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Messages - roybrox

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Because things didn't go badly last time and I can't learn from my mistakes, we'll be having our 6th MassDestruction in two years at the end of January!

The Charles River Museum of Industry has been hankering to have robots for a while and now thanks to Connecticut Yankee Screw Machine Salesman, you can display and fight your electrical toys right next to steam-powered machines that pre-date transistors! The very cool museum has dozens of antiquated but still running tools and toys from automatic scraping beds and model T's to watch lathes and ride-on trains!

We'll be coordinating via Facebook again, and expect a registration via Eventbrite to go out soon:

https://www.facebook.com/events/149911915489892

Spectators are as always welcome, although you will have to pay admission to the museum in the first place.

Robonerds - I should have the Eventbrite up today or tomorrow. Catagories are once again:
1lb
1lb Plastic
3lb
12lb Sportsmans
Please see NERC for generic rules (http://www.nerc.us/rules.html).

MassD Unique Rules:
Plastic Ant: The vast majority of construction elements in your robot must be made of plastic. This goes especially for weapons and armor. Carbon fiber, kevlar, and fiberglass are not plastics so you should not put them in your robot. 3D printing is heavily encouraged, but not required. No fiber or epoxy reinforcing allowed on prints though, or chopped-suey carbon fillament!

12lb Sportsman's: To continue to see the growth of this class, the active weapon requirement and anti-wedge clauses are once again removed. However, kinetic energy weapons are still limited and you'll totally get more points if you do have an active weapon and no wedges AND if you hastily make everything from Harbor Freight parts the night before. What good are the points? Not really much, maybe to avoid the....

Wheel of Misfortune: I'm bringing this back but better this time. If your robot is marginally overweight or somehow offeneds me, the judges, or the audience, we will make you spin the "Wheel of Misfortune".

All standard NERC rules will still apply, and we will try to have a testing box in the pits. Let's keep being safe here!


Tournament Structure:
We will once again be running our modified-Swiss style of competition, ensuring every 'bot gets to fight at least 4 times. Highest-scoring four will be entered into a short double-elimination tournament to crown our winner and King (or Queen) of Denmark!

Tournament structure is subject to change without reason, but time-permitting you will be able to fight your robot at least 4 times if it's up to the task!

Scheudle is shamlessly copied from previous events:
8:00 AM Doors open. Come in, Get check in and inspected
9:30 AM Check in for combat Ends
9:45 AM Drivers meeting and match schedules distributed
10:00 AM Round one of fights start
1:00 PM Approximate lunch break for combat
6:00 PM Approximate Semi Finals period
6:30 PM Arena break down

As always, we'd appreciate any help we can get from kind volunteers showing up the night before for arena assembly or who want to serve as judges/staff for the event! We will be sending out a volunteering form in the weeks ahead for you cool people!

Any questions or concerns? Feel free to leave them on this page, or contact EOs directly at massachusetts.destruction (at) gmail. We're really looking forward to seeing you all again!

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Hey all!

We'll be starting MassDestruction Quarterly again in Boston, Massachusetts! Our next event will be at Artisan's Asylum in Somerville, MA on November 12th. Weight classes are 1 and 3lbs, $25 registration fee and unlimited spots (for now!). Event details are on Facebook:

https://www.facebook.com/events/324137631264560/

Registration will be up in the next week or so. If you have any questions, please post them here or email the EO's directly at massachusetts.destruction at gmail.

Thanks, and we look forward to seeing you!
Fred

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Questions / Re: spark for flame bot
« on: September 09, 2016, 03:23:05 pm »
Hey dude, in the interest of you not doing this, which is still a really bad idea, I'll turn you on to two avenues you can check out that are much much much safer and infinitely more reliable. We're not hating on the idea, we're trying to convey to you how actually dangerous this is to your property and person and how very few event organizers will allow your robot into their event for safety concerns.

First, try a "glow plug" or "glow igniter". NiChrome resistive wire can also be used. Hook it up to a BRUSHED single direction ESC to regulate power, and vary the power the same way you would to a motor. They are usually able to get to the point of glowing red/white hot, which is the auto-ignition temperature of whatever gas you're using for fuel.

Second, try taking apart an old disposable camera. They use a boost circuit similar to a taser to create several thousand volts for the flash, but with low power draw and regulation. By messing around with the leads going to the flash, you should be able to make a very reliable, and very safe spark gap.


