For your viewing pleasure (or, if we’re lucky, fear), I’ve posted a few photos in the robot gallery of our team’s triple-motor gearbox. In response to a post in the TechnoTank thread about whether three motors help, our drive system this year is certainly a vast improvement over last year (where we had a drill motor and a custom gearbox on each side). I don’t think we have ever managed to stall the motors this year, we have never once flipped a circuit breaker, and we can run the motors a lot longer without them getting hot. Anyways, the pictures:
Thats impressive, but how much dose it really help? Don’t all the motors start to work against themselfs after a point? It seems to me that 2 is the right number of drive motors, but hey, if it helps put em in. Either way thats a great looking gear box.
Trust me…the more motors the “better”…this year using 6 motors we have noticed a very large increase over our previous years using 2 motors or even 4… we’ve also noticed a considerable increase in speed and power…
I’ve gone through the same discussion (about the motors fighting each other) with my team numerous times, and I’m quite certain that they don’t - and the more load you apply, the less likely it is that the motors will fight each other. Obviously, all the motors are going the same direction, so the only way they could fight each other would be if one was actually being pushed by the others faster than it “wanted” to go. Therefore, if a motor is going less than its free speed (where it “wants” to be), it is not being fought against. Under even a little bit of load, none of the motors are approaching their free speed , so they are all contributing driving force. Perhaps some are contributing a little more than others, but that’s really not a problem. My only initial worry was that we could flip the main 60A breaker with six very powerful motors driving at once, but we have tested quite rigorously and never once done it.
*Originally posted by ianmackenzie *
**I’ve gone through the same discussion (about the motors fighting each other) with my team numerous times, and I’m quite certain that they don’t - and the more load you apply, the less likely it is that the motors will fight each other. Obviously, all the motors are going the same direction, so the only way they could fight each other would be if one was actually being pushed by the others faster than it “wanted” to go. Therefore, if a motor is going less than its free speed (where it “wants” to be), it is not being fought against. Under even a little bit of load, none of the motors are approaching their free speed , so they are all contributing driving force. Perhaps some are contributing a little more than others, but that’s really not a problem. My only initial worry was that we could flip the main 60A breaker with six very powerful motors driving at once, but we have tested quite rigorously and never once done it.
-Ian Mackenzie **
I disagree, forcing a motor to go faster then it wants to takes work, i’ve had this disscussion with transmission engneers. My team’s robot will have 4 drive motors (if we finish the drill mounts) and we were VERY careful to mechanically match the rpm’s. We will still have to fine tune them with electronics.
I think the more motors the better, but any more then 6 would be overkill. It’s not worth the fuse’s and speed controlers (not to mention you run out of motors to put in there).
Let’s say we have two different motors mounted to the same drive shaft. If they weren’t connected, let’s say the RPM’s are a slight mismatch. For example purposes:
Motor 1: 100 RPM, 100 N-m torque
Motor 2: 110 RPM, 90 N-m torque
What will the result be? This is not easily intuitive… But the way you do this is you treat one of the motors and how fast it wants to spin the shaft as your frame of reference. For example, if motor one is our frame of reference, we have motor two wanting to spin at 10 RPM with 90 N-m torque. Since power = torque x speed, we have 10 * 90 units (900 units) of power being applied to motor one by motor two. If we look at it from the perspective of motor two, motor one wants to spin at -10 RPM at 100 N-m torque, or 1000 units of power. Thus motor two is losing 1000 units of power to motor one. These motors are acting against each other to a certain extent, and 1000 + 900 = 1900 units of power are being wasted.
HOWEVER, the net result is still great! With both motors combined, we have 100 *100 + 110 * 90 units of power, or 19900 units of power. 1900 are lost, thus our NET POWER OUT is equal to 18000 units. If we compare this to simply using one motor, motor one, we gain 8000 units of power by adding the second motor. Although it is true the RPM is mismatched and the motors do work against each other, for the most part they are still working towards the same goal, and we have a 180% increase in torque.
