Brushless motor, ESC, Battery so many choices

[BradG]

I recently have gotten back into RC after seeing that Tamiya had re-released all the kits I had as a kid. I've now got two Lunchbox's, The Frog, and a Blackfoot III. Since I am new getting back into the hobby I want to try to keep up with the new technology. With that being said, I've got just a question or two that I can't seem to find anywhere about which lipo to use with a brushless setup.

I'm pretty sure that I will be ordering Novak motor and ESC. I like the fact that you can buy the motor and esc as a combo which takes a lot of the guess work out. My question is how do I decide which Lipo to run with it? I was looking into getting the Venom 7.4 Lipo batteries. I like that they come with the different plugs for Tamiya or Traxxas which eliminates having to solder on connecters. My question is how do I find out which mAh to get and I also don't under stand what 20C and 30C etc means? Sorry this may be a very basic question, but I still do not have a full grasp on understanding it all. It was so much easier 20 years ago! I also don't understand kv fully. Is there a kv to turns simple conversion out there?

[Wooders28]

This sounds like me not so long ago!

There has been advances in batteries and motors in the last few years (I say a few, 20+ years lol)

Lipos are great, took me a bit to swap over but never looked back. They store a lot of energy, but as they store a lot of energy they need to be treated with respect.

Each Lipo cell is 3.7v (NiCad's are 1.2v each ,6 cell= 7.2v)

mAh hasn't changed,the higher the mAh the longer the car will last per charge (I remember 1800 mAh being the one to get!)

Hard case needed as a must for RC cars to take the knocks.

The C rating is the amount of power it can deliver in a burst (20c = 20 x discharge rate , 30c is 30x etc) only really something to worry about if racing.

I went for the castle 5700 brushless combo for the same reason.As far as I can gather for each volt the motor will turn 5700 RPM so running a 2s Lipo would be 7.4 x 5700 = 42180 rpm. Don't know if there is a chart / conversion for turns to Kv.

Hope some of that helps and if I am a bit off the mark then no doubt someone with more experience will educate me a bit more too!

[BradG]

That's perfect! Thank you so much for the reply.

[Gruntfuggly]

Remember you'll need a charger that can balance your LiPo's too. I bought some Turnigy LiPos similar to these a couple of years ago - they've been excellent...

http://hobbyking.com/hobbyking/store/__21006__Turnigy_5000mAh_2S2P_40C_hardcase_pack_ROAR_APPROVED_.html

[BradG]

I was looking at the Hitec x1 touch. The reviews all seem good and only $99.

[super gripper]

there is one golden rule to abide by to make sure you do not damage the lipo.

Find out what amp rating your esc is ...............

then use the following formula to make sure the lipo is up to the esc's needs.

take the following example.

my esc is 100amps.

my lipo is 4000mah and 25 C.

so A x C = esc current

change the milli amps to amps ...... 4000 =4.0

4.0 x 25 = 100

so simple.

use a lipo that produces less amps than the esc's rating at your own risk.

[Klausen]

Novak is an excellent choice. They make high quality brushless esc's and motors. On top of that everything is produced in the USA. Tekin and Castle creations also make high quality combos. In my Clod Buster i Have 2 x Castle Sidewinder3 combos with 4600 kv. motors. Combined with a Turnigy Nanotech 5200 mah. 2s lipo and dialed down to 70% power ,they provides the needed power and topend, and delivers more than ½ an hour of driving.

In my Avante 2011 I have a Turnigy Trackstar combo. China produced motor/esc, and it works fine as well. I prefer the US brands though, even if I have to pay a bit more.

For just playing around, buy some 2s lipos with high c rate and high mah. If you are gonna race, still get a high c rating, but only the mah. you need to complete the minutes each heat lasts, as the more mah. the higher weight.

When using brushless setups compared with lipos, I will advise to use goldplugs, Deans or Traxxas connectors. The Tamiya connector might overheat and melt.

Regarding kv, the higher kv = the faster motor. For a cooler set up, choose lower kv, and then maybe a 3s lipo instead of 2s. You will get the same speed, but a cooler setup. In most Tamiya 1/10 it might be difficult to fit a 3s lipo though.

