Handling (Arm) Gear Slip

VEX V5 General Discussion General Forum
1

What are feasible ways to handle the gears on an arm slipping? For contextual purposes, the arm is very heavy (probably about 5 pounds) and we are using 4 High Strength Motors geared externally at 1:5. We are able to lift the arm all the way to 30 inches but a lot of times the gears will repeatedly click and the arm will start to drop before it catches again and starts to raise. A lot of times the clicking is completely harmless and the arm will keep rising but I’m worried that we will destroy the gears this way.

Right now we have two C-Channels bolted together with Delrin Bearing Blocks for each of the four arm axles. During the tournament we also took a couple of zip ties and connected the axles together which was enough to make our arm usable for the day. Does anyone know of a more permanent solution that will hold the axles and gears to make sure that they don’t slip?

I’m not sure of it’s importance but the top and bottom axle are all bending under the weight of the arm. (Mildly)

The arm itself is essentially a 4 bar.

2

There are lots of previous threads with same issues, and lots of discussion, including pictures.
Main points are

  • using compound gearing reduces tendency to slip (I didn’t follow the math)
  • gears slip because the axle to axle spacing increases;
    – redesign the axle brackets to keep the axles from sliding apart
    – for example, increase the number of shear joints at the shoulder pivot.
  • use elastic springs to reduce the effective torque needed to pass through the gear train
3

Im not sure if it would work for your design, but i would consider putting a middle brace down your gearbox to reduce the amount of possible unwanted movement in the gears. Also, try doubling up the gears and as jgraber said use elastic to reduce some of the load on the gearing/motors.

4

Here’s an example using 1x strap with bearing blocks to keep the axles from spreading (which is what leads to gear slipping). This is an OLD robot :slight_smile:

https://vexforum.com/gallery/files/2/0/9/1/dsc_0121.jpg

5

yes exactly what i was trying to describe. also this image appears to demonstrate the use of elastic/rubberbands to assist the lifting.

6

There are two main things you can do:
Reduce the effective weight of the arm using elastics.
Support the axle, as the image above demonstrates. The closer to the gears the axle is supported, the less slipping you will get.

Zip ties like you mentioned have worked for us, and they could very well be a permanent solution (not very elegant, but it works very well).