# Hanging with a four bar lift system

Hey everyone, I’ve been thinking about changing from my vertical scissor lift for a four bar lift. One of my issues with this is how much potential is there for hanging with 2:1 or 3:1 using four motors? And I may post videos of the current robot at some point

I remember a thread where someone (127?) tried a 1:3 and they said it worked but not very well. I think hanging stalled the robot. Would someone post the thread if they find it?
[EDIT]
Found it:
https://vexforum.com/showpost.php?p=338578&postcount=27
[/EDIT]

I think a 1:3 might be possible; 18" bar, 10 lb, 4 motor, 75% torque, well tensioned elastics…

I would suggest starting out with a 1:5 personally.
http://polynomic3d.com/user/smith/vex-lift-calc.html

[/EDIT]

I think a 1:3 might be possible; 18" bar, 10 lb, 4 motor, 75% torque, well tensioned elastics…

I would suggest starting out with a 1:5 personally.
http://polynomic3d.com/user/smith/vex-lift-calc.html
Our robot is all aluminum with a 4 motor drive. With 4 motors on the tower I think it would be reasonable for 10-15? It’s not been weighed. How fast would it lift at 1:5? Our intake is fairly light too.

My estimate with a 1:5 is 2 seconds.

Just from my experiences I would say that your best bet would be a 5:1 ratio on your 4 bar. This all depends on the length of the lever arm and weight of the robot, but it would still give you a very quick lift time, while allowing you enough power to lift your robot (I would think).

I don’t think anyone will be hanging with a ratio below 1:5. Our first lift system at 1:3 was barely able to raise the fully Aluminum base of our robot a couple of inches. Go with 1:5. We’re rebuilding into that now (Chain Bar), and I’ll let you know how that goes if you’re curious.

Ok thanks. I’d love to hear how that goes I assume the results would be similar with the chain and 4 bar?

Yeah, I would think so. The Chain Bar will be slightly lighter (which is why we’re doing it), but the amount wouldn’t be significant.

How long would each arm of your four-bar be? If they were 18" from pivot point to pivot point, and your robot weighed 12.5 lbs, with four 393 motors (in their factory setting) at a 5:1 gear ratio… :

Now, please keep in mind that we should probably size this down a bit due to the inefficiency of gearing. Let’s give the VEX gears the benefit of the doubt and say that they have a 90% efficiency. That would leave us with 159.408 inlbs*.

So, if your robot meets all the above requirements, you’d be fine. However, your robot could only weigh 8.856 lbs. But you could possibly use rubber bands to pull your lift down rather than up. I don’t know much about how much extra power you can get by adding rubber bands, but I doubt you’ll get enough to hang even a 10 lb robot (while still being able to lift the intake with game objects in it…).

Do keep in mind that you will be lifting the weight of your intake (and game objects) while raising, but while lowering (hanging) you will not.

~Jordan

From past experience, I’d recommend 1:7 for hang
the obvious downside to that is the slow and overpowered arm throughout the game

One of my team mates have a 6 bar that is compound geared 1:15 and they lift in about 4 or 3 seconds. They don’t shift gears so they run a constant 1:15 (pretty slow) and they made it to semis in the last tournament which is pretty good! I would not count that option out! I can post a video if any wants to see!

Yeah post a video. I don’t think I’ll try that but it sounds interesting:)

It is very possible to hang with an arm geared 1:5. I would mess around with it. Do you have elastics on your arm? Those help a lot. We can talk more on the 26th Jarred

On a plane ride, heavily drugged by the lack of sleep, I did a calculation of a 10:1 torque arm powered via winch and elastic. Elastic raise and winch lower. When I did the math, it took about a second in a half to raise throughout a match. The problem is, it would probably take 3 or so seconds to lower(didn’t do math, just relying off of experience and intuition) in a match. I didn’t do time calculations for hanging, but I assumed that I would push 3 motors to about 70%.

There’s a chance I conceptualized wrong however. I assumed the motor would have 150 rpms when lifting simply because elastic would raise the system. Going down wouldn’t be much of a problem because I rationalized that the robot would need to turn around anyways and sap more time

With 4 motors on a chain bar at 1:5 (Torque) we were not able to hang. The hook was about 28 inches from the gear with elastics pulling down. This is a large reason for my team switching our lift.

Ever think of doing a 8 motor PTO?

whats a PTO?

http://en.wikipedia.org/wiki/Power_take-off

I think this is what he’s referring to.

A “PTO” or Power take off, is where you shift gears that are connected to your arm into gears that power your drive… giving you added motors to lift or “takeoff” of the tiles creating less stress on your motors and possibly a faster and more efficient hang.

I think i got this right … please correct me or add to it if i am wrong :o