Just finished a pair of adaptors for my VEX-Bot using the Arduino.
All parts available at Radio Shack for a little cost, though I did find one item cheaper at another place (a hobby store).
Items:
7.2V 3300mAh Ni-MH RC Battery (RS Part# 23-319) (strongest battery I've found, and for the lowest price!)
9.6V RC Battery Repair Kit (RS Part# 23-445, though I found same at a RC Hobby shop for $2.00 less.)
Type-M Female Coaxial Power socket (RS Part#274-1577)
Type-M Male Coaxial Power plug (RS Part #274-1569, 2-Pk)
Simply take the Male end of the RC Battery repair kit, and clip the crimp connectors off (on the Hobby-shop pair, I didn't need to as they were bare wire ends) Insert them through the plastic cover of the male type-M coaxial connector. Either strip (or clip back) to 1/16" of wire on the ends. Solder the Red wire to the center connection, and the black wire to the outer connection. You might need to put some plastic or paper between the contacts to prevent them from shorting. (which is why I chose the 9.6V repair kit, smaller wire, as the 7.2V kit has much larger gauge.) Replace the cover of the connector, making sure nothing shorts, and the connections will fit inside. Using a Volt/Ohm meter, check all connections for continuity or possible short circuits. Connect the 7.2V battery to the mating connector of the new adaptor. Plug the Type-M connector into the power socket of the Arduino. You now have power to your project/sketch!
The VIN pin on the Arduino will now carry 7.2V power, Plenty of power to move servos! (Do Not rely on the +5V output, as the draw could potentially burn out the +5V regulator.)
Are you advocating to power servos with 7.2vdc? Most all hobby R/C servos are rated for 4.8 to 6.0 vdc voltage, and 7.2vdc is very likely to damage them. Also using the Vin output pin to power projects is subject to the polarity protection series diode on the arduino board, rated I think to 1 amp maximum current flow. As servos can draw an amp each depending on mechanical load and specifc model, you might want to rethink your power management proposal.
retrolefty:
Are you advocating to power servos with 7.2vdc? Most all hobby R/C servos are rated for 4.8 to 6.0 vdc voltage, and 7.2vdc is very likely to damage them. Also using the Vin output pin to power projects is subject to the polarity protection series diode on the arduino board, rated I think to 1 amp maximum current flow. As servos can draw an amp each depending on mechanical load and specifc model, you might want to rethink your power management proposal.
Lefty
Not to mention that the traces and header pins on the Arduino are likely only rated to 1A, if that...
I wouldn't discount it entirely... 1st of all, the battery itself was intended for RC cars in the 1st place. Also, as far as the traces, take into effect how much most RC receivers are wired with even tinier, and short-length traces.
Objective here is longer running life of a project, (read larger battery, compared to a 9V transistor battery. Possible hours of run time compared to 30 minutes on the transistor battery.) the project I'm working on, only has 3 servos. 1 regular, and 2 constant rotation. (which are for the tracks.)
Load at most is not that high.. I'm not trying to create a hyper-speed racing vehicle. This is a tank on a lite frame.
gelfling6:
I wouldn't discount it entirely... 1st of all, the battery itself was intended for RC cars in the 1st place.
The 7.2v packs are used in electro-rc cars. They use an ESC (Electronics speed controller) with intergrated BEC (Battery eliminator circuit).
The servo's will be fed 6volts max.
7.2v will fry servo's easily. If you want more runtime, that's cool. But don't hook up your servo's to 7.2v, limit it to 6v.
There's enough ways on limiting them.
And as stated, I wouldn't power this over the Arduino, find a different way to power the servo's, to make sure you can handle the draw from the servo's.
Like people said above. You really need to drop your voltage to 6V. i have burn at least 4 servo because 7.4V directly.
You need one of this or something smiler or few diodes to reduce voltage:
