URGENT - No power from backup battery/PWM port voltage

We’re getting no power from the backup battery. One of the terminals fell off the RC and has been resoldered. We noticed that we have continuity from backup battery ground to PWM grounds, but not from backup battery + to PWM +V. I am guessing that this voltage is regulated bt the RC (i.e. is disconnected when the RC is off), but I could be wrong. So two questions:

  1. Can someone see if they’re getting +V from PWM ports when the RC is off?
  2. Any ideas as to why we’re not able to use the backup battery?

We have an offseason comp on Saturday and are trying to train drivers. This is urgent. Thanks for your help.

The backup battery is not always needed to run the robot. its only function is to power the RC and radio when the voltage in the main battery voltage drops. so you should be able to run your robot without it. as for the positive volts from the pwm i can check and let you know tomorrow. there is more info on the backup battery on page 4 of the robot controller reference guide at http://www.ifirobotics.com/docs/rc-ref-guide-01-31-2005.pdf

I think the battery supplys the power to the servos - the little hobbie servos. If you are not using any on your bot, you should be able to run without the backup battery.

Yep, that’s right. We had ours on the bot but not charged, and we could not use our one servo. Everything else worked perfectly. Soon as we charged it, the servo worked. The only other thing the backup does is to keep the controller powered if the main battery somehow fails. So as long as 1) you have no servos and 2) you keep your main battery charged, you should be fine wihtout the backup.

We’re mainly worried about a dip in main voltage and a reset.

I’m looking forward to John C’s test.

What’s happening now is very strange. I’ve done continuity tests on the RC, and backup +V is getting to a cluster of a relatively small, yellow cap and a small IC chip. The RC and OI are both showing no backup battery. This is worrying.

Our battery voltage is currently dropping greatly while running the four drive motors. We will plug the battery in and the OI reports the battery to be at 12.6-12.8 volts. We can go forward and reverse with no problem and not a significant voltage drop. It is when we go to turn and reverse on a carpet pad we use for testing that the voltage begins dropping below 9V and the robot can barely turn. Normally the backup would kick in then, but it isn’t. To further this, we know the backup battery isn’t turning on because it doesn’t activate after we kill the main power.

It is also able to take over powering the RC completely in times of low main power.

By the way, I hope you are doing this with a fully charged backup battery. Also it is possible for the main batteries to get a surface charge if they are heated too hot (don’t ask), or you may be drawing way too much current with your drive motors.

We do sometimes have current draw “issues” when turning with this bot :smiley:
The backup battery always saves us.

It is charged, by the way… or so I was told.

The backup battery might be bad. At the L.A. Regional this season, we were told that we had no back-up battery by a ref, when we knew we had one there. We found out that that the pack couldn’t hold a charge. It was our older one from 2003 I believe.

Hopefully, maybe you can try getting a new pack, they should carry them at your local hobby shop, and that might work. Good luck.

The backup batteries do have a finite life. If you have been using this battery for a long time and it has gone through many charge/discharge cycles it could be defective. However, it is relatively easy to check the voltage while connected to the RC. Make sure that the voltage remains constant by inserting your meter probes in the back end of the battery connector while the RC and OI are communicating. The backup battery is used to power all PWM outputs but the voltage is not used in Victor speed controllers, only in servos. The battery also powers the radio and primary circuits in the RC during main battery brownouts. It shuts itself off after 2 minutes. If you broke off one battery connector then resolder the other as well. One thing to remember is the RC and OI are multilayer circuit boards and pulling a pin out of the board may damage internal connections. If this happens some of the board may be powered when other parts are not. Additionally, there is reported to be a fuse in this circuit to protect the RC and power switching electronics. You may have burned that open or there is a short (two pins touching on a PWM port) and the voltage regulator is in over-current protect mode. Finally, there is reverse power protection for the battery input. Are you sure when you made the repair that the connector body was installed correctly? Check the wiring, the black battery lead should go to board common.

The backup battery is fine, it is the one we got in the kit last year, and I doubt it died that fast (it is still holding a steady power). Our drive has always taken way too much power, dropping our voltage from 12.9 (after sitting off the charger for 15-20 mins to burn off the surface charge) to 7.9 while trying to turn (doesn’t seem to matter how far the joysticks are pushed), but it is only dropping to around 10 when going full power forward or back.

The re solder job was done correctly and we are about to re solder the +terminal just in case.

We also found a dead relay last night, a dead speed controller now and more things are likely to be found.

It isn’t the speed controllers and relays, it seems to be a progressive failure of the board. We drove the bot down to our auto shop to work on it and now PWM ports 3, 4 and 6 aren’t working. We are going to try and reprogram the bot to compensate, but it seems its going to keep developing problems.

Time to fundraise for a new RC.

I can infer that you are doing tank style turning with sticky tires or treads. This is the inevitable result of this type of steering. Omni wheels would help or center trucks on a tread system that are slightly lower than the front and back.

For anyone reading this post, 12.9 volts out of this battery is a temporary reading following charging. Within seconds of a load being applied, this voltage will fall to 12 volts nominal or 2 volts per cell. With a battery nominal internal resistance of 11 mohms, a four volt drop indicates you are drawing in excess of 350 amps during a turn. ( if you were looking with a scope you would see spikes exceeding that amount.) With a four motor drive you are near stall on all motors. (which coincidently is what happens when you turn tank style with sticky tires or treads.) For reference, the RC drops out at just under 8 volts and runs off the backup until the main power rises to more than 8 volts. (This is a design tradeoff to get a regulated 5 volt rail from the main battery. The regulator requires at least two volts higher on the input than the output to function plus the reverse polarity protection diode.)

Before you buy a new RC, make sure there is nothing metallic shorting out any of the pins on the RC. We had an incident this past year where a metal shaving was causing a short between one of the 5v pins and a ground pin. We found this shaving underneath the black plastic of the pin connectors (the plastic that holds the pins together). It was between this plastic and the PCB of the RC. It took a while to find this problem since a “normal” inspection didn’t reveal anything that would cause a short. We had to hold it at the right angle to the light such that we could view down this very narrow gap to identify the shaving. Once we got it out the RC was fine (those IFI guys do a nice job of making hardware that is resistant to things like that).

Anyway, the point of the story is that you might want to spend some time with an airhose and make sure the board is fully cleaned of any debris and then bench-test it before you declare it dead.

Hey Everyone
We got the bot to drive again and the PWMs to work by reloading the code. The bot still does not recognize the backup battery.


I checked the pwm voltage with the RC off and also did not get any reading. so i think you were right about not getting any power because it is regulated by the RC.

I’m just posting this for closure.

We found the problem a week or so ago… somehow the backup battery was wired up backwards!

We were assuming white