Competitive Motor Options

Motor Talk
#1

What am I looking for in a competitive motor?
I am running a 12s Li-Ion setup with plenty of discharge available. From my understanding, everything will run cooler if I opt for a given wattage at a higher voltage/lower current, and I see a lot of the top karts running 12 or even 13s packs. Hopefully that variable can be set aside.

Brushless seems like the move here.

The motor controller is undecided. VESC scares me a little bit, but then again, I have done BLHeli_S and BLHeli_32 tuning for combat robots.

Current thought process
My best guess is that because of the 30A fuse limit, it’s better to have a system capable of shooting past that in bursts. The current plan would be to monitor the temperature of the fuse at all times so our driving style can change appropriately. It’d at least let us open up on the straights when the current draw starts to come down.

Because I am stuck at 48v and a 30A fuse, motor efficiency seems like the key to extracting as much as possible from a given wattage.

In combat robots, I am familiar using high kv motors with gear reductions when needed because it’s more power dense. Looking at forums talking about efficiency for R/C planes, they talk about using a high voltage/low kv motor to spin a large prop for the most efficiency. High RPM setups aren’t as efficient.

Applying that to a kart, it sounds like getting a high torque motor and running less of a gear reduction will be the key. (Of course, I’ll still gear the kart to accelerate quickly, but it’s the difference between 5000rpm 2:1 and 2500rpm 1:1.)

A preference is to avoid hall sensors, but something tells me that’s going to be necessary if I go this low RPM high torque route.

Given that this is brushless, the answer I’m dreading is that I’ll extract the most motor efficiency out of ESC tuning, but I’m open to it in the name or learning new skills and not getting lapped by the leaders.

Is this the right line of thinking? Any suggestions?
I’m not opposed to the idea that most of the stuff I mentioned might be for miniscule gains not really worth chasing. I’d love a simple motor setup if something really isn’t worth it. I just want speed too. lol

#2

Hey,

I suck so I might not be the best to give advice, but have gotten multiple fourth places hahaha.

Being competitive to me, means staying in the race as long as possible. I would prioritize reliability above top speed. Better to have a fast kart in the a full race than a super fast kart that breaks.

Also, I use a flipsky vesc. In my opinion it is pretty good for the price and very customizable. But you are gonna want really good cooling.

#3

First off totally agreed with the previous comment that reliability is the overall most important aspect. The karts that win are frequently not the overall fastest, particularly when it comes to the endurance race.

As for the question about the controller, yes the motor controller is one of the key ingredients to success. Having some level of bus (battery) current limiting, or better yet dynamic control, is of the utmost importance. You need to control bus current to keep from blowing fuses. The closest you can run the blowing the fuse without going over is where all the power comes from.

Using an off-the-shelf RC style esc won’t work effectively because:
A) They rarely have any battery current limiting
B) Many are for senseless operation and assume little to no system inertia, which is okay for an RC car but no where near correct for a car that is moving a human with a handful of horsepower.
C) Most are not meant for the voltage levels you are talking about, and if they do support 12/13s they are pricey.

Your “standard” to compare against should be the cheapy ebay Chinese ebike controller with some mold modification of its shunt resistor (sometimes can even be ordered directly with the correct current level). That will take the voltage levels you are talking about, provide decent battery current control, and works correctly and reliably in a system with high inertia.

You can move up from there to a VESC or to any number of custom solutions. But IMHO for a new build that is a good place to start.