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12 V bat replacement for practice
http://www.robotc.net/forums/viewtopic.php?f=52&t=872
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Author:  chuckmerja [ Thu Oct 30, 2008 11:15 pm ]
Post subject:  12 V bat replacement for practice

We know that we have to use the 1.2 x 10 ORION bats for FTC competition, but we have a plethora of 7.2 V Vex bats and chargers on hand, and are wondering if we could use a couple of those in series for practice, or is 14.4 too much? If it is too much voltage, might we use a 1 or 1.5 amp LM7812 linear voltage regulator to drop that bat combo to 12 V?? thanks

Author:  Dick Swan [ Thu Oct 30, 2008 11:40 pm ]
Post subject:  Re: 12 V bat replacement for practice

I am only a simple software designer so cannoit guarantee the following.

All my initial development for the HiTechnic Controllers was done using two 7.2V battery packs connected in series to get a 14.4 supply.

There was also a 20 amp fuse connected in series as well for protection which you should also use. An inadvertent short circuit is not something you want. I don't know that the battery will explode, but at a minimum will get extremely hot.

And an on/off switch is a nice extra.

I bought appropriate connectors and wire to build my own harness at local R/C hobby shop. It cost me under $5.

You might find in easier to use a single 7.2V battery (or 9.6V) instead of wiring two in series. You won't get full power on the motors, but the wiring may be slightly easier. The controllers themselves are powered by 5V derived from the external battery. One small note if you go this route. ROBOTC checks the external battery voltage and silently disables the 12V motors if the voltage is below 10V; this is to prevent deep discharge of the battery. You will have to adjust this voltage threshold. You can do it from the "System Parameters" debugger window in ROBOTC: Open the debugger, open the "system parameters" window (available in "expert" user level), scroll through to find the appropriate variable name and set the value to 5000 (i.e. 5000 millivolts).

Author:  chuckmerja [ Fri Oct 31, 2008 6:13 am ]
Post subject:  Re: 12 V bat replacement for practice

thanks for the software, Mr "simple software designer" :o))! I had real reservations about moving from EasyC to RobotC, but thanks to you and others we are doing alright. Boy, is it cool to see what's going on through the debuggers!! MANY THANKS!!

On to the 12 - 14.4 V. We plan to make a wiring harness using the RC connections and still go through the kit switch and fuse, so I'm thinking we are going to be good. Thanks for the reply.

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