ESC ESC and BEC question

Derek

Derek

Well-Known Member
I'm looking to order electronics for one of my scratch-build planes. However, I'm still learning how to "pick-and-choose" the correct parts. I have a motor picked out from Hobby King and I think that I want a particular ESC, but it requires an external BEC. In the specifications for the particular ESC, it doesn't say what size BEC to get for it.

How do I know what size BEC to get to match up with the ESC that I'm thinking about ordering?

Here is what the site has listed for the Specs:

Max Amps: 60A
UBEC: none
Cells: 2-7S Lipo
Size: 83mmx15mmx39mm
Weight: 63grams (including wires)

That's it! A bit less than helpful, I'm afraid.
 
murankar

murankar

Staff member
If this is for the toys r us glider, that esc is way over kill. You should need no more than 30 amps on the ESC. I have never used an external bec but I would want to know the output power so I do not over power my servos. You may also want to know how many servos it can support. I know that my ESC puts out 5 volts for up to 4 servos which is right where I am at.

other than that I am not sure what else you would need.
 
Lee

Lee

Well-Known Member
Give us a link to the motor, which prop size/pitch, which plane its for, what size battery you're using. All these things will help to guide us on what to advise.
 
Derek

Derek

Well-Known Member
oh no, lol, this ESC/BEC combo is not for the toys r us glider. I have a scratch build plane that I'm wanting to get flying soon and I'm shopping for electronics.
 
Tony

Tony

Staff member
I'm sure we can find you a motor and ESC right here in the good ole US of A. Much faster shipping and if anything is wrong, you can actually send it back without it costing more than the part. If you have read my past posts, I"m done dealing with china and will not suggest any parts from there. However, some parts that are made in china but sold here in the US are okay and I still run them in my planes.

Let us know the exact specs on the plane and what you are wanting to do with it and we will get you a motor/ESC combo that will work great. Hell, I may just sell you the motor and ESC off my trainer.
 
Derek

Derek

Well-Known Member
ok...here we go.

I did watch the video that was made on "Matching the motor to the esc to the battery." That was "tons" helpful. It definately explains alot. I wrote down alot of the important parts for future reference. I surely don't know much about electronics, I can admit to that (i sure wish I had paid more attention in high school, lol). I understand how to match the ESC to the Motor and I understand how to match a battery to the ESC. The trouble I'm having now is determining what motor to even start with because all my planes are scratch-build, therefore no manufacturer's recommendation. I have 7 planes right now and only one of them has electronics, so how to I determine what motor to even start with? I can give you any information that you need about the specs on my plane that I want to start with. Just let me know what you need..weight, length, width..whatever.

I do have a plane that is complete now, with the help of some YouTube buddies (this is prior to knowing about this forum) and I will be doing the maiden flight this week. However, during the build, I had ordered parts, not knowing that the ESC that I ordered required an external BEC. I was frustrated for sure. How would I determine what kind and what size BEC to get when an ESC requires a BEC?

Damn...there was something else that I wanted to ask, but I can't remember what it was, so I guess we'll just start with what I've listed above.
 
Tony

Tony

Staff member
Most of the time for a foamie with a 30-40" wing you can get away with a 50g motor 1000kv on a 3s spinning a 10x6 prop. If your plane is bigger, you will need to go bigger on the motor. smaller, go smaller. The way you do this is to look at the max thrust for the motor with a given prop. Match that thrust with the AUW (all up weight) of the plane with servos, batteries and Rx, then add the weight of the motor and ESC and match them up. Takes a bit, but works.
 
Derek

Derek

Well-Known Member
ok, so what you are saying is that I would weigh the plane (with parts and all) then add the weight of the motor, esc, and battery. Then take the sum of all that and I'm looking for a motor that has at least that amount of thrust. Am I understanding that right? If so, the amount of knowledge that I've gained from this forum is "staggering."
 
Tony

Tony

Staff member
That is correct. That is if you can find the thrust ratings with a specific prop.
 
Derek

Derek

Well-Known Member
alright, sounds good. Thanks for your help. I'm sure I'll be around to hassle you guys with more questions in my "Pursuit of Air-worthiness" lol.
 
Derek

Derek

Well-Known Member
ok, here's another dilemna. I have a brushless motor that is rated at 175 watts. Divide that by my 3cell voltage, 11.1 and i get 15.765 amps. I have a 20 amp esc. no worries there. I have two lipos here that I'm afraid won't work with this combo of motor and esc. My 800mAh x the 15C rating, divided by 1000 equals 12 amps. Not really enough for a long flight with the above motor...right? My 1100mAh x the 20C rating, divided by 1000 equals 22amps. Surely enough for the motor, but I think it would toast my esc, right?

Any thoughts??? Am I doing the equations right?

These two lipo's are what I had intended on using with this motor and esc combo before I joined up with this forum, so please excuse my ignorance. They are just left overs from my last styrofoam glider but since I did go to a bigger motor and bigger esc, I don't think I can use these two lipo's.
 
murankar

murankar

Staff member
no, I have a 55 amp battery with a 45 amp esc with a motor pulling around 42 amps. The esc will handle what the motor is requiring. I was thinking of going to a 30C pack from a 25C pack just because. Remember the battery will only give what is being requested by the motor and the esc needs to handle that request.

My first setup had a 55 amp battery with a 40 amp esc and a motor pulling 27 amps everything ran cool and stable.

I was also informed by the folks at a main hobbies that the esc rating is a continuous rating and may be able to handle a spike. You would need to confirm that with the manufacturer of your esc if that is possible.
 
someguyinsandy

someguyinsandy

Crash Test Dummy
There are a number of calculators available for free use on the web. I have tried many of them, but this one: http://www.ecalc.ch/motorcalc_e.htm?ecalc seems to give fairly accurate numbers based on my inputting known numbers from tests I did on equipment that I have. These software tools require a bit of patience and research on your part to get any sort of accuracy. You really need to have the specs from the motor, esc, prop, and battery to input the correct data. But, it is kind of fun to "see" what your stuff will do before you actually buy/use it!

A power analyzer is a valuable tool to give you real world data on a combo as you are building it. I have this one: Extreme PA-010 Two Power Analyzer Watt Meter Battery Checker/ Equailizer and that site has it for a great price! Note that you may have to build yourself a set of test leads since it has Deans female connections for the source and load connections. It also doubles as a battery tester to check the amount of charge in your Lipos before flying!
 
Chris O'Hara

Chris O'Hara

Thermal Padawan
An excellent source of *high quality* Chinese made motors and ESC's is rcplanebuilder.com. They even ship out the same day if you order before 4pm! Check them out!
 
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