FW electric crusher build

[Draper]

Hello everybody, I am planing to build a new feather weight crusher for live events later this year. To start with I have began designing the crushing mechanism and will build the rest of the robot around it. Currently a 24V Linak 6000N linear actuator is being used to power the weapon.

Spec of the actuator:
IMG_20180528_145000.jpg

Here are the CAD drawings of the mechanism:

claw design side.pngclaw front.pngclaw top.png

The claw will be 10mm thick steel, and the mounts 20mm thick HDPE.

For the setup and holes used in those examples these are the performance calculations:

bite force spread sheet.png

Effectively the jaws open 225mm high and 60mm low, with close to 4000N of tangential bite force across the whole movement. The vertical bite force is lower at start of the cycle but ends up at 4000N at the end of the cycle, this is not so much of an issue as this force will only be used after the tangential force has pieced the armor.

Anybody with more battle experience be able to tell me if i have enough force and bite width to be effective with this set up?

To continue the design I plan to use a low tornado like body in line with the weapon mounts 130mm high and four wheel drive drill motors. I would ideally like it to be capable of self righting but i'm struggling to think of a way that wouldn't involve massive wheels or a heavy powered solution.

I though about roll bars but i'm worried the heavy actuator would give it a poor center of gravity for self righting as its mounted high in the robot.

[James Williams]

Hi James, welcome to the forum.

Your weapon looks pretty impressive. My robot Neophyte is approx 200mm tall & is one of the bigger FW's so you should have a big enough bite for most opponents.

I'm no expert so I can't tell you how effective your weapon will be at piercing armour but I do know that most robots use HDPE for top armour so you should have enough power to at least get a good grip.

[Al_]

Hi, and welcome to the forum. I have a FW hydraulic crusher so I'll have a stab at answering your questions.

225mm jaw opening will fit most featherweights in it. There will always be the odd one or two too big to fit, but it you go chasing every last one its not worth the trade off in increased weight or less crusher effectiveness.

Does it have enough bite force? Impossible to say really. As before there will always be bots you can't crush and there are so many variables such as different armour types, thicknesses, where you grab a bot and so on. Put a good drive system on it and at worst you have a crusher for lightly armoured bots and a capable control bot for the heavier armoured stuff. More crush is always good but you'll add weight to yourself to make sure your own bot can take the forces too, and crushers have to be very sturdy to do this to begin with. Are the 20mm HDPE bulkheads going to be up to this?

Just as important as the amount of crushing force, I would say is the speed at which the crusher closes. There is no point having the most powerful crusher if you never get to use it on anyone.

I would also suggested you think about at least some form of self righting, you will end up flipped over at some point. Also, try and get a good estimate of weight for the whole robot before you start, it disappears fast.

Please don't let that put you off, crushers are an ambitions bot for a first build. (It's your first post, I'm guessing it's your first bot?) It's always good to see another crusher in the works!

[Draper]

It would be my second robot, I also have a thwack bot made from steel box section.

I was unsure if the bulkheads would be strong enough, not worked with hdpe before, I could double the thickness around the anchor points or strengthen it with steel. I was also concerned if the 10mm thick steel would be thick enough for the claw.

How does your bot self right? I was thinking of roll bars to passively self right it, they would also protect the actuator from attack as well.

[Al_]

I would think that the 10mm steel would be thick enough for the claw, depending on the grade. I use 6mm thick tool steel, but only for the last 100mm or so due to weight, the rest is all aluminium.

Roll bars could be a good option for self righting if your bot has the right shape for it, and added protection for the actuator is good too. Mine uses cable actuated arms to self right, but I had lots of problems with them last year due to not having enough weight for the self righting system. I worked on it over the winter and this year they have been much better in the couple of fights I have had with it so far. There is more info in the build diary if you want it.

[Ocracoke]

Roll bars could be a good option for self righting if your bot has the right shape for it, and added protection for the actuator is good too.

Downside of roll bars is that it will potentially limit the height that your crusher can have. Won't affect performance but it may stifle getting hold of taller robots.

[Retroman]

For self-righting, could you create something similar to Razer? Linkage actuated wings could be made to push pretty much any way you wanted.

[PaulusSmallus]

Hi James,
from the pictures you attached, it looks like you will be able to adjust how fast the claw comes down by choosing what hole to attach the actuator to. I like this idea a lot
From the top view of the robot, it looks like the claw comes down in front of the robot. My thought is, if this comes down on top of a robot, it will just tend to lift your robot up. You will need something for the claw to push down against, like the front scoop of razer.


This makes me want to build a crusher robot

[Draper]

Cad robot 2.pngfirst cad picture.png
Update on progress

the CAD design is coming along nicely but still a long way off finished.

I went for the simplist solution for the self righting by making it invertable. When it is finished it will be able to run off the top of the claw and the rear wheels and unable to stay on its side.

triangler wedges still need to be added to the front wedge as well to catch robots and prevent the claw lifting the back end up.

biggest problem at the moment is that its already 2.5kg over weight! Without any electrics, top lid, fasteners or the front wedges. Some work needs to go into reducing the size of the design.

[AdamST180]

Nice design! Will look forward to seeing it progress

[Roboteernat]

You could prob loose 'some' weight by using 2wd and a belt between drives. saves weight on motor gearbox (but gains on belt and pulleys?

also you wouldn't need those large plates to hold the motors in place, something like these will do: https://www.youtube.com/watch?v=kDS28q6QwIQ (shameless plug - i do sell some)
also the plastic casing around the linac could be striped back a bit. i have a couple of those actuators and although i haven't striped mine, they do look as if they can be.

[Draper]

full new robot.pngfull robot inside.png

Update on the CAD. I have created a final design that clocks in 1kg under the weight limit including batteries and ESC's. Hopfully all the fasteners will be less than 1kg.

The frame will be assembled primarily using barrel nuts with some standard nuts and screws as well.

The motors are 15.6v drill motors and I plan to run them on 4s lipo for testing with the option of overvolting them to 7s later. For the 24v actuator i'm unsure if i should use 6s or 7s currently.

For ESC I was going to use two of the feather two controllers as I think 5s lipo may be too much for the dual version to handle.

[Draper]

Work has been started on the build. The base has been cut from 6mm hdpe using a hacksaw. The holes were done with a pillar drill allowing for the counter sink bolts to sit flush on the bottom.

[Draper]

The back plate made from 15mm hdpe has also been made, this plastic was ordered to the correct height so only had to be cut to length, which was done with a chop saw. The holes for the barrel nuts were done with a pillar drill with the marking and measuring done on tape.
IMG_20181001_135442.jpg

[Draper]

Two parts joined together.
IMG_20181001_135823.jpg