Hey all,
In the final stages of buliding a scissor lift and am wondering what would better to use for 2 of the 4 motors (one per side) powering my lift, an IME or shaft encoder. Also, does anyone have any sample easy c code for programming either of these sensors under the operator control tab. The idea being that having these sensors for autonomous would be great and all, but im really just looking for even lifting on both sides while under operator control. Thanks for any and all suggestions.
-Anthony
Neither. The issue with IMEs or Encoders is that they count up or down as you move them, meaning they measure the distance a shaft travels, not the position of it. Therefore, at the beginning of the match or if they reset they are always at 0, regardless of the position of the lift.
For the lift, I would use potentiometers. They are much more exact and also smaller. They measure the position of the shaft, so you can always tell at exactly which position the lift is at.
It all depends on the design, using an IME is often easiest. A pot will give an absolute reading as Kevin points out. Sometimes I use an encoder with a limit switch to create an index that resets the encoder count. For example.
https://vexforum.com/showpost.php?p=324534&postcount=1
Thanks Kevin and JPearman for your comments. While I dont have any pictures of my lift at this time this video shows a design very similar to mine:
based on that, would you still suggest potentiometers over IME’s? Would either of you know of a good resource (meaning any sample code) for programming either of these into the operator control of the lift? (im not interested in autonomous at this time). Thanks,
Anthony
You could probably easily add a potentiometer to a scissor lift at one of the joints. An IME would be just as easy to install, since it goes on the outside of the motor, but you’d then need to mount a limit switch, which might be easier than mounting a potentiometer. A potentiometer has a slight edge over the IME/limit switch, but I wouldn’t force it upon a design (i.e. if you’re using screws instead of axles on the scissor lift).
“You could probably easily add a potentiometer to a scissor lift at one of the joints. An IME would be just as easy to install, since it goes on the outside of the motor, but you’d then need to mount a limit switch, which might be easier than mounting a potentiometer. A potentiometer has a slight edge over the IME/limit switch, but I wouldn’t force it upon a design (i.e. if you’re using screws instead of axles on the scissor lift).”
Thanks for the comment, and I am using screws instead of shafts for the joints. Would a potentiometer on the shaft that my 60 tooth gear is on work (since it doesnt undergo more than 90 degrees of rotation anyway)?
In terms of the limit switch/IME combo, would the limit switch be somewhere stationed at the bottom of the lift and serve to reset the IME everytime the lift activates the LS? Or were you thinking of the combo working in some different fashion? Thanks,
-anthony
Yes.
Yes, what you said. The limit would serve to reset the lift encoder once it was pressed (and therefore bottomed out).
Another thing to also consider is that with pots you only need to wire them to 2 analog ports. However, with Encoders you need 4 ports or with IMEs you need to daisy chain them, and the limit switches take up another two ports.
However, if you have the space and ports, I would still put the limit switches on. They offer an extra bit of protection, especially if you have the lift going down to a specific value and the pot were to be unplugged, the limit switch acts as extra protection.
"Another thing to also consider is that with pots you only need to wire them to 2 analog ports. However, with Encoders you need 4 ports or with IMEs you need to daisy chain them, and the limit switches take up another two ports.
However, if you have the space and ports, I would still put the limit switches on. They offer an extra bit of protection, especially if you have the lift going down to a specific value and the pot were to be unplugged, the limit switch acts as extra protection."
Couldnt I just use one IME and set it as the master of the other 4 using Smart Tasks. Also, wouldnt I just need one limit switch (on one of the 2 sides) and just set all four motors to shut off when the limit switch is tripped? Would this not suffice? Thanks.
-anthony
Yes, that is true, you do only need one. We just had two as it allows you to move the sides separately if one is slower or be able to send if one were stuck.
P.S. On each post there is a button on the bottom right “Quote” which allows you to automatically quote a post the way I am right now.
thanks and my bad 
-anthony
+1 to using potentiometers. Worked great before and you could dial into fractions of an inch way up high.
An IME may result in too much movement of the scissor with greater height differences near the top or slop. This is dependent upon lift configuration. Pot is actual angle of the scissor regardless of slop.