To address you design elements directly:
1. Battery damage happens instantly when you short a battery. There's no "if I move quick enough" to it, you damage the battery permanently every time you short it. The mechanism that you'd need to ensure leads don't weld to each other would also take up significant mass.

2.Adding resistors to the leads will decrease your voltage at the gap. More volts = More sparks, as voltage is just a fancy way of saying "electrical potential energy". The higher the volts, the more willing the electrons are to jump across a gap, which is why tasers and flashes use volts in the thousands.

3.Shorting your battery will cause all of your electronics to cease functioning. Most, if not all RC parts have system low-voltage cutouts designed to turn off the parts when a serious voltage drop is detected. Shorting your battery will cause your system voltage to drop well below this level and will turn off everything.

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Questions / Re: spark for flame bot
« on: September 08, 2016, 06:12:50 pm »
This is a really, really bad idea.

To get a sizeable spark, you'll need some serious power discharge from your battery. When you're touching it off, you're shorting the circuit, which is to say putting the battery in a circuit in which the highest resistance is found in the battery itself. This will exceed your battery discharge rate and damage it, every time.

Furthermore, at the current you need to put in a spark at those "low" voltages you'll have enough power to melt your wires but also your leads. There's a very good chance that your two leads will weld shut and you'll be unable to separate them while your battery promptly melts your wiring completely and or catches fire.

Most sparks that you see in Tesla coils or taser are generated by using a boost converter to get an enormous voltage between the terminals, but a relatively low current. They also use cut-offs to stop the power when it detects something's gone wrong, like a short or low power input.

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I could probably take a look at it. Feel free to send me an email with your time restrictions and other specs.

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Progress Reports / Re: Team Tamper Resistant
« on: August 26, 2016, 11:34:20 pm »
I'm going to go look into a venue tomorrow, but expect the next MassD to be around early November! I'll start posting official dates and locations as soon as I get more of the details worked out

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Event Videos / Re: Clash of the Bots 2016
« on: June 29, 2016, 11:14:41 pm »
You cut out the part on my fights where I had a crowd of children chanting "BEST KO-RE-A BEST KO-RE-A"  :'( :'( :'(

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Event Videos / Re: Motorama 2016
« on: February 25, 2016, 10:11:35 pm »
No one does it better than Mike, but if you want some different views, check out Xo and my Youtube playlists. Xo has a fair amount, and I've got select GoPro shots in and out of the arena.

https://www.youtube.com/playlist?list=PLtFGTIaDRrU5rE6d_I1RFgnYiuSOuCBrl

https://www.youtube.com/playlist?list=PL2zGKGH-B5ap0T7Ug4WR3SWvTW5NAymhq

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CAD Zone / Big Guy Motors
« on: December 11, 2015, 11:51:03 am »
Here is a CAD file for an NPC Black Max
https://dl.dropboxusercontent.com/u/32861468/Black%20Max.x_t

And here's one for a Motenergy ME0708 (E-Tek)
https://dl.dropboxusercontent.com/u/32861468/ME0708.x_t

Will update this list with a short/long mag as soon as I steal them from Charles next week. Also taking suggestions.

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Event Results / Re: NERC Franklin Institute 2015 fight results
« on: October 26, 2015, 10:27:06 pm »
You're all wrong, it was BEST KOREA, all caps.

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Questions / Re: 6061 vs. 7075 Aluminum
« on: October 22, 2015, 11:12:14 am »
I was going to post some cheeky response, but numbers don't lie and I'll go ahead and eat my hat

6061-T6
http://www.matweb.com/search/DataSheet.aspx?MatGUID=1b8c06d0ca7c456694c7777d9e10be5b
7075-T6
http://www.matweb.com/search/DataSheet.aspx?MatGUID=4f19a42be94546b686bbf43f79c51b7d

I still want to emphasize temper really quickly, you'll want to make sure that what you get is a good "T6". 7075-O is just about as good as 6061-T6.
http://www.matweb.com/search/DataSheet.aspx?MatGUID=da98aea5e9de44138a7d28782f60a836

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Questions / Re: 6061 vs. 7075 Aluminum
« on: October 19, 2015, 11:11:32 am »
While McMaster is a really nice convenient-to-use source on materials, I'd check on Amazon (particularly with SmallParts) for aluminum and steel. Their tool steel bars can be a little sketchy but I've had a lot of success with their O1. Their aluminum (7075 and 6061) is straight from Kaiser, the same guys you'd get from McMaster, but can cost up to 50% less and if you have Prime still with next or two-day shipping. Their bolts and bearings are pretty crappy though, and their plastics cost 2x what McMaster does across the board which really weirds me out.

