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 Advice on Insect weight (3lb) robots

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rdubard
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Location : Ransom Everglades, Miami, FL

PostSubject: Advice on Insect weight (3lb) robots   Sat Mar 26, 2011 6:41 pm

A movement is afoot is Miami to start up 3lb. combat robots. I already have a Middle School Parent (eeek!) asking me to 'help their son out" with one.

There's just one problem--I have never even tried to make one that small. Sure, I've helped out with LOTS of 15's (maybe as many as 30 of 'em), and we have evolved one 120lber into a competitive robot, but I'm not sure how to move success in the smaller direction.

So, I'm asking:
1) Any special TX/RX recommendations, or will DX6, DX6i, and DX3E, or more importantly the receivers (BR6000, AR6250, SR300) be OK?

2) What about ESC's--I know BaneBots has a little blue thing (not sure of the exact part number) that some folks use, but is there something more standard or just plain better? What are most people using in 3 lbers?

3) This is the biggie for me right now, I think--what drive motors? I recall someone saying "Maxons" are good, but what part number? (Maxon apparently makes a LOT of motors) What are the leading other options?

4) How much battery voltage and capacity? I know this really depends on the weapon system and it's current draw, but at least the voltage will need to be limited by the choice of drive ESC's, and the capacity will probably be limited a bit by size and weight.

5)Which brings me to the next point--in general what is the enclosed volume of a 3 lb bot? I realize there is a lot of variation, but for instance, a 15 battlebot generally has a footprint between 1 and 2 sheets of notebook paper, and usually isn't more than 3 inches tall. How large is a 3 lb bot? I guess I could assume equal densities, and calculate that a 3lb. bot has 1/5th the volume of a 15, but I ain't sure, so I could use the voice of experience.

6) Armor? Is Aluminum OK at this level, or do I look into Titanium or Steel (very thin, I suppose), or can I go the other way and use some sort of 'plastic' like polycarbonate or UHMW?

7)Lastly, how much might it cost? Again, I know the variation is wide, but assuming I have chargers and transmitters and tools, what's it gonna run in parts to put a decent 3lber together (brushless weapon, Lipo batteries, and whatever you recommend for the above?)

Thanks, and sorry for the extensive questions (I at least hope they are good ones!)

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Koolaid64
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PostSubject: Re: Advice on Insect weight (3lb) robots   Sun Mar 27, 2011 1:47 pm

1) you can pretty much use and system you want i would just recommend 2.4ghz and that you use the smallest receiver you can find. i use a dx5e for my bots now. and i have been trying out this recently and so far im really impressed with it, especially for the cost and size http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11972

3) as for drive motors ebay has blessed the 3lb builders with its latest surplus of chines slave labor technology. you can usually find a a pair of these for around 8-14$ each depending on how well you ebay just search "1000rpm motor" http://cgi.ebay.com/2-x-12V-DC-1000RPM-Mini-Torque-Gear-Box-Motor-Hobby-/320569452140?pt=LH_DefaultDomain_0&hash=item4aa36da66c#ht_5232wt_978

2) i use the bb 3-9's for the motors i listed and they work perfect for my application, if you were to make a pusher you might was some bigger controllers but thats assuming you will be using bigger motors as well
http://banebots.com/pc/ELECTRONICS/BB-0309

4) i like bigger batteries then i need most of the time mAh wise. that said i use a 1000 mAh 3s pack in my beetles, but some people have gotten away with using 3s packs as low as 350 mAh though i wouldn't recommend it.

5) just try and fit the parts in the most compact space as possible, i've built for about three years without the advantages of weight calculating modeling programs and i've always managed to get things within about 2-3 oz of the target weight. for you first couple of bots i would recommend using UHMW for your frames 1/4" and 3/8" thickness go along way

6) depends on how much money you want to spend, again the UHMW is cheap and easy to machine, i've made a beetle in as little as two days with the stuff and managed a 2nd

7) if you build like me (cheap) you can probably put together an entire robot from scratch for 150-200$ - the transmitter. that will cost you an extra 100 or so.

and i also use this motor and speed controller for my weapon system http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=3885
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=2165


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rdubard
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PostSubject: Re: Advice on Insect weight (3lb) robots   Mon Mar 28, 2011 6:20 am

Wow, Kyle, that's a really excellent set of answers! (Ever consider teaching this stuff?)

Thanks so much for the information. I am meeting with the parents on Tuesday afternoon, and while I was prepared to show them the shop and talk about the kinds of systems their kid is gonna have to buy and build, I didn't have any specifics. Now I can send them some links, and have their son take a look at those.
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SenaiERI
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PostSubject: Re: Advice on Insect weight (3lb) robots   Mon Mar 28, 2011 10:48 pm

Wow, nice job koolaid. Awesome work.
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