Ok, that helps a lot.

1:45 is a massively strong gear ratio. I don’t think I’ve ever heard of a ratio that strong before . So if none of the gears skip and the motor is putting out full torque, then the torque on the arm will be pretty huge.

As you said, the most likely set of gears to skip is the very last set in the chain (5:3 on your robot).

**Technical explanation starts here - For anyone who’s reading, if my poor drawing skills mean this doesn’t make sense then that’s ok. You can just read the rest of the post and skip the explanation**

What makes the gears skip isn’t actually the torque on the arm, but the tangential force at the gear interface. Here’s a diagram (possibly confusing, but hopefully not):

**A** is a tooth on the driving gear, and **B** is a tooth on the driven gear. **A** pushes **B** with a tangential force **Ft**. Torque = force * distance, so we know that **Ft** = (torque of **gear A**) / (radius of **gear A**).

But that force doesn’t convert directly into a tangential force on **gear B**. The force between the gears can only be transferred across the point where their surfaces touch, and since the surfaces are designed to have minimal friction the force can only be transferred perpendicular to the surface.

This is what is represented by **Fab** (the force of tooth **A** on tooth **B**) and **Fba** (the force of tooth **B** on tooth **A**). These forces can each be represented as two perpendicular components: a tangential component equal to **Ft** and a radial component that we can call **Fr**. The radial component **Fr** pushes the gears away from each other. The gears will meet at the same angles whatever amount of force is applied to them, so increasing **Ft** will increase **Fr**.

**Technical explanation ends here. tl;dr: increasing the force where the gears meet increases the force pushing them apart.**

Of course if there is more force pushing the gears apart they are more likely to skip, so we want to reduce the tangential force between the gears. Force = torque / radius, so we need to decrease the torque and/or increase the radius.

A simple way to increase the radius is just to use a larger gear on your arm. Use an 84-tooth gear attached directly to the arm, and move the 60-tooth gear that’s currently on your arm to an earlier point in the chain. That will reduce the force pushing the gears apart by about 30%.

Reducing torque isn’t quite as simple, but the general idea is that you want to bring the load closer to the “shoulder” of your arm and increase the angle that your arm has to travel through. If lifting a robot to 12" requires your arm to rotate by 45 degrees, then the arm needs more torque than if it was rotating through 120 degrees.