Lifting mecanisms
 

My team is looking at a winch with some sort of telescoping mecanism to get a hook up to the top of the platform.

does this sound logical? and do any other teams have ideas for lifting their bots up on the tower?

Re: Lifting mecanisms
 

Sounds reasonable.

I'd like to encourage teams this year to go back and look at the last two times there's been hanging: 2004 and 2000.

And, a tip from someone who built a robot to play the 2004 game, make sure that you can get your hook out of places you don't want it and then still hang, if you can. (Examples: the floor, another robot's lightening holes (actually happened once in 2004), the bar itself, the ball return, a tower pole...)

Re: Lifting mecanisms
 

You are going to need a lot of power to lift even 70 pounds up there. The process will be slow, you may have a hard time doing that within 20 seconds.

Personally, I have none at the moment. I have gone from pneumatics, to scissor lifts. I'm still considering the best way.

-Rion

Re: Lifting mecanisms
 

2 FPs with a stock gearbox and a 3-inch diameter winch directly connected to them is enough power to get a 130 lb robot up quickly, like inside of 10 seconds. That's hook at the bottom to robot at the top.

I've seen some other fast ways too.

(P.S. We have another CIM motor available this year, for a total of 5 maximum.)

Re: Lifting mecanisms
 

Ok. I withdraw my statement then. Now i need to look into other ways to hang the robot. :D
(I seemed to have over looked the extra CIM... :yikes: )

-Rion

PS. Is that a typo or did I over look the weight change limit?

Re: Lifting mecanisms
 

It's not a typo. Back in 2004, there was a slightly different weight rule: 130 max, battery included (and bumpers, if you really wanted them). It wasn't until 2005 that the current 120 lbs sans battery was introduced. (Either that, or I'm a year late and it was 2003/2004 for the change.) I was basing my estimate on one particular 2004 robot.

And the extra CIM happens to be located in <R52-D>.

Re: Lifting mecanisms
 

150lb would be the number to use this year with full weight bot + 20lb bumper allowance + ~10 lb battery

Re: Lifting mecanisms
 

Ah okay, now I'm not so confused.

Ah see, there is my problem. I am on <R08> at the moment. I am not an extremely fast reader...

-Rion

Re: Lifting mecanisms
 

I preferred a van door motor direct driving a 1" spool, but we don't have that option this year. :mad: It is definitely possible to lift a 150 lb robot with motor(s), just remember to think about back driving when the power turns off at the end of the match. ;)

Re: Lifting mecanisms
 

well my dad mentioned the winch on the front of a 4 wheeler to be possible, we would have to adapt it to a cim motor but it should be able to lift like 500 lbs

Re: Lifting mecanisms
 

One could easily overcome this with a simple pneumatic locking mechanism, or even a passive tension powered lock.

Re: Lifting mecanisms
 

You could also use a worm gear.

Re: Lifting mecanisms
 

You would be surprised at how fast some robots made it up. I remember team 501 had such a swift movement for getting up.

And to echo what Eric said, make sure youe hooks are secure on your robot. A lot of teams lost their hooks before they made it to the bar from collisions.

Re: Lifting mecanisms
 

To bring a little more "training" to the discussion... you just have to look at the maximum power of your motors to determine the absolute fastest you can get a robot up.

Power = Work / Time
Work = Force * Distance
so
Power = Force * Distance / Time
or
Power = Force * Speeeeeeeed

The CIM motors max out at 343W = 252 lbf*ft/s

So the fastest an optimally geared CIM will lift a bot is about 1.5 ft/s. Or you lift in about a second.

Mind, this assume you're instantly at the max power point, no friction losses, spherical chickens, the works. But, lifting your robot 20" in, say, 5 seconds is easily doable if you gear it right. The gearing it right being key. Max power occurs at 1/2 stall torque. But I'd really aim for 1/4 - 1/3 stall torque for your full load, for safety and losses and all that.

Re: Lifting mecanisms
 

Remember that the more you gear down the more time it will take to lift...

Re: Lifting mecanisms
 

Kevin,

Our team would like to purchase a set of these spherical chickens. We think that they will be the key to success this year.

