Pneumatic Scissor Lift wont work with PSI below 60.

With already using 6 motors on drive and 4 motors for intake and lift there is not much of a question to whether or not we should use pneumatics for our scissor lift. Everything is built and we cant seem to get back to our starting position once we fire the 4 pneumatic pistons powering our scissor lift. we have 6 tanks mounted and hooked up but once we drop below 60 psi we cant bring it back down, or up(this is without any sacks or mechanism on it) Obviously we have a bit of a problem and we were just wondering what some of you all would do. Would you get more tanks or would you sacrifice intake motors and lift motors?(taking motors off drive isn’t an option considering our weight continues to increase.) But the most motors we could sacrifice would be 2. If anyone has any suggestions they would be greatly appreciated. Thank you and Good Luck!

Yeah that’s the problem with heavy, complicated robots (I’m guessing). It sounds a lot like my team’s first gateway design, which was a intake box, pivot arm, and scissor lift.

My advice is to get a simpler design with fewer moving parts that can do the same things as your design. That way you could have more motors on each part, ex: 4 on drive, 4 on arm, 2 on intake instead of, 4 on drive, 2 on arm, 2 on lift, 2 on intake. Fewer, more efficient mechanisms also means less weight and easier driving.

I can’t really say more than that without knowing more about your robot. If you are really attached to your design, you could move two of the motors to the lift and make sure it’s geared down really low (at least 20:1 torque). Hope you can figure something out.

The six motors on drive cant really be changed considering the weight of the robot is approximated at 25 lbs not including the sacks. and i know we can easily get rid of 2 motors from the intake and lift but this years game is going to be about speed and if we’re going to be slow with our lift that will be a pretty big disadvantage. Pneumatics are bam up, bam down. We want to stay original too. We haven’t seen many pneumatic scissor lifts at worlds or competition. Do you think more tanks will fix our problem or should we ditch the idea of a pneumatic scissor lift?

I disagree that that the deciding factor in this year’s game will be speed, I think it will instead be a combination of descoreing into your robot and high capacity.

How many lifts can you get with the pistons? One? You could get six more tanks and then you would have two. If you already get five or so then this could work. But there is also the problem that each tank is more weight on your already-heavy robot.

Actually I think picking things up off the ground and then halfway through the match lifting to trough height and descoring until the end, where you then score it all, could be a viable option. Then you would only have to lift once. What I would do is have a four 393 motors for the drive geared 1:1, which should work especially without pneumatic tanks. Then have two on the intake and 4 on the scissor.

Is your robot aluminum? If not, you could get some aluminum and maybe the pneumatic lift would work then. Otherwise you could just make sure you have no extraneous metal on the lift and it is built as lightly as possible.

We are going to do some fine tuning, put some regulators on, and fix leaks. but if all that doesnt work you have a very possible option. THANKYOU AND GOODLUCK! I hope to see you at worlds :stuck_out_tongue:

I recommend that you do not use a pneumatic scissor lift. Having plenty of experience with pneumatic lifts, we barely got ~3 pounds of game pieces to go up with perfect rubber band tensioning. Creating a lift with pneumatics is not going to be the best way to get 10 pounds of sacks up 15", even if pneumatics are fast. What would be the point of having a fast manipulator if your lift doesnt work by the end of the match? I think the best way to power the lift is taking 2 motors off of the manipulator and 2 motors off of drive. Also, if you eliminate the pneumatic lift, you would take off the 6 tanks and all other pneumatic parts, cutting about 6 pounds from your robot.

You can take 2 of those drive motors and put them on your lift. You’ll want to gear them with a heavy torque ratio, though. Our Gateway scissor lift needed 4 269s with a 1:21 gear ratio (for torque). We tried a motor/pneumatic combo for a while, but since the motors move so much slower than the pistons, it wasn’t very practical.

Don’t worry about losing pushing power when you take those extra two motors off. Our Gateway robot had plenty of that with a 4-motor drive. The key is to add some extra weight. Your six tanks should make you heavy enough; could you use your pneumatics for a different purpose?

Also you may want to think how you are powering it. If you are powering it vertically you have a constant torque causing the lift to run with less maximum torque. If you are powering it horizontally then the torque is variable and the maximum torque is much higher.

from the looks of it, scissor lifts are very inefficient. it needs more power to lift them. try adding horizontal elastics to pull the scissors together.

If pulling the lift down is a challenge for the pneumatics, then I’d assume they’ve already got elastics. Either that, or they have an inordinate amount of friction in their lift.

the lift wont have elasstics unless you put on elastics. that is more than likely your friction. scissor lifts are not the easiest to perfect.

Yes, we do have elastic and we are powering it horizontally. and there isnt much friction. but once we fine tune them and put regulators on the other pistons we are using and fix the leaks we should be good.

take into account leverage. you can do alot if you get some leverage working for you.

Perhaps something I’m missing, but when you say four motors on “intake and lift” does that not incude the scissor lift?

IMO, having a lift and then a scissor lift mgiht be a little…excessive. Try to cut out the middle man. With the two free motors, there really shouldn’t be a problem raising the scissor lift.

Additionally, I’m not the leading authority on pneumatics but 6 tanks sounds like a lot. Perhaps it’s best to do a bit of a redesign.

  • Sunny G.

Cedric’s “plenty” is based on his trials and tribulations in getting that great 599D robot working. It was worth it, but not easy.

Before deciding, lets take a quick look at what theory would say re lifting 10 lbs up 32 inches with pistons.

Energy needed 10lbx32in = 320 in lbs.

Typical piston energy at 100 psi pressure:
12 lbs x 2 in = 24 in lbs. extend
10 lbs x 2 in = 20 in lbs. retract

Minimum number of pistons = 320/24 = 40/3=> 14 pistons

Pistons must be geared with 16 to 1 to get 2 in piston movement to a 32 in lift movement. Suppose the scissor lift has 4 stages and you actuate it at the midpoint of the first stage and each stage has a delta height of 8 inches. The mid point would move 4 inches. This gives a gearing of 8:1 so you would still need a 2:1 gearing between the pistons and the scissor attach point.

So no one wants to use 14 pistons…

What about 6 pistons?

Add lots of rubber bands and reduce the number of pistons to 6.
Piston up energy (assume piston is retracting ) = 120 in lbs
Elastic energy needed = 320 - 120 = 200 in lbs.
Piston down energy needed to work against the elastic = 200 in lbs

Maximum down energy available (piston is extending) = 6*24= 144 in lbs
net deficit = 56 in lbs
So you cannot get the lift down!!

Well… now try 8 pistons
Piston up energy (assume piston is retracting ) = 160 in lbs
Elastic energy needed = 320 - 160 = 160 in lbs.
Piston down energy needed to work against the elastic = 160 in lbs

Maximum down energy available (piston is extending) = 8*24= 192 in lbs
net excess = 32 in lbs

So you can get the lift down now… but at the cost of 8 pistons.

Now repeat with 60 psi and you can see the problem. Essentially the number of pistons would go up by factor of 1.7

Trade offs must now be made to make the lift work. If you operate with 60 psi you might be able to lift 6 lbs with 8 pistons or 3 lbs with 4 pistons which now gets closer to the 599D capability.

In summary, it is possible to make your lift work without motors but you need to do this type of calculation for your lift geometry and payloads.
Having a lot of pistons can make things easy but money, space and weight constraints soon make a very hard problem.