What is the optimal motor loadout for a scissor lift?
It depends upon how much you need to lift, how many motors you are willing to use, how fast you want it lift, etc. From there you just need some calculations and you will be able to know what gear ratio you need.
If you are referring to the motor placement that simply depends on how much space you have or where it is easily positioned. You can power it at the cross-section of the scissor (usually the lower stage), at the base (there are 2 ways) by either directly gearing it to the arm or using a rack and pinion system to move a slider or bracket along a rack by powering a gear.
Hope that helps. And if their is a chance that I did not answer your question I will not be able to help you further without a more detailed question.
The answer to this is a complete “it depends” and well, it depends upon a ton of things - the style of lift, the placement of the lifting mechanism, the style of lifting mechainsm, etc.
When attempting a scissor “friction is wicked mistress” came to mind over and over again. So be prepared for some rework and give yourself plenty of time.
Vamfun has written quite a bit about scissor lifts on his blog and has posted in the forums here. Read these here.
Two papers are referenced in his blog to tell you about type of lift mechanism and effects on their placement. Very good illustrative graphs showing the forces based upon their type.
http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA225220
The downside is that Vex has discontinued two of the parts commonly used in scissors - the old style linear lifts, and the slotted metal. However the slotted metal I believe is available in larger kits still. Although using the new style sliders for rails works much nicer.
So once you decide upon a lift style that will show you the forces for that style on the graph in the papers listed above. You want vertical force for lift in most cases. But cramming under 12" will force horizontal forces into play. Mechanical coupling between the two sides is also helpful if not needed 100%.
If you choose the 60 or 84 tooth gear on the central X method, watch for gear skipping.](http://www.worldcat.org/title/mathematical-analysis-of-actuator-forces-in-a-scissor-lift/oclc/227815555?title=&detail=&page=frame&url=http%3A%2F%2Fhandle.dtic.mil%2F100.2%2FADA283906%26checksum%3Dee80908eb5da01fb7bd791b190ab5d73&linktype=digitalObject)
Thanks for the help!!! We’ll probobly use 2 393’ and 269’.
It’s not usually a great idea to mix n’ match motors
Why not? I mean, 269’s and 393’s have the same rpm.
High torque, yes. High-speed, no.
I personally can’t see anything wrong with mixing motors assuming they’re going the same RPM. We’ve done it before and haven’t had a problem.
What are you guya running foe your drive, as in getting over the bump
Everything works. We’ve done X, Mechs, 4 Omnis, 6 Omnis and the 5" traction wheels. They all got over no problem.
So, whatever works for the strategy you want to use.
People mixed and matched 269 and 393 during the Gateway era and prior. It worked fine for me and my team.
You should be fine using different motors.
Alright, I stand corrected. Mah bad :o
Scissor lifts are pretty good, but having a 6-bar lift system would be better!
We appreciate your enthusiastic posting today, however, a little more substance to some of them would be beneficial to the community.
For instance, tell us why do you think that having a 6-bar lift would be better?
If built well a scissor lift can impress judges, and be effective. For example: 9090c, both effective at scoring and the number one programing skills (according to robotevents.com). Hanging is good too with a scissor lift.
I, too, would love to see justification for this statement.
I take the position that a well-working scissor lift is akin to the “Holy Grail” of robotics. It lifts fast, lifts high, can carry semi-substantial weight, and lifts vertically (<- that’s the important part).
If you lift vertically, then programming becomes much simpler–you don’t have to worry about being 10" away from your target when you’re at a 40deg inclination, or 12" away when you’re at 45deg inclination. If it’s simple for a program, then it’s also simple for a driver. Well-done vertical lifts–on teams I’ve seen–tend to perform better than rotary lifts (e.g. 4-bar/6-bar) because the driver doesn’t worry as much about alignment, especially for games with different goal heights.
Yes, 6-bars can lift more weight (possibly), but they also take up a large amount of “always-occupied” vertical space to start, and take quite a bit of forward clearance to lift.
I’m sure you can see why I’m curious about the motivation for your statement… 
//Andrew
I agree with the above post. Our Scissor Lift bot is far and away more stable than the six-bar we built. The fact that it lifts straight up means that during Auto, you can get basically right up on the goal without having to stop as the arm raises, saving you half a second. It’s taken us a few months to straighten out, but the end result is a very stable design that’s basically immune to tipping.
Scissor lifts also combine really well with Mecanum wheels. Because the weight is centered on the frame, your strafing is nearly flawless. And, because the scissor lift goes up vertically, that doesn’t change when your lift is at any height. You also don’t have a ton of dead space above your wheels; every inch of space is used effectively. There’s also the opportunity to build a descore mechanism, something that’s much more difficult with a Six-Bar. We don’t currently have one on our robot, but it’s nice to have the option.
Throwing out blanket statements like “N-Bar > Scissor Lift” contributes nothing to the discussion, and they’re also generally untrue. Most designs have a use somewhere, on someone’s robot. Just because it’s not what YOU found to be best doesn’t mean another team hasn’t pulled it off. Considering the team with the highest Skills scores in the world is using a Scissor Lift, you really can’t write the entire design concept off.
Regarding your scissor lift vs your 6 bar, ephemeral, at the competition on Saturday I saw your scissor lift tip multiple times yet I never saw the 6 bar tip once. . . The 6 bar seemed like a much better robot to me.
We have a few teams using scissors this year but more with 6 bars.
Be careful with your scissor designs. Team 81J ran into this with the 8912[A-c]Shanghai Hangpu Tenage Activity Center Round Up style scissor lift we like so much. You need some more structural strength this year it appears.
Notice the lower arm is bent inwards…
Set of three pics:
Needless to say, 81J re-designed their robot a bit after this.
Another one of our teams, 81G went the aluminum c-channel route and can high hang without a dedicated lock motor/piston since it’s light enough. They can’t grab a big ball yet, but maybe next week.