While we're at it, we'd also like to purchase any infinite planes of uniform density and frictionless vacuums you may have for sale.

Thanks,
Jared

Re: Lifting mecanisms
 

We've only been able to find planar chickens for sale this year, so we're figuring that the 1.5 second number will end up being around 8 seconds

Re: Lifting mecanisms
 

It's going to be harder than most think to elevate a robot above the platform. As it's lifted the robot is going to swing toward the tower assemble and a bumper will most likely snag on the underside of the platform.

Re: Lifting mecanisms
 

Every time I ask a serious question, I get 6 people telling me to read the manual, search the pdf, browse the FIRST site...

I have looked, read, searched, and found NOTHING on spherical chickens. Are they available from AndyMark? They were not on the kick-off inventory list.

Thanks

;)

Re: Lifting mecanisms
 

My students would beg to differ with you on that.

Also, yes, a 1 second lift is unlikely. Mostly because gearing to max power means you stall your motor if you double the load. But c'mon. Aiming for a paltry 12.5% stall torque on a CIM still gets you from 0-20 in under 2.5 seconds. 5 seconds just to lift yourself with a CIM means you're doing something wrong. Using a different motor will obviously be slower, of course. But still, it's just 20".

Re: Lifting mecanisms
 

I have been running some numbers on lifting with a single CIM motor.

Seems perfectly reasonable for a robot to be able to lift itself in ~4 seconds. Now you just need to figure out how high is high enough to hang (keeping in mind you need to get down without powering on the bot, and also staying in place when power shuts down).

Remember to consider the current being drawn by the CIM while your lifting. Gear down too much and you will lift too slowly, but not enough gearing and you will blow your breaker. We are limited to 40 Amps continuous load per motor.

Hope this is helpful,
Rob

Re: Lifting mecanisms
 

This was brought to our attention with the idea of a winch, and frankly, I'd agree that this could be a huge problem.
We're now considering something other than a winch that we saw in 2007 by many robots.

Re: Lifting mecanisms
 

As long as you don't center the robot in front of the tunnel (keep your bumpers up against one of the poles) this shouldn't be a problem.

Re: Lifting mecanisms
 

During the finale, robots can come out into and around the bumper zone, and with an unlimited number of servos, the top tier teams will easily be able design a mechanism to prevent bumper snagging.

Talking with my physics, he has assured me that using a CIM to lift the robot would definitely suffice, and it'd be fast too.

And for those who are considering a worm gear, a worm gear will rip itself apart before it goes against the motor, but they are extremely slow. And I mean EXTREMELY slow. IMO, it'd take at least 10-15 seconds to get up beyond the 20".

Good Luck,
- ttl

Re: Lifting mecanisms
 

Any thoughts on gear ratios? We're looking at using a CIM with a planetary gearbox from Banebots and a spool winch, but the only ones we've ever used are 12:1 reduction -- probably inadequate for the job...

64:1? 128:1?

Advice would be appreciated.

Patrick

Re: Lifting mecanisms
 

Patrick,

There are many things to consider when selecting your gear ratio.

Specifically, what method are you going to use to lift yourself? I presume a spool and cable system of some sort. So you need to consider the radius of that spool. Changing the radius of the spool will affect the linear speed of your cable system, as well as the required input torque to lift the robot.

If you were to share a bit more information and specs on your proposed system, I am sure someone could give you more clear advice on what gear ratios to run.

Also consider how the mechanism will back drive after power has been cut off.



That aside, something I have not heard much about yet, is if anyone plans for their lifting mechanism to be able to work with multiple robots hanging off their bot.

Rob

Re: Lifting mecanisms
 

Also, Banebots cautions that the higher gear ratios on their planetaries are for speed reduction only. A CIM is capable of tearing the gearbox apart if the shaft is too heavily loaded. What that load is, they don't say.

Re: Lifting mecanisms
 

I personally wouldn't use a CIM on a BB planetary to hold high loads, as I've heard lots of stories about gearbox failure. Perhaps Andymark's GEM500s are worth a look?

