Selecting motor + pinion for Cat SX?
 

Hi guys,

Decided to treat myself to an RC car after not having had one since I was about 12 (Optima Pro!). Having always liked the CAT and dreamed about getting one as a kid, I thought I'd treat myself to the new model.

Anyway, things have moved on a lot and whilst I've decided to get a brushless, I'm still trying to find info on how many turns motor I should run and what pinion?

From looking at race results on here with people running Cat SXs, it seems a 5.5 turn is pretty much the most popular. How will this be different to a 6.5 turns unit or 4.5 in terms of acceleration, torque and driveability?

Considering the Losi Exleroin + 6.5 combo as they don't do a 5.5. Any recommendation on which pinion would suit?

Also planning to get a trakpower battery. My understanding had been that the capacity dictated runtime + weight, but I've seen comments suggesting they affect acceleration too? Is that just because the smaller capacity lipos don't supply enough current for the motor? Or, if I compare a 5900 vs a 3200, will its be same performance but better run time?


Thanks for any help, read almost all the threads on this forum, but can't find this kind of basic info!

6.5, 5.5, 4.5 etc means nothing as every motor is different. Brushless is not like brushed and turns don't mean anything really. For some reason the rc car industry is still using them.

Anyway with brushless you can basically gear for top speed anyway, so depending on what system you go for, 4.5, 5.5 or 6.5 will be fine. Acceleration is not greatly affected like it is with brushed motors. As for LiPo, you are right, bigger packs can supply more current. I use a 4900mAh Trakpower in my cat, as this is BRCA legal. The 5400mAh are not BRCA legal, so you won't be able to run at places that follow BRCA rules. It's good to have some weight in, as LiPo is lighter than traditional NiMH/NiCad stuff.

I would recommend the Tekin stuff, it's awesome, but Losi is fine. My brother races with a 6.5 losi and it's good for 1/10th off-road so you will be fine with it. :)

I would have to disagree about the turns not making any differance, its just the same as it used to be in brushed, one brands 9T would be as quick as a lesser brands 8T

basically yes, lower the turns you loose some torque for RPM, but you would gear the lower turn motor lower so you would get your torque back and even on the lower gearing you would have more top end. the loose here is run-time.

in addition to brushed motor 'tuning' you have rotor size, its basically the size of the magnet inside the brushless motor, bigger magnet more torque less rpm and vice versa for smaller magnet/rotor.

you have it pretty much right on about the LiPo capacity, the higher mAh is able to deliver more current.

depending on your level of skill, level of competition you want to be doing and your budget will determin what turn motor you want.

as you say you are just getting back into it, it would not be wise to go with a 4.5 or 5.5 LRP X12 motor just yet.

Well I was considering the Losi 6.5 mostly because I like the PC programmability and to be honest it seemed more modern and a lot newer than the novak I was also looking at. The price is a bonus and whilst not the deciding factor, I couldn't really see any reason it was inferior?

I read your review which is one of the things that helped me decide on a CAT so thanks for that.

So spec I'm considering is :

Cat SX
Spektrum DX3R
Trakpower 4900
losi 6.5 system http://www.m-k-racing.com/product_in...8&%3CosCsid%3E
Savox servo http://www.m-k-racing.com/product_in...1&%3CosCsid%3E

Any idea if that Savox servo is any good as not heard of them before?

Guess I should downgrade the battery then :(

Thanks for the comments.

the savox servo's are very smooth and plenty fast enough. They seem very good build quality too!!:thumbsup:

Ah thanks for the explanation. Was trying to work out what the losing variable was. Are the lower turn motors just less efficient even if you don't use all their extra top end? (i.e. if I set the ESC to limit to 50% throttle would it run as long as a motor half as quick?).

I think you are right about a 4.5 or 5.5 in my hands. Was planning to get started with the ESC setup to limit full throttle whilst I work out how to drive. Decided to switch from stick to wheel too, which I may regret. Then again its been years so probably no difference!

Which would you recommend for the CAT, the 12kg or 20kg? I guess the trade off is speed?

Great thanks.

Comparing a tekin, or more expensive brand, will it actually make any difference when I drive the car, or is it more intangible things like massively overspecced+ high build quality?

I'm not adverse to paying for quality if there is a tangible benefit (getting a CAT Sx after all!), its just I haven't worked out what that benefit is on the motor+ESC front as the losi units seem ok for most people (problems I've read about online, seem to largely be user error).

People will say different things, some people say they can feel the differance, others say they can't. you also hear so many different opinions on forums and at the track, some say something is ace, others say its not.

Answering your other question about efficiency, limiting the top end on the radio would make it less efficient than a motor of that desired rpm but with LiPo and brushless efficiency is one of those things that is never really considered anymore.

wheel Vs stick - strongly consider sticking with what you have been familar with, you would be suprised how many connections in your brain would still be wired up for using a stick radio, even after a 10 year break!

True, but its a 20 year break (I'm getting old lol) and I've spent a lot of time with real steering wheels since. Will take my chances I think as can always swap back to stick.

Thanks for all the advice everyone. Anyone know what pinion I should be using with that 6.5 motor?

I'd start off on a 22/23 on kit spur :)

G

The lower turn brushless you go the more 'savage' it is to drive, so a 4.5, with limited top end electronically will be MUCH harder to drive than a 6.5 selected and geared appropriatly.

A 6.5 motor (any brand) with a decent cpacity Lipo will be plenty fast enough for any UK track, I chose to motor down to a 7.5 at Worksop on Sunday (to improve dravability) and that has a pretty big straight.

Ref Novak motors, they have been around a while but you might want to consider than they haven't been changed much as there is nothing to improve. Wasn't the Novak system the only Brushless system in the A final at the last 1/10th off road worlds? ;)

ok thanks, seems 6.5 is plenty for me.

There were a few systems run in this report (see end table) including the losi:

http://www.oople.com/rc/photos/worksop191008/

I guess because novak have been about so long that may skew numbers for long standing top class drivers?

Well in that case you are wrong. It just so happens that a lot of systems have just copied the first to markets systems like the Novak. This is partly because the lack of innovation for most RC companies is low and also, probably mainly, due to the stupid rules put in place for electronics to comply with for motors. This is the only reason there is correlation between a few of these motors.

If a 6.5 turn motor from one brand is slower than a 6.5 turn motor from another it does not make it lesser quality as you suggest. That is just poor logic. There are so many factors in determining power output, and turns is just one. The RC airplane, helicopter and marine industries all realised this a long time ago, and instead rate their products in terms of power rather than turns. This is all that really matters, along with Kv which helps you gear for the most effcient rpm band.

I run a RedLine 4.5 turn (not BRCA legal) in my CAT SX and it's about equivalent to a 6.5 turn Losi system. Kind of proves the point in itself. And being less turns for the same speed doesn't make it lesser quality, in fact I would bet the system is actually much more effcient.

Anyway back on topic

A higher end system, in terms of the Tekin at least, will be better than the Losi. However it's all about relative value for say, and in my head the Tekin and Losi come out at equal value for money. The Tekin system is more effcient, so you should get longer battery life and less heat. Also it can easily handle much more than a 6.5 turn, so the system will be under less strain and should operate faltlessly.

I have a Tekin 1/10th system powering a big 1/8th buggy on 4 cells and a big motor. Just shows it's quality, and overspecced really which isn't a bad thing. On the other hand the Losi is much cheaper, and does the job just fine. So it's just something to weigh up in your head. I personally would go for a Tekin system but the Losi really isn't a bad option and can save some £'s.

How do you know the tekin is more efficient? have you done back to back tests?

Yup certainly have :)