# Gear configuration for a legged hexapod

I have an assignment for my Mobile Robotics course to design the drive mechanism for a legged hexapod and demonstrate its gait in motion.

The idea is to design the hexapod as per the following schematic:

There are 2 motors in the mechanism, each driving 3 sets of wheels. Wheels 1,3 & 5 are connected to one motor and wheels 2,4 & 6 are connected to the other. The wheels work as sort of a crank to produce motion in the legs and both the motors are 180 degrees out of phase to enable a working gait.

The part where I am having trouble is designing a gear mechanism that connects the 3 wheels in this triangular configuration to a single motor. If anyone has ideas for that, or further suggestions, it will indeed be very helpful.

• Do you think that is the thinking part of the exercise? So perhaps we can comment on what you suggest. Commented Apr 3, 2021 at 12:10
• No this is not the thinking part of the exercise. My professor is just interested if we understand the sequence of motion of the legs since this is a Mobile Robotics course. I could just animate the wheels without focusing on the mechanism driving it but I want to take a more practical approach. Commented Apr 3, 2021 at 12:26
• And getting that to happen from one motor is the critical part... Commented Apr 3, 2021 at 12:28
• Can you help me with some resources or hints which could help me figure this out? I have no problem figuring this out myself that would be a fun exercise, I am just blank as to where to start and who to ask Commented Apr 3, 2021 at 12:31
• You do realize that being out of phase adds 0 additional complexity right? Being out of phase does not mean that you turn in the opposite direction.
– Abel
Commented Apr 3, 2021 at 14:36

Ok I think I understand the intention now. Here is a thought of how to do it with timing belts. 6 half axles and 2 common shafts M1 and M2.

All 6 half axles would all need to be horizontally adjustable to tension the 6 belts. Everything could mount to "2D" vertically oriented sheet metal or laser cut parts, and the same shafts, bearings, and sprockets could perhaps be used throughout. The trick is getting the tensioning process to be reasonable. Bit of a mess as a concept, to be honest, compared to 6 individual motors.

PS- if the range of angular motion is finite, like 120 deg or less, then replace the belts and sprockets with linkages to drastically simplify

There are several possibilities depending on what it is you are trying to achieve with your motors.

As Pete pointed out, just syncing all your wheels would KEEP things the same phase (180 deg) apart.

Next up: the thing your diagram seems to represent - two sets where two outer 'wheels' and the middle 'wheel' of the opposite side are in sync. This allows you to vary the phase between the two sets if you desired and have all 6 'legs' down if you desired.

My hypothetical 'highschoolers' would likely motorize the middle ones, drive-sha ft power to the opposite side and then chain it to the two outer ones. They might try something annoying, in some effort to mirror things in the top view, they have to offset in a different view to make room for the two drive shafts. One of them might then realize they could have rotated the 'left' to the 'right' and built identical parts for both sides rather than mirroring. That's about it for hurdles not related to the strength in their materials.

There's also a third option where the left and right are each in sync. This lets you potentially have 4 'legs' down if you so desired ( middle ones would always be out of phase of their outer ). Hypothetical highschoolers would chain each of the two sides together.

WWHHSD