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Project Squirrel
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.
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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!
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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.
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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.
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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!
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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. :)
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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.
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Do you need pilot holes to screw into hdpe or can you just screw straight into it like 2x2?
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You can screw straight in if you have to, but a pilot hole helps a lot, as does drilling a countersink.
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.
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When you talking about 2 ESC's to one receiver are you meaning both on to one channel (like 2 ESC's running 2 motors at identical speed on one stick) or separate channels like drive and weapons seperate?
You can comfortably do both, if you wanted to run two ESC's off one channel, like 2 motors running one weapon, you can use a y lead like this
http://m.ebay.co.uk/itm/Servo-Extens...%257Ciid%253A2
And there's similar y leads that reverse one of the ESC's (eg if you had 2 motors facing each other but wanted them spinning the same way).
If your talking about different channels it's also fine, As said by lowndsy you only want one power source (BEC) running the receiver, so chop (or Unwire/disconnect from plugs) all the red servo wires a part from one. It's sensible to choose your most reliable BEC / Esc to power your receiver as your robot will stop working if that esc breaks, so using a drive esc is normally best, also means you can easily run the robot with the weapon disconnected (like for testing).
of your using seperate drive ESC's (one for left side, one for the right side) you can use a thing called a mixer to combine the signal from two challenges, meaning one stick runs both sides in the right directions (duel ESC's have this built in)
As with Q1 that radio seems to be the same as a radio from"Giant Cod" which was a cheap set that people use to suggest buying a few years ago. it works fine, but I've had 2 receivers break over the years, I think others have had mixed experience with them too. From what ive seen, recently people have been suggesting a hobby king radio as a cheap first set. However I've not bought one myself, so someone else would have to confirm if that's a better choice.
If getting lipos, make sure to buy a proper lipos balancing charger, and always store and charge in a lipos guard (a special fire proof sack). Follow the fra rules regarding fuses etc, and have a Google about there safe use, and care (for example it stresses them to store them fully charged for long periods of time) . They can be a bit nasty if used incorrectly so learn about them before you buy one
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So I was just checking the drills in question... and they don't get them restocked in my area until the start of July... Which means I either...
A) Wait for a month which, although wouldn't be too bad, makes things a little frustrating.
or
B) I splash out a little more and go for this particular drill [LINK]... which I'm not sure if it's a decent drill or not for this kind of application.
Thoughts or advice?
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I personally don't think it's worth it for only a 10V rated motor. I would have a look on eBay for much cheaper cordless drills.
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Ah. Right. Thank you Rory. Well... I found another drill, taking into consideration your advice. It's from Terratek. Now I'm not so sure about this one as well, but it looks promising... then again, I said that to the last one and I overlooked it being 10v. This one's 18v at least, I made sure to check it but I'd love another second opinion on this particular drill from Ebay. [LINK] Or would there be a better alternative, and if so, is it possible to get a link to it?
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That one would probably work, though it's still a tad pricey. The ones I bought don't seem to be on eBay any more, but this one is similar, and £10 cheaper than the alternative. I know it looks a bit rubbish, but they all have basically the same motors inside. http://m.ebay.co.uk/itm/18V-Electric...257Ciid%253A23
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Thank you, those are on my list of things to buy.
Now I just need to wait for Rory Mangles to get back to me so I can buy the two ESCs from him.
EDIT: The alternative ESCs would be the Sabertooth Dual 12A's. I have heard that they're a bit hit and miss but it would be a decent alternative if I can't get some FeatherTwos.
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Alright, so drills, HDPE, a Sabertooth Dual 12A for movement and a Botbitz 85a V2 for the weapon ordered... I know where to get an RC, and now I just need some connectors, screws and batteries. And a soldering iron.
Question is... should I go for some ec3 or ec5 connectors to connect all my wiring together? And what thickness of wiring would be the best? 12 awg? 14 awg?
Also, on another side note... which side of the battery should the safety link go on? The + or the -? It's been a while since I've done any wiring of the sort.
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The ready made fuses sold by Gimson go on the red side, so my money is on +
https://gimsonrobotics.co.uk/categor...tomotive-fuses .
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i had asking which side to mount the Link as well, it doesn't matter but people prefer on the positive side
http://www.fightingrobots.co.uk/thre...t-robot/page20
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Oh boy...
So, I got the Botbitz ESC, the Sabertooth ESC and the drills in. Just waiting on the HDPE to come in. But (here it comes), I've looked at the little sheet that comes with the sabertooth, and although it says on the technobots website that it's good for 30lb combat robots, on the little sheet, it says at least half of that. This is the thing I'm talking about. Did I make a big mistake buying this? Or is it suitable for what I want to do, which is power two motors for the movement of the robot? :?
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Forgot to add on here, thank you for the help on the safety link Steve and Mark. It's very much going to go on the positive side.
And the reason why I ask this now about the ESC is that it looks a little small, considering what it needs to do. :(
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I'd say they would work relatively okay for a featherweight. They were used very frequently a while ago, and they used very similar motors. I just wouldn't run them on 18v. There are better ESCs but given the lead time of feather2s, and that they cost the same as one Botbitz controller and half the price of a scorpion, their advantages outweigh their shortcomings.
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12A per side is on the low end of handling capability for featherweights but it would probably manage. I've never used Sabretooth controllers (and never will) but I ran a 2WD drill drive robot on a Scorpion XL for several years - they're also 12A per side - and it coped fine. It does have current limiting, so if your motors try to draw too much current, the speed controller will prevent them from doing so rather than blowing up. Best thing to do though is test it out in practice once you've got a functioning drive setup. Run it for a few minutes at a time to get a feel for it and see how it copes.
