[FW] Hydraulic Crusher Bot

Me and a work buddy, Dave, are working together on a featherweight for the champs in April. We're going to post our progress here, will probably just be working on spare weekends up until the event.

Here is a very rough idea of the kind of design we are aiming for. Nothing is set in stone yet, just trying to think of a shape that works, and this is our best effort so far:
http://www.fightingrobots.co.uk/atta...tid=5553&stc=1

http://www.fightingrobots.co.uk/atta...tid=5554&stc=1

We're going to be running two Satern-16's with 775's from Ranglebox with a belt driven 4WD setup. Powered these things on for the first time on Saturday and they are absolute beasts! Can't wait to get something driving around on them.

For the weapon, we're using a hydraulic pump from a convertible car roof. This pump is nice and compact, with the motor, pump and reservoir all combined into one block. Spent the weekend figuring out which valves and wires do what, it works in a strange fashion, with different flow directions controlling different outlets. It works a treat though, one ram had no trouble lifting a fully grown man off the ground, and we plan on using two of them :)

We used a pretty ghetto set up for testing... a computer power supply with all the wires soldered together and croc clipped onto the motors!

http://www.fightingrobots.co.uk/atta...tid=5555&stc=1

That is all for now... more soon!

What car is the pump/motor combo from? Looks good btw

It's out of a Mitsubishi Colt, not sure which exact model as we just got it from Ebay. Weighs 2.5kg in total for the motor, pump and res. Good bit of kit!

thats a good find, will watch with interest

Should look into that.

Agree the saturns are phenominal. They made my robot scream around on 60mm wheels and were good as new after a spinner hit pretty much wrote off the frame.

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Originally Posted by Giles

It's out of a Mitsubishi Colt, not sure which exact model as we just got it from Ebay. Weighs 2.5kg in total for the motor, pump and res. Good bit of kit!

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Those pumps, using a quick google search, are good for 1750 PSI max.

http://www.jagrepair.com/HydSystemEvaluationXK8XKR.htm

Still 120 bar tough. A 32mm bore ram will develope 1 ton of force on that pressure.

The main question, how much oil is in that tank?

I'm not sure what the norm is for feathers, but that seems pretty good to me? With our two 20mm bore rams we should be pushing out around 700kg of force (Force = Pressure * Area * nCylinders).

The tank is pretty small. Doesn't seem to require much liquid. Once we remove two of the rams (it currently has 2 big and 2 small rams, we only want the big ones), then we'll be saving even more fluid.

Hmmm, this is looking very good! Little Nipper came 4th this year so Crushers have their place. I'm sure it will produce enough forced to scare off most opponents.

if you're going to use the rams it came with, I think you'll bend the rams before you bend hardox. get yourself one fat ram.

Crusher norm for feathers. No clue
Ram power ain't the main thing. Pressure on the tip is what counts, combined with the shape of the tip.

Also, stroke and speed have their place.

The 20mm rams, what stroke are those? If the stroke is longer than 40, the forces impared in robot combat will bend the rods.

On the other hand, Tiberius uses a 70*148 ram, with a 20mm hardened steel rod, and it seems it's still going strong, even build by me in 2003.

Hmmmm yes the rams are extremely light, which leaves me to wonder what they are made from... The big rams have a stroke of 140mm, was planning to use these on a 3:1 lever ratio to help with grabbing speeds.
Will look into sourcing a single, fat ram. 32mm would be ideal. I'll see if anything crops up on ebay that will fit the bill.

Is there a standard in how to prevent the pump from overworking when the ram is at its full extent? The rams i'm using at the moment are sensored, but I can't imagine many second hand rams on Ebay having such features.

EDIT:
Something like this seems to fit the bill.
http://www.ebay.co.uk/itm/Flowfit-Hy...item3a7cb3126c

That one will be heavy.

To avoid burned out motors or burst parts, an PRV or current limiter is in order.