Re: Lifting mecanisms
 

While checking the Harbor Freight web side for cheep winches to play with (hint hint) in the search was a couple come-along. The thought of powering one of these with a pneumatic cylinder briefly crossed my mind. I might have to try that just for kicks.

Re: Lifting mecanisms
 

Team 2508 is planing on a robot that can pickup two other robots using a forklift like device to pick them up, but we are still sketchy on how we are going to lift all of the weight off of the ground.

Re: Lifting mecanisms
 

http://media.atc.wpi.edu/News/Events...errage2004.wmv

In 2004, 190 had a telescoping arm/winch system.
The cable controlling the telescoping action was a light weight line, that only had the weight of the telescoping arm applied to it. The weight of the entire robot was lifted by a second steel cable. These were both powered/spooled by the same motor.

Re: Lifting mecanisms
 

*ahem* A 30:1 reduction with a 2" pulley will lift a bot in under 4 seconds. In fact, a 2" pulley needs at least a 14:1 reduction just to get to half stall torque. So you need a reduction in the worm gear range unless you're using extremely small pulleys and beating up your motor.

Re: Lifting mecanisms
 

picking up other robots would be cool but how would you center the weight of your own robot so that you wouldent swing on the bar. when you try to pick them up
we are also looking at using a spooled wire and winching ourselves up but the problem is getting the arm that deploys the wire to fold up small enough to fit through the tunnel

Re: Lifting mecanisms
 

What would be the safest amount of weight a single CIM Motor could lift 20"? We can easily lift ourselves in just a few seconds but I don't know how hard it will be for the motor to lift us and a second robot at the same time.

Re: Lifting mecanisms
 

3 sec x 200 watts is 600 Nm. A full weight robot is about 667 N so,
You could lift 1 robot 0.9 meters or 2 robots 0.45 (17.7")

Of course you need frictionless bearings and what not...

CIMs are somewhere between 200 and 300 Watts depending on battery voltage and ...

Re: Lifting mecanisms
 

A fully loaded robot (120 + battery + bumpers) is closer to 150 lbs, which would put you closer to 750N

But that's a rather small difference.

What's important to remember is that although the PEAK power of a CIM is over 300W (I think), that requires it to be run at ~40% stall torque. If you run at at ~80% stall torque, you'd probably not even get 100W of electrical energy out of it (but you would get tons of thermal =D). So, although on paper the CIM has plenty of power to lift in 3 seconds, you need to effectively use that power.

Re: Lifting mecanisms
 

1lb=4.448N ... 150*4.448=667.2N...
Yep small difference indeed. ;)

Agreed on the importance of effectiveness. Not only proper gearing, but don't forget real-world losses. 1-5% per gearstage and/or chain drive. Properly designed and supported systems can get quite efficient. Gearboxes made with hand drills and drill-presses often are not.

The 200W is quoted off of MK's motor database that uses 10.5 volts from a power-supply. Yes your battery may be as high is 15 volts (300W), but by the end of the match, with a high load, I wouldn't count on it.

Re: Lifting mecanisms
 

We had no problem lifting ourselves in about four seconds with a single CIM on a 4:1 Banebots plus a four-start screw for reduction. (We engineered it for a 3:1 gearbox, then put on the 4:1 just in case).

Wouldn't a more effective strategy be to lift yourself, have something mechanical lock into place, and then let the other robot use their own lifting mechanism?

Re: Lifting mecanisms
 

2foot long 2in bore pneumatic cylinder

60 psi * 1in radius * 3.14 ~ 188 lbs of lifting.

problem solved. if u already have a pneumatics system in place on your robot or can afford the weight. i can see a lift in the sub second range (with enough accumulators on the robot)

Re: Lifting mecanisms
 

It's not nearly that simple...

The air usage of such a cylinder is a huge issue. Also, retraction force is less than that theoretical value, and if your robot is dragging up the tower you may need to provide more force than you expect. Also with that short of a throw you need to make sure to keep the robot pretty level to get it all above 21"

This is not to say it can't be done (I really, really hope it can), just that there may be more to it than first glance would suggest.