COTS Elevator in Action

[Mike Marandola]

Originally Posted by Mr V

I don't understand why you would think that it would slip on the drum. The "string" should be anchored to the drum so no possibility of it slipping. You should not just wrap the string around the drum and tie it.

I think he may be talking about a continuous lift in which case you would want the "string" wrapped around the drum a few times (to prevent slipping) instead of anchored.

[BryceKarlins]

Does anyone know a source for the delrin wheels from this lift kit? We are interested in fabricating our own roller kit from the CAD files, and we're trying to avoid lathing our own.

[Gregor]

Originally Posted by BryceKarlins

Does anyone know a source for the delrin wheels from this lift kit? We are interested in fabricating our own roller kit from the CAD files, and we're trying to avoid lathing our own.

Do you or a team near you have access to a 3d printer? These seem like neat parts to make on them if you don't have a lathe. Most universities and many highs schools will have 3D printers too if you can't find one.

[lynca]

Originally Posted by Mr V

Having used a chain driven lift on a number of competition robots over the years and using paracord and pulleys for the Team [REDACTED] Ri3D machine I would never choose a chain driven set up again. It is heavy, a pain to attach to and a pain to properly tension and problematic to repair quickly.

Thanks for the feedback.

There are definitely tradeoffs between a chain-lift and cable-lift. Let me see if we can summarize the differences.

Chain-lift:
handles more torque but heavier
needs more structure and pieces to implement

Cable-lift:
lighter but has the potential to slip or snap the cable with too much torque
easy to implement but more prone to failures


Teams can see some of the differences between the robots in Ri3D.
Team Indiana is a Chain Lift
Most of the other Ri3D teams are cord-lift

[1988]

Competition Robot Parts has found another supplier that should allow us to get more parts out the door beginning Jan 16. Spread the word!

[Mr V]

Originally Posted by lynca

Thanks for the feedback.

There are definitely tradeoffs between a chain-lift and cable-lift. Let me see if we can summarize the differences.

Chain-lift:
handles more torque but heavier
needs more structure and pieces to implement

Cable-lift:
lighter but has the potential to slip or snap the cable with too much torque
easy to implement but more prone to failures


Teams can see some of the differences between the robots in Ri3D.
Team Indiana is a Chain Lift
Most of the other Ri3D teams are cord-lift

What do you base the thought that the cable lift is more prone to failure. I've seen chain lifts fail too and when they do it can be difficult to fix them quickly.

Properly designed they will not slip. Again I've seen chain lifts slip if the design is not done properly and tension not properly maintained.


As far as strength goes, chain does have a slightly higher ultimate strength that is for certain but don't discount the strength of paracord, the 1/8" stuff we choose from Home Depot has a 160lb working limit or ~3x what we determined we needed and most have a break strength of between 3 and 4 times their working limit. The chain I found on Amazon is rated for a 900lb break strength.

I'd rather have a cord fail than cause damage to the mechanisms and replacing the cord can be done very quickly. Replace it every few matches if you are afraid it will fail or you see signs of abrasion.


Now granted our machine had a very short life but when we discussed what we had done differently none of us even mentioned that a chain would be a better choice. A way to power it down would be a possibility of an addition.

Again my regular team has done chain lifts in the past and the fact that they are doing one for this season just makes me cringe. I would never choose to to a chain lift again after my Ri3D experience with a lift using paracord.

[adityaag]

For either chain system or the pulley system, what do team typically do to keep the load off the motor while not actively lifting? I'm assuming you don't want to have the CIM be constantly supplying force to the lift mechanism in order to keep it going. Anything remotely COTS that someone can link to or previous designs? I'm a relatively new mentor and our team has never built a lifting mechanism like this in the past.

[Mike Marandola]

Originally Posted by adityaag

For either chain system or the pulley system, what do team typically do to keep the load off the motor while not actively lifting? I'm assuming you don't want to have the CIM be constantly supplying force to the lift mechanism in order to keep it going. Anything remotely COTS that someone can link to or previous designs? I'm a relatively new mentor and our team has never built a lifting mechanism like this in the past.

Check out this thread. Some people are using bike brakes. We will be using a dog clutch system.

[Mr V]

Originally Posted by adityaag

For either chain system or the pulley system, what do team typically do to keep the load off the motor while not actively lifting? I'm assuming you don't want to have the CIM be constantly supplying force to the lift mechanism in order to keep it going. Anything remotely COTS that someone can link to or previous designs? I'm a relatively new mentor and our team has never built a lifting mechanism like this in the past.

There are multiple ways to prevent the lifted weight from drifting back down or at least controlling the speed at which it drifts.

Using a high reduction gear box and the motor controller set to brake will cause it to come down slower than it goes up. Note the brake setting is a dynamic brake, the braking force is directly proportional to the speed of the motor. Once the motor speed approaches zero so does the braking force. With this method you can get away without the need to stall the drive motor, just lift say x inches higher than you want it let it fall x inches before applying more power to raise it back up again. With the right ratios and some practice you will be able to get away without burning up the motor particularly when using a CIM or mini CIM. We did this with a RS-775 for Team [REDACTED]'s Ri3D machine. The RS-775 is a fan cooled motor and it didn't heat up that much even with 5 minute "matches".

A worm drive transmission will not back drive, or at the very least it is very hard to back drive. The Window motor is a worm gear, my team used this in Overdrive with success. The Window motors are not that strong but there are now some COTS worm gear boxes available.

You can attach a bicycle rotor to your drive and use brake caliper that is operated by a pneumatic cylinder as Mike mentioned. We have done this in the past. We used this for the climber in Ultimate Ascent and the lift for Logo Motion.

