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Thread: Project Squirrel

  1. #1
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    Hoo boy, here we go again.

    So after a long debate (with myself more than anyone else), I'm going to attempt to build a featherweight robot, just on the basis of cost constraints, that and it'd be my birthday present that I'll be giving to myself, but it's going to need a lot of thought, and quite a few questions, which I hope you guys would help me out on.

    So, the name of the robot will be called Ratatoskr, in kin to the messenger of Yggdrasil of Norse mythology. Two wheeled, drill motor driven and more than likely, HDPE chopping board/sheet in every way... possibly. Maybe. Who knows.

    Things I know would be in the final design/product as it were...
    - The motors will definitely be drill motors. They're either going to be second hand, or super cheap from Argos, or Homebase or something similar shop wise.
    - The baseplate/chassis will be entirely made out of HDPE. No need for welding, just a lot of drilling.
    - My best bet for ESCs would be either getting them from Ranglebox, or from Rory Mangle's site, as his FeatherTwo ESC looks like it would be a nice fit for the robot.
    - For the controller, I'd love to get a Pistol grip controller. I'd have to do a little more research into that but my good friend knows of an RC place that could help.
    - Tab and Slot. It'll be easier to replace wrecked pieces of armour or chassis, cut out new pieces and screw them in.

    Things I'm a little sceptical about:
    - The weapon. I'm not sure if I should go with my original idea of a vertical spinning blade, similar to the famous Pussycat Series 4 version, or make it an axe similar to Hatchet.
    - Armour. I'm honestly not sure if I should splash out on getting some Hardox or mild steel sheet for side and front armour, or just make it entirely HDPE. I'm on the fence about it because I could always start off with HDPE then move on to metals.
    - Batteries. I'm not sure if I should go 6 cell or 4 cell, and a decent charger to go with it all.

    Questions about all of this, and fingers crossed when I get the chance to make a video...

    Would 10mm HDPE be enough to cover all bases of the chassis? Or will I need to go a little thicker? And what's the best place to buy sheets of HDPE? Or should I just buy big ol' chopping boards and cut them down to size instead?

    What would be the best screws, nuts and bolts for this kind of thing? As I need the base to be flat to the ground as much as possible, so the flatter, the better. And how thick do these things need to be to withstand heavy hits from spinning weapons and general wear and tear?

    Wiring. How thick should the wires be to withstand the current going through it?

    For the weapons, will I need bearings or bushings, depending on what I go with? And if so, what would be the best bet to get them from for a decent price?

    And whenever possible, fingers crossed, I'll be able to post a video on some design work of it all, as I have been using cardboard from old soda drink boxes to cut up and use for design purposes. Not exactly prototyping, but to form shapes and such, so hopefully I'll be able to explain more with that.

    If anything is confusing, then just give me a nudge, and I'll try to explain it as best as I can. Writing sentences isn't exactly my strongest aspect.

  2. #2
    Bodge Job's Avatar
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    Sounds like a good first robot plan, spinners may be better to avoid for first robots though as there much more dangerous and expensive, (can only be run at certain events as well). For good design ideas have a look at other robots and watch out for how there made and there main advantages and failure points (eg do they always land on the wheels, or get stuck on their back/side) and keep these in mind when designing yours.

    Battery wise, what kind of batterys are you talking? (lipo's, nimhs or Lead acid etc) if your new to things, nimhs are a better choice as there cheaper and safer. Lipos are lighter for the same energy so are slightly better, but dangerous if damaged or miss used (can catch fire) so require special equipment and have extra rules, and will end up coming much more expensive so I'd avoided using those at first unless you have prior experience. lead acid batterys (sla) are generally too heavy and only supply a low current so I'd avoid them altogether for feathers. (you may know all this already, but wasn't sure)
    From the cell count your mentioning, you seem to be referring to Lipos (3.7 volt per cell). so a 4s is probably a good bet for 12v drills, a 6 cell would be 22.2 volts so would probably kill your motors and esc very fast so I wouldn't use that. Most motors can survive a 50% overvolt eg a 12v motor could survive being used at 18v, but would massively shorten it's life, (currents would be much higher, so every thing will get much hotter) some motors can't cope with any overvolting though so be careful.
    If using nimhs, there 1.2 volts a cell, so 10-14 cells is a good bet (could use two identical 7s packs in series to achieve a 16.8 volt pack.
    always make sure to keep below your ESC's max voltage, keep in mind lipos peak at 4.2 volts per cell when fully charged.

    Plastic related questions:
    https://www.directplastics.co.uk is where I get my plastic from, chopping boards maybe be cheaper but are often made from LDPE, which tends to crack/split when hit by spinners. Thickness is difficult to judge (depends a lot on shape and how it's used etc) 5-6mm will generally be enough for your top and bottom (little hitter only managed to make it though my 6mm top once), not sure how that survives against crushers though. For side armour some robots rely on thinner plastic (I think some bits of explosion are 5-7mm, but spinners can often make it through that, 10mm can be enough, but still a tad on the thin side. I've found 15mm+ is a safe bet, and is thick enough to be screwed into end on, so you wouldn't need angle section or mounts to hold the plastic together (so thicker plastic can save weight if used in the right way)

    Some chunky countersunk wood screws works well in this plastic, and you can used threaded metal inserts with bolts if you want a longer life ( good for commonly removed parts like a baseplate). Hdpe is too soft to be threaded for normal bolts though, so avoid that.