Just wanted to test out the rams/pumps under load to make sure everything worked as expected. Seems to be working fine. Will need to explore the strength of these rams though until I can find a good 32 bore one which isn't too heavy (suggestions anyone?)

https://www.youtube.com/watch?v=6cWS...ature=youtu.be

What stroke is wished for?

Anything between 100mm and 140mm would fit well into the current design. We currently have two 80mm ones (as seen in video) and two 140mm ones. Wouldn't really want anything longer than the 140's.

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Originally Posted by maddox10

The 20mm rams, what stroke are those? If the stroke is longer than 40, the forces impared in robot combat will bend the rods.

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What about if the rams are pulling in, rather than pushing out?

Then the rod size will detract from the power. Bore 20mm, rod size 12mm

1*1*pi*120bar=376.8kg of force pushing.

Pulling it's (1*1*pi*120) - (.75*.75*pi*120)= 165,85 kg


But in tension steel is better than in compression. One of the reasons we have longer suspension bridges than single arch bridges.

OK, so if the bore cross section is smaller, then the ram will be moving faster for the same pump flow - couldn't the leverage ratio on the jaws be changed to make up for the lower force while keeping the closing speed about the same?

Yep, speed and torque are interchangable, with only the mechanical losses interacting.

But what isn't interchangable is the total available force. A retracting ram has less force to mutate from speed to power or the other way around.

Another thing to think about is reach.

If you have a slow, high force cylinder, then you can increase the speed with a 3:1 lever ratio, which also increases the reach of the claw.
If you have a fast, low force cylinder, then you can increase torque by using a 1:3 lever ratio, which will reduce reach, and for the most part not be as useful.

So ideally, a slow, powerful cylinder on a decent lever ratio would be the thing to aim for.

I was looking at the build thread for Cobalt, who uses a really nice custom made titanium cylinder. I don't have anywhere near the tools or skills to make something like that. So its looking like im going to need to go with one of the heavy steel cylinders out there. Or stick with my two thin ones and hope that between them they can bare the load :P

The guts of Cobalt are now inside inside Little Nipper, you could ask the Big Nipper team what ratio/force/pressure they use. I know they swapped the brushed pump motor to a Scorpion HK4035 to up the power/speed of the pump, maybe you can do something similar.

While I love anything made of titanium, 7075 aluminium is probably just as good for a light weight cylinder and much easier to fabricate.

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Originally Posted by maddox10

Yep, speed and torque are interchangable, with only the mechanical losses interacting.

But what isn't interchangable is the total available force. A retracting ram has less force to mutate from speed to power or the other way around.

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Good point. So that would mean that you could have a larger, possibly hollow rod that would give you a faster return stroke, assuming the crusher doesn't need nearly as much power to get the point out of the opponent. Would I be right in saying that for the same weight, a wider hollow rod will be stiffer than a smaller diameter solid rod? Sorry for all the questions, I am looking around for something a bit unusual for a sportsman weapon for next year.

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Originally Posted by overkill

Would I be right in saying that for the same weight, a wider hollow rod will be stiffer than a smaller diameter solid rod?

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Yes :) If the weigh was identical, the wider hollow rod would be stiffer. But I think (since the cross sectional area would actually be the same, just distributed differently) they would have identical compressive and tensile strengths.

A wider, thinner walled tube is stiffer and tougher in compression, weight for weight compared to a solid rod or thicker walled tube.

TAN uses a D60 d50 rod since day 1 for its 100mm bore ram. Just to give an example.

I Still have the 32mm Bore Cylinder from Cobalt if your still looking for one, Gear pumps have a motor matched for the correct flow and pressure for the size of the pump, you can overspeed and create Cavitation so don't overvolt (https://en.wikipedia.org/wiki/Cavitation)

Hi Kenny,
Potentially interested in the cylinder, yes, havn't found anything else to fit the job yet. Just been continuing with other parts of the build in the mean time. Do you have any pictures of it? And how much you might want for it? PM me if you like.