Scissor Lift Update Issues

[CHS_Robotics]

Since posting I have added elastics to the X’s of the scissor lift and know the lift goes up great but still having bad issues of it going down. I checked with my advisor and we can’t seem to get the idea where the friction is at anywhere and is hard to mess with because it tears the gears apart. I have attached some videos of how it goes up but going down is horrible and need some help with what could be causing this.

http://youtu.be/nbHicmobGkg

http://youtu.be/RGAo5jDqyzc

[Kevin_Boenisch]

Since posting I have added elastics to the X’s of the scissor lift and know the lift goes up great but still having bad issues of it going down. I checked with my advisor and we can’t seem to get the idea where the friction is at anywhere and is hard to mess with because it tears the gears apart. I have attached some videos of how it goes up but going down is horrible and need some help with what could be causing this.

http://youtu.be/nbHicmobGkg

http://youtu.be/RGAo5jDqyzc

It seems that now you have elastics that allow it to go up well, but are too much for it to go down, which the motors can’t handle.

The reason they are stripping is because they are not tight enough to the racks, allowing them to move away from them and strip. Try to see if you can make them mounted more solidly.

[CHS_Robotics]

I will have to try to create a tighter fit between the gears and the racks. Thanks!

[Procrastination_pls]

Have you considered the suggestion of having the rack power between two centre pivots of the X’s rather than on centre pivot and the base?

You asked for clarification about what I meant on your previous thread on the topic

on procrastination pls can you provide a more explained way? I’m not understanding what your trying to explain but you got the problem I’m having correct.

At the moment, your lift is powered by a vertical rack and pinion set up. You have one end of this mounted to your robot’s base and is fixed relative to your horizontal slide rails, where the friction is occurring, and the other end is mounted to the centre of one of your X’s. When your arm get’s closer to full height, this starts to lift the whole arm, slider blocks included, up slightly relative to the robot’s base, rather than causing the X’s to rotate and the green slider inserts to slide.

If you were to mount the slider with one end on the centre of one X and then the other end mounted to the centre of the next X, I think the problem would be solved as there is nothing that actually pushes the arm up away from the base like how your current system does. This way, the power system will only cause the lift to raise by the X’s rotating. You can also have one side of the X on a fixed mounting this way, with only one side rotating.

[CHS_Robotics]

If we did a pivot point on the first and second one I don’t believe we have the height or room to do it to get the height we need to build the tower. I will see though if we do.

[Team80_Giraffes]

Skipping can be introduced by the length of that driven shaft having room to wiggle.

We’ve had some lifts like this and have a 12 tooth gears on top of the one driving the linear slides. So sandwiching this gear in place keeps the driven gear smashed on to the linear track. Putting another linear rack bracket on top or attaching C-channels gets you the room to do this. 81J is doing this type of rack design this year but with a different lift placement.

Another means of reducing shaft flex is to use bearing blocks as it passes through the rack brackets. This gives some bracing on the long shaft.

From a lift force perspective, using multiple smaller #32 rubber bands can get less force per rubber band allowing you to tune to a sweet spot of lift assist with what needs to come down. But stopping the skips is need number 1.