Quote:
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....
