- Sun Oct 16, 2016 7:11 pm
If you're going for speed runs, higher kv is better. However, the higher the kv, the fewer LiPo cells you can run.
Back to lower vs. higher kv. The lower the kv, the more torque that motor will produce. Higher kv is less torque, but higher top speed.
Brushless motors don't work like brushed motors do in this regard, where lower turns equals more torque. I've posted this before, but it's worth posting again: "A high power capable brushless motor in electrical engineering and physics terms, has unlimited torque. We live in “the real world” so technically for us that’s not totally true, but – a brushed motor has a torque level that due to its design has an upper limit, regardless of how much power is being applied to it. That limit is low enough that you can see it clearly on an average track. On the other hand, a high power brushless motor’s limit to torque in an RC vehicle is not within the bounds of the motor itself so much, but rather falls on the ability of the battery to deliver current to it. We generally don’t describe these motors in terms of “one has more torque than the other”, but rather “the 7700Kv motor is faster and draws more current than a 5700Kv motor in the same vehicle”. It draws more current, because it’s making the car go faster and doing more work than the 5700 motor is. As long as the batteries used are very good at supplying current without an excess of voltage depression (low internal resistance is good) both motors will appear to have the same torque, even though one is much faster than the other. Battery technology is constantly improving, and the first thing you’ll notice when you use a very good battery pack (or perhaps trying a Lipo pack for the first time) with these systems is a more “punchy” feel when you accelerate. The faster you set up the car to go at full throttle, the more reliant you are on good batteries to flow that current into the motor and maintain acceleration performance. So think of torque as a function of battery capability only." That was pulled directly from Castle's website, in case you wondered.
With equal battery packs the 5600 would be the faster motor. However, since you can run more power though the 3500, ultimately, in terms of top speed, the lower kv motor has a slight edge by virtue of the power it can handle. You can run the 5600 safely on up to 3S, and 4S if you want to push the system to it's limits. The 3500 you could safely run on 4S if you geared it correctly, and you could run up to 5S (which again is pushing the system's limits) if you have the nerve, and the ESC that could handle it.
A low kv setup is the better all around choice imo. They are much more flexible than high kv motors are. If you want to run off-road, it will happily do that all day long--just adjust your gearing accordingly. If you want to do speed runs; throw in a larger battery pack, gear up, or both, and tighten your chin strap. It's the best of both worlds, really; at least imo--torquey when you need it to be, or fast when that's what's called for.