The choice of a Scaler/Crawler motor can be a difficult one for even the most experienced modeller, especially since this category of radio-controlled model cars knows no crisis and is always coming up with new models and fashions.
All existing types of motor are valid choices because each has its own strengths, and in this article we will explore the most important aspects to evaluate according to the application of your hillclimbing car.
Crawler motor types
There are 3 types of motor used in Scaler/Crawler models, namely
Brushed motors (with brushes)
SD brushless sensored motors (brushless with sensors)
SL brushless sensorless motors (brushless with sensors)
Cogging of electric motors
Cogging is a resistant torque that occurs in some electric motors and presents itself as an irregular or jerky rotation, especially at start-up and during low-speed rotation, which is why Scaler and Crawler models are the cars where this phenomenon is most visible.
Cogging in the brushed motor
The brushed motor is totally free of this defect, so much so that the model can be held stationary, hung uphill with the motor stalled without noticing any uncertainty or irregularity in operation.
Cogging in the brushless motor
The sensor system (SD) is almost cogging-free and can stop and restart without hesitation, like or almost like a brush motor.
The sensorless system (SL) is the one most susceptible to cogging because every time the model stops and restarts, the ESC has to read the EMF return signal and synchronise the phase supply; even at low speeds, this type of power supply can perform poorly.
A practical solution to reduce cogging in SL systems is to adopt a high gear ratio, because even when the model is almost stationary it allows the motor to turn just enough for a good signal reading. Conversely, too high a gear ratio limits maximum speed, which is why the use of SL systems in scalers is often associated with the use of 3S or even 4S batteries, to recover speed that might be needed in other circumstances, such as jumping over a rock.
Purchase costs
When we talk about brushless or brushless SD motors for Scaler/Crawler model cars, we normally refer to motors with 540 or 550 case, also classified as 3650-3652 and 3660 (the latter acronyms indicate the dimensions of the case, (e.g. 3652 diameter 36mm length 52 excluding axle).
The choice of the brush system is undoubtedly the most economical solution for both motor and ESC. The cost of a good SD brushless combo can even double that of a similar brushless combo.
SL brushless motors for scalers are almost always rotary can models (outrunners), which have more torque and less revs than fixed can motors (inrunners) for the same power and are therefore more suitable for the scaler category. There is a wide range on offer and it can also be a fairly inexpensive and slightly superior choice to a good brushless system, as long as you are familiar with the technical characteristics of both the motors and the regulators (ESCs), which must be matched wisely and sometimes also require ESC programming.
Weight
For the 540 and 550 brushless or brushless class systems, the weight is comparable and between 180 and 210 grams, excluding ESC.
The brushless SL outrunner systems, on the other hand, can boast unbeatable lightness, with a reduction of at least 100 grams compared to their brushless and brushless SD siblings.
Waterproofing
Brush and brushless SL motors can be considered waterproof as long as they are subjected to trivial splashes of water. Immersion is not recommended, however, as the water may contain abrasive dirt.
SD brushless motors are susceptible to damage if water enters the sensor assembly. Therefore, they can only be used in a wet environment if declared waterproof by the manufacturer.
Regulators (ESCs), on the other hand, of whatever type, are not waterproof unless they have been manufactured according to specifications.
Power consumption
It is almost nonsensical to talk about consumption in a scaler model, because this is a category with very low power output. But at least from a formal point of view, it should be emphasised that the brushless motor has a higher consumption than a brushless motor of equal power, due to the friction of the brushes on the commutator.
It is also true, however, that to appreciate an advantage in terms of fuel consumption, a brushless combination must be well tuned and well configured. When, for example, cogging becomes evident, efficiency is greatly reduced and heat and battery consumption increase.
Conclusions
As is evident, there is no universally valid rule for the choice of a motor in scaler models. It is therefore necessary to orientate yourself according to the expense you wish to incur or the use you wish to make of your RC car, taking into account the technical characteristics and the pros and cons that characterise each type of motor.
Comments