Scissor Lift Help

Hi,

We’re a fairly new team and are going to be attempting to build a scissor lift for the first time. Due to insufficient funding, we want to design the lift ahead of time before we buy parts. Despite the funding issues, we’re willing to spend a reasonable amount of money (approx. $750 - 1000) to build it and we already have some parts.

What are some parts that we should definitely have for a scissor lift? We are thinking of the following:

  1. 4 393 Motors (2 of them should have IMEs to control the lift?)
  2. 4 Rack and pinion sets so we can have the sliders on the bottom and top of each side of the lift
  3. Gears (What sizes? We’re expecting to gear it for torque as I know scissor lifts tend to have a difficult time initially when going up so a gear ratio of something around 1:21 is what I’ve seen some teams do but it does depend on the weight)
  4. Teflon Washers (Spacers?)

Also I have some questions regarding building the actual lift:

  1. I know that we should be using screws instead of axles for joints but have them loose enough so it can go up and down. Whats the best way to get right tightness?

  2. Whats the best way to use elastics and how many?

  3. Should we use a rack and pinion horizontally or a linear motion slides horizontally?

  4. Where should the motors be located ideally? Split up between the stages?

  5. Whats the ideal gearing that most teams have had success with? We plan on carrying 2 cubes or 1 skyrise.

Thank you and any additional help would be appreciated.

  1. Spread them out on each stage, enough that it can support itself without motor power

  2. You’ll probably need both. Both joints of scissor attached to U-brackets attached to slide-block that slides on slider (one U-bracket can be fixed to the slider), with a rack-and-pinion next to it or below or above or something, don’t remember exactly how it goes. Top should have a slider assembly too, I don’t think you really need a rack-and-pinion if you’re not motorizing the top.

  3. I guess it depends, I think the less weight the scissor has to lift the better, so I would do all 4 on the bottom.

Scissors are relatively complicated and I recommend CADing it out in Autodesk Inventor or Solidworks

Do you have a picture of what you mean for question 3?

  1. The number of motors depends on the number of stages. I have found that 4 motors is good for 3 stages, and 6 motors is good for 4 stages, but by all means, find out for yourself.

2/3. This really depends on how you power your lift, but you definitely do not need both the rack and pinion set as well as the gears.

  1. You’re definitely going to want teflon washers, as well as spacers. I would also reccomend the shoulder/pivot screws where necessary.

  2. There’s nothing wrong with using shafts. This is easiest, since they are made to rotate.

  3. Ditto to FarceSolid.

  4. Whatever you want.

  5. In a spot that makes sense, which includes maintenence and wiring.

  6. Your ratio ultimately depends on how many stages you want, which is dependent on how high you want to go. The more stages, the higher the ratio.

Tighten the nylock nut until just tight so your fingers can’t turn the screw via the nut side. Then back off about 1/8 of a turn until you can turn the screw by hand.

Using washers on both sides of the screw assists this movement so it does not stick to the metal scissor component

We have discovered that waits on this robot are also acting screwy. A wait of 150 is working normally, but a wait of 1000 is hanging the program up indefinetly. Is it possibly a problem with the microcontroller’s timer?

That’s fairly unlikely. Can you post the code?

Did you actually stopped the motors in the program?

No, it’s your code.

I can’t remember if RobotC uses wait10Msec(150) … wait100Msec(150) etc., but make sure you are actually using wait1Msec(1000); and not something like wait100Msec(1000) .