Finally considering brushless for my Summit. What KV? 1600ish?

[fyrstormer]

At long last I'm seriously considering switching to a brushless motor in my Summit. I'm currently running the stock Titan 775 motor, modified with ball-bearings at both ends which let me gear-up a bit without the motor getting hotter than before. I'm content with the speed and power I'm getting from this slightly-modified stock motor. What KV should I aim for?

Hypothetically I could do a couple speed runs and do some math to figure out the motor's top speed. And indeed, I have actually done that -- the motor's top speed is 21901rpm on 4S, give-or-take a few RPM. That would seem to suggest I should aim for a motor in the 1300KV range, which is surprisingly low -- but that assumes the battery was maintaining a perfect 16.8V during the run, and we all know that can't be true. If I assume the battery was sagging all the way down to its nominal voltage, 14.8V, then that would put the motor closer to 1500KV. The problem is, I don't know the voltage the motor was running on at the exact moment it reached top speed -- or the exact speed of the motor, for that matter -- because I have no way of measuring those values in realtime.

I don't want to dump a bunch of money into a telemetry-enabled receiver and sensors just for this one instance, especially since realtime RPM and voltage readouts wouldn't be able to account for things like a difference in torque or power efficiency when switching to a brushless motor. But I also don't want to dump a bunch of money into buying one motor after another just to test with. I also don't want a monster motor that will shred my Summit's drivetrain by accident. So what should I go with?

 

[fyrstormer]

Nothing, huh?

Well, I did some more math based on the gearing and top speed of the E-Revo Brushless Edition, compared to the gearing and top speed of my Summit, and concluded that 1600KV should be just about right. Approaching the question from two different perspectives and arriving at the same answer gives me enough confidence to spend money on a 1600KV 4475 motor. It's gonna be a big boy compared to the 3650's and 3660's I've held in my hands over the past few years.

 

[LincolnofDeath]

It’s gonna be a total monster. I look forward to hearing how this works out for you. My only reference point is going from, like you said, 1410 3650 and 3660’s in the 3-4K Kv range to another four-pole 28650 Castle, so tenth to eighth scale power stuffed and dremmelled into a SCT...and yeah, drivetrains had to be reconfigured, along with almost everything else. I’m late to the crawler game for any intimate knowledge regarding Summits, except randomly reading about them in the past over on the Traxxas forums. But I think I can see what you’re going for here.

The notes you left me regarding 4S with an WP880 are super insightful and encouraging, for sure. Thanks for that, amigo.

 

[fyrstormer]

I doubt it will be a monster. I'm aiming for the current speed of ~25mph in high gear. I won't be running any crazy gearing, just 17/65, same as I'm using with my modified Titan 775 motor. Mostly I'm looking to future-proof my truck.

I wouldn't say you're late to the crawler segment. I'd say you arrived at its peak. There are more really good scale trucks available now than there ever have been before, and I don't think the current huge selection can last very long. In any event, Summits are still in-production, and everyone should own one as a general-purpose basher whether they want to or not.

 

[fyrstormer]

The motor arrived today, and...oookay, everyone has ways in which their brain just doesn't work right, and one of mine is I always underestimate the size of products in photos. The motor I got is as wide as the Titan 775 and quite a bit longer too, in addition to the inherent power efficiency increase that comes from being a brushless motor. I can't envision a scenario in which this motor wouldn't be complete overkill for my purposes. Now I'm wondering if I should've just gotten one of Traxxas' 540XL motors that they use in the new Maxx truck. My goal was to get equivalent power in a brushless motor, not a huge increase in power.

 

[rockhugger]

The longer can will add more torque (AFIK). Summit has big heavy tires and 1600kv is what is the xmaxx for comparison (only larger motor). Your success may be largely based on controlling your throttle finger, you've math'd pretty well here and reached your own conclusion from the looks of things. You could likely adjust your gearing due to the added efficiency of the BL motor. "thumbsup" Looking forward to your results. A summit has been on my radar for many years....

 

[Sammy_Yay]

@fyrstormer hey brother, I realize that it's been quite some time, but have you ever seen this build through? With that setup? Regardless, what was your outcome and concluding thoughts?

Sent from my SM-N975U using Tapatalk