running bot off car battery?
 

there are some parades that we are thinking about going to and we would like to bring the robot. The problem with this is that it would drain the battery something fierce. Would it be possible to run the bot off a car battery, would it damage anything, and any estimations on how long it would run? we would only be using 2 drill motors. thanks!

As long as it's 12 volts (and nearly every car battery is), it won't hurt any of the electric components.

Since most car batteries are not sealed, you would have to be careful on how its mounted- it must be straight up and no chance of it getting tipped over. Battery acid sucks.

It's also likely to be heavier which might reduce your speed, just keep that in mind. Your motors are also likely to get nice a toasty if you run them long, you might invest in a can of coolant.

-Andy A.

we've run robots using one of those battery portable jumper kits- it worked fine.

Be warned though, typical car batteries are not designed for deep discharge cycles. If you drain the battery, chances are you will cause harm to your car battery.

Deep cycle (typically marine) batterys don't have this problem. They're more expensive though.

You might also consider hooking up your competition batteries in parallel to double your runtime.

Those have a battery not unlike what we are given by FIRST. I wouldn't expect it to last any longer than what we have.

Perhaps you should find someone with a truck to hold your team and a trailer to hold your robot like we do!!!

Most of the team sits on the truck and the drivers sit on the tailgate...

We have a few people on the trailer and they usually collect the scoring objects (balls or boxes this year) we demonstrate the robots abilities instead of just drivin the bot down the road!!!!!

The people on the trailer also change the batts if needed!

The problem is that we were a stacker and that never worked so all we can do is drive..... hehe. :rolleyes:

It will work
 

Car batteries will work fine, just be sure the battery remains in an upright position becaus most are not sealed cell batteries!

This is what I would use although it is quite pricey. It is the only one you would have to buy for a long time though.:]

Parade in Canton?
 

Parades in Canton? I live in Canton and I don't know about any parades. You should let us know what parades you're talking about so I can show up.

-Chris

We did this for our homecoming parade: Get a big enough trailer where you can drive the robot around resonably well. Then you can drive the robot around on the trailer. Make sure there are side railings you don't want your bot to fall off a moving vehicle! We had like a 15ft. x 6 ft. trailer.

do what we did
 

we made carousal of six robotics that ran off of two cip motors and we (6 teams) walked behind the float. It also had a FIRST symbol that was suspended in the air which almost hit street lights..i cant find pic right now...but i will post it soon. It was awesome.

We ran just fine in our memorial day parade last year with 3 batteries. I believe the entire length was around 2 miles or so.

A typical car battery should work just fine. Be advised that the safety issues with FIRST batteries are multiplied with a car battery. It is much heavier and higher available current than the robot battery. Be very careful not to short across the terminals. Insulate very well, all wiring from the battery to the robot. I would suggest removing the breakers for motors that won't be used so that they don't accidentally get turned on when people are close by. (i.e. just drive motors and light because the light is cool) Try to give the robot some rest throughout the parade, especially if it is a hot day and the sun is beating down on the robot. Motors and speed controllers that get hot during driving will smoke during constant use in heat and sun.

As an extra added precaution, you might want to add a high current fuse near the battery, in case the wiring should short in the robot before the 120 amp breaker trips. Always secure the battery so that is does not tip over. Add flags, that's always cool!

We drove 980's 2002 robot in a parade that was 2 miles long using only 2 batteries. It was cool driving a robot through the streets of Downtown Los Angeles. We were going pretty slow most of the way. The robot ran only on drill motors which didn't really get hot. We followed in a chase vehicle with the radio and OI powered off a battery.

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