Fozzy D

What does boosted esc mean?

ibuffo

Firstly a basic description of a brushed motor: In a brushed motor the permanent magnets are glued to the can, and the rotor – the part of the motor that spins – contains windings of wire (called the armature). It works by inducing a magnetic field in those windings, turning them into electro-magnets that attract/repulse the permanent magnets at different points in their spin. To do this electric current is passed through the brushes, and into the commutator which is connected to the wires. The commutator is split into 3 parts, so that only two may be in full contact with the brushes at any one time.

Because the current supplied to the motor is direct current, one brush is positive and the other negative, and the magnetism induced in the different windings flips depending upon which corresponding tab on the armature is in contact with which brush. This flipping is the reason the magnets don't just attract each other and freeze the motor in position. The angle the brushes make to the permanent magnets is called the timing. By advancing the timing the attraction/repulsion of the electro-magnets is induced at different points in the cycle. If the rotor is spinning slowly this is a hindrance and makes the motor less efficient. If the rotor is spinning quickly however, then its momentum means this arrangement is more efficient and the rotor will ultimately spin faster.

Ok, now that we've gone through that detour on a brushed motor, let's talk about brushless motors. In a brushless motor the permanent magnets are on the rotor, and the windings of wire are on the can (or stator). So, now we don't have to get the current into the spinning part of the motor things are much simpler (at least with fast electronics). What happens in a brushless motor is that different amounts of current are supplied through three wires. Basically one supplies positive current, one negative, and the third is ground at any given time. This makes two of the windings of wire into electro-magnets that once again attract or repulse the permanent magnets and the rotor spins as a result.

The trick with a brushless motor is how does it know what current to send to each of the 3 different widings of wire (or coils). Well, in a sensorless motor one of the coils, one that is not getting any current supplied, is used as a sensor. A back-emf (small current) is induced in that coil by the spinning magnet. This tells the speed control where the rotor is and it sends out current appropriately.

However, a sensorless motor is very bad at starting up and running at low speed. This manifests as a stuttering of the motor or "cogging." It's very difficult to use the back-emf system to work out where the rotor is initially. A sensored motor gets around this by using Hall effect transistors as sensors – this is just a device that a current is induced in when it is exposed to a magnetic field.

I hope that mostly makes sense.

A zero timing ESC follows a 6-step pattern where the input of the Hall sensors corresponds to a very particular phasing of the electro-magnets. I know that doesn't make much sense without a diagram, there is one in the AARCMCC rules in Section 11 (http://www.aarcmcc.org/docs/AARCMCC%...les%202011.pdf).

The thing is though that by dynamically changing the timing on a brushless motor you can have a motor that has small or no timing when it is running slowly, and high timing when it is running faster, giving you a fast and efficient motor at high and low speeds (if you see what I mean). This is the bit that Phill is going to teach us to do well. It is important for Onroad Stock and in Modified classes.

Timbulb

iTrader: (2)

A boosted ESC simply has a "boost" feature, kinda like turbo boost. You can set the boost to kick in at a certain RPM for a noticeable boost of speed.

Fozzy D

Do Linear and Exponential curves have anything to do with it?

Dave H

No, exponential typically refers to the throttle curve, how sensitive the throttle is at low throttle vs. high throttle. A transmitter adjustment normally, has no real impact on the acceleration or top speed capability (perceived maybe, but not real). Typically used as an aid to get more control over a partial throttle condition, and is simply a personal preference.

A boosted ESC in it’s simplest terms is just a way to make a rules limited stock motor faster than it would be otherwise.

In detail it can be a combination of the previous posts. The timing advance is varied with RPM, and then some extra might be added after a time at full throttle (or perhaps a RPM). I think some brands might use the term boost for the full throttle extra, perhaps what Tim was referring to, but the term is used generically too for the overall concept, both forms of timing.

Boost ESCs are sometimes referred to as ramping, as the timing ramps up with RPM. Dynamic timing is another as mentioned earlier.

Classes that outlaw this mode are frequently called “blinky”, as the ROAR rules require the ESC to clearly display it is operating in a no boost mode, frequently indicated by a blinking light.

Fozzy D

Wow! The thank you guys for the response. Timing and boost are the same thing. I never knew. This afternoon I tweaked the white "Blinky" on my esc. Not too much. Just enough...Got some pretty good speed.