Quote:
Originally Posted by ICE_Bear
What motors work to lift the weight of a robot? Of course some have to, but we are at a loss as to what we could use.
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Given the correct gear ratio and infinite time, any motor can lift any load.
There's an absolute minimum amount of time any motor could do any amount of work based on the motor's max mechanical power, assuming perfect efficiency and perfect gearing and everything like that. In reality you'll never get close to this speed but it's a good way to get a rough idea how much faster one motor can potentially be compared to another.
Some back of the napkin numbers: You have to lift a 140 pound (63 kg) robot (counting bumpers and battery) about 3 feet (1 meter). This is a change in potential energy of 618 Joules. The work required to do this is thus also 618 Joules (work-energy theorem).
Motor mechanical power is measured in Watts, or Joules per second. Here are some max mechanical power ratings for common FRC motors:
CIM: 336 W
Mini-CIM: 216 W
BAG: 148 W
775Pro: 348 W
So if we divide the work needed to lift the robot by the power of each motor, we will get the
absolute fastest possible time that motor could possibly lift the load. Again, this in real life depends on any number of things that will make the real number fastest, so this is only useful as a basis for comparison:
CIM: 618 J / 336 J/s = 1.84 sec
Mini-CIM: 618 J / 216 J/s = 2.86 sec
BAG: 618 J / 148 J/s = 4.18 sec
775pro: 618 J / 348 J/s = 1.78 sec
What this tells us is, even if we get the perfect gear ratio for each motor, and a 100% efficient gearbox and everything, an optimally-geared BAG motor will take more than twice as long as an optimally-geared CIM or 775pro to climb.
So what motor should you use? Clearly, the higher the power, the faster you may be able to go if you get the gearing right. CIM style motors are generally more durable than fan-cooled motors like the 775pro, particularly if you end up stalling them for any period of time, so they are likely a safer bet. Aside from that, the CIM and Mini-CIM have much more power available than the BAG, so I would use at least one of those. The 775pro can work, but you have to be careful not to stall it.
More on gearing later if anyone's interested.