How Do you Climb the Rope?

[who716]

775 do a nice job lifting the robot quick

[Crew Cox]

Originally Posted by who716

775 do a nice job lifting the robot quick

Careful not to let them stall though they'll burn up quick.

[Ari423]

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.

Shameless plug here. If you aren't sure what motor(s) and reduction to use for your climber (or any mechanism), check out the spreadsheet calculator I just posted here. It lets you vary motor type & number, force, and moment arm and calculates the reduction that will put the motor at peak power output. Then you can check the top speed and see if the chosen motor is strong enough or you need a stronger motor. Technically, any motor will lift the robot's weight if you gear it low enough, but it will be insanely slow if you choose to lift the robot with a throttle motor.

[edong4273]

I believe that our team is gonna try the velcro method, using loop side velcro as our rope and then having a drum on the robot that has hook side velcro.

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.

I think we could be way overshooting what we need, but we are thinking of using 2 bag motors at a 100:1 reduction using a VersaPlanetary Gearbox from VEX.

[Bruceb]

we are currently planning on a 1 inch drum powered by 2 bag motors at 25-1 and a 3-1 belt reduction

[Team 288]

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.

Our team has done the calculations and we have decided to use the Bag Motor for climbing.

[Chris is me]

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.

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.

[Oblarg]

Originally Posted by GeeTwo

We're working four different prototype tracks for climbing. We figured out pretty quickly that securing the rope would be the fiddly bit.

• "Keyhole" (knot)
• "Hook Drum" (loop)
• "Wringer" (plain end)
• "LevelWind" (plain end)

All but "wringer" involve pulling the rope with a winch/drum/spool. Wringer is more like a continuous intake mechanism.

449 would like to assure you that securing the rope via the "hook drum" approach is actually quite easy.