You could use multiple FIRST batteries at once...power each drill motor off of a separate battery. Would be safer than a car battery, although it still depends how far you will be driving.

If you use the 120mm muffin fans on your drill motors, they shouldn't get too hot. The speed controllers, on the other hand, might fry. Try to mount another fan in there.

I couldn't put my finger on what looked strange about this suggestion and then it came to me. Powering each motor with a separate battery would not allow you to have one single shut off in case the robot went nuts.
There might also be an issue with the controller and speed controllers being on separate power sources. I have had some problems with current flowing through logic blocks when the power source was different.

If the signals to the speed controllers are cut off, they wouldn't be able to run the motors. As long as the RC is connected to the battery with the main breaker connected, I don't think that should be a problem. Also, when the robot is disabled through the Competition port, the RC ceases to send signals to the speed controllers.

In other words, the Disable function of the Competition port should work fine.

I need to just sit down with an RC, and OI, some other odd pieces of the kit, and a scope, and figure out exactly what happens.

The problem with there not being a central emergency cut-off would be when you allow custom circuit boards to supply PWM signals to speed controllers. That would effectively bypass the emergency controls, and allow your robot to operate at any time, only considering there's power to all necessary components.

It's way too early, so I apologize in advance if I'm wrong.

Yes there are a lot of things that could effectively be used to shut down the robot, but we are talking about a parade situation where children especially are going to run up and look at the shiny thing on the road. I tend to look at these things from a safety first, good ops second, and let's just get it running third. From where I stand it's not safe and it's not good from an operation standpoint (unknown effects from different power sources). But it will get it running.

Is it possible to setup a series of AA batteries with enough juice to run the robots? Of course, they would be in a nice little package when you have the hundereds that you'll prolly need to run it.

Somebody check me on this. (Remember, I'm a programmer, not an EE.:cool: )

At 1.5 V* per AA cell, you would need 8 AAs in series to get 12V. And at 2850 mAh* per AA, you would need more than 6 parallel 8-battery series to equal the 18 Ah of the Exide batteries. So by my calculation, you would need a minimum of 56 AAs. I'll leave it up to someone else to engineer a package for all those batteries. :)

I have a feeling though, that this still won't get you the instantaneous current you may need to be fully equivalent to the gel cell Exides. Any comments, anyone?

*The 1.5V, 2850 mAh are Eveready's advertised specs for their Energizer Advanced Formula Alkaline AAs. This is not an endorsement. It just happened to be the first Alkaline AA specs I found on the WWWeb.

I highly doubt that you would get 2850mAh out of a single AA.

This page says 2850, and Eveready's own page says 2707, so it's not far off, I would guess. My only concern is whether my premise is correct.

I may be wrong, but I am quite sure this wouldn't work. AA's (dry cells in general) can't deliver high current draws like the kit battery. They are made to give a steady low draw for a long time, not a 100+ amp draw, then 20, then back up to 100 with some 150 spikes just for flavor. I suppose we could do some tests and see what a AA short delivers, but I imagine it will be very, very low compared to what we need, even when multiplied by 56. Maybe this is already documented. I can't find any data, but everything suggests that if you do put high draws on dry cells, they very quickly derate and your 2800 milliamp rating drops. No one defines what 'high current draw' is. In any case, you would need an obnoxious number of AA's.

I ran into this problem with a model rocket ignition system I made up. Despite having 3 times (eventually 5 times) the power of a normal ignition system, it couldn't ignite 3 engines at the same time. Plenty of power, just couldn't get it to the engines fast enough. I grabbed a 2000 kit battery (only half charged) and it worked just peachy.

-Andy A.

Andy, Greg, et. al.,
You would be surprised at how much that little AA cell can deliver. (Anyone out there drop a 9 volt battery into their change pocket?) Just check out DC-DC converters at the MAXIM website for data on how to get 5 volts from a chip and a 1.5 volt battery. Yes you are correct that several battery strings in parallel would be required to deliver the current of our battery. Now here is the killer... Batteries wired in parallel will deliver current from the more charged battery to the less charged battery constantly alternating until the batteries are drained and all the current has gone off to heat. To prevent this from occurring, you can put diodes in series with each battery string such that they only deliver current to the load. The down side is there is a voltage drop across the diodes. (0.6 volts for standard silicon diodes, less for power Schottky diodes.)
As for the ignitors, these are required to be heated to a temperature that will eventually ignite the coating on the wire. With three in parallel I am not surprised at the outcome. To compare apples to apples, take 8 AA cells and compare to the kit battery which is 6 cells and anyone can see that the current density/cell is going to be much higher.

BTW, I asked the question about the change pocket above because I know of several people who have done that and suffered minor burns from the heat generated by the battery and change shorting out.

I work our pit and I do all the batteries, For a parade a car battery is dangerous in the respect that most aren't sealed. Our team got a giant battery that is heavy but can do a deep discharge. It's one of the batteries that are used in racks as backup power for companies w/ computer networks; it worked fine for us with all of our tests unfortunatly our memorial day parade was cancled and rescedualed twice