6.5T Lipo vs 5 Cell

[nickyrhodes]

Hello,

Just wondered what peoples thoughts are about the difference between the 6.5t limit on lipo and the more relaxed 5-cell motors in this years rules.

Apart from run time issues on large tracks, 5-cell seems to beat lipo all the way, i constantly get caught up on the straight by my 5 cell rivals... I know speed isnt everything, but at the next SRCA meet at Stonehaven, 6.5t cant keep up down the straight unless you gear it up to melting point!!

[Steve Cann]

At the beginning of the season I [sort of] predicted a win for 6.5/Li-Po this year at a National [even with a perceived weight dis-advantage ;)]... It very nearly happened at Cotswold... Colin Price still took TQ setting a new track record in doing so... Be interesting to see what happens at Snetterton but my money is on the win coming at the wide open and fast Mendip track...

For the Ansmann GP we've decided on weight parity for the Super Tourers as we felt at medium speed circuits like West London there won't be a lot to choose and hopefully no advantage for either Li-Po or 5cell [with weight parity]...

[Skiddins]

At the beginning of the season I [sort of] predicted a win for 6.5/Li-Po this year at a National [even with a perceived weight dis-advantage ;)]... It very nearly happened at Cotswold... Colin Price still took TQ setting a new track record in doing so... Be interesting to see what happens at Snetterton but my money is on the win coming at the wide open and fast Mendip track...

For the Ansmann GP we've decided on weight parity for the Super Tourers as we felt at medium speed circuits like West London there won't be a lot to choose and hopefully no advantage for either Li-Po or 5cell [with weight parity]...

And if we're lucky more Mod drivers will book in to come and test that theory :D

Nicky, when I was at Cotswold watching the top guys you couldn't tell who was running what just by watching what was happening on the track, you actually had to look at the cars in scrutineering and as Steve has said, Lipo 6.5 took FTD there.

Skiddins

[MikeS]

Don't forget the weight penalty that Lipo is having to run with, it makes a difference ;)

[Steve Cann]

Don't be overlooking the voltage 'penalty' 5cell has... Suspect that makes a difference also ;);)...

[Jonny Aird]

In my opinion I don't think there is too much difference between 6.5t and 5 cell. With any "spec" brushless class, the motor is pushed to the limits of its temperature range to get it fast enough and its the same with 6.5t.

At Cotswolds Colin Price and Chris Grainger were both extremely fast down the straight, one used 6.5t and the other 5 cell.

I tested 6.5t earlier this year and found that you need to be quite aggressive with the throttle to get the most out of it. It seems to suit some people more than others.

I think the main difference in straight line speed at the moment is the ESC, because in my opinion there is one available that is much better than the rest.

[PDW]

...when he says that the issues with motor and speedo stress are down to voltage. 6.5T is just 27T and 12T written large - the lessons of history are that, whether you have competition or not, a 'spec' motor class will always test that motor to destruction.

Now add in the voltage, and the problem just gets bigger. In 12th and GT10, with a 4.8v limit, those problems do not exist. In 5-cell, they are much less than with 6-cell/LiPo. Whilst I appreciate that you all want LiPo, the lessons of history are that it will burn motors out - fast.

As to the point of the thread, there cannot be equivalence between two different voltages since the track and the grip on the day may favour one over the other. Play with weight, play with motor wind, play with anything - it cannot be equivalent. However, it does make for good racing - the ebb and flow of the cars as one plays their advantage and then the other.

[Skiddins]

The lessons of history are always there - things that don't adapt die.

Whether anyone likes it or not Sub-C's are nearing the end, speak to any of the Mod drivers and they can't wait to go to lipo for that proper 'hassle free' feeling :D

The weight limit will quite likely be reduced at the AGM for 6.5 lipo, then that will be that, you wont be seeing Sub-C's in any competitive TC's. If any of the other classes decide to follow ROAR's example etc. your beloved 1/12 will go lipo as well.

The argument has been that we'll get more entries in Mod when 6.5 lipo is competitive.....time will tell.

Skiddins

[nickyrhodes]

Hmmm, interesting topic!! :-)

Perhaps i need to update my motor and esc then.... What recommendations for 6.5 motors and which esc are you talking about?

