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-   -   Elevator counterweight / constant spring and ability to lift different number of tote (http://www.chiefdelphi.com/forums/showthread.php?t=132158)

lamk 05-01-2015 13:32

Elevator counterweight / constant spring and ability to lift different number of tote
 
It's easy to figure out the counterweight/constant spring if we have only one single load like tubes used in previous year. Now we have to deal with loads that varies from 8 lb to 50 lb. How can we precisely move the elevator up and down and not fried the motor when holding a position. A linear electrical actuator(worm screw) with no back drive will be nice but we don't have the machine capability.

Jon Stratis 05-01-2015 13:43

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Instead of trying to counterbalance, think instead of applying a friction brake of some sort. Try thinking about how you brake a bicycle tire, and see if you can do something like that with your spool that lifts the elevator. Pneumatic would be a great way to generate that braking force without burning out a motor!

vps 05-01-2015 13:43

Re: Elevator counterweight / constant spring and ability to lift different number of
 
window motors, snow blower motors, and van door motors (these have the most torque) have worm drive. Use those.

JDGallagher 05-01-2015 13:51

Re: Elevator counterweight / constant spring and ability to lift different number of
 
CIMs or mini-CIMs with a RAW box from andymark could work well

JesseK 05-01-2015 13:53

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Quote:

Originally Posted by vps (Post 1422032)
window motors, snow blower motors, and van door motors (these have the most torque) have worm drive. Use those.

These are 30 watts or less, meaning they are very slow.

Given lack of machining, I agree with the bike brake idea. Otherwise I would say use a steel punch into a hole in a 1st stage gear in the gearbox, pneumatically actuated. 1538 did this with great success in 2013. Requires some precision machining to line up the punch with the hole though.

Scott Morgan 05-01-2015 13:54

Re: Elevator counterweight / constant spring and ability to lift different number of
 
In the past we've successfully used both bicycle disk brakes and ratchet/ pawl systems to hold loads at position without running the motors.

cmrnpizzo14 05-01-2015 13:59

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Theoretically couldn't you just design for the heaviest weight that you expect to hold? It wouldn't be ideal but if you think about it, 40 lbs is actually quite a small range so it should work.

Sh1ine 05-01-2015 14:12

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Quote:

Originally Posted by cmrnpizzo14 (Post 1422052)
Theoretically couldn't you just design for the heaviest weight that you expect to hold? It wouldn't be ideal but if you think about it, 40 lbs is actually quite a small range so it should work.

Even if you split the difference (0 lbs with no load and 50 lbs full load) and put a 25 lb CF spring your motor would always be working, but at 1/2 the force and 25 lbs should be able to be held by a cim (or bag motor) without too much issue.

nixiebunny 06-01-2015 00:06

Re: Elevator counterweight / constant spring and ability to lift different number of
 
The fusee pulley is one solution. It automagically changes its "gear ratio" as the distance traveled increases, so you can use a gearmotor and optimize its lifting speed for the small stack but still have plenty of torque for the tall stack.

pmangels17 06-01-2015 00:20

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Why not use a worm drive? We used an Andymark Wormbox in 2011 for our elevator with decent success (we had other racking problems irrelevant of the gearbox) and the RAW Box, as already suggested, could work. We actually used a custom worm drive last year to winch back a really heavily loaded catapult arm, but if you don't have resources to custom build, use a COTS worm gearbox. You can mate with a CIM and get a ton of power out of a reliable box.

lamk 06-01-2015 00:38

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Quote:

Originally Posted by pmangels17 (Post 1422490)
Why not use a worm drive? We used an Andymark Wormbox in 2011 for our elevator with decent success (we had other racking problems irrelevant of the gearbox) and the RAW Box, as already suggested, could work. We actually used a custom worm drive last year to winch back a really heavily loaded catapult arm, but if you don't have resources to custom build, use a COTS worm gearbox. You can mate with a CIM and get a ton of power out of a reliable box.

We actually use the said gear box for our aerial assist bot to arm a catapult but we have to use a one way bearing and clutch to arm and fire it. For an elevator we want to be able to move up and down at will. However if we only aim for 3 totes and use 2 sims we may be able to get away without a braking system.

pmangels17 07-01-2015 10:31

Re: Elevator counterweight / constant spring and ability to lift different number of
 
If you use a worm you don't have to use a one way bearing, they can be driven both ways without a braking system. They are also a good way to have a compact gear reduction that slows the CIM motors down slow enough to be usable in an elevator.

Cyberphil 07-01-2015 11:55

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Quote:

Originally Posted by nixiebunny (Post 1422472)
The fusee pulley is one solution. It automagically changes its "gear ratio" as the distance traveled increases, so you can use a gearmotor and optimize its lifting speed for the small stack but still have plenty of torque for the tall stack.

I have never heard of one of these. Although I am not working with a team this year, I may use this on my own practice design. Seems like it will do the trick.

Jared 07-01-2015 21:27

Re: Elevator counterweight / constant spring and ability to lift different number of
 
Worm drives CAN backdrive- especially multi start worms. As they wear in, they can backdrive a vibrating and shaking robot.

pmangels17 08-01-2015 11:39

Re: Elevator counterweight / constant spring and ability to lift different number of
 
While yes that is certainly true, depending on the number of starts (or threads) on the worm, the torque required to backdrive is often much higher than will ever be seen in an FRC application, though vibration could foreseeably unwind a worm drive at a very slow rate.


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