"Creep" - Middleweight Walker - First build

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8th April 2023, 19:47
Daniel Vernall

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"Creep" - Middleweight Walker - First build

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.

Attachment 10017

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
10th April 2023, 12:44
Ocracoke

Hey there Dan, welcome to the forum! Great to see another potential MW competitor and especially a walker!

Quote:

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.

I used 100x50x3mm as the frame for my previous iteration of my current Middleweight, Jibril and that held up "fine". It took a direct impact from a vertical spinner and yes, it did penetrate but it wasn't terrible, certainly didn't punch a hole all the way through the box section. Its heavy but if you can make it work, it is a very straightforwards building material block to work with.

Quote:

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.

That honestly is a decision you need to come to on your own, practically any active weapon would work on this but if I was building it, saw arm or lifting mandabels.

Quote:

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.

So MW/HW events are either Robots Live or Extreme Robots really speaking and they follow the OOB FRA rulings (ref: http://www.fightingrobots.co.uk/docu...uild-Rules.pdf). Now in the past it used to be up to double the weight for walkers and 10% for shufflers but rule 2.2 has been changed to be EO specific. For the AW event I run, I typically allow double but I would aim to be as inline as possible with the roller weight limits. Alan and Jonno are quite flexible though (the EOs for Robots Live! and Extreme Robots respectively).

Quote:

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!

Hahahahaha, so long as it can get through the doors, you're good. 130cm I think, from memory, is only just wider than Raphael, another MW competitor.
10th April 2023, 15:28
Daniel Vernall

2 Attachment(s)

Quote:

Originally Posted by Ocracoke

I used 100x50x3mm as the frame for my previous iteration of my current Middleweight, Jibril and that held up "fine". It took a direct impact from a vertical spinner and yes, it did penetrate but it wasn't terrible, certainly didn't punch a hole all the way through the box section. Its heavy but if you can make it work, it is a very straightforwards building material block to work with.

That's good to know!

Quote:

Originally Posted by Ocracoke

practically any active weapon would work on this but if I was building it, saw arm or lifting mandabels.

It's funny you should mention lifting mandibles, because I was working on a design last night which had something like this. The idea is to have two fixed forks on the front that almost touch the floor, and a pneumatic spike on the top which crushes down on whatever is on the forks to grab it (and hopefully puncture it), then the hexapod can raises its whole body height lift it slightly off the floor and drag around the bot. It definitely has insect vibes that are really cool!

Attachment 10020

Attachment 10019

I imagine there may be issues of counter balance when lifting, but I only really need to lift the bots very slightly off the ground to be in control. There's also the worry robots won't fit between the front to actually reach the mandibles! It would be nice to have an invert mechanism of some variety, which is why I was also considering a 180 degree hammer/axe, but it might not fit very well with enough reach to hit as far out as the legs.

Quote:

Originally Posted by Ocracoke

So MW/HW events are either Robots Live or Extreme Robots really speaking and they follow the OOB FRA rulings (ref: http://www.fightingrobots.co.uk/docu...uild-Rules.pdf). Now in the past it used to be up to double the weight for walkers and 10% for shufflers but rule 2.2 has been changed to be EO specific. For the AW event I run, I typically allow double but I would aim to be as inline as possible with the roller weight limits. Alan and Jonno are quite flexible though (the EOs for Robots Live! and Extreme Robots respectively).

Yeah, the double weight limit was epic, but that would make this a heavy in a middleweight group :rofl: I think I remember seeing a 25% bonus on the Robot Wars reboot rules a few years ago, and a 33% bonus on Robodojo's Beetleweight tournament ruleset posted somewhere around here. So I think you are probably right. I'll aim for no bonus and use 25-33% bonus if it's not possible. That will hopefully be reasonable for event organizers.

Quote:

Originally Posted by Ocracoke

Hahahahaha, so long as it can get through the doors, you're good. 130cm I think, from memory, is only just wider than Raphael, another MW competitor.

Ha I hadn't thought of that! Are they double doors??
10th April 2023, 15:43
Ocracoke

Quote:

Ha I hadn't thought of that! Are they double doors??

This depends on the arena ;) Robots Live is definitely double doors, Extreme Robots is a sliding single however Gabriel and the like will go through those so you are probably OK with your proposed dimensions.

Quote:

Yeah, the double weight limit was epic, but that would make this a heavy in a middleweight group :rofl:

Heh, I've fought HWs with MWs before :P It is a victory just getting a fighting machine to survive 3 minutes in the arena in the first place.