Personally i am very careful with overgearing, the hottest mine has been was about 45c at Stonehaven. I always build up the gearing during practice the day before...

[Skiddins]

I believe the Schumacher guys run the GM motors and ESC's.
As for temps and gearing, what you're doing sounds very sensible to me.

[MikeS]

These statements thrown out by various posters regarding the voltage effect and differences between 5 cell SC and LiPo are terribly misleading since they appear to totally disregard the motor power and load the motor will have to move (mass). The fact is that the pack voltage will only affect the maximum rpm potential of the motor NOT the power, the power output is a function of current draw of the particular motor, and the performance of ANY vehicle is a function of it's power/weight ratio, assuming the CoD, aerodynamics are the same!

However none of this is easy to "prove" as most manufacturers don't publish all the relevant information on how they "measure" the numbers they publish, even worse there is no proof that the same measurements/calculations are actually being used between manufacturers are the same either!

The things we DO know are the calculations and electrical coefficients regarding DC motors as these are set in stone!
Torque constant: Kt=Kb x 1.345
Current draw of motor: I = [V-(Kb x kRPM)]/Rm
Torque output of motor: J = (Kt x I) - (Kt x Inl)
RPM of motor: kRPM = (V - RmI) / Kb
Power output of motor: Po = (J x RPM)/1345
Power input: Pi = V x I
Motor efficiency: Eff = (Po/Pi) x 100
Current at peak motor efficiency: Ie max = Sqrt [(V x Inl)/Rm]

Where:
Eff = Efficiency
I = Current
Iemax=Most efficient current
Inl = No load current
J = Torque (oz-in/A)
Kb = Voltage constant (Volt/1000 RPM)
Kt = Torque constant (oz-In/A)
Pi = Power input (Watts)
Po = Mechanical power output (Watts)
Rm = Terminal resistance
RPM = Revolutions/minute
V = Voltage

So lets debunk some of the stuff that gets posted with regard to this topic.......the starting point is to use the figures published by ONE manufacturer as this assumes that whatever process they use to determine these figures, the same one is used across their range.

The basis for comparison has to be the power output of the motor - Po (Watts). this is the stated power output of the motor. So taking Novak as a well known and respected manufacturer they state the following for the following 2 motors, of the same design and in the same range:

Novak Velociti 3.5R BL Racing Motor [Nov3403]
Input Voltage: 4-6 cells (1.2 volts/cell)
Watts: 490
KV (unloaded) 10,500 RPM/Volt

Novak Velociti 6.5R BL Racing Motor [Nov3406]
Input Voltage: 4-6 cells (1.2 volts/cell)
Watts: 340
KV (unloaded) 6,400 RPM/Volt

As they also state the input voltage and on the assumption that they will use the values that produce the most impressive Po, I am going to assume that the voltage used for these numbers is going to be another "constant", that of 7.2V
As there is a direct linear relationship between the Po and the voltage, another constant, then it is easy to reverse engineer the numbers:

So taking the 2 classes:
5cell SC @ nominal 1.2V per cell @ 1425g (however we know that for todays SC cells that 1.2V/cell is in fact much lower than that actually achieved, since most SC cells run at 1.5V+/30A)
LiPo @ nominal 7.4V per pack @ 1500g (however we know that 8.4V is the controlled initial pack voltage)

IN all this we take no account of the voltage drop of the pack during a run as this is impossible to measure reliably, and varies according to many external issues, such as ambient temp, motor efficiency, drivers thumbs, grip level etc.......so the numbers resulting will be calculated at the initial starting point rather than an overall value.

Adjusting the Po for the no load starting voltages of the packs:
5C @ 7.5V @ 408W @ 1425g = 0.2863
Li @ 8.4V @ 317W @ 1500g = 0.2113

Which appears to show that all other things being equal, which they would be if this is the same chassis and same body, but different motor/battery/weight, the 5C/1425 class has a higher potential power to weight ratio over the Li/1500 one. However the difference is not going to be as high as the numbers appear to show since there will be a significantly higher voltage drop in the 5 pack as the load is applied compared to the Li pack.

