How many seconds to climb the rope?

[MrForbes]

I guess there are a couple different ways to look at what is "proper gearing". If you design it so the motor has to run at maximum power, then you don't have much of a safety margin. If you design it so the motor runs at maximum efficiency, then you will still be able to climb at maximum power when things go wonky...like a low battery at the end of the match, more friction than you anticipated, etc.

[Chris is me]

I don't think the number of seconds from "secured the rope but haven't left the ground yet" to "up in the air pressing the button" is particularly important. The time from starting the entire rope climbing process to the end of it, somewhat.

I don't think it's the worst thing in the world to have a climber that takes a couple seconds to get up there, but ideally your entire climb cycle should be under 10 seconds at least.

Gear your climber conservatively. Max power for these motors is usually well over 40 amps and leaves little margin for error or for your breakers to not trip. You also have to consider you are climbing when your battery voltage is at its lowest.

[Ari423]

Originally Posted by Chris is me

Max power for these motors is usually well over 40 amps and leaves little margin for error or for your breakers to not trip.

I'm going to go ahead and disagree with this statement. I just did the math and the only two motors that are over the 54A limit that a 40A breaker can provide indefinitely at max power are the CIM and 775pro. Both of these draw about 65A. For all other motors, you can run them at max power (i.e. 50% free speed) indefinitely on a 40A breaker. The BB-RS775 is close at 50A, but I wouldn't be worried too much because the breakers don't trip immediately, they take a few seconds, especially when the current is only slightly over the limit.

Those three exceptions aside, you can run all of the other motors at max power without really worrying about tripping breakers. Whether you actually want to depends a lot on how big of a FoS you want and what options you have as far as motor choice.

[Chris is me]

Originally Posted by Ari423

I'm going to go ahead and disagree with this statement. I just did the math and the only two motors that are over the 54A limit that a 40A breaker can provide indefinitely at max power are the CIM and 775pro. Both of these draw about 65A.

54A is on the very outer edge of the current breaker tolerance band; I would not rely on your mechanism being able to consistently pull exactly 54 amps. If you have a slightly out of spec breaker, or your mechanism has marginally more load than you expect (various ineffiencies, etc), you'll have a bad time, especially since that doesn't even factor in voltage drop. It is reckless to give people the general advice that they should expect and plan for their motors to draw 54 amps under design load.

With that all said, the other motors with max power drawn at more than 40 amps include the mini-CIM, BB-775, BB-550, etc. Basically, any motor you should be climbing with.

The other danger with gearing at exactly mass power is that once you tip over that critical point, you're getting less and less efficient performance out of your motor as your load increases.

You also don't want to run fan-cooled motors at 50% stall generally; it's not great for them to run that hot. Be conservative here; you're not going to win the World Championship with a climb that's 300ms faster than your opponent if your motors smoke.

There's some benefit to climbing quickly, to a point, but this isn't a race, and you just want to complete it reasonably quickly. You can easily get there with 1 CIM / 775pro geared conservatively for less than 40 amps under load - add a second if you really want those sub-2s climbs; don't overwork 1 motor.

[bobbysq]

Originally Posted by s_forbes

What is the diameter of that spool that the strap is winding around? Also it sounds like you have some kind of speed control on the motor, have you tried going 100% throttle as it climbs up?

With a 100:1 reduction on a 775 and a full weight robot, you'll start to draw more than 40 amps when you're spool reaches about 2.5" in diameter (which is kind of the limiting factor with the breakers, but they won't pop immediately if you go over 40 amps). With that size of spool it should take just over 2 seconds to span the distance from the top of the robot to the davit.

I believe we weren't gunning it, but we were going maybe 80%-90% speed. The tube was a PVC pipe around 1.5" in diameter. Our test rig actually used an ATC fuse box, so it only had a 30A breaker and we were surprisingly able to stall it for a little while. The full robot will probably use a 40 amp breaker though.

[JesseK]

Time to pony up and make it official. Go vote!

[Ari423]

Originally Posted by Chris is me

54A is on the very outer edge of the current breaker tolerance band; I would not rely on your mechanism being able to consistently pull exactly 54 amps. If you have a slightly out of spec breaker, or your mechanism has marginally more load than you expect (various ineffiencies, etc), you'll have a bad time, especially since that doesn't even factor in voltage drop. It is reckless to give people the general advice that they should expect and plan for their motors to draw 54 amps under design load.

With that all said, the other motors with max power drawn at more than 40 amps include the mini-CIM, BB-775, BB-550, etc. Basically, any motor you should be climbing with.

The other danger with gearing at exactly mass power is that once you tip over that critical point, you're getting less and less efficient performance out of your motor as your load increases.

