What does it all mean?

[pacman]

OK, I’m not the greatest boffin but I can do elementary maths and I can tinker with most things mechanical, but this electrickery has got me stumped.

I want to dabble in electric helis by converting an old shuttle. Just for laughs really, I know it can be done, I love tinkering with stuff and I want to get on the learning curve of the black art that seems to be electric power, BUT…..

I took a look around, did a bit of googling, and I just seem to be getting myself more and more confused….

Batteries: I can cope with and understand them being different voltages, but there are Ni-cd, NiMH, LiOn, Lipo. They come in strange designations, such as “6S 1P (16C continuous and 20C burst)”. Then there’s “mAH”, the rule seems to be the more the better, and it has to be matched to the motor, etc etc etc, but why? I’ve read stuff that says more mAH gives greater head speed, so maH = power? Oh, and there are so many warnings about overheating, catching fire, exploding etc. What’s that all about?

Batteries, charging of: Trickle I understand, but now there are balance chargers, chargers that are for specific battery types etc

ESC (I worked out that’s the Speed Controller for the motor), but they seem to be rated for number of “cells”, but at the same time have to be compatible with the motor.

Motors: Brushed, brushless, outrunner, Inside outrunner (?). Carrying wonderful designations such as 10L, 8 pole, 1100Kv, 2000W power, and requiring certain ESC timing and switching frequency. And they seem to range between $50 and $500+. Crikey!

And what else is there that I don’t know I need to know?

So here I am with a 30 size heli that lends itself to conversion. I have seen the kit here: http://www.ewtech.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=hhi&Product_Co de=QUISP72C&Category_Code=Upgrades+for+HIROBO

but what does it all mean? Is that 3530 a decent motor, same for the esc, or would I be better off (and cheaper) sourcing them myself. I want to give it a go, I’m determined to give it a go, but this is driving me nuts. Before I do something I like to understand what I’m doing, how it works and why.

Can anyone point me in the direction of a laymen’s guide to all this? Is there a simple way of explaining any or all of the above? A nice little comparison table that says “Motor X plus ESC Y plus battery Z = 30 size”.

Sorry to have wittered on for so long, verbal diarrhoea borne of frustration.

Oh, and if I’ve posted this in the wrong place then mods please feel free move it.

[Andy from Sandy]

This should help you with batteries?

http://www.batteryuniversity.com/

Wiki for brushless motors http://en.wikipedia.org/wiki/Brushless_DC_motor

[jiberjaber]

Pacman... the head speed is linked by the pinion and main gear teeth making a ratio which you multiply by the rotational speed (RPM) of the motor to give you a head speed - no different to how you would calculate a Nitro heli headspeed from engine rpm and gear ratio.

I would forget the brushed motor technology, old hat now... brushless is far more efficient and easier to understand.

They have a number of ratings, in relation to the headspeed, the rating you want to look at is the KV rating, this shows you how many revolutions per minute you will get for a voltage applied to the motor by the ESC.

So a 1000KV motor will produce 1000RPM on the motor.

This link might seem like double dutch to you untill you get some more answers, but you might find it useful at a later date for doing some calculations:

http://dhrc.rchomepage.com/calc.htm


Your ESC will be a calculation on how you want to fly the heli, two options, high voltage or low voltage. Basic elecrical theory covers the amount of power being a function of the current and voltage, power=voltage x current.

If you run a high voltage setup you need less current for the same amount of power.

Power also shares a relationship with weight and size as well. The modern lipo battery comes in "cells" (3.7ish volts per cell). You can have high capacity cells or low capacity cells, that is low mAh or high mAh.

So from the last couple of paragraphs, you can have lots of smaller (mAh) cells (a high voltage) or a few larger cells (low voltage) to achieve the same power, but this might give different weights or sizes to the combinations! This will also effect other characteristics such as how quickly that power can be provided etc.

There are some set sizes though, if you look at the majority of battery sppliers, they do certain configureations, so there is some of the decision process taken care of. You might want to look at what is fitted to the Atom 500 and Trex 500 as they are fairly close to the class of heli you are looking to modify. Alternatvly, you might want to just get one of them instead.

Where do you fly at the moment? (were you at CMFA on Sunday? Charrles??)

[TimmyB]

C x ah = max amps hence higher the ah the better they hold voltage under load hence more power/higher head speed.

I would just buy the kit and go from there, havnt used the motor before but the esc is good quality so I presume the motor will be ok. It looks like it needs a 4000mah 8s batt or 2 4000mah 4s linked together in series to make a 8s 4000mah.

I wouldnt worry about exploding batts, provided you buy decent quality and charge them correctly you should have no problems.

[scallybert]

So from the last couple of paragraphs, you can have lots of smaller (mAh) cells (a high voltage) or a few larger cells (low voltage) to achieve the same power, but this might give different weights or sizes to the combinations! This will also effect other characteristics such as how quickly that power can be provided etc.

High voltage is generally going to be more efficient, as the current is less, and that is generally going to mean less battery energy wasted as I^2R heat.

You can also have thinner wires as they carry less current.

AFAIK, HV is better all round.

[cjcj1949]

The mistake you're making is adopting this layman approach. There's no such thing. You will find it difficult to answer lots of questions at the same time and there is a lot of confusing information. Some of the stuff you've been told is wrong. I used to tutor people in maths and physics and they were usually confused. To undo the confusion you have to listen to what they think they know and highlight the contradictions. Once you've done that the usual response is " Is it that easy". I think the going rate is £30 a hour or you can just pm me. The easier answer is to ask people who've done it before what they did and just copy them.

[TimmyB]

The easier answer is to ask people who've done it before what they did and just copy them.

Or just buy the kit someone kindly put together for you, use it and forget about the ins and outs.

[cjcj1949]

Exactly. Preferably one that's known to be good. Some people are interested in how things work, some like using them. I'd like rtfs to show you how to put it back together and I don't think I've seen a kit that doesn't have something misleading or just wrong.

[jiberjaber]

Well which ever way the OP decided, there is plenty of help in here and also in Essex

[cjcj1949]

I'm a bit addicted to explaining things. I sent pacman an explanation and he's now happier.

[jiberjaber]

If he is who I thought he is, then the chap who was stood next to him at the flight square also has a Trex 500 he could look at, if he is stuck with the build, then I could help...