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  • Unnamed FW crusher build diary

    Hi everyone, so what does a chap, who has very limited mechanical engineering experience, no tools more advanced than a battery drill and jigsaw, who last built an antweight over 10 years ago and who has been bitten by the bug again since watching the last series do? Build a featherweight crusher of course!

    I started generating some ideas a couple of months back and in hindsight, I should have started this build thread back then so you could have all told me about the mistakes I no doubt have made. I decided that I wanted to make a FW crusher. Crushers have always been my favourite type of robot and having a good read of the forum it doesn’t seem like there has been too many of them built, and I think it should push the limits of what I am capable of. I decided to aim (for no particular reason) to try to get around 1 tonne at the tip of a vertical crusher, as this seems reasonable.

    I set about finding a ram and means to power it that would give me the force needed at a sensible ratio at as light a weight as possible.I’ll put some details of that in a later post, but once I had the sizes of this, I could set about designing the chassis and the rest of the bot around it. I have never really used much CAD software, but I downloaded Fusion 360 and after a bit of messing around I was able to get the hang of it. After about amonth of design and re-design, I came up with something I was fairly happy with. Again, I’ll put some pictures up of the CAD in another post when I get on the other PC. The thing that became apparent very quickly was that it was going to be difficult to get something in the weight limit that doesn’t tear itself apart if it bites on something it can’t crush.

    Fusion 360 has some simulation capabilities built it, so after watching the tutorials I set it to model the chassis sides with the expected loads the ram and crushing arm will put on them. I still don’t really have much idea what I’m doing, but at least I could see if each iteration of my design was better or worse than the previous one. It seemed to make something strong enough and within the weight limit, that I was going to have to use titanium for the chassis. I spent a lot of time refining the design and then I had a look at the availability and cost of the titanium. Wow. I know it is expensive but I had no idea just how bad it was and I should have checked this before putting too much time into the design. After another read of the Riobotz manual and some more research into materials, I have changed the chassis to 7075 T6 ali. Still not as cheap as I would like, but much more reasonable than the titanium. Anyway, a couple of weeks back the designs went to waterjet cutters and yesterday I picked up this:

    IMG_20161116_185201374.jpg


    That is one of the chassis sides and it has come in on weight budget, yay! Its on the dining table as the shed isn’t ready yet. I have some more bits of the bot that I need to take pictures of and add to this diary, but I think that’s enough for the first post, comment and critique welcome!

    P.S. As per the thread title, I don’t have name for the bot yet, any ideas on that welcome too.

  • #2
    I'm very much in the same boat as you... building / designing a fw crusher as well. Just wondering about your choice of material there for your chassi. How thick is it? And how much force will it have to take / can it take.... to achieve your 1tonn at tip.... 3 tonn from your ram maybe?

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    • #3
      Hi Matt. The chassis is 8mm thick per side, which theoretically means I have 16mm total thickness to resist the forces of the ram and arm. However I think this would only work if you happened to crush everything perfectly vertically and in line which wont be the case. Therefore I have tried to design it so that one side could handle the forces on its own. I think the material for it will be ok from having a read of the Riobotz manual. Its one of the best aluminium alloys, especially with regards to yield strength which I think is was I need for the chassis and arm where the forces are. The arm is mainly made of the same stuff, but I plan to put a tool steel (or similar) tip on it. Titanium was way too expensive and the steels were too heavy so I don't think I had much choice.

      The ram should give out 2.6 tonnes so I'm working on a 2.6:1 ration. Speaking of the ram......

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      • #4
        Here is the business part of the design, 100mm stroke and weighing a shade under 3kg. I think that longer term there is scope for a smaller bore ram running at higher pressure to save some weight. However that would require a power pack that can produce greater pressure than any I have found so far.

        IMG_20161117_191941362.jpg

        Here is the power pack I’m using, it should make it as simple as running the motor one way to extend the ram and the other way to retract it. The pack comes with a heavy, fairly low power brushed DC motor on it. So I have removed that and I’m going to replace it with a smaller, lighter brushless motor, which should save on the order of a kilogram of weight and give me faster flow rates.

        IMG_20161117_192027587.jpg

        Lastly, a few spacers, one of the few turned items in the design, one of the guys at work was kind enough to make these for me, just some grade of aluminium and acetal plastic. There is another bit of turning to do, so I’m crossing my fingers he can do these for me too in a quiet time or I’ll have to look for alternatives.

