New to the hobby- Where to get parts on the cheap?

[npolanosky]

Hello all,

I'm brand new to the hobby and I'm looking to build a robot and find some competitions to shoot for. I'm a mechanical engineering student at Embry-Riddle Aeronautical University in Daytona Beach, FL, and if I can build something for a reasonable amount of money to demonstrate I am going to attempt to start a combat robot club here and maybe, if all goes well, get an east coast intercollegiate series going.

Big plans aside, I have about two weeks before I'm on winter break. I have years of experience building and flying RC airplanes, I can weld, I've worked with carbon fiber and fiberglass before, etc. I don't have a ton of time or a ton of money to work with, but I'd like to build myself a robot.

I'd like to be able to compete, so basically the active competitions will dictate what class robot I attempt to build. I think I could do anything from featherweight to middleweight, depending on how much equipment repurposing I am able to do and what components cost. I already have a nice 1500W 24v power supply and an FMA powerlab 6 charger that can do all chemistries, a JR x9303 2.4g 9ch airplane radio as well as a 7ch 72mhz radio, all kinds of large 3s-6s lipo and SLA batteries, and other misc RC gear.

Basically, I just need a rundown on what is active where, where to source cheap or repurpose-able parts (motors, ESCs, wheels, chain, stuff like that), and I guess any other advice, tips, and resources you have.

In the future if I can build a demo bot or two I may come back seeking advice on starting a club or team, but that's down the road.
Also, I know this is a UK forum but I'm sure you guys can help at least partially, and if you know of an active US forum that would also be fantastic.

Thanks in advance,

Nick

[harry hills]

Hey Nick.

http://forums.delphiforums.com/n/mai...gid=2008950046

Just a point, you'll almost certainly have to upgrade your Tx to a 2.4ghz set.

Cheers.

[geeza]

When looking at the rules, our rules are different to those in the states. Robot marketplace is a good start point to buy components over there. Could suggest loads of sources for parts but probably not much good to you over there. Best advice would be pick a category and then ask some specifics. Get a drive system going the think about a weapon for it after. There are some events going on in the us, best check on their forums for details though.

[npolanosky]

Harry,
I have one of each- The X9303 is a 2.4ghz DSMX radio, and the other is a futaba 7ch 72mhz. I didn't know if one was preferable to the other due to the large quantities of RF-blocking metal involved and the fact that 2.4 doesn't like that too much.

For that matter, I am a licensed ham radio operator and I can also use UHF frequencies in the 433mhz band for RC control as well if I wanted.

Thanks for the link to the RFL forum, I'll start there. Are there any other good forums out there?

It seems like a lot of the US activity ended years ago and there are only a few isolated events.

[Shakey]

Mostly 2.4GHz is used purely on a safety basis. With robots like these safety is a big issue so radios that won't be interfered with and are fairly standard are high on the list. I know you have concerns over putting a 2.4GHz system in a metal armoured robot but it never really comes up as an issue even in robots that are just pure metal boxes! No idea how a UHF system would play in the setting but going with tried and tested is a good idea.

[npolanosky]

Got it, makes sense.

So I want to build something on the larger side, I'm thinking lightweight ~60lb class. That way I have power and mass to use it for other experiments than battles. I'm trying to get a feel for what size motors, batteries, and ESCs are needed for something of that size. Are drill motors or wheelchair motors better suited for this size? Some of the drill motors have massive stall currents, but what size ESC is suitable for regular operation?

I'm very familiar with electric power systems, but usually in aircraft, so I'm not sure where to start sizing things on the ground. Once I have a baseline example of a working setup I should be able to feel it all out myself from there.

[Flag Captured]

If you want cheap, a featherweight class drill-box would be a start*. Using drill motors/gearboxes for drive is very cheap, and there's loads of robots out there that use them, or a modified version of. Plenty of those in the build diaries section, check those out if you want inspiration!

As for electronics, a 3/4s Lipo and a set of Botbitz TZ85A speed controllers, along with an Orange R620 receiver (or equivalent 2.4ghz one, if you have one) will get a machine up and driving about, paired with drill motors. Gives a nice base then to add weaponry, if indeed you want to even add any!

Also, reiterating what else has been said, rules are different in the US but it really won't harm to look at the UK rules as well - they're not THAT different but there's a couple of notable changes, like I don't think fuses for LiPo batteries are a requirement in the US, and the removable link can be tool-assisted over there, whereas it can't in the UK. Little things like that I guess.

Good luck with the build!

(*the only drawback is that I believe Robogames in the US don't do featherweights, the lightest they go for the non-insect classes are lightweights, but there's always Motorama and a few other events which do take featherweights...)

[npolanosky]

Great, thanks for the advice. I'll do some digging as far as rules and regs go, but yeah worst case I'll build a 30 pounder this winter for fun then do a 60 pounder or larger once I have additional funding to do it right. Except for the motors and ESCs, I should have everything already laying around the shop at home.

[john_frizell]

You can often get cordless drills for free or dead cheap when their battery fails. Try swap meets. Ask friends. The motor/gearbox combination is ideal for a 30 lb machine and works for a 60 lb one. There are lots of tutorials on how to lock the clutch and convert a drill gearmotor for drive. The output shaft is 3/8 UNF so you will either have to make an adapter for your wheels or buy wheels that take that shaft. For a first machine a relay based H bridge will get you going but a proportional speed controller is much better.

[npolanosky]

That's actually what I did today! I picked up two cordless drills on sale from harbor freight for $15 each today. They're good enough to get started and if I find some higher quality ones for cheap or free later I can always upgrade.

I can run them off of one of my lipos between 3-6s and I'm thinking of grabbing a pair of the bot bits 85a controllers to run them.