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Hi everyone. Am having ideas about building a heavyweight robot once I finish the car I'm building (supercharged V8 Volvo 240 estate) and one of my questions is about motors. My budget is tiny and so I was thinking of getting some brushless pallet truck motors from work, as they'll most likely be free! My first question is this: what power is considered adequate for a relatively agile heavyweight robot?
Hey there, welcome to the forum!
It depends on the gearing, especially if using brushless motors. From my experience with my Middleweights, a pair of brushed CIM motors going through a 6.35:1 single stage reduction gives me ample speed (so much so that I've bad to turn it down slightly). That is on 8S LiFe batteries.
Speed will also be affected by wheel sizes and the KV rating the motors themselves. Bigger wheels mean more speed but draw more power. Smaller limits the speed but I would figure draw less power overall and possibly be more controllable. Since these sound like industrial motors, I figure they'll be fairly big and have a low KV rating as a result?
It's always good to hear another Heavyweight Robot is been considered to be built.
If you can get those motors for free you should and 2 speed controllers from 2 would be ideal-
that way you could either have 4 wheel drive or at least an independent controller for both sides.
I imagine the controller is lever or twist grip so save that too-you may be able to run it from a auto
return servo to keep costs low.
In terms of power most good Heavies scoot across the arena in 5 seconds and weigh 110kg
just to give you an idea
I'll have a look at the KV rating next time I'm servicing one. Unfortunately the ESC's are integrated into the ECU's on all our forktrucks, pallet trucks, etc.
I'm thinking of getting around the bar spinner problem by building a whole body flipper with a bit of flexibility in the hinge and ram, so that if it gets a hard whack and goes slightly out of line it won't stop it working. Is this a stupid idea?
Like I said in my initial post, I can't start building anything until I get my 240 on the road. I think a 400bhp/400ftlb Estate would be the ideal transport for a heavyweight. :lol:
Hahaha, I'll be transporting my MW (and a planned HW) in a 2001 Smart City-Coupe CDI. A Volvo 240 is positivietly cavernous in comparsion so no issues there. :p
ESCs... Given the overall size I think these are, try looking at Triforces ESCs here (I'll see if I can find the thread later). The full body flipper idea doesn't sound bad to me. The slack might become an issue if not kept an eye on between fights but I can't immediately think of why that wouldn't work.
Thanks for that, Ocracoke. Yes, I wasn't thinking of a floppy flipper, so to speak (heaven forbid!), more of one that could still work if misaligned by a whack from a spinner. Many flippers fail when faced with a spinner as it bends the flipper into the body and stops it from operating properly. IMHO, with a whole body flipper a misalignment wouldn't be so much of a problem before repairs could be completed.
Here you go for the ESC (go to the last couple of pages): https://www.fightingrobots.co.uk/thr...estions-wanted
Look forwards to seeing the design for this, be interested in how the misalignment would be handled.
I'm sure I'll think of something. It's just an idea which I might realise is a bit daft further down the line. Now to look into full pressure rams. Is there somewhere you'd recommend I look on this forum to learn about the systems? I really should go hydraulic given my background, but I'm not sure if a hydraulic system could be fast enough to fling competitors around.
Motor I was thinking of using (from a pedestrian controlled pallet truck) is an Asynchronous 24V 1.2kw 113KV motor, drawing 76A at full whack. I was thinking of using two- one for each drive wheel.
Have just been offered some free CO2 fire extinguishers in various sizes. What size are people typically using, please?
For heavyweights, 2kg cylinders are the common size used (usually one 2kg bottle as a supply and one or two modified bottles as buffer tanks) and for featherweights, 600g/20oz paintball bottles tend to be the go-to option. The key point is if you can get them with screw valve handles on them rather than lever ones; this will make it easier for adapting the valve to take an M10 nut which will allow you to use a 17mm socket tool to turn on the gas.
So, even if you may not find it suitable to use the extinguishers in your build, it is worth while taking them - if they are filled, as you will get through CO2 quickly during testing, and having access to them FOC helps out during the build and testing stages. Plus some smaller events do not supply CO2 - so you can bring along your own supply to fill up your paintball tanks.
For buffer tanks in smaller builds, get hold of 7oz or 4oz paintball tanks - difficult, or get hold of fire extinguisher co2 cartridges (these are the things inside water, powder extinguishers that make them work) these asre good for small buffer tanks - google "fire extinguisher cartridge co2" for several stockists including zoro.
So, is there an idiot's guide to full pressure flippers?
Not to be too serious here but I wouldn't use Idiot and full pressure flipper in the same sentence and definitely
not in the same room, I have seen when they go wrong.
It's nice to understand the Robot you are using but I would outsource high pressure systems at heavyweight level
even though I myself have a good knowledge of those systems and engineering in general, they are highly dangerous
which is why I have stayed clear of them along with the build costs.
I've been a mechanic since leaving college over 30 years ago and currently work with hydraulics and LPG systems all day in the world of forklifts. A bit of CO2 holds no fear for me. I'm well aware of the precautions you need to take around this kind of stuff, but didn't know if anyone had done a walkthrough of how to build such a system. Yes, the pressures in a CO2 bottle are higher, but at least it's not flammable!
Slight hiccup when it comes to motors. The pallet truck motors are massive and not suitable (never really clocked their size before).But I've noticed that the steering motor is about the right size and has about 4:1 down gearing. they are however, brushed and not brushless. I've read that brushed motors are, due to their inefficiency, much more tolerant to stalled conditions, so they would possibly make better motors for a robot. they are only 185W @ 24V, but being industrial motors will be massively over engineered so they don't fail over thousands of hours of use. Would I be correct in thinking that the torque increases at a linear rate with the reduction ratio?
Yes, I believe this is the case. That is why I went with such a high (perhaps too high) a ratio on my axe for my MW, to ensure it'll definitely self right.
To be honest, it's over three decades since my theory exams, but that's what rings a bell