[super gripper]

I have 2 Turnigy Trackstar 100amp esc's now and they are both proving to be great value for money, my old power plants the Losi Xcelorin's served me well but I only have 2 of those left.

What ever you choose that's within your budget just make sure you get a sensored system.

[BradG]

Thanks for all the help guys. I definately feel more like I've got a game plan now. Just as I have bought every hop-up option available, I just couldn't stand the thought of putting the old school 540 silver can in my builds. I wish Tamiya would start putting a brushless motor / esc combo in their kits.

[Wooders28]

One thing (i could be wrong though!) about Brushless motor 'turns' is that '.5' turn motors (ie 27.5t) are 540 size motors and 'whole number' (ie 27t) are 380 motors in 540 size cans.I dont think it makes much difference on a 2wd dasher,but i think the reduced torque in a 380 in a 4wd may start to heat up a bit.I think its a bit like single,double and tripple windings in the old skool brushed motors.

[WillyChang]

One thing (i could be wrong though!) about Brushless motor 'turns' is that '.5' turn motors (ie 27.5t) are 540 size motors and 'whole number' (ie 27t) are 380 motors in 540 size cans.

some makers use an "adopted convention" to rating from early days

But physically, brushless windings are stationary in the can so wires dont have to

terminate at the same end as they started out with... it's how they're joined up between poles.

Half turn are Star/Wye wound. Full turn are Delta wound.

kV ratings are "measured" so there's no biblical conversion table between winds & kV.

kV of Wye to Delta style also differs.

[Wooders28]

Thats just how i had it explained to me.Good to get a better insight.

So given the half turns are star wound,they would give more torque? The delta wound higher RPM?

[Daves956]

there is one golden rule to abide by to make sure you do not damage the lipo.

Find out what amp rating your esc is ...............

then use the following formula to make sure the lipo is up to the esc's needs.

take the following example.

my esc is 100amps.

my lipo is 4000mah and 25 C.

so A x C = esc current

change the milli amps to amps ...... 4000 =4.0

4.0 x 25 = 100

so simple.

use a lipo that produces less amps than the esc's rating at your own risk.

Is there an original source for this formula? I've never heard of anything like this before

[super gripper]

Yes there is..............

I found it on oople years ago

not sure where to find it now though

Its basic common sense anyway, to use a battery that is not powerful enough for your esc is not very clever really

[Daves956]

Yes there is..............

I found it on oople years ago

not sure where to find it now though

Its basic common sense anyway, to use a battery that is not powerful enough for your esc is not very clever really

There's something new all the time

I'd always figured the battery was to power the motor and the ESC was basiclly a switch to control it and sized the battery to the load not the switch. Interesting

[super gripper]

There's something new all the time

I'd always figured the battery was to power the motor and the ESC was basiclly a switch to control it and sized the battery to the load not the switch. Interesting

Things have changed and moved on with the introduction of 3 phase brushless systems and lithium polymer batteries.

Old school ways of thinking no longer apply.

[Daves956]

Things have changed and moved on with the introduction of 3 phase brushless systems and lithium polymer batteries.

Old school ways of thinking no longer apply.

The motor design is older than I am and DC power is DC power regardless of the battery. Electrical basics don't change, I've been working on real scale polyphase inductives for over 30 years now. RC motors and drives are just the miniature versions of what I fix for a living,

[super gripper]

The motor design is older than I am and DC power is DC power regardless of the battery. Electrical basics don't change, I've been working on real scale polyphase inductives for over 30 years now. RC motors and drives are just the miniature versions of what I fix for a living,

Three phase brushless is AC , is it not ?

[Daves956]

Fanuc and Yaskawa went to DC in the 80s. Reliance was building two, three and four phase DC drives here in Denver back to the 60s. Back then they wouldn't fit in the back of your car but now they're smaller than half a sheet of paper. It's primarily Tesla's designs but improved on with miniaturization. What is considered sensored for an RC, Fanuc and Yaskawa now have controlled down to the arc second. You can tell the AC to DC difference by the color of the end caps on most of the industrial motors. It's still transistor driven and phase shifting technology.