Experience shows that the 5C pack will suffer an initial voltage drop of approx 1V as soon as a load is applied, where as the li battery only drops by .25V:
5C @ 6.5V @ 354W @ 1425g = 0.2483
Li @ 8.15V @ 330W @ 1500g = 0.2199

Which shows how fairly close the 2 classes currently are, however the 5c class still has an significant advantage, not least the lower weight resulting in less engery required to accelerate the car and the handling benfit that the lower weight provides.

Reducing the weight of the Li class to the same as the 5C class brings them closer together still:
5C @ 6.5V @ 354W @ 1425g = 0.2483
Li @ 8.15V @ 330W @ 1425g = 0.2316

So as you can see, all other things remaining the same, reducing the weight of the Li/6.5 class brings the 2 much closer together...but would in reality probably result in the Li package producing a faster car over 5 minutes simply due to the lower voltage drop curve of the packs during a full 5 minute race.

I agree with the comments that having a lower voltage reduces the chances of motors being blown up, however I have always been of the opinion that this is a drivers mental and throttle control problem and responsibility and that you can't blame the equipment for what is basically a driver failing! Reducing the voltage does reduce the chance of failures, but for the wrong reason! If you overgear a 5C car then you dump, if you overgear a Li car you may blow the motor - we need to stop nannying and drivers need to take responsibility for their actions and stop blaming the equipment and learn to gear correctly as we used to! I see no valid reason why drivers should not be responsible for the gearing decisions they make........I also understand that proposals may be made for the next worlds to be Li/Open class. It will be interesting to see what they propose to do with the weight limit as well, as the cars will be ridiculously fast even at 1500g, far to quick for lots of people even at worlds level and sort of totally contradicts one of the main reasons for going 5C in the first place - to slow the cars down and reduce the loads on them!!!

[nickyrhodes]

Thats a bit of an eye opener!!

Be interesting to see what happens next season with regards to the weights...

[Skiddins]

Mike, I take it that brushless motors are not effected by voltage drops the same way that brushed motors were, i.e. with brushed, when you halved the voltage you also halved the amps drawn so you actually got 1/4 of the power from the motor, it also works the other way, double the voltage and you quadruple the power.

So BL motors are more linear with their voltage/power requirements?

[KennyClark]

I dont think you analysed that enough there Mike.

[Ben Cosgrove]

5 Cell was introduced to stop the problem of blowing up unreliable brushed motors and the weak bonded rotors. Reducing the voltage made it safer.

No problem anymore with those issues. Sintered brushless is fine.

Speaking to the key players at the Euros they all want LiFe bringing in for EFRA next year! 6.6V.

Long term maybe the best way forwards?

[Jonny Aird]

5 Cell was introduced to stop the problem of blowing up unreliable brushed motors and the weak bonded rotors. Reducing the voltage made it safer.

No problem anymore with those issues. Sintered brushless is fine.

Speaking to the key players at the Euros they all want LiFe bringing in for EFRA next year! 6.6V.

Long term maybe the best way forwards?


Yep and the ones I spoke to said "LiPo is done". It will die out in 1 year, or we will have problems.

[Skiddins]

If lipo was wiped out completely at the end of the year and we had to use something else I wouldn't mind that much, I've had more use out of my lipo's than I ever did from any Sub-C packs without any problems whatsoever :)

[MattW]

......and the word on the street is that LiFe cells actually have a longer usable life than PiPo does. Currently I'm not sure they have the capacity or quite have the discharge current compared to LiPo at this moment.

[Steve Cann]

Is that having two choices of motive power for same class is in the long term not good... [Mr G has told me that on many occasions ;)]... It means if your being serious you most probably need two cars and spend most of your time testing just to decide which way is best for any particular track and or situation...

Think at some point [sooner the better] a decision is gonna have to be made as to which way to go with regard this... And whatever the direction is... Make that a decision to attract the 'middle order' drivers back into Super Touring... 'Cos at the moment all thats happening is the creation of an 'elitest' group which in the long term ain't good for the sport...

And my final thought... I hate that word equivalency... It sucks :mad:...

