We are designing a sumo bot and would like to ask for your input on the topic of picking the best electric motors for the job.
For those not familiar with Sumo bots: They are a type of autonomous robot created for competitions where two competing robots are placed in a circular ring and must push their opponent out to win. The maximum mass, width and depth are defined by category, while height is unlimited. We will be building a bot for the Mini Sumo class, which sets the limit at 500g and a 10x10 cm footprint, like the robots in this video.
It is desirable to have a motor that creates just enough torque to make use of all available ground friction while static (such as in a pushing match with another robot), while also having good acceleration and top speed, so that when the opponent is detected at range, maxium momentum can be developed before impact.
DC motors are a popular choice and there are a few advantages I can see, one of which is that manufacturers specify stall torque and freewheel RPM, which combined with a wheel diameter can give an estimate for forward ground force, accceleration and top speed. Geared DC motors are easy to find, so we are spared having to make our own transmission.
On the other hand I am considering brushless motors as they seem to offer much greater power in a smaller package, and also have high speeds. My concern is that there doesn't seem to be a way to know how much torque to expect, causing fear that it might be inadequate, or that we will need to build a pinion sprocket transmission into the robot. Also, is my understanding correct that they would have to be sensored motors and ESCs, because of regular stalling during fights? Still, the low weight and high power make brushless seem like a tempting option.
So what is your take on this? Could brushless be a strong option or is it not worth the hassle, and we should stick to the tried and tested brushed DCs?
Thank you for your time.
OK, so I've been trying to figure out brushless dc motor sizing and I just don't get it. Can someone in simple terms explain how to get torque values on a brushless motor? I made the assumption it was a hp equivalent, i.e. watt/746 = hp. But that doesn't seem to be the case. And I really don't understand why you would rate a motor in volt per rpm. Why do I care how fast it will go at 2v when I don't even know if it can spin the necessary load at any speed?
Or another way to phrase this, does reactive power loss affect a DC brushless motor?
From what I learned in circuits 2, the reactive power doesn't affect a motor in terms of efficiency, but we want the PF to be close to 1 because the power meter reads W, not VA.
Given some supply which can only provide so much power, I have to imagine that the reactive power loss in a very long cable means the motor gets less power. Conservation of energy says this is the case.
However, torque is only proportional to current. And in my simulations, the current remains the same.
So where is my misunderstanding?
there is tutorial video about this topic in the matlab website, but I can't seem to find the file anywhere. If there is anyone has the file I would really appreciate it.
https://www.mathworks.com/videos/pid-control-of-a-brushless-dc-motor-1523009772696.html
Hey!
I have a system that uses a brushless DC motor (24V at 0.1 amp average current). I measure RPM of the motor in order to perform feedback control. Here is my question:
I want to be able to detect and measure degradation and failure of the motor. Is there a need to actively measure the current drained by the motor or can all types of failure and degradation be detected and measured by RPM measurements alone? Will current stats provide some information that RPM stats can not and v.v. ?
Hey!
I have a system that uses a brushless DC motor (24V at 0.1 amp average current). I measure RPM of the motor in order to perform feedback control. Here is my question:
I want to be able to detect and measure degradation and failure of the motor. Is there a need to actively measure the current drained by the motor or can all types of failure and degradation be detected and measured by RPM measurements alone? Will current stats provide some information that RPM stats can not and v.v. ?
