Motor / Speed Controllers
There are two main technologies here. Brushed and brushless. Brushed equipment is DC based where as Brushless is AC based. The table below gives a comparison between the 2 technologies:
For touring cars running brushed motors, you must make sure your speed controller can take a motor of the appropriate “T” number. The “T” relates to the number of winds on the rotor, the lower the turns, generally the faster and more powerful the motor is so the more current it will draw – the speed controller needs to be able to handle this current otherwise it will overheat. Brushed systems are not really used in competitive racing anymore but some mini and GT12 classes still legislate their use.
For brushless equipment, there is a lot to know about but we will try and make it easy! There are 2 main subsets, sensored and sensorless. The sensorless systems can be cheaper but are not as fast, most people use sensored systems for touring cars – so much so, we won’t cover sensorless systems any further here.
Within the band of sensored systems there are then 2 main differences between the types of speed controllers available. The basic “sportsman” speed controllers offer fixed timing which is easier to setup and set the gearing so you don’t overheat the motor – these are normally called “Sportsman” or “blinky” speed controllers – blinky comes from the fact that when in sportsman mode, there is a light that blinks to indicate it is in such a mode. The newer competition speed controllers have what is called “timing on the fly” or “boosted” or “supercharged” or “variable timing” which is where you have several settings that determine the amount of timing applied to the motor depending on its rotor speed. Timing on the fly systems can be very quick but they take a lot of practice and time to get a software setup and gearing ratio adjustments to obtain optimal motor temperatures. Similar to brushed motors, the lower the T rating of the motor, the more powerful it is. Due to the extreme speeds brushless systems can run at it is important to never rev the car off the ground other than with slight power to check it works – other wise the motor can be damaged (you can also rip the tyres apart!). It is possible to buy speed controllers where you can change the firmware on them so that you can buy one unit and change the firmware so it has either has or does not have timing on the fly capability. Why is this a good idea – well it means you can use the speedo in different classes – for example you could start off in Spec class with a non boosted speedo and change firmware to boosted if you progress to open modified.
What does timing do? Well the lower the timing, the more torque the motor can generate but the lower the top speed will be. This means the motor will be quick out of the corners when torque is needed to achieve the acceleration levels required but when you are on the straights, the speed will be lower. “Sportsman” type speedos give the option to give the motor a fixed amount of timing which is applied no matter what the speed of the motor is and so is always a compromise between torque and speed. If you put so much timing on to get top speed, you will be very very slow out of the corners. With timing on the fly systems, the amount of motor timing applied is dependant upon the motor speed, so when you are at low motor speeds, the timing can be low but when your speed picks up, the timing can increase to give the top speed as well. It is typical to have more than twice the number of adjustable parameters on a timing on the fly speedo than on a sports man type.
So what do you buy? Well don’t fall into the normal trap, a fast car does not necessarily give a quicker lap time. What you buy depends on what you can afford, what level you want to race at, if you want it to be future proof (as much as electronics can be these days) etc. It is also helpful if someone at the club has a similar speedo so they can help with settings. Before you buy, make sure you get what you need to update firmware and change settings as most of the timing on the fly systems need a separate program card or need to be connected to a laptop to program!
There are literally hundreds of possible speed controllers / firmwares etc so it is worth taking a little time over your selection. If you are using LIPOS make sure the speedo has a LIPO mode other wise you need to get a lipo cut out, this is to prevent your lipo voltage getting too low when you are running (a potential issue on long runs or using low powered lipos for racing).
Speed controllers tend to have a continuous current rating advertised. The table below gives you an idea of what continuous current rating speed controller you should look at for the different classes (note peak current can be 4-5 times the continuous rating – make sure you are looking at the correct number!). These obviously depend on what motor you are running but I have based it on something sensible!
