1:5 lift stalling

So we changed our lift to a two motor 1:5 torque and for some reason it starts stalling after stacking like 8 or so cones. We know other teams have a similar lift, but no stalling issues. We gave the motors time to cool down, but it still stalls easily. We have tried distributing the motors across the cortex and power expander evenly, but still receive this annoying stall. One thing we suspect it to be is friction, but we don’t really know how to get less friction in the joints of our lift.

Anything helps!


Also, we know 2 motors should be able to handle the weight of our lift as it is made of all half cuts including the transmission, and we are using rubber banding.

Do you have enough rubber bands on your lift for it to hold its position without motor power?

Yes, we do

If you remove the motors, how difficult is it to move the lift up and down?

Can you post a picture of your gearbox?

it isnt very difficult and the lift holds its position at all points, but I do feel some friction. I dont have any pictures of the robot currently

If there are no motors on your lift, it should move relatively effortlessly, otherwise there is too much friction. Perhaps your joints are too tight? Usually people tighten them all the way and then loosen by a quarter or half turn (if you’re using screws, which I’m hoping you are).

EDIT: Another thing that could be happening is your rubber bands causing torsion. I know this happened to my team’s lift in the early season, and it made running a 2 motor 1:7 hi-speed ratio difficult, it could only run 1:7 torque. What was happening is that since we only rubber banded one side of the metal on each side of the lift, it was causing torsion on the metal, and because of that the gear that it was attached to also leaned. This causes a lot of friction when moving the arm, as the gears aren’t perfectly straight. I would highly recommend rubber banding both sides of the metal in order to reduce as much torsion and friction as possible. Once we did this, my lift ran 1:7 hi-speed beautifully, and if it was built a little better could probably run 1:5 hi-speed lol)

Thanks I will try rubber banding on both sides of the metal, we didn’t have much space this time so we will Have to increase the spacing on the transmission
I was wondering how you make the joints, we do use screws, do you just go screw and regular nut or use something else like 2 thin nuts( 1 before the bar and 1 after) And do you use bearings on both sides for the bar, will that even help?

We use spindles (you may know them as pulleys) on both sides of the metal. The spindles are 3/8" wide, and the spacing on the lift due to the gears is 1/2". If you count the screwhead sticking out of the spindle, you’ve got about 1/16" clearance. My lift functions fine even with such a small clearance, but if you want to conserve space without widening your spacing, just use standoffs with a circular piece of lexan instead of spindles like in this video so that you have more clearance, since you can control how long your standoffs are.

We just go screw to nut, although you want to make sure that metal is not rotating against other metal. We like to leave 1/8" space between the metal. And yes, use bearings on both pieces of metal, as it fits a screw perfectly and eliminates a lot of slop.

oh ok thanks, also do you know how to deal with a lift that has already stalled once, because at our competition, it stalled in the beginning, and no matter how much we cooled it down/ let it rest, it still stalled every match. we would have stacked more, and been able to use the practice field in between matches if it weren’t for this lol.

one point though, we did not have much air duster spray left in the can so we could only cool in the beginning, and we are thinking it is the ptc in the power expander that tripped or perhaps the cortex, what can we do about that, we tried changing ports around

After a PTC trip, motors can take anywhere from around 20 minutes to an hour to properly cool down. I haven’t dealt with sprays much, but if you played every single match after, I doubt they were able to fully cool down. If this isn’t the issue, and they were working perfectly fine before, then it sounds like something changed permanently. Perhaps a motor controller went bad, or something mechanical changed when you overstressed it, like some gear skipping. I’d recommend switching out your motor controllers and seeing if this still happens.

Oh and also, what’s your ports setup for this lift?

I am wondering what your joints are? The best joint in VEX (especially to reduce friction and slop) is a single rotating screw joint. Basically you would firmly attach a screw to one of the bars with a fully tightened Keps nut. This will remove a lot of the slop and keep the screw perpendicular to the bar. Then you would run it through a bearing on the other bar so it can rotate, and then hold it all together with a Nylon Lock nut, just tight enough to keep it from coming apart. This joint only rotates in one place and you don’t have to compromise between a tight lock nut to remove slop and a loose lock nut to prevent friction. Please use this wherever possible. But also make sure not to have any metal rubbing on metal! The other cause for a lot of friction are bent axles. I have had a lot of cases where an axle that was ever so slightly bent was causing all of my friction issues so make sure to check your axles! If neither of these are the case and you don’t have metal rubbing on metal I would need pictures/video to help diagnose the problem.

I actually never thought of using a keps nut to hold the screw perpendicular. Either you’re really smart or I’m completely clueless (or both haha). Just curious, is there a way to accomplish this if both of the outer faces of the metal are facing each other (like this: ] )? If they’re like this or ]], you can use the space in between to put the keps nut, but if they’re facing each other, I can’t seem to figure out a way to accomplish this. I’m probably just missing something really simple, but if you know a way that’d be great haha

@Mystellianne I usually just put a keps nut and a teflon washer and it works great in that orientation