20mm HDPE - no
20mm nylon - yes BUT I would do what I did with hornet 2 and have hardox or steel braces around the front to strengthen it.
I could have fitted the drills inside but putting them outside gave the machine more ground clearance and more space inside.
Just got a couple of quick questions:
Does this switch count as a removable link or does it need to be a whole section of circuitry?
http://www.fingertechrobotics.com/proddetail.php?prod=ft-mini-switch
Does a smaller disc work as well as a bigger one if the rpm is higher? When does the disc become pointlessly small/should be replace with a drum for a better attack?
Quick CAD update:
I found that the original disc was ~250mm, so the disc will have to be smaller (hence above question). I would like to keep the robot within ~45 degrees because I think that otherwise it will start to look too tall.
That switch is against FRA rules as used in europe.
The Australians and the americans do use them.
The FRA rules specify that a link has to be removed from the machine as a clear way of disarming the machine.
An action that is aided by the use of the indication LED that will turn off once the switch is removed.
Well, the way I see it is that if you get a larger disc with a slower rpm, and a smaller one with a faster rpm, they may well have the same tip speed but at lower rpm ranges the disc will get more bite and engage more frequently, if that makes sense?
It all depends on your design though, you want to maximise bit as much as you can - even though 720's drum spins at about 15k and is only about 100mm diameter, it has a single tooth design and well over 10mm of bite if I recall. That plus the speed it runs into other machines at means it can get monstrously large hits. (Again, all what I've heard, apologies if any of that is wrong!)
If your disc ends up pushing 10-12,000 rpm then I'd consider a larger disc to be honest. There's lots of variables though like weight and how much of the mass is towards the outer ring... That's why Archangels bar has those heavy tool steel teeth, it contains more energy at lower RPMs, so may get similar/better performance than one with more equal weight across the bar hit-wise but will also have the perk of getting regular engagements.
Theoretically, I think anyway. The extent of my robot building really goes as far as the computer game, so I'll probably need someone to verify haha.
ha 720 would get nowhere near 10mm of bite unless it was moving forward at a rediculous speed *waits for smart arsed comment from mouldy*
Tooth engagement is a balance between forward velocity and rotational velocity. I wrote a big post on it a while ago.
Energy in a disc is all about the moment of inertia of the disc. A useful tool to work it out is here, granted it's all in US units but you can do a quick conversion
http://www.teamcosmos.com/ke/ke.shtml
For reference, the original hypnodisc had around 6kJ of kinetic energy, typhoon 2 could store 40kJ, boner's drum when it was doing a few thousand rpm was 0.7kJ, supernova in robot wars was around 30kJ, middleweight typhoon could store around 12kJ.
The belts that come with cheap bench drills are usually complete crap. Try replacing the belts with cogged versions as they have more grip. You can usually get cogged belts at engineering or auto spares stores, or on line. There should be a short tensioning lever somewhere of the drill head; adding a length of pipe to the lever lets you get much higher tension on the belts.Originally Posted by Max
Brave man!720 would need to be travelling at 18KPH to get a 10mm bite depth with a two tooth drum spinning at 15,000 RPM.
I always do the sum for a robot moving forward at 1m/s as it's most indicative of what a robot will likely be doing before a collision
I noticed at the last Nats event that Mouldy usually likes to drive 720 quite a bit faster than 1 m/s so the maximum bite depth is going to be deeper than the 2.22mm he would get at that low speed.
Sure you get big hits now and again, but the majority are slow speed. It's an interesting problem. I did consider a while ago having an axe with the head being a disc or a mechanism acting on CO2 to shove the disc forward quickly but building it strong enough would be a night mare
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