Brushless help please

[Feight]

Hi, I posted my thread in the electrics section when I had intended to post it in this section.
Probably the result of a lack of sleep and way too much coffee.

http://www.oople.com/forums/showthread.php?t=37870

I'm quite tempted by the tekin, it's one of the two systems I've really been looking at, the MMM is the other that floats my boat.
I was just thinking that I'd probably need to cram 4s under the shell to make 1700kv be worthwhile.

[Marvin]

1700KV is primarily a 5S motor.

You are under the misconception that 4S is bigger than 3S - only so if you just add an extra cell. Taking a 3S pack and a 4S pack that have the same power, one should be no bigger than the other. A 3S 6600mAh pack has the same power as a 4S 4950mAh pack. They should offer the same run time when combined with an appropriate motor and gearing.

In fact, a higher voltage set-up will give a higher efficiency, assuming that the two set-ups are geared for the same speed, therefore the higher voltage will give a slightly longer run time. This is why you run lower KV motors on higher voltages, and higher KV motors on lower voltages, to achieve approximately the same overall motor RPM, then use the same gearing to get, say, 40mph. They use the same power as each other - the same job is being done. However, the equation Power = Current x Voltage, shows us that the higher voltage results in lower current, which means less heat, and therefore higher efficiency - less power is wasted. Therefore, the lower voltage set-up will use a tiny bit more power - and so the run time will be longer with the higher voltage.

Have a read of the guide, then I'll help with anything you don't understand, or have problems with.

The Tekin is fine, as is the MMM. For higher voltages (5S, 6S) definately go with the Tekin, for lower voltages (3S) go with the MMM. The lines fade with 4S, and either will do nicely - though the Tekin may just have the edge - but it is more expensive and the motors are more fragile. Conversely - the MMM's case is poor as it may split unless braced, and the fans are weak.

[ek9russ]

Where is the best place to get the Tekin systems from? Are Much More Racing distributing them in the UK?

Thanks

[JonyNitro]

Aswell as fusion hobbies, But if i was you I would buy from RC monster, if you are getting the tekin combo, maybe the 1900 combo, then get the hot wire, and still have money left over after import duties, and anyway it is only warranted for 120 days after purchase, but still can send it away? if anything does happen

[jamiekerr14]

Have a tekin RX8 1700Kv combo in the for sale section for cheap and hotwire!

[Feight]

I first read your guide a few days ago and I keep coming back to it. It's what's been making me think 4s is a much better option. But I wasn't sure I had the space under the body for it, but I've had a play with some cardboard and a ruler. I've got options

I had originally thought that the 2500kv would be the best option for a 3s setup.
I've been told by some that it's too much and by others that it's too little.
The problem I was having was most of the higher kv motors I could find had small shafts.

Anyway as 4s is on I'm thinking the 2050kv is a good option.

The only reason I asked about the 1700kv is because I'm eyeing up Jamie's system. Might have to go for it and replace the motor

[jamiekerr14]

Go for it, Im not just saying that.. Marvin will tell you how hard to come by the Tekins are in the UK.. And if you really wanted you could get a mm moter after.. but its your call! ready for the taking!

[Marvin]

5S on 1700KV is a great set-up. Just check this out if you're worried about space:
A Hyperion VX 3300mAh 5S pack (61.05Wh) is 136.3x43x36mm
A Hyperion VX 5500mAh 3S pack (61.05Wh) is 158x46.8x30.7mm

Overall volume of the 5S: 210992.4mm^3
Overall volume of the 3S: 227008.08mm^3

Cost of 5S: £104.95
Cost of 3S: £104.95

The 3S has higher volume, is wider and longer than the 5S. From my experience, the higher voltage packs are just as easy to fit as the same power lower voltage packs.

In fairness, 3S is a crap voltage to run on. It is very inefficient, even when compared to 4S. The extra current produces a lot of extra heat - a sure sign of inefficiency. 4S or above is a far better option. 5S even better.

[Feight]

Wow, today has been an education.

There have to be some down sides to running 5s over 3s to get the same power.
Do charging times come into play at all?
I notice people running 4s and 6s tend to run in 2x 2s and 2x 3s respectivly, is there any real reason or is it just personal preference?

[Marvin]

No they don't. The experienced 1/8 brushless folks run single packs - the cells are all matched within that pack (only 1 matched pack vs two matched that have been shoved together).

Downsides of higher voltage. You might need a better ESC (a factor if you get a Novak or LRP), but as you want either an MMM or RX8 this won't be a problem.

The packs are a different shape - the higher voltage lower capacity packs tend to be shorter and wider than the lower voltage higher capacity packs. Whether this is a disadvantage is up to you.

Charge times.

