Chief Delphi - Lifting mecanisms

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- - Lifting mecanisms (http://www.chiefdelphi.com/forums/showthread.php?t=79901)

Matt C

13-01-2010 16:45

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.

Kevin Sevcik

13-01-2010 17:21

Re: Lifting mecanisms

Quote:

Originally Posted by ttldomination (Post 898012)

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

*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.

JosephBurns35

13-01-2010 17:50

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

nskerven

16-03-2010 15:26

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.

IKE	16-03-2010 15:35

Re: Lifting mecanisms

Quote:

Originally Posted by nskerven (Post 938125)

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 ...

Jimmy Cao

16-03-2010 16:22

Re: Lifting mecanisms

Quote:

Originally Posted by IKE (Post 938131)

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.

IKE	16-03-2010 16:44

Re: Lifting mecanisms

Quote:

Originally Posted by Lostmage333 (Post 938169)

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.
.

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.

pfreivald

16-03-2010 17:46

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?

qwertyuiop[]\

16-03-2010 18:08

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)

Vikesrock

16-03-2010 18:11

Re: Lifting mecanisms

Quote:

Originally Posted by qwertyuiop[]\ (Post 938248)

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.

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