another through bolt in the wtc , or can the noise wire be connected to the neg. bolt on the wtc ? further could i come off the neg. bolt on the inside the wtc. with a buss wire to connect all the noise wires ? There will be quite a few !
next, if i understood you, any metal in the wtc needs a noise wire but these can be ganged together and run to the neg. post?
finally, i am using the robbe navy 14 radio w/ the expansion modules so for appearance purposes i plan on making a pc board to mount the bec's on and leads off the pc board to plug into the rx and modules. can the motor power leads (twisted) be connected through this pc board or do i still need to hook up directly to the battery bolts? neil

[ramius-ii]

Common Point Ground

Hi Neil,
What is idea is to have the noise wire be both as large and as direct to the battery negative as possible. Think of it this way. I see you are in New York and in you home or apartment when you plug in an appliance, the receptacle on the wall has three wires. Two slotted blade types and a round. The round is the “common ground” even though you would find the larger blade is actually connected at you meter box to the same point. Your computer has a three wire plug on it to eliminate unwanted signals from affecting other electronics.

Your motors turn in both directions, clock-wise and counter clockwise, therefore there is no negative as either wire can be the “negative” depending upon the direction of the motor. Yes, you can gang the “noise drain” wires together and it is not the ideal way. Each noise wire has noise on it and you end up connecting one noise source to the next noise source. So you end up passing the noise from one to the next to the next and so on.

What you could do is use the connection point (bolt) from the battery negative into the WTC as your “common point”. And, yes, you are correct it is a few extra wires. For me, I mounted all my stuff (servos, BEC’s, etc.) on a thin brass plate. Each servo is mounted inside a small metal box to this plate. Thus, each servo is “shielded”. In most configurations this may seem extreme and I have a transmitter and computer boards so it seemed best to do this from the start rather than trying to find noise sources later. Again, this is optional. Try, whenever and wherever possible to go direct to the battery negative. If you find you have problems, you can take an AM radio, put a loop antenna on it and “sniff” for the problem.

Below is a picture of “common point” grounding.

Best, Ed

[cstranc]

A co-worker published an excellent

A co-worker published an excellent article on supressing radio frequency interference in an RC boating magazine.

He is looking into getting it into the SCR now thanks to some hinting

If anyone wants to get a sneak peak then e-mail me and I shall get it to you.

I learned lot's I could apply.

Chris

[ramius-ii]

Thanks Chris

Thanks Chris
Actually, “noise” comes in two basic flavors. There is EMI (Electro-Mechanical Interference) like a motor and RFI (Radio Frequency Interference). A third “attack” on our electronics is from “back emf". (Electro-Magnetic Force) This is when you forget to add a diode across the coils of relays or solenoids. As the magnetic field in the coil collapses, a major voltage is generated and “back fed” into the circuits!

If this were not enough to worry about, there are also the infamous ground loops and the “I did not realize” voltage that comes from two dissimilar metals and water! Best example for anyone reading this who may not know, is if you take a penny and a dime, put them together, add saliva or a liquid and you have a battery!

I am looking forward to reading the article.

Best, Ed

[subshop]

noise

ed, then most of us will have this "battery" in our wet areas of the sub since most shafts are ss and the stuffing tubes are brass. what effect does this water battery have overall? and will having batteries in the wet section of the hull have any other adverse effect ? what happens if we add a third metal, say aluminum ? neil