[Mark Stiles]

Is that having two choices of motive power for same class is in the long term not good... [Mr G has told me that on many occasions ;)]... It means if your being serious you most probably need two cars and spend most of your time testing just to decide which way is best for any particular track and or situation...

Think at some point [sooner the better] a decision is gonna have to be made as to which way to go with regard this... And whatever the direction is... Make that a decision to attract the 'middle order' drivers back into Super Touring... 'Cos at the moment all thats happening is the creation of an 'elitest' group which in the long term ain't good for the sport...

And my final thought... I hate that word equivalency... It sucks :mad:...

Amen to that bruv! :D

[Mark Christopher]

as a point................ in off road thay dont use light cars and super fast motors with lipo, simply the cars are undrivable and a light car can not put the power down to the track as much as a heavey one, so would you not end up with the same senario would drivers not chose a motor thats easier to drive and put power down? or are tc drivers a different breed?

[Ben Cosgrove]

you are correct Mark, drivers would find a steady level of speed and performance for their ability. If that was a 3.5 because they wanted to go fast then cool. I think most would end up around 4.5/5.5 due to driveable power.

The end result would be.........motors will be geared in the correct range not to blow them up, speedos would work in the correct temperature range as there would be less stress from highly tuned motors/gearings and batteries would never be pushed to the limit.....

Basically we would use the products as they were designed to be used, sensibly!

The only thing that happens in control classes is that you have to spend lots of time and money to go fast, simple. Proven with brushed motors with skimming comms down and having loads of brushes etc, proven in 10.5 where you have to push motors and lipos to the limit with drivers now finding they have to buy fresh lipos to be fast!

I personally think that opening up the 'mod' class would attract more 'mid level' drivers as they have been referred to because they will be able to have FUN! It would bring a smile to anyones face passing Chris Grainger on the straight but lets not think about the corner bits lol.

Mod is currently broke worldwide. Simple rules are the way forward.

IMO LiFe batteries with no motor limits would get my vote. Possibly turn the mod class into an 'EFRA spec' class. Designed for the elitist drivers to race and qaulify to race the best drivers in Europe at the Euros. Leaving the BRCA National series as 10.5 only but having a few heats for the elitist serious runners. This new class would be proving grounds for new technologies. That would also allow the 'mid level' drivers to have a play in that class if they wanted to go fast!!

AGM Proposal Forms will be in circulation soon ;)

[nickyrhodes]

If lipo was wiped out completely at the end of the year and we had to use something else I wouldn't mind that much, I've had more use out of my lipo's than I ever did from any Sub-C packs without any problems whatsoever :)

Be a bit of a bummer for those who've just bought a £100 charger and 3 x £50 lipo packs though.....:'(

[steveonamission]

I dont think Lipo should be wiped out for Pro Stock, as too many people have invested in them.

However, i think Li-fe cells being 6.6v are perfect for modified with an unlimited motor wind as Ben says. Modified should be modifed right,unlimited motors!... ive never really liked the 6.5 limit, its like half way inbetween mod and pro stock in my opinon, even if track records or specs say otherwise........5 cell should be banned now as thats crap, i have no time for that what so ever, its a wallet game, no fun in that.

Also most of todays chargers have settings to charge Li-fe cells aswell as Lipo, most are multi-functional......

[Skiddins]

Be a bit of a bummer for those who've just bought a £100 charger and 3 x £50 lipo packs though.....:'(

Haven't seen a Lipo charger yet that doesn't have the option for LiFe cells.
It's all hypothetical though, as has been pointed out, at the moment liFe cells aren't up to the job yet so no need to worry :)

[nickyrhodes]

Unfortunately the muchmore silent charger doesnt lol, maybe they could offer a firmware upgrade service...

Agree with the modified should be modified... and shouldnt be a wallet game.

[Ben Cosgrove]

hopefully I can test the GM 3400 LiFe cells this weekend at some point with Mod at the Juniors...demo run maybe??

Will also test them round Snett with open motors, that way at least we may have some feedback for discussion at the AGM.

[Chris ODonoghue]

I don't care if it's LiFe cells or Lipo cells or Nimh cells, but it should be the SAME cell for everyone, pro-stock and mod, otherwise there's a needless barrier in place for people to move between classes easily.