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Well if that's the case I would've gotten myself the 25A instead, haha. Thank you Theo and thank you Jamie for the insight. If it doesn't really work that well, then I can at least use it for... like a distraction bot just for silliness, I guess, and I'll have to dive back into the wallet for the 25A one.
So with that out of the way, I'm just waiting for the HDPE, then I'll make a list of what else to buy.
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I think Antazz is/was selling one for £60. I saw it in an old for sale thread (about a year old by now) but it didn't say it was sold.
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I've got one of those ESC's and it seems to cope with two drill motors fine. If I were you I'd add an additional heat sink/fan, just to keep the heat down. And there a bit exposed/ delicate so I'd give it a cover of some sort (so bolts and other rubbish doesn't damage it) and shock mount it somehow.
Other than all that their really good ESC's, have lovely low speed control and lipo cut outs etc. There a fee different settings (like exponential ramping) so have an experiment with those and find what you like driving best.
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I may have to look into that, thank you Theo, and thank you for the additional information Alex. I was planning to put it into a cheap, small Tupperware box with holes drilled out for the wiring to go through and such, and use maybe a couple of rubber washers to keep it steady and not shake itself apart when other robots smack into it.
Aaaand unfortunately I have to go back to asking questions about batteries... again. But instead of it being the batteries itself, the questions are for the chargers.
I found this thing from hobbyking, and I'm just wondering if that'll charge up say... this battery? Or are there any other battery/battery charger combos that're cheaper and get the job done just as well? Because I don't want to buy them and find out that they're utter... well, you know, haha.
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I have the Accucell T100 charging that exact battery and a couple of other 5S packs. Not used it lots yet, but no trouble so far.
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I just realised that the charger that I found is for 4 cell batteries... and the zippy's a 5 cell. Almost shot myself in the foot there.:eek:
So I'm still looking for a charger/balancer. There's one by Overlander that's around £45, so I could end up buying 2 of those so I can charge said batteries... And I tried looking up what Alan said about the Accucell t100 and it looks a little sketchy... Does anyone have any recommendations/thoughts upon this?
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So I looked up some reviews on the Overlander charger, and suffice to say that a lot of people say that it's a good one. And I spied one that was about £5-£10 cheaper, so that's good at least. So I bought two of them, along with 2 Zippy 5 cell LiPos, a pack of EC3 couples, 2 LiPo bags, and 2 metres of red and black 14AWG RC wiring, along with a cheap Hobbyking 4 channel RC controller with receiver. All that's left are screws (would chunky wood screws work with 15mm HDPE? I can't remember), a soldering iron, grub screws, a multimeter, and some good ol' fashioned elbow grease.
Only question is... how thick should the countersunk wood screws be? And is it possible to get them from B&Q? Or would it be better to just find better ones somewhere else? Same question goes with the Grub Screws.
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I recommend cross nuts (sometimes called cross dowels) over wood screws:
https://elraco.com.au/images/XD616-1.jpg
These are impossible to rip out until the plastic itself breaks and unlike wood screws, the thread doesn't wear out if you have to disassemble them.
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Oh yeah, I remember that now. Those would do excellently. Thank you Nick. I'll have to take a trip to Screwfix at some point for some of those. Would I need an insert, or just drill a hole directly vertical into the plastic? And if so, should the hole be a little smaller so that the screw has a little bit of a bite to it and be able to hold onto the plastic?
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You shouldn't need any inserts, just a slightly oversized hole for the screw and an exact or slightly under-size hole for the nut so they don't fall out. Laying out the hole positions is super important so the screws & nuts line up.
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Slightly oversized for screw, and slightly undersized for bolt. Excellent. Easily a Screwfix job. Much appreciated Nick.
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If you pass an Ikea any point, head to the customer services area where you can pick up 'spare fixings' for your ikea stuff.
They have those cross nut things as part of it, and its free...
Disclaimer... please dont abuse that and its for your IKEA stuff........ :)
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Okay, I'm coming back to this thread once more for a quick question...
So if I remember correctly, the robot has to have an indicator of when it's on, and the supposed easiest way is to use LED lights.
Question is, how would one go about linking said LED's to the robot, when there's 18 volts buzzing through the system? And what LED's would be the best for the situation? As the ones I looked at was extremely low voltage, and I don't want to waste money.
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Or would it be easier to buy a couple of LED strips and run them in series on the positive side of the battery leading to the ESC? Or is there a better/easier way of linking the LED strip up to show that it's an active robot?
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You should get away with using some 24v led strips and hen wire them directly after the removable link and ground so that they are always on when the link is in place.
If you can't find any I'm sure I have a small strip could use?
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I shall definitely look into that, thank you Nat. But now I have another problem.
Just read the build rules again, and it says I need a fuse for the batteries. Problem is I don't know where to buy and place the fuse and housing in question... any help would be fantastic once again.
The batteries I have are Zippy Compact 35C 2700mAh 5 cell... which means I need a 94.5 amp fuse? Did I calculate that right? Or am I completely off the mark and in need of some simple math lessons?
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Car fuse holder and fuses from Halfords or Maplin are spot on.
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Thank heavens, just took a look at Halfords and they have a 100 amp fuse on there. You're a saint, David, thank you. :D
Well, as soon as I figure out how to wire it all up, then I'll be able to do all the soldering and such... just need to make a circuit blueprint so I know what's going on as such. As soon as I got it all worked out on "paper" so to speak, I'll post it up on here and hopefully get feedback on it. But that'll have to be tomorrow, as it's way too late to do anything about it today.