    With weapon mounting, Hdpe is a bit soft for spinner shafts to run directly onto , so it will warp over time. It may be fine for axes though, provided you can keep the chain tensioned. I believe some People have had success with spinner shafts going directly into Nylon 6 (tougher, but more expensive plastic) haven't had any experience with that my self though)
    Bearing wise, some people swear by bearings (less friction) , others by bushings (less to break) , I don't have enough experience with spinners to tell you either way. If your going for bearings I've found https://www.technobotsonline.com is pretty good, others companies like bearing boys also have a large selection. Not bought bushings before so don't know of a good source.
    For wires, I normally use 2.5mm, but that's pretty over kill (it's what I have laying around) I think 1.5mm is enough for drill motors but probably to thin for battery wires so go for somewhere in between. If you want a cheap source of wire I've found buying a cheap 13amp mains extension lead and chopping a chunk out of that, is cheaper than buying rolls of wire at hardware stores ( you can then wire the plug back on so the extension lead still works, be careful doing that if your not use to wiring mains stuff though).

    Sorry, someone else will have to answer the rest of your questions as I'm out of time!
    Last edited by Bodge Job; 19th May 2017 at 14:06.

  3. #3
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    To answer the HDPE question - before I joined a team and started working on a heavyweight, I found a lot of HDPE providers on eBay that cut to your specification and then ship it out to you either free or at a pretty reasonable cost, just type 'HDPE' into eBay and marvel at how many sellers there are! If you have the tools to cut it at home, you can just order a huge few metre sheet then draw on patterns for your robot and cut them out yourself.

    I think we'll also end up using HDPE for the base of our bot for easy access for repairs etc.

  4. #4
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    Hi guys. Thank you for the advice and comments upon such things. But, as per usual with me, I've made a couple of decisions, but I have a lot of questions... and I have to rewrite them all again because the forum decided that I needed to... aaargh...

    So, decisions I've made...
    It's going to be an axe/hammer bot instead of a spinner. I think this'll be easier and could probably get me going in the right direction considering costs and such.
    LiPo seems to be a better choice for me, but if anyone can tell me the best way to make a rechargable NiMh pack, then please do so.

    Questions... oh boy, need to retype this lot again...

    1) RC. Would this be a good rc set? LINK If not, then what rc set would be better?
    2) Drill motors. Would these be a decent set of drills for the motors? LINK Once again, if not, then what would be a better choice?
    3) Batteries. If I do go down the LiPo route, would a brand known as Overlander work for the application?
    4) The screws. How would one go around finding threaded metal inserts? And what would be decent for 15mm HDPE? Or would I be better off going with the chunky wood screws?
    5) Weapon control. This one's been on my mind for a little while... Is it possible to link two ESCs to one receiver? Or will I just be blowing the poor sucker up?
    6) Wires and wiring. Would Homebase or B&Q hold such wiring that I need? As I'm not entirely sure myself...
    7) Connections. Would it be better to solder everything together? Or would it be better to buy a bunch of connectors?

    Any and all help will be greatly appreciated, and if anything needs clarifying, then give me a nudge.

  5. #5
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    I can have a go at some of your questions for you:

    2) The drill you linked is thoroughly reviewed by one of the forum regulars here

    3) I am using Overlander batteries in the FW I am building and have used them in other applications in the past and never had any issues with them. I don't know if anyone else has used them in combat but I would imagine that some people must have. Looking at the quality of their packs I see no reason why they wouldn't be suitable. Also note that if you join the FRA then you can get a discount from battery supplier/sponsor Optimax.

    4) Barrel Bolts are a good way of joining HDPE (and some other materials) together. Here is the first link that popped up on ebay for example

    6) No idea what Homebase and B&Q stock regarding wire, but avoid the stuff intended for home/diy use with low strand count. I like the silicone insulated wire typically used in RC applications as it is very flexible, so easy to run, and the insulation is good for high temperatures.

    7) Connectors to make it easy to test, prototype, upgrade parts, swap out damaged parts etc.

    Good Luck!

  6. #6
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    Thank you Alan for the advice. I think I'm going to series run two 2s overlanders, so I get the same power for cheaper.

    Only 1 and 5 remains. And I would much like to know about 5 the most if anything, because I don't want to fry a receiver on my first go.

  7. #7
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    And I just realised that I need 4 batteries if I'm going for the two 2s overlanders. Two for the movement and two for the weapon drive. This is the reason why I'm a little concerned about using two ESCs connected to one receiver. As said before I don't exactly wish to burn the devil out of it.

  8. #8
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    Do you need pilot holes to screw into hdpe or can you just screw straight into it like 2x2?

  9. #9
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    You can screw straight in if you have to, but a pilot hole helps a lot.

    There was some discussion a few weeks ago about multiple BEC power supplies from multiple escs on one receiver. It boiled down to "cut the red wire on all but one receiver input to protect the receiver", but you should probably go find the full details.
    Last edited by lowndsy; Yesterday at 21:48.

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