Going back to my 5S 3300 and 3S 5500 example - it still relies on power output - IE - you end up with the same requirements power wise. However, you don't need a charger with as much current to charge the higher voltage packs faster (assuming the power is adequate). To charge a 5S 3300mAh pack at 5C, you need a charger capable of 18.5V, 16.5A and 346.5W (21V x 16.5A) - readily available. To charge a 3S 5500mAh pack at 5C, you need a charger capable of 11.1V, 27.5A and 346.5W - very hard to come by.

With chargers, the current is often the limiting factor. So, in reality, the same charger will charge the 5S faster than the 3S.

[Feight]

Thanks Marvin

It's alot easier to understand once someone who knows what they're doing tells it to you straight.

[Marvin]

Glad to be of service. I wrote the beginner's guide as a hopefully non opinionated guide - and for further advice to come here.

[jasonwipf]

Good explanation Marvin. Like he said higher cells better for cooler but no cost savings I agree.

[Feight]

Yeah the savings seem to come with getting an MMM over the Tekin or even getting the hobbywing 150A for the seriously skint.

This is the cheapest I've found the escs new

Tekin £120 + p&p + import
MMM £92 + p&p + import
Hobbywing £85 + import (if you're unlucky)

I'm not sure what Tekin's oversea's C/S is like and how easy it is for repair, the same for hobbywing. I know Castle just want $70 + postage for the MMM

Castle should do a 1700KV package deal, it'd make life easier

[Marvin]

Castle have got the 1800KV motor - and they're thinking about doing a combo with it: clicky

Another thing to bear in mind is that the Tekin does not come with a PC link - must be bought seperately for about $30. The Hobbywing doesn't either but has a programming card. The Tekin's programming (without PC) is very easy though, so it's not too bad.

Tekin's warranty is only 4 months (120 days), compared with the year that Castle offers. Tekin's CS was fine with me, though I shouldn't have to be writing to them multiple times. They are happy to send replacement parts to you though - Castle, less so.

Hobbywing would be an unknown quantity as for repairs - I guess it won't be too good.

[adrictan]

3 Tekin RX8 systems and no problems so far. I'm getting my 4th one soon. 2000kv on 4s is nice. I don't think u've indicated you're getting one for the buggy or truggy. But Marvin has said. Running lower kv with higher cells will be more efficient and draw less mAh. I personally go for 4s cause I already have many 2s lipos. 1700kv is ideal for 5s. There are guys in the U.S using the Castle 2650kv on 4s for races.

[jasonwipf]

Originally Posted by adrictan

3 Tekin RX8 systems and no problems so far. I'm getting my 4th one soon. 2000kv on 4s is nice. I don't think u've indicated you're getting one for the buggy or truggy. But Marvin has said. Running lower kv with higher cells will be more efficient and draw less mAh. I personally go for 4s cause I already have many 2s lipos. 1700kv is ideal for 5s. There are guys in the U.S using the Castle 2650kv on 4s for races.

Ya I'm one of them, but 2650 is sorta overpowered for our shorter tracks here in the states. We usually turn them down 30-40% to stay manageable. I recently tried the 2650 on my truggy and it was extremely unmanageable and did wheelies so bad I could almost do back flips at the 100% setting. I got 2 tekins and 1 castle system. They both do a great job but Tekins are cooler running and more one the spot tunable.

[Marvin]

Originally Posted by adrictan

3 Tekin RX8 systems and no problems so far. I'm getting my 4th one soon. 2000kv on 4s is nice. I don't think u've indicated you're getting one for the buggy or truggy. But Marvin has said. Running lower kv with higher cells will be more efficient and draw less mAh. I personally go for 4s cause I already have many 2s lipos. 1700kv is ideal for 5s. There are guys in the U.S using the Castle 2650kv on 4s for races.

Only thing with running LiPos that 'you already have', and pairing them up, is that if you're running them down low, the possibility is there that one of the packs could be destroyed (the older pack can't sustain the same current draw and puffs, or the older pack's voltage drops faster - it has less capacity, and so the cells could drop below the 2.7V safe limit whilst the newer cells 'balance' these out so the LiPo cut-off doesn't kick in, but the older cells are destroyed).

One of the reasons why I always recommend buying either single packs, or a new set that'll only be used together.

[Feight]

Right, well things haven't really gone to plan this month.

So I've had to go with a cheaper option

On the other hand, someone I know had an MGM esc for sale at crazy money. I nearly bit his arm off for it. I saw it powering his buggy and was really impressed with it.

I went for the flightmax lipo 5s, 30c 5000mah 2 packs with import duty was cheap enough.

I'm currently stuck with a 12T pinion, which is low. The stock clutchbell on the hyper is 14T.

I'm about to get a motor to get the show on the road.

[Marvin]

The stock gearing as a nitro isn't neccessarily what is good when electric. When you've figured a motor, I'll work out what pinions would be best for you.