Depending on the design of your lift you can use a "pin" that is engaged by a pneumatic cylinder to lock the position. You may have to power the lift back up slightly to get it to disengage. You could also use a pneumatic cylinder to force a high friction brake "shoe" attached to the cart against your mast. You would want to attach the brake so that the act of falling tends to wedge it in place rather than push it out of place.

If you wish to hold it at the top of its travel you could use a gate latch to lock it in place and then a pneumatic cylinder to release it. Depending on the latch geometry you may need to power it up slightly to be able to release it.

[asid61]

Originally Posted by BryceKarlins

Does anyone know a source for the delrin wheels from this lift kit? We are interested in fabricating our own roller kit from the CAD files, and we're trying to avoid lathing our own.

Just a quick note, the correct tern is "turning", not "lathing". I only say this because if you talk to professionals you come out as more knowledgable. I actually fell into the trap of saying "lathing" a while ago, but I've been trying not to do it.

[adityaag]

Originally Posted by Mr V

There are multiple ways to prevent the lifted weight from drifting back down or at least controlling the speed at which it drifts.

Using a high reduction gear box and the motor controller set to brake will cause it to come down slower than it goes up. Note the brake setting is a dynamic brake, the braking force is directly proportional to the speed of the motor. Once the motor speed approaches zero so does the braking force. With this method you can get away without the need to stall the drive motor, just lift say x inches higher than you want it let it fall x inches before applying more power to raise it back up again. With the right ratios and some practice you will be able to get away without burning up the motor particularly when using a CIM or mini CIM. We did this with a RS-775 for Team [REDACTED]'s Ri3D machine. The RS-775 is a fan cooled motor and it didn't heat up that much even with 5 minute "matches".

A worm drive transmission will not back drive, or at the very least it is very hard to back drive. The Window motor is a worm gear, my team used this in Overdrive with success. The Window motors are not that strong but there are now some COTS worm gear boxes available.

You can attach a bicycle rotor to your drive and use brake caliper that is operated by a pneumatic cylinder as Mike mentioned. We have done this in the past. We used this for the climber in Ultimate Ascent and the lift for Logo Motion.

Depending on the design of your lift you can use a "pin" that is engaged by a pneumatic cylinder to lock the position. You may have to power the lift back up slightly to get it to disengage. You could also use a pneumatic cylinder to force a high friction brake "shoe" attached to the cart against your mast. You would want to attach the brake so that the act of falling tends to wedge it in place rather than push it out of place.

If you wish to hold it at the top of its travel you could use a gate latch to lock it in place and then a pneumatic cylinder to release it. Depending on the latch geometry you may need to power it up slightly to be able to release it.

Thanks Mike and Mr V. Both very helpful thoughts. Will definitely check out the various means of mechanical braking. Mr V, to clarify the use of the brake setting on the speed controller (we actually do this on our drive train so do know what it is now that I've looked it up... with it, you're basically just banking on the drop happening slow enough? In your experience with the RS-775, how slow did the drop actually happen? We'll likely use a Mini-CIM for this drive if we end up doing it. Are the Ri3d "matches" online anywhere? Would love to check them out.

[Mr V]

Yes we were banking on it dropping slow enough to "catch it" and power it back up. The fact that we used a 775 meant that we used a 20 to 1 planetary because that was what we had available, IE we had Versaplanetary and a 775 as our best motor that we could easily attach to it. Because of that and a small drum the braking was good enough. I don't know that with the gear reduction needed for a CIM or Mini CIM to still have some speed if it would work good enough. The 775 was definitely warm at the end of a 5min or so "match". Of course the 775 is a fan cooled motor.

You can find our videos at www.teamredacted.org. From there you can find a link to the Ri3D website where you can find videos from all of those who participated in Ri3D this season.

A mechanical brake would certainly be preferred and if we found the drop rate to be too fast we certainly would have looked at implementing one.

[adityaag]

Originally Posted by Mr V

Yes we were banking on it dropping slow enough to "catch it" and power it back up. The fact that we used a 775 meant that we used a 20 to 1 planetary because that was what we had available, IE we had Versaplanetary and a 775 as our best motor that we could easily attach to it. Because of that and a small drum the braking was good enough. I don't know that with the gear reduction needed for a CIM or Mini CIM to still have some speed if it would work good enough. The 775 was definitely warm at the end of a 5min or so "match". Of course the 775 is a fan cooled motor.

You can find our videos at www.teamredacted.org. From there you can find a link to the Ri3D website where you can find videos from all of those who participated in Ri3D this season.

A mechanical brake would certainly be preferred and if we found the drop rate to be too fast we certainly would have looked at implementing one.

Awesome. Thanks for the tips and the links. I've definitely been watching all the Ri3D videos and am no stranger to your team's bot. We've gotten some great insight already from your build. Seems like the best bet would be to just build a prototype of the system and see how much load it can hold. The team's come up with some good ideas for mechanical braking if it's necessary.

We're looking at using our remaining 2 CIMs for the elevator system which should give us a pretty powerful lift. Hoping to get it prototyped out tomorrow!

[Mr V]

Originally Posted by adityaag

Awesome. Thanks for the tips and the links. I've definitely been watching all the Ri3D videos and am no stranger to your team's bot. We've gotten some great insight already from your build. Seems like the best bet would be to just build a prototype of the system and see how much load it can hold. The team's come up with some good ideas for mechanical braking if it's necessary.

We're looking at using our remaining 2 CIMs for the elevator system which should give us a pretty powerful lift. Hoping to get it prototyped out tomorrow!

Thanks, our intention was to provide inspiration and not a canned solution. I certainly recommend prototyping it and see how it plays out just as we did. If it isn't deemed good enough then go to work on prototyping some mechanical brakes.