        IMG_20161117_192126799.jpg

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        • #5
          I get what your saying about the steels... how much that chassi side cost then?
          i was planning on making my arm chassi and arm out of 3mm stainless steel becuSe I have someone who will give me some and laser cut it for free... but I think it may come in too heavy.
          i need to get myself that riobotz book I think and have a read.
          i too am planning on using a different material for the tip.... I made a crude test of my weapon system and used a hss tip. It pierced through some 2mm mild steel. But found it difficult to contain sideways movement once the pressure really starts, but that may have been down to the crudeness of my test rig. Lol.. Going to be very tough in the weight limit for me I think. Lol

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          • #6
            Looks like your off to a great start!, look forward to seeing how this progresses

            Have alook at my build dairy on my featherweight crusher Cobalt i built in 2012 and message me if you have any questions

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            • #7
              Just looked at your build diary kenny... looks amazing.,, no real info on the materials you used tho, chassi, tip, or real figures on what force your ram is producing and what downforce is at the tip....... i need these figures so i can aim higher ;-) lol

              Comment


              • #8
                Originally posted by MattLampitt View Post
                Just looked at your build diary kenny... looks amazing.,, no real info on the materials you used tho, chassi, tip, or real figures on what force your ram is producing and what downforce is at the tip....... i need these figures so i can aim higher ;-) lol
                7075 Grade Main bulkheads and 6082 T6 Aluminium everything else, P20 Tool Steel Claw, 32mm Bore ram (1.6t at the pressure i run it at), i had different pivot points to adjust the pressure at the tip but limited the stroke of the claw depending on the opponent, the highest point was 1:1 Ratio and 1:2 at the lowest.

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                • #9
                  Hi Kenny, I've just had a read of your build diary, thanks for telling me about it, cobalt looks a very impressive machine! What happened to it? Did you get the new ram and self righter working and how did it get on after that?

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                  • #10
                    Al,

                    Thanks for the compliments, It was split apart due to a redesign of the drive system and then sold the hydraulic system and ram which is in little nipper later that year, Over the years ive been designing and making bits for a new Cobalt which isn't so far away being ready for battle

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                    • #11
                      Bits of progress on a few areas to report:

                      First up, I have received and tested the speed controller for the weapon motor. I have tested it with the motor that I am fitting to the hydraulic power pack a Turnigy Aerodrive SK3 brushless and confirmed I have full forwards and reverse operation. The speed controller itself is one of the Hawk Fusion ESCs intended for RC cars. Failsafe tested and working on it too.
                      IMG_20161119_124933017.jpg

                      Next, thanks to some advice from Kenny, I have checked the speed of the Aerodrive compared to the motor it replaces in order to avoid pump cavitation from running it too fast. I had calculated the Aerodrive to be about 20% faster than the old motor to give me some headroom for increased flow if possible. After measuring them it turns out the Aerodrive is about 25% faster, so this means I can limit it to the same speed as the old motor by limiting the throw on the TX and still get a big increase in power, and I still have speed headroom if that’s needed/possible.

                      I have had the pins for the ram and crusher arm made and test fitted together, and the parts for the front wedge and arm tip are at the water-jetters.I hope to have these soon to start mocking the parts up.

                      Probably the biggest bit of progress since the last update is one of these:
                      IMG_20161126_134932338.jpg
                      Unfortunately this means leaving behind the comfort of a nice, warm dining room with a dining table as a workbench. The plan is to wire it up, insulate it, board it out and get some work benches in over Christmas so that bot construction can continue in there in the New Year.

                      Finally, the drive for the robot is sort of modular, in that it can bolt on and off the rest of the machine. Its designed to run on a pair of Saturn 16s with the 775 motors but these are currently out of stock. By changing a couple of motor mounts I can run a pair of the Argos finest drill motors/gearboxes just to get me running around, so I have got a couple of these. I have also received one of the 2 TZ85a ESCs and successfully modified it for brushed operation. However I have a question about the drill motor/gearboxes. Ahem. How do you get the balls out? I mean a few fell out when I turned it upside down, but the rest of them wont come out even though they move freely in their holes. I have tried shaking it, I have tried sucking them out, and I have tried taping it on a hard surface (but not so hard as to damage the l/h screw)all to no avail. Any tips for doing this which don't involve taking the whole thing to bits as I can’t lock the gearboxes up with grub screws untill I remove the ball bearings.

                      Cheers!

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                      • #12
                        I turned the gearbox so the bb's dropped down... then I bored the hole a little at the top with a slightly wider pozi screwdriver.. then turned it back the other way and they dropped out...
                        you could also use the tip of a new Stanley blade.
                        I need a shed too... desperately ..... and time.... lol.

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                        • #13
                          Thanks Matt. I had considered having a go at the top of the hole but I was weary about creating a burr on it and making the situation worse, (or at least no better!) I'll give it go.

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                          • #14
                            If you don't need much power/speed on the drive, and wait for ranglebox restock for your final version anyway, the neptune-28 could be an alternative to the saturn-16.
                            They're not listed in the shop, and also out of stock (ellis hasn't much time for the shop with robotwars going on, last info i got was "early next year" or something like that), but smaller and lighter.
                            So for a feather that doesn't want to push or be really fast, they could be an alternative. Planning on using them, too.

                            Neptune Gearbox Maße.jpg

                            Just take in mind they have a 28-1 gear ratio, not the 16-1 of the saturns. Sooo... either faster motor, bigger wheels, or slower bot.

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                            • #15
                              I wasn't aware of the Neptune gearboxes, so that could certainly be an option if weight is an issue or I don't need as much power. Would you say they are similar to the typical drill motor/gearbox in terms of power, as I understand the Saturns are much more powerful than this? Either way I finally have the ball bearings out and the drill motor/gearboxes locked up. I can have a run around with these when I get the rest of the bits and then make a decision on final motors/gearboxes from there.

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