5S gearing in a Savage Flux

[Ascender]

OK, I've heard every gearing theory on the MMM/2200kv that there is, so I'm actually looking for the info straight from the horse's mouth here. The horse, of course, being Pdelcast.

I'm currently running a stock Flux trans, 44T spur, 29/9 diffs, and Proline MT Mulchers that are taped down to keep them from ballooning. I was running a SMC 4S 6000mah 28C setup and the fan hardly ever came on, so I figure I hit the right combo.

Now I'm going to 5S, with Hyperion 2S/3s 5000MAH 35/65c batteries. I've been told variously to gear up or gear down, and everything from a 13T to 23T pinion.

Not wanting to release the CC genie, I ask you, what do you think is the right pinion for 5S?

[RC-Monster Mike]

While there is no universal "right pinion for 5s", there may be a "right pinion for you". As you go higher in voltage with a given system, you want to go lower with the pinion ideally. What is "right" will ultimately depend on your particulars(terrain, driving style, tires, etc.), along with your intended purpose(bashing, speed runs, racing, etc.). If it performs as as desired and results in acceptable heat(or lack thereof), then it is "right" by most standards. :)

[Ascender]

What I'm looking for is really the right range of pinions to start with. I know 16 is going to be too low, and I know 21 is going to be to high, but that still leaves me with four options, and that's discounting the guys who insist that you have to gear up with more cells, and insist that you HAVE to use the 25T with 6S or your truck will obliterate the Eastern seaboard and plunge the world into nuclear winter.

I'd like to run this weekend, and I don't feel like spending $40+ on pinions just to have them all there to test.

BTW, I should add that my truck is about a half pound heavier than stock, and is primarily a basher.

[Arct1k]

Use the speed calculator and gear for 40 MPH...

http://scriptasylum.com/rc_speed/_top_speed.html

[Ascender]

Originally Posted by Arct1k

Use the speed calculator and gear for 40 MPH...

http://scriptasylum.com/rc_speed/_top_speed.html

I already used it, and I know the right pinion for the speed. But with all the contrary advice floating around out there on this particular combo, I want to check it against what the CC guys say.

No offense to anyone else, just that I'm getting conflicting advice. Use the 25, never use the 25, gear for 40mph, gear for 45mph, gear for amperage, gear for wattage, weight doesn't matter, weight is everything; everybody has their own theory, and I just want to get confirmation from the guys who designed the darn thing.

[skellyo]

FWIW, I've been happy with the stock 20T when running LPR Crime Fighters on 5S. For a little larger diameter tires, 18-19T is where I would probably want to start.

[scarletboa]

i think an 18t pinion would be your best bet. you will get a little more top speed while still lowering the amp draw a little. that is if you use the stock tires though. for mulchers, keep the same gearing or drop down to a 19t.

[suicideneil]

Originally Posted by Ascender

I already used it, and I know the right pinion for the speed. But with all the contrary advice floating around out there on this particular combo, I want to check it against what the CC guys say.

No offense to anyone else, just that I'm getting conflicting advice. Use the 25, never use the 25, gear for 40mph, gear for 45mph, gear for amperage, gear for wattage, weight doesn't matter, weight is everything; everybody has their own theory, and I just want to get confirmation from the guys who designed the darn thing.

Where & who?

The only real theories as such ( as discussed recently actually ) revolve around gearing up a more powerful but slower motor, or gearing down a smaller but faster motor, on the same voltage. As for the rest of it, there shouldnt be any confussion, since here at RC-M we all tend to observe & agree on what to do in any given situation. I'll expand a little:


Given all other factors remain the same ( vehcile, weight, wheels, motor kv, gearing ), if you use a higher voltage you should gear down in order to improve system efficiency. Your top speed will still increase slightly, but it wont reach the max possible. This is for the puposes of bashing with a sensible topspeed around the 40mph mark, in order to keep things running cool but with lots of torque on tap.

When doing speed runs however, you should use the max voltage possible and gear for the desired, but realistic, topspeed you hope to achieve. With the MMM system ( Blur ) and 2200kv motor, this is about 60-65mph, as thats the max speed possible in a 4x4 MT weighting about 10lbs, gearing higher just increases current draw and therefor temps.

A bashing setup is typically 4s lipo and 40mph, speedruns being more like 6s lipo and 50-60mph.

