# Mechanically increase motor torque

An electrical engineer here. Using a stepper motor for a robotic arm. A stepper motor at the base of the arm has a max holding torque of 6kgcm. The arm is around 30cm in length from this base motor meaning that the max weight that can be supported at the end of the arm is 200 grams. There are other motors along this length that the base motor has to support too. How can i mechanically increase the torque of the motor so it can support 800g to 1kg ? The max torque (6kgcm) is provided at the highest rated voltage on the electric side of things, Is there any mechanical methods to improve torque of a stepper motor without wrecking its precision/step accuracy? I've heard gearboxes increase torque but I want to know all options and find the best one.

• A good gearbox won't wreck precision. It will also cost a lot. Commented Apr 10, 2021 at 23:53

Actually if you want to keep accuracy and increase the torque you can use a gearbox that reduces the input Rpm.

So you will be Sacrificing the speed for the increased torque and precision.

Its also linear so if you need to go from 200gr to a kg you need a great ratio of. 5.

If you had to go higher than 10 then the forces would be significant and you'd need to check the strength of gear teeth. However for your application you should be fine

Gearboxes are very convenient to integrate with stepper motors, and sounds like the most likely solution by far. Just for completeness, some other options are:

• Don't know if this counts, but something fairly common that is a gear, but not a "standard NEMA-xx gearbox", would be a worm gear.
• Timing belt with the appropriate reduction. The belts have some layout possibilities that complement those you can get from gears, and (IMO) would usually be done for reasons of mechanical layout rather than cost. Usually gears are the first try.
• A different motor and/or driver. In particular larger diameter will help torque, but same diameter but longer length, may also help. If the existing motor is fine-pitch, like 400 steps/rev, then a standard 200 steps/rev motor might give more torque also. Other than increasing stepper motor diameter, these are all relatively small improvements, like +50% can be expected if it was not already optimized.
• If range of angular motion is small, a lever mechanism, combined with cams, or linkages, or some other kind of simple high ratio gear (like a worm gear again), could be used. There is an endless variety of "old-school" mechanisms with usually very narrow/specialized applications, so would need to know about the situation.
• Adding an external force to support part of your load, e.g. a spring of some kind