"Creep" - Middleweight Walker - First build

[Daniel Vernall]

Hi all, I'm a long time lurker and I've decided to start work on my first bot this summer. At the moment I'm just in the design phase, so any help you could offer would be appreciated


I'm Daniel, I'm 29 years old and I'm a software engineer based in Spalding, Lincolnshire. I've not had much experience with metal fabricating, but there is a makerspace nearby with over 100 active members in Peterborough, so I'm considering joining that community and getting access to the machines and education there. My Dad and uncle are proficient welders of steel, so I might get them to come and give me a hand with the chassis.


I know it is not a good idea to make a complicated build for my first robot, but I've always been fascinated with walking robots that I just can't resist giving it a go .




Here is my work-in-progress design idea:


"Creep"
A 3dof hexapod robot with locomotion controlled by pneumatic air muscles. I haven't settled on a weapon system yet, but I imagine a pneumatic weapon of some variety will be a good fit as I will have half of the kit already installed for the locomotion pneumatics.


The reason I chose 3dof for the legs is because I think that a walker which is not maneuvrable will be awful. And 3dof hexapods have amazing opensource code available for walking gaits which allow them to move quickly and in all directions. Including strafe (crab-walk) etc. I believe this is a key advantage a walker bot has in its own right, that isn't gifted to it (aka. weight bonus).


The reason I chose air muscles is because they can be fabricated DIY and they are cheap to make/replace. They are very compliant, so they will bend and stretch without breaking (within reason) and this allows them to be bent around so they can squeeze in tightish spaces. Servo motors are very expensive and too fragile to be exposed in the legs of the robot. I considered a complicated system of pulleys/chains/sprockets but it seems way too brittle to withstand any form of beating without mega expensive parts.


I am currently considering using liquid CO2, which is regulated down to around 45PSI in a buffer tank, which is the necessary pressure needed for the air muscles. If I go for a pneumatic weapon, I'll have a second buffer tank and with its own regulator set at whatever pressure the weapon design calls for.


I have attached a mockup I've been working on in Sketchup. I haven't modelled the brackets/supports/piping for the CO2 tanks etc yet. And some of the chassis is just overlaid instead of modelling the joints. I plan to add some chains/cable from each leg to the chassis which are sized to be taut at the maximum joint motion to attempt to protect against over extension of the joints when the legs are rammed/attacked.

Creep.png


Key parts of the design:


Chassis and legs are 70mm x 60mm x 3mm thickness Steel Box Section. This allows me to house the air muscles and joint rotary sensors inside the box section.


The central bank of modules is 18 x 5/3 way double solenoid valves. Each of these control a pair of air muscles. As one muscle is pressurised and contracts, the other muscle is vented and relaxes.


I'm not certain of the top armour yet, but I'm considering some kind of roll cage at the moment depending on the weapon system. I'm thinking that the base armour can be fairly thin.


A few questions for you lovely people please:


How well do you think 60mm x 70mm x 3mm Steel Box Section will withstand to Middleweight weapons? I understand a sheet of 3mm steel might not be great, but box section is very sturdy.


Which type of weapon system would you think compliments a design like this? I originally considered a couple of big spinners which were angled as armour over the legs and met in the middle above the center of the body, but the only way that would fit would be on a massive heavyweight.


Can anyone point me to any events which offer weight bonuses to walkers with 2/3dof. I was originally aiming for a featherweight, but the mini components required which reduce the weight significantly enough are just too expensive. So, I'm looking at squeezing into a middleweight category and using cheap mass produced industrial components from alibaba.com etc.


If Creep manages to fit in a middleweight class she'll be a behemoth! With the legs out it's 1.5m long x 1.3m wide!

I'm definitely needing a weight boost to squeeze in middle weight. The weight of the chassis and legs is looking like its nearing 30kg!

Thanks for your help in advance!
Dan