I myself run 5s lipo in both my trucks; one is a 13lb Gorillamaxx geared for 40mph, the other is a TXT-1 geared for 35mph. The Gmaxx tends to run hotter with its Medusa 36-80-2000kv motor ( roughly equal to the 2200kv castleneu ), but the 1518 1800kv motor in the TXT-1 runs much cooler. This is because its geared lower, has a lower kv and is larger, so produces more power, more efficiently.

When it comes to the power side of things, its actually a very simple concept:-

power ( watts ) = volts x amps.

To move any given truck a certain speed, you need a certain amount of power, and making that power from high voltage & low current ( amps ) draw is much more preferable to low voltage and high current draw. This is because more current = more heat, poorer efficiency & shorter runtimes. This is the same reason why using a lower kv motor ( that pulls less current ) and higher voltage is very popular for larger vehicles, especially 1/8 scale and upwards. With a HV setup like this ( 1600kv motor and 6s lipo say ) your gearing will remain roughly the same as a 2200kv & 4s setup ( roughly- check the gearing calc for exact numbers ), and so will your speed; if you use the same mah capacity lipos you will find your runtime increase- you can even use smaller capacity packs and achieve the same runtime more or less.

Obviously, the faster you want to go, the more power you need, so higher voltage and larger motors are called for; in a speed run situation you arent too concerned about runtime and efficiency, moreover just topspeed without blowing the esc skyhigh. For racing and bashing though these things are a concern, so the best answer I can give you is to gear for your ideal speed with any given cell count, let your temps dictate if you are pushing it too hard or are geared to high. If temps are fine and you're happy with the speed, then thats all that matters really- I figure 5s lipo with the 2200kv motor is the sweet sopt, nice mix of power and speed with good temps, with a wider window for gearing up a bit if you so desire ( you can only gear up so much on 4s lipo before the batts and motor run out of puff due to lack of raw wattage ).

Hopefully that clears a few things up for you- be warey of advice from some places, they are populated by noobs and plebs with little real experience & very little practical electrical knowlegde; many of the guys around here are industry insiders, beta testers and electrical engineers/ gurus who know exactly whats what when it comes to electrons and mechanical advantage through gearing. Im just a skilled blagger....

[Jahay]

nice explanation neil!!!!

[Ascender]

Originally Posted by suicideneil

many of the guys around here are industry insiders, beta testers and electrical engineers/ gurus who know exactly whats what when it comes to electrons and mechanical advantage through gearing. Im just a skilled blagger....

Exactly why I'm asking here, I want the opinion of the company insider.
I've done the math, I know where to gear for speed/wattage, I just want to make that my gear choice isn't going to cause my MMM to go FOOM like so many others. With all of the conflicting advice, I want to get the advice of the guy that builds and tests them, since he is available.

[suicideneil]

There isnt any one-person with a magic answer, I think you're over complicating things because of all the conflicting opinions out there. Stick to one good forum and you'll find 99% of the guys with applicable knowledge & experience will agree on a suitable setup/ setups for any given application.

As for escs going FOOM, its generally down to a few simple things:-

1) noobs. They gear for 120mph and cover the esc with an airflow restricting dust filter, with massive tyres & then wonder why their esc went pop ( true story ). They also do poor solder jobs and use poor batts, which stress the esc and cause it to fail ( see: 'ripple current' ).
2) Dodgy component(s). These are impossible to detect & will only show up once you start using the esc in a real-world situation; as a general rule, if you survive the first session or two, then the esc is a good'un.
3) Exceding operational limits. If you take a wild guess at gearing & dont check/ ask if its a good setup for your needs, then you can potentially cause the esc to fail through over gearing or pushing it too hard- such as repeated speedruns without checking temps, or testing the setup by jamming it into forward-reverse-forwards repeatedly and/or doing repeated backflips > massive surges of current that will pop Fets and TVS devices.

Learn to trust the advice of gus who've been running their setup for while- if its anything like what you want to achieve, then it will be a good solid setup.

So, use the calculator ( you can trust that too- BrianG is a legend in his own right ), settle on the gearing that gives you your ( sensible ) desired speed with your setup, allow for ballooning & heavier than normal tyres or stretched chassis etc ( gear down a notch as such ), then go ou and buy the required pinions and spurs. Buying a selection of gears allows you to finetune your setup- a couple pinions say that are 2 or 3 teeth apart and a couple of the available spurs either side of the ideal sized one will allow you to gear up or down a bit, depending on the temps, ambient temps, and the terrain ( long grass or sand vs hard dirt and tarmac for example ).

I would gear for about 40-45mph with 5s, works great for me