Another question about scissor structure

I finished my scissor structure using some of people’s advice. It’s very help for me, thanks. And the stucture can lift and descend very smothly, also it can hold at any position.
Howerver I found it’s difficult for me to lift two sides of scissor stucture at the same place verytime. I try to use one channel to control both of two motors up and down, but sometimes the structure can lift up evenly,some times it will lean to one side. Then I use Y wire to join two motor, it doesn’t work. At last I use two channel to control motor seperately, but it’s hard to operate.

Another question is I use four motors to drive each of tyre directly, and software easyC to program. When I program Arcade-2 motor and joystick to control chassis, I found the robot move quickly, and hard to control.

I am the first time to take part in this competition, I don’t know how to use sensors to program automatically. Does there have any recommended teaching materials for me to study?:slight_smile:

I would advise reading up on how to use potentiometers to measure the angle between the parts of your scissor lift. To ensure that both sides of the lift reach the same height and stay there, I would use two potentiometers, one on each side of the lift. You could use a simple program that would have both sides of the arm reach a certain “setpoint” and then once both sides reach it, the motors would still be fed some small amount of power to keep the scissor lift at that position. An LCD Display would definitely help you in finding those setpoints you want to use

Examples of setpoints would be: on top of the posts, the various heights needed for scoring skyrises, ground level, etc. You would use whatever the potentiometer values are when the lift is at each position as your setpoints.

Using potentiometers or sensors and then a control for the two sides would work, but we have found it tricky, and unless it is perfect won’t work well.

I would try to mechanically connect the two sides at multiple stages as solidly as possible. Also, at the top and bottom, try connecting the sliders or like so they can only slide alligned, so one slider can’t be farther than the other. Then you can just hook up the motors to multiple 3-wire ports (don’t mix 2 and 3 wire ports) and just run them at full speed.

Stiffer cross members can also help keep left/right together. The 1x25 bent about has a bit of flex. Try standoffs chained together (with locktite on the middle screws especially) or some other angled metal piece that has greater strength.

Also adding some bearing blocks on the lower parts will eliminate some slop from side to side. The less room you have for slight movement on those critical points are exaggerated as you go up on a scissor. Multiple bearing blocks along the path can also help keep that shaft within a tight tolerance.

Rubber bands also help control the left right lift movement to “tune” the lift by adding one at a time to balance the left/right lift capability. The black bands are harder to tune but can be done. You just can’t pop one of those black bands off and see if it makes a minor difference, changes tend to be more major on those.

Then you have the pots on both sides as well. But making it mechanically sound will help a bunch.

To add to this, one good method of “tuning” your lift with elastics that I heard about is completely removing the motors, and putting enough elastics on the lift to the point where you could have it at any position and it will hold.

I am glad to see your improvements. Balance issue is always the most detrimental one in scissor lift. There are few tips from my experience that may help you.

First, use stiffer structure to connect both sides. Using 1 inch wide C channel or chassis rail is definitely not overdoing it. If you look at 400x, they used 2.5 inch wide c channel to connect two sides. I cannot emphasize this enough. Try to design it so that you can not even manually make it wobbly. That is the goal of structure.

However that is not always possible. Another good approach is to use elastic assist. Take off your motor when you are placing rubber band and do so in multiple angles. You want your elastics to help balance your sides so that when the motors are not installed, the two sides are tuned to stay at any height and balance decently. This reduces motor load and helps the balance.

Programming is possible to assist balance, but I will always make that the last resort because there are easier ways. But if nothing works, try programs. Usually the use of potentiometer is recommended. You can design a program like, if one side is higher, slow it down when activating it. Or you can do what I’m experimenting with, PID. There are a few great articles about this method and you can definitely look into it. It allows the motors to intelegently control and balance themselves. It is also something possible.

Any way being another huge scissor lift fan, I wish you good luck building and competing!

Martin, 3921

I agree. Theoretically works great and it makes me so happy reducing motor load!

Team 80N in Gateway I think had 40+ rubber bands across their lift.

The no motor balancing method is the way to go. Keeps the motors pushing the lift up with the proper help. It’s still a big push initially from the lowest folded section.

One last thing: look for errant screws that fell into in the track that can stop the sliders. You will get left/right differences as this point needs to be overcome.