As far as the difference goes I'd say 7075 is 20% "better" than 6061. It's a firmer, slightly stronger material that I think is worth paying the premium for. That being said, the difference between 7075 and 6061 is not really enough to make or break your design, it'll just provide an incremental improvement. If you're seriously budget-limited, 6061 is just fine, especially with a T6 temper.

With respect to your design, I would suggest putting a layer of full-hard spring steel on top of the aluminum and get it firmly bolted down. It can be incredibly thin, but the hardness and toughness of it will tend to deflect scary MOI weapon tips, whereas they'll cut into aluminum, grab it, then throw you. Straight tool/spring steel will shatter, but the combination of the two holds up remarkably well combining the ductility and shock-absorption of aluminum with the hardness of spring steel. I had Stance Stance Revolution parked on top of a wedge like that with .01" spring steel for a good 15 seconds with no appreciable damage, and even Silent Spring's hit which shattered my tool steel armor did minimal damage to the spring steel/aluminum wedge.

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Progress Reports / Re: First Beetleweight
« on: August 28, 2015, 12:16:44 pm »
"Better safe than sorry"

Not when that's space or weight that's on the line. It goes like this: Copper is a great conductor of electricity, but its not perfect. Given a long enough strand of wire and you'll be able to actually measure the resistance in it, which scales with both length and wire diameter. Construction type and purity of the wires also factors in as well, with higher-purity being more conductive.

With any resistor on a DC circuit, it "saps" power coming out of your batteries to reduce current draw by Ohm's law V=I*R. With copper wire, 'R' is extremely low but in our combat applications, 'I' can jump up to be quite high. This leads to a power loss, which can be measured also pretty easily with P = V*I (This is also how Hobbyking rates the power on their motors). This power loss goes into heat, which heats up the copper. Vinyl and silicone are both great insulators of electricity, but also do a great job of insulating heat so that heat tends to stay where it is in the wires, until it rises to great enough levels to melt the insulation, which is your failure point. Large gauge single-core wires have the bonus of both a lower resistance as well as have more 'thermal mass' to distribute resistance power heating across, but will cost more, weigh more, and are much harder to work with, as well as having fatigue issues if you bend them too much. Therefore, its prudent to size your wiring to your application such that everything isn't overkill. Thankfully all of the big engineering standards associations have already done the hard work for you: http://www.powerstream.com/Wire_Size.htm

"Billion Strand" wire like wet noodle and other silly-silicone ultra-flexible options have different wire gauging/amp rating requirements than standard house/car requirements; we care a lot more about burst rating than overall lifetime. Our wires are only conducting for 2-5 minutes, which is often not enough time to really get a thermal buildup. Additionally, the small strands means that there is more conducting cross-area than with other types of braided wire, although it's not as good as solid single-core. The silicone insulating jacket also has a higher temperature to fail than standard cheaper wire options, all of which combines to make a different wire-gauging chart that Hobbyking recommends:

8AWG = 6.5MM = 200 amps
10AWG = 5.5MM = 140 amps
12AWG = 4.5MM = 90 amps
14AWG = 3.5MM = 60 amps
16AWG = 3.0MM = 35 amps
18AWG = 2.8MM = 20 amps
20AWG = 2.0MM = 12 amps
22AWG = 1.7MM = 10 amps
24AWG = 1.6MM = 6 amps

As with all Hobbyking specifications, you should try to de-rate it by about 50-75%, as they're more or less lying to you and not taking impurities into account with their manufacturing. However, its sized for constant use instead of burst, so I tend to de-de-rate it and just trust it at face value. This chart is also only a rule of thumb, not a guarantee.

To size your wiring, find the stall current of your motors (my 1000 RPMs tested at around 10 amps) and add up the stall currents through the relevant wires. Your batteries and main power switch should be sized to take 40-60 amps, so you're not far off the mark with using 12 ga for that although I personally use 14. Each of your ESCs ought to be sized to draw around 25 amps, as they're running two motors each, so those wires should be around 16 ga. Finally, your motors can pull 10 each, so I'd use at least 18, although I have gotten away with 22. Anything smaller than 22 should be used for communication or accessory only; those run at lower voltages and don't draw a whole lot of current (miliamps).

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Questions / Re: NERC sportsman spinner limits
« on: August 14, 2015, 12:26:55 am »
Colson-bot-off. Winner gets sportsman, loser gets Triggo in the first round of regular 30s.

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