It's kind of funny that the newer Beta systems run at temps over 170 degrees with more torque and accuracy. I wonder if that will trickle down to the RC world?

I'm a field service tech in the CNC industry.

[super gripper]

Fanuc and Yaskawa went to DC in the 80s. Reliance was building two, three and four phase DC drives here in Denver back to the 60s. Back then they wouldn't fit in the back of your car but now they're smaller than half a sheet of paper. It's primarily Tesla's designs but improved on with miniaturization. What is considered sensored for an RC, Fanuc and Yaskawa now have controlled down to the arc second. You can tell the AC to DC difference by the color of the end caps on most of the industrial motors. It's still transistor driven and phase shifting technology.

It's kind of funny that the newer Beta systems run at temps over 170 degrees with more torque and accuracy. I wonder if that will trickle down to the RC world?

I'm a field service tech in the CNC industry.

It is good you know what you are talking about ref your job and industrial motors.

and I refer to your previous comment of 'you learn sometime new everyday'

I was always under the impression RC 3 phase motors are AC.

[Mokei Kagaku]

I'd always figured the battery was to power the motor and the ESC was basiclly a switch to control it and sized the battery to the load not the switch. Interesting

The Golden Rule mentioned should rather be considered a "Golden Rule of Thumb" and not exact physics, and I reckon both Oople and Super Gripper intended it to be a practical approximation for suitable combinations of components. As such the "rule" is good, but it's totally unusable for a physics exam.

The short circuit current of a 25C battery will in reality be higher than the rated (permissible) 25C, and a 100A rated ESC will pass more than 100A (unless a strict current limit is set), but will hardly cope with the thermal conditions caused by 100A for an extended period of time. Also, I guess you mean that the load will be a current limiting factor too, which of course is correct.

Example 1: the combination of a 4000mAh 25C battery and 100A ESC will generally be safe if the maximum motor current is 50A.

Example 2: the combination of a 4000mAh 25C battery and 100A ESC will not be fully safe if the maximum motor current is 200A, as the battery will deliver more than 100A at full load, unless the ESC has a current limiter set at 100A or lower. The 100A rating of the ESC itself won't stop a higher current from flowing if the load "demands" so and the power source is capable of delivering more than 100A.

[Mokei Kagaku]

I was always under the impression RC 3 phase motors are AC.

You are of course right.

The "DC brushless motor" is, despite its name, an AC synchronous motor, with the difference being in how the power is supplied. In most pure AC-applications, the power is supplied as a sinus wave current as supplied from the grid, whereas DC brushless motors have the power supplied as square wave current, in RC-applications chopped up from a DC power source, very much the same way the "old" brushed ESC work, but putting out AC square waves instead of DC square waves.

[super gripper]

I am also an electrical engineer.

I am interested to know more about these motors please Dave.

[Daves956]

Just as an example, a Fanuc motor manual is around 300 pages. Same is true for each drive type manual. Then you have a control manual that's a bit thicker and a connections manual a little thinner. So roughly 1400 pages of info on how it all works together. You also need a parameters manual that's around 500 pages and the maintenance manual at another 400 to tune them and keep them running. An overview description is that they are a closed loop system fed back to the control and monitored by an A quad B encoder. Command is output from the control and set by a number of parameters. The newer DC systems have a power supply that's bussed to all the drives and all of this is daisy chained with a fiber optic control and feedback network. A lot of the newer motor types have a mag or hal effect ring sensor in them for a second feedback or a rotary glass scale. I'm way off topic and going geek again but working on this type of stuff makes the RCs seem pretty simple.

[Mokei Kagaku]

I am also an electrical engineer.

Ignore the muppit who has just jumped in, he is a known internet troll.

This is utterly rude of you and totally out of place! I'm an electrical engineer too and graduated on AC electric motors, so though I'm not an expert in this field, my contribution is anything but trolling. I wonder why you repeatedly attack and insult me whenever I post a factual and reasonable comment in any thread you are participating. In this thread I even supported your opinion! How would you feel if somebody here would treat you with the same disrespect and aggression that you treat me? I have reported you to the mods as I'm sick and tired of your abuse.

And btw, if you had even basic knowledge about AC motors, you would know that my comments are correct.