Yesterday, we were pretty sure sure that our tweaks for Worlds were finally over, but when we tried to raise our lift during a practice run, it barely went about ten inches before the gears (specifically a 60-tooth gear and a 12-tooth gear) began to slip, causing a lot of clicking and no movement. We’re worried that this could be a serious issue that could take a lot of time to fix, time that we really need for practicing.
Here are some images of our lift gearing, which is a 10-1 gear/chain system
Well we tried making a scissor lift before and same problem. How we avoid this is by simply using turntables (which are remarkably strong) and if we need to increase torque we just gear once outside the turntable, because the higher ups are more likely to slip.
You need to gear the system for more torque. You have a lot of metal to lift, and the farther out the arm extends, the harder it is to lift.
I would also suggest not using the 6-tooth sprocket to lift like that. The larger the sprocket, the better at pulling it becomes. Honestly, I would consider using two 1:5 HS gear combinations in place of the sprockets. We’re using a 3:25, but our arm is vastly simpler than this, so we don’t need quite as much torque.
I can’t see enough of the robot to give you really good help, but here some standard things I would ask or look into:
I really dislike using small sprockets for high-load applications, especially when mounted vertically. I guarantee the chain is going to slip on that lower sprocket. Are you sure the gears are slipping and not the chain? If you want some advice, ditch the chains and go to gears. A 36:60 ratio will give you pretty much the ratio you want, and spur gears work a lot better in this kind of application.
When you pull the axle out of the motor, how hard is it to lift the arm by hand? I’m guessing that the rubber bands I’m seeing aren’t doing you much good and that you are dead-lifting a lot of weight. Set your rubber bands so that they support all the weight of arm (at least).
What is holding your towers in alignment with each other? If your towers are not held pretty close to perfectly in line, you can get a lot of shaft friction as they twist and rack. Here is a picture of a Clean Sweep robot with a terrific “sheer plate” which keeps the tower in alignment:
If you have FOUR 393 motors on your arm and still cannot lift, you DO have a design problem you need to fix. The footballs in Clean Sweep were lighter than the sacks this year, but the robot in the picture above scored very quickly with two 3-wire motors. You do not have to have massive motor power if you design around the engineering design limitations of your parts.
This is not particularly directed to your robot, but I see a lot of teams this year using a lot of motors to make up for inefficient designs.
Im surprised nobody has posted this. The using a nylon spacer next to a pinion gear is could be the source of your problem. The diameter of the white spacer is slightly greater than the inner diameter of a pinion gear. This not only often causes friction, but also lifts neighboring gears slightly away from the pinion gear. Try using the plastic spacers or washers directly next to the pinion gear instead.
I would agree that a prime point where the skipping could be coming from is the distance between the towers. The axle with the pinion on it has a lot of room to bend, especially if the chain is pulling too tight, so I would suggest adding in some kind of structural support between the pinion and the chain.
I would also agree that chain is not ideal for this situation, but if you must, please don’t use the 6 tooth sprockets unless you absolutely have to. We prefer to use them as tensioners only.
all great points.I would make sure and connect the 2 sides of your tower securely and make sure that everything is spaced with the exact same type of spacers as mentioned before. I don’t think it is the 6 tooth sprocket that is the problem.
I would suggest aligning your gears because they are slightly off, or atleast appear to be. Make sure your sprockets are aligned or it will not be efficient. It is hard to pin point a problem without the entire robot in the photo.
the left tower “bar”
put the bearing blocks on the outside, and get rid of some of the black spacers
now you can shift the entire left tower bar over a few holes
and make sure there is some play in the axles (dont over-stuff with spacers)
In Science Olympiad, they may refer you to Euler’s Buckling Theorem(cutting distance in half between column supports quadruples the force necessary for column failure or something like that) on the issue of the bending of the axle supports which appears to be the root cause of the problem. The resolution to shorten the distance between supports is not always possible but there is always vex duct tape, e.g. cable ties. You may have separation between the axles with the top bending up and bottom bending down–zip tying the two may add the support necessary to stop the clicking. You are not going to win a build award with them but there should be a Mc Gyver Award in it for you.