You also don't want to run fan-cooled motors at 50% stall generally; it's not great for them to run that hot. Be conservative here; you're not going to win the World Championship with a climb that's 300ms faster than your opponent if your motors smoke.

There's some benefit to climbing quickly, to a point, but this isn't a race, and you just want to complete it reasonably quickly. You can easily get there with 1 CIM / 775pro geared conservatively for less than 40 amps under load - add a second if you really want those sub-2s climbs; don't overwork 1 motor.

When I'm designing mechanisms I like to use all of the edge case values and incorporate my FoS into the load. For that (especially with climbs not taking longer than 6s) I would use 54A and make sure to include a significant FoS in my load. If you do it differently, that's fine.

I agree with pretty much everything you are saying; my team's climber is powered by 2 BAGs which gives us plenty of power and the ability to add more if needed by switching to a different dual-motor VP input. That being said, while I agree a blanket statement saying you can run all the other motors at max power probably wasn't the best idea, a blanket statement that you shouldn't run any of them at max power isn't really called for either. I'd be interested in seeing data about running fan-cooled motors at half speed. There are a lot of factors here that need to be considered on a case by case basis imo.

[Gravity]

Our robot this year is pretty darn lightweight. We plan on climbing in under 5 seconds.

[Chris is me]

Originally Posted by Ari423

That being said, while I agree a blanket statement saying you can run all the other motors at max power probably wasn't the best idea, a blanket statement that you shouldn't run any of them at max power isn't really called for either. I'd be interested in seeing data about running fan-cooled motors at half speed. There are a lot of factors here that need to be considered on a case by case basis imo.

One blanket statement results in people tripping breakers or damaging motors. The other results in reliable mechanisms that err on the side of too conservative. I don't think they're really equivalent.

BAGs are an interesting case here; they should be more durable than fan cooled motors and stall at like 75 amps or so. I just assumed people would go for more mechanical power if they are interested in optimal solutions (you can do a 775pro / CIM / mini at less-than-max power that outperforms a BAG even on a less ideal point on its motor curve).

[qscgy]

The mean of the poll responses seems to be 3-6 seconds. Now I feel bad about our 8 second climb. Of course, from what I've seen, most climbers have CIMs. We are using a single Mini CIM with a 50:1 VersaPlanetary, although we have space to put 2 in a 2-CIM VersaPlanetary mounting if those few seconds look like they will make a significant difference.

[JesseK]

Originally Posted by qscgy

The mean of the poll responses seems to be 3-6 seconds. Now I feel bad about our 8 second climb. Of course, from what I've seen, most climbers have CIMs. We are using a single Mini CIM with a 50:1 VersaPlanetary, although we have space to put 2 in a 2-CIM VersaPlanetary mounting if those few seconds look like they will make a significant difference.

There are many factors that go into climber design, including how much space and power you can allocate it. If it goes up every match in 8 seconds, I'm sure you'll find a valuable home on an alliance.

If climb time is still a concern, then you may be able to replace the MiniCIM with a 775Pro through a VP CIM-ile and adjust your gearing slightly.

Yet in our testing, it is time to line up and time for the rope to catch that actually takes the longest. From liftoff to touchpad ours is under 2 seconds. Yet from rope touch to rope engagement it's about another 2 seconds. There are still a couple of things we can do to minimize it further, but our target is under 4 seconds (place gear at 5 seconds remaining).

[Chris is me]

Originally Posted by qscgy

The mean of the poll responses seems to be 3-6 seconds. Now I feel bad about our 8 second climb. Of course, from what I've seen, most climbers have CIMs. We are using a single Mini CIM with a 50:1 VersaPlanetary, although we have space to put 2 in a 2-CIM VersaPlanetary mounting if those few seconds look like they will make a significant difference.

I just want to let you know that if you're referring to the 2-motor VersaPlanetary adapter, that adapter is not compatible with the mini-CIM as the motor is much larger than what the adapter is designed for. If you are actually referring to the BAG motor instead of the mini-CIM, then the adapter will work with that.

I don't think a fast climb is incredibly important at all levels of play this year; a consistent climb is far more valuable if that's the tradeoff you're making. Since you're using a VP, you can always try a smaller reduction later if you want, such as 40:1, and see if the motor still does a good job lifting with that amount of torque. (I don't know if it will, I'm just throwing it out there).

[Hgree56]

Originally Posted by qscgy

Of course, from what I've seen, most climbers have CIMs. We are using a single Mini CIM with a 50:1 VersaPlanetary, although we have space to put 2 in a 2-CIM VersaPlanetary mounting if those few seconds look like they will make a significant difference.

Our team is using miniCIMs also. Granted, we are using three, but it's a 10.71:1 gear box. We are getting a ~4.5 second climb consistently.

[scott.smith]

We are using a PTO, so we are looking at 1 second for climb once it grabs on.