[Steve Cann]

Create a class for all!

Been done before...

[Ben Cosgrove]

yup i agree with Steve.........for the UK Nationals I think it should be all Pro Stock as is now (maybe lower weight)

Although I do think we need to cater for the elitist at nationals by having an 'open heat' of efra spec to qualify for the Euros etc.

I personally would like it all to be 1 class again. But I am also worried about our World Class superstars who only race at nationals going abroad and getting spanked by the Europeans because the rules are totally different.

The switching between classes is a valid point.

People dont race Mod currently because of 5 cell. LiPo is way more fun all round for people to use and work with, much less hassle.

So heres a question for all you Pro Stock runners.......

Would you race in MOD if we used LiPos and no NiMH cells regardless of the motor rules?????????

If so then we could drop 10.5 class altogether?

Remember some one like Andy Moore would win the Mod class and would also win the Pro Stock class at a national. So dropping in the top 20 from MOD could potentially through the top 20 in Pro Stock into the 20-40 area.

Do current Pro Stock drivers like making the A/B Finals or racing against the best drivers on a fair playing field (i.e open motors)?????

[Mark Stiles]

yup i agree with Steve.........for the UK Nationals I think it should be all Pro Stock as is now (maybe lower weight)

Although I do think we need to cater for the elitist at nationals by having an 'open heat' of efra spec to qualify for the Euros etc.

I personally would like it all to be 1 class again. But I am also worried about our World Class superstars who only race at nationals going abroad and getting spanked by the Europeans because the rules are totally different.

The switching between classes is a valid point.

People dont race Mod currently because of 5 cell. LiPo is way more fun all round for people to use and work with, much less hassle.

So heres a question for all you Pro Stock runners.......

Would you race in MOD if we used LiPos and no NiMH cells regardless of the motor rules?????????

If so then we could drop 10.5 class altogether?

Remember some one like Andy Moore would win the Mod class and would also win the Pro Stock class at a national. So dropping in the top 20 from MOD could potentially through the top 20 in Pro Stock into the 20-40 area.

Do current Pro Stock drivers like making the A/B Finals or racing against the best drivers on a fair playing field (i.e open motors)?????

I have always wanted for there to be 1 class for all.:)

How many nationals are there in a year? 5... so it's not like they're every weekend. I understand the superstars wishes to 'practice' for the Euros, but to be Frank if thats all they turn up to the nationals for then they can go play somewhere else for all I care. I turn up to a national in any class to race on a level playing field against the best drivers in the UK - not to watch others practice for a bigger event later in the year. Forget the 'elite' heat or whatever - everyone should have to race against everyone and earn their place at the Euros.

I can't answer your question aimed at the Pro Stock runners Ben as I never raced it. However, if tc was made into one class only at nationals for next year then I would probably come back to play; the prospect of racing 120 other drivers appeals to me more than racing against 30 or so others.

[Skiddins]

If you were to open up the nationals to effectively become a modified only, you won't see 120 drivers!
I don't race Mod because I'm not good enough, simple as that.

We've seen quite a few drivers have drop back into the 13.5 class from Pro Stock (perhaps the volateg reduction in LiFe would solve this!)
I continue in Pro as I want to push myself that bit more and try to become good enough to run Mod. Fat chance :D

One class sounds great until you're actually trying to compete. Yes we could put whatever motor we wanted in but you'll then end up with people who have to run slower motors because they can't cope, or those that crash a lot with more powerfull motors. Those that run the slower motors will know they won't be competitive so might not bother in the first place.

Please nobody mention off road only having one class, they don't have the grip levels and speeds that we do so they can't be compared.

I don't think we are going to see enough development/testing of liFe cells this year to make a definite decision on them at all.
Next year perhaps.
If we then get pushed towards LiFe across the board, the voltage reduction would calm down the Pro-Stock class and more people might try Mod.

One thing at a time though, we have a new technology that makes things a lot easier and is helping to move the hobby forward, lets allow that for then we can test and plan for the next revolution in electric RC.

Maybe I will try Mod later i the year at a bonus meeting or something.

Make sure you give everyone a shout Ben if you do get to test the liFe, I will be there Sunday :)

[PDW]

Haven't seen a Lipo charger yet that doesn't have the option for LiFe cells.
It's all hypothetical though, as has been pointed out, at the moment liFe cells aren't up to the job yet so no need to worry :)That's what they said about LiPo in 2006/7... ;)


I don't care if it's LiFe cells or Lipo cells or Nimh cells, but it should be the SAME cell for everyone, pro-stock and mod, otherwise there's a needless barrier in place for people to move between classes easily.That's where leadership from the National Associations is needed. I appreciate that we all want our democratic vote at the BRCA AGM, but a racehorse designed by a large committee of people always comes out as the camel we have now!


Create a class for all!

Been done before...Hear hear! The antipathy in this country towards having multiple classes so everyone can race mystifies me. In the US they have six or eight classes on their Club nights, some as low as a handful per heat, yet scores turn up to race every week. In full-size motor racing there are more classes than you can shake a stick at, but if the class is 'pre-1990 Touring Cars' then drivers turn up in everything from a big Rover to a small Mitsubishi, and race together.

There's nothing wrong with one class with open Rules and people just race what they want. Equally, there's nothing wrong with three, four or five classes where people race each other within closed Rules for each class.

One thing I certainly agree with - I want to race against the best drivers. I don't mind that I race with a 10.5BL in the Sports Class, I want to see where I am compared to the best drivers on the same track. If I thought I could do justice to a Mod, I'd race one. I can't, I don't, I won't make the same lap time, but that doesn't stop me checking my 'difference' compared to Griff, Styles and Hale - one day it'll be 0.3 secs, one day... :)

[Steve Cann]

The way I look at it... If all the mobile 'phone makers [with all their vested interests] can get their heads together to achieve what I thought was the un-achievable [common charging lead]... Then putting together a set of rules for a single class for TC should be relatively easy peasy...

The trick is to make 'it' [the class] sufficiently challenging for the cream of the crop without putting 'it' out of the reach of the 'improvers'...

And, I reiterate it has been the case before and not everybody used the same motor wind in lemming like fashion... And the entries were full both at nationals and clubs... And everybody had "a good day out"...

[Skiddins]

It has been suggested by many people that one of the reasons why we don't seem to have so many youngsters coming into the hobby is that they can't win straight away, with the instant gratification of PSX's and Xbox's etc. the effort to learn the skills to setup, maintain and drive a TC just seems like wasting time.

If you remove the lower classes they are even less likely to put the effort in as it would be too steep a learning curve.

Mod want rid of Sub-C's, and those racing Pro Stock would like it to be easy to try Mod.
I think Lipo 6.5 would be fine for next year, then if LiFe cells make progress perhaps Mod and Pro Stock could end up using those and we'll all be on 6.6V
Perhaps that would help reign in the speed from the timing boost type speedo's in 10.5 etc.


That's what they said about LiPo in 2006/7...

In racing development, that's an eternity, BL systems then were barely in use. :D


And, I reiterate it has been the case before and not everybody used the same motor wind in lemming like fashion... And the entries were full both at nationals and clubs... And everybody had "a good day out"...

But everyone was slower then as the technology limited the capacity of cells and the speed. In my opinion the gap between the top guys and the also rans has just gotten bigger over time.

Skiddins

[spmcc]

As we seemed to have wandered a bit on this thread and LiFE cells have been mentioned, has anyone else read the "blurb" in the September edition of Race Car on the Max Amps LiFe cell. Makes for some interesting reading. There is also a link to there website.

[Chris ODonoghue]

I continue in Pro as I want to push myself that bit more and try to become good enough to run Mod. Fat chance :D


Sorry Damien, but I've seen you drive.. you're more than capable of running mod !
Maybe the Ansmann would be that perfect opportunity you're looking for to give it a run ? ;)

I've not been doing this hobby for very long compared to a lot of people, but I gave mod a go very early on (sorta skipped 19t/10.5 in that sense). It's been a steep learning curve, but I'm getting better.. still nowhere near the sharp end of things, but that's not what the hobby is about for me. I want to challenge myself against the best there is. That's just how I'm wired, it's the same in every hobby/sport I've done in the past.