Need help with making my first bot

Well, since you asked. . .

Batteries are rated in several ways. The most fundamental rating is the VOLTAGE. With LiPo batteries, each part (or cell) of the battery package will be rated at 3.7volts. Thus, a 2 cell battery will be 7.4V, and a 3 cell (more commonly called 3s, for reasons beyond this discussion) will be rated at 11.1V. 4s is 14.8V, 5s are rated at 18.5V. etc.

A battery will deliver current when placed in a circuit. We measure current in units called amps. The things (like motors) that you have in the circuit will determine how much current the battery will deliver. Obviously, the more current, or the more time you have it connected, the weaker the battery will become until it is drained.

SO, you can rate the CAPACITY (or "C" ) of the battery by how much current you can take from it to drain completely in one hour. Thus capacity is rated in Amp Hours, or, since most batteries cannot deliver a whole lotta amps for an entire hour, we use milliamp hours, which is abbreviated mAh. A battery with 2000mAh rating can deliver 2000 milliamps for 1 hour. A battery with a C of 4000mAh will last twice as long in any circuit as the 2000mAh battery.

If you draw MORE than 4000mA from the 4000mAh battery (let's say three times that amount, or 12000mA, which is the same as 12amps), then the battery will not last an hour. (in the example it will last only one third of an hour, i.e. 20 minutes)

There is a maximum current a battery can withstand to deliver. Try to drain it too fast, and it will overheat and possibly burst into flames (no kidding). These maximum ratings are usually expressed as a multiple of the capacity rating. For instance, a 4000mAh battery with a 10C rating will not safely deliver more than 40 amps at any one time. There are some LiPos out there that are rated at 65C. This means you can drain the battery in under one minute!!

Hope this helps some. . .

Hey again guys. My college just gave me a pair of banebot 20:1 transmitions and a pair of banebot rs555 I was wondering since these are 12v motor will my 14.8v battery burn them? Also how much bigger are these when compared to the PDX60 26:1 gear and duratrax motor and would these also hold 14.8v or am I limited to using 12? What would be a good speed control for either of these? They gave us a saberthoot but this might be a bit annoying to have inside my bot.

if you have the money to replace the sabertooth with something else you should.

you can run a 5xx size motor on anything up to 18v or 5s lipo. if you run it on more than that the brushes tend to disappear.

Any suggestions on ESC?

KyoRinsuu wrote:

Any suggestions on ESC?

If you want something cheap botbitz (or directly hack Hobbyking ESC), more pricey rage bridge, banebots 12-45 if you can find one, or torque master.

For a while there, the BaneBots BB12-45 seemed to be the best option for 12-to-15 pound robots. However, two problems have arisen
1) they HATE voltage above 3s. For reasons I do not understand, they seemed to run just fine the first year or two when we were running NiMh 14.8v (two 6 cell packs) and the occasional A123 two-6 cell setups, but once we went LiPo, they became increasingly unreliable--overheating in under 2 minutes and then doing weird things like working only one direction.
2) You cannot buy them anywhere. I've heard all kinds of rumors about how the mfgr is 'just waiting on parts,' but they have not been commercially available for at least 18 months.

They are were really small, and not terribly expensive, and pretty much 'plug n play.' They never did handle much current (rated 12 amps continuous--tho I suspect this isn't quite true either), but that's about all you need per wheel in a 12 or 15lber.

Honestly, there really hasn't been a good replacement on the market. Because we have the money for it, and I know they last, I have had our team begin purchasing the Castle Creations Mamba Max Pro for our 15's this year. You can program them brushed reversing (crawler mode) using the free software and a USB thingy that we seem to have a lot of (I think they used to come with the ESC free, but now require $$). Or if you wanna run brushless motors with them, they can do that just fine too. They are a bit large and a touch heavy, but definitely no more so than anything else that can handle 6s and lots of current (100 amps? I think?). The big drawback is the price--THREE TIMES what a BB 12-45 used to cost us. Yeh--a hunnert an fitty. Each.
But I have not had one blow up. . . yet.

I do not like the SabreTooth 2X25, Scorpion XL, or the IFI Victor 883 (if you can still buy them?). For varieties of reasons you can find elsewhere on the web.

I have never tried the botbitz, HobbyKing,
ragebridge, or Holmes Hobbies TorqueMaster BR-XL.

Actually, after that listing, I guess there ARE a lot of options out there. . .

Well guys i have 18 days left and im really just having doubts about the ESC will the Saber tooth survive my battery? or will it burn into pieces? is there any ESC that i can buy that cost less than 150 for a pair to control 2 wheels? really need a bit of help here thanks for everything so far guys ^^

sabertooth will survive the battery, it will not survive combat.

ragebrige and torquemaster both are way more esc than you need for a 15lb robot.

http://www.botbitz.com/index.php?route=product/product&path=59&product_id=57

would be what i would use.

if you need something with more voltage capabilities another option might be a single channel vantec.

http://www.robotmarketplace.com/products/VT-RET411P.html


vantec's have been known for being rock solid and impossible to kill.

Will those ESC work with banebot motors?

yes

Will these work?
ebay.com/viewitem?itemId=190736681800&index=13&nav=WATCHING&nid=47663774956

It says 071 50A 400W Brushed ESC W/Reverse for 2-4S lipo. 1:10 RC On/Off Road Car / Boat

Thanks that's what I wanted to know 85 amps peak didn't know that bit of info. Do you have any suggestions on a good esc? Or could you explain to me if the sabertooth will handle these motors using a 4s lipo battery? Or will it catch on fire? Thanks for your help so far.

Ill be using a 20:1 gearbox with a 2 and 7/8 banebot wheels.

Oh i see the only thing i was wondering is if the extra voltage wont kill the sabertooth. Because my professor gave us a 12v battery and im using a 4s lipo to replace it. But yeah i guess if you guess that it will survive ill use it then.

I think it will survive the voltage just fine. It may go weird after a hit, or take 20-30 seconds to 'link up' when you first power up, but it's really better than any other ESC you have right now (which is none, amirite?)

From what I've seen in most competitions, Lipos are banned beyond 3# bots because of overdischarge/shock fire hazards associated. A123 cells are li-ion like what is found in your phone, only these are much more shock resistant.

As for ESC's, I personally have little experience in the field of larger bots, but I would say your ESC should be rated continuous current for what the motor's burst current is to be totally safe. My particular setup has the ESC heat up about equal with my drive motors.
The Sabretooth should hold out, but no experience here, so i'll shush.

For your drive, make sure each individual motor can handle the entire bot's weight at the point of contact between the wheel and the arena - Meaning if you had just one tire and it was attached to a wall, it could pull the entire robot up without stalling the drive motor. This will ensure you never burn out your motors and reduce burning an ESC. my drive ESC's barely get warm because of this.

One thing about FBS i discovered: 2 wheel centered drive is very finicky and usually unstable, but if balanced properly will handle amazingly. If you find you cannot evenly distribute the weight over your wheels, try to opt for a 4 or 6wd version. Note also because it is a FBS, your wheels are protected (make sure the shell/tooth is low enough to stop an undercutter), and can be made very lightweight.

Best of luck!