Electronics

Motors: Brushless vs. Brushed

Here’s the differences, pros, and cons of both.

Brushed uses mechanical method to generate current. Current flows through the brushes and those brushes make contact with with a commutator shaft causing the rotor to spin (watered down definition). These motors are measured in “turns”. Lower the turn, faster the motor.

Pros
• cheaper!
• easier to wire
• can switch motor rotation by switching wires.


Cons

• usually needs some maintenance
• more suseptible to wear and tear since it’s mechanical

Brushless uses a non-mechanical method. Instead of brushes generating current, it uses electro-magnets to turn the rotor by turning the magnets on and off in sequence. These are also measured in turns, but are not equivalent to the same turn on a brushed motor. An 8.5T brushed motor is not the same as an 8.5T brushless! Most of us us the kV rating. Higher kV rating means higher power output.

Pros
• more consistent power
• almost no maintenance since there’s no mechanical parts

Cons

• expensive….biggest con of all
• need lipo battery to get the most out of motor
• not all esc’s can take brushless motors

Sensored vs. Unsensored
Go here if you want to know more…novak does a pretty good job explaining it. Just know that the biggest difference with an unsensored motor is that it stutters, or “cogs” at low speeds because it does not know the position of the rotor (as well as other things). Sensored motors are monitored by the ESC..the ESC knows exactly what that motor is doing, which is why sensored motors require a separate sensor wire running to the ESC.

So which is better? If you look at it from a technology standpoint, of course a brushless is better. But you don’t need it to drift well. There are plenty of drifters out there that run brushed. The same applies between sensored and unsensored motors. The XERun system is unsensored and used by a lot of drifters. So do your research to find which is better for you. Note that you don’t need to have a lipo to run a brushless setup. Nimh battery will run fine. I’ll explain all this in the next section.

Battery Types

There are 2 different batteries in an RC car: Nimh and Lipo. By now you all pretty much know NiMh, so I’ll go over lipos. Here’s the pros and cons:

Pros
• provide higher power output to motor
• more consistent power
• does not suffer from “battery memory” (explained below)
• much lighter than nimh

Cons

• usually expensive..but this is changing with companies like Tenergy who sell at almost wholesale prices
• requires a charger that can charge lipos and a balancer unit
• requires a little more care than NiMh. Yes, they can be dangerous, but any battery is if you disrespect it.

“Battery memory” is exactly what it sounds like. Nimh are known for this. As the battery gets older, when you charge a battery it will “remember” the last peak charge capacity and minimum discharge point and use that as a baseline for the next time. This is why you need to fully discharge a NiMh battery every time you run. Lipos are not as susceptible to memory. They also have a slow discharge rate, so if you leave one lying around it won’t discharge by itself as fast as a Nimh. Note, you should never ever fully discharge a lipo. Always store them between 7.2-7.4v charge if you’re planning to not use them for more than a week (thanks TA03, goots). Running a lipo down to 0 risks damaging the battery.

Do I need to balance my battery every time I charge?

No. Although it’s highly recommended to balance when you can. Put it this way, the better you take care of your electronics, the longer they’ll last…unless you crash.

How is lipo capacity measured?

Lipos are rated in mAh (2400, 3800, 5400, etc..). The higher the number, the higher the capacity, and the longer the run time (depending on motor size). Also, lipos can be 2 cell or 3 cell (2S or 3S). Note that IMO, a 3S lipo is a bit much for drifting. Also on a lipo is the “C” or discharge rate. This is how fast the battery can be discharged safely. The higher the C rating (10C, 15C, 20C, etc), the faster the battery will discharge. So in other words, more “punch” at the throttle.

Can I run Nimh on a brushless system?

Yes. Although keep in mind that depending on how fast your bushless motor is, it can drain a nimh pretty fast. Also, once a Nimh hits that point where the charge is low, you’ll notice it on the throttle. Lipos deliver a more consistent output and the power drop off when the charge is low isn’t as dramatic.

Can I run lipo on a brushed system?

Yes…technically you can. I’ve read that grip racers have done this. Although I was always told that it wasn’t recommended, and to be honest I wouldn’t recommend it either unless you knew someone else that has a similar setup.

Picking an ESC (electronic speed control)

The guys can go on and on about different ESC’s. This is the brain of your RC. It controls the throttle, breaks, etc. When shopping for one, you need to figure out the following:

Do I plan to run lipo batteries?
Do I want a brushed or brushless motor?

If you are planning to run lipo (or know you will eventually) it’s important that you find an ESC with a “lipo-cutoff”. The ESC will basically keep track of the batter voltage, and shut down once it’s reached a certain point (usually around 3.6v per cell) . Again, you never want to run a lipo dead. Note that most brushless ESC systems will run both brushed and brushless motors, but the motor limits are different. Most brushless ESC have no limit on the number of turn brushed motor, while ESC’s like the Havok pro have a brushless motor limit of 3.5T.

Servos

Again, there’s lots of servos to choose from coreless, brushless, ball bearing, etc etc…the most important thing that you want to look at when you’re picking up a servo is the size. Not all servos are the same size, so be sure to look at the specs of your chassis to make sure it will fit.

Servo Speed The speed of a servo is measured in sec/60 degrees. Meaning how many tenths of a second it takes for the servo to turn 60 degrees (corner to corner). So how fast is fast? My opinion, servos with a speed of 0.13 sec/60 degrees or faster is pretty damn fast. Most digital brushless servos have this rating and faster.

Do you need a fast servo? Depends. a servo with a 0.06sec rating is pretty quick, maybe too fast. The faster the servo, the more responsive it tends to be when you steer, especially with a digital brushless servo. For noobs, i always recommend starting off with a basic servo, like .17 sec. Get a feel for how you drive, learn how to steer, and then upgrade when you’re ready. The best electronics money can buy doesn’t make you a good driver. It takes practice!

Radio and receiver-the Digital Age

Definitions

Controller:The thing that controls your car
Reciever: the thing that has the antenna that you plug your servo and ESC into.

Digital receivers/controllers are getting more popular for many reasons. If you can afford it, or save up for one, it’s worth the investment. Unlike FM systems, digital systems are less subject to interference, have a longer range, and you don’t have to worry about who is running on your channel. Of course, they’re more expensive. But if you plan on sticking to the hobby, it’s worth it. In my opinion, Futaba makes some of the best controllers out there. The 3PM and 3PL are great controllers, and will last you a long time.

One of our guys, Project-c2 on the forums described digital controllers and recievers like a bluetooth headset. Instead of using crystals to get the controller to communicate with the reciever, they are “paired” the 2 together. In addition, many digital controllers can accomadate more than one chassis. Meaning it’s possible to run more than one RC on the same controller. All you need is another digital reciever (must be the same as the one that came with the controller) or you can swap the one you have into the other one. So if one of your RC’s breaks, you can select your backup with the controller and run like nothing happened. Each kit can be programmed with settings (steering trim, throttle EPA, etc) on the controller so that you don’t need to figure it out all over again. The Futaba 3PM can program up to 10 models.

The thing to remember about any receiver is that its placement in your chassis can affect performance. Try to put it somewhere away from the ESC and power wires, as electrical current creates “noise” that can interfere with with signal. Also, carbon fiber is conducive to static electricity and noise. Try not to place the antenna wire on a carbon fiber part. And NEVER cut the antenna wire…EVER.

Chargers

Just like shopping for an ESC, figure out what type of battery you’re planning to use. And just like controller, this is one of those things that you’re going to want to invest in. A lot of guys buy a charger that can’t charge lipos, and eventually buy a lipo. Next thing you know they have to buy another charger. There are plenty of good, inexpensive chargers that will take all batteries including lipos. Better to get one that can charge something you don’t have now, than to have to buy another one later. Unlike chassis parts, a charger will last a long time, and can be used for different types of RC’ing, whether it be grip, crawling, or flying. So even if you get out of drifting, you can still use it.

Source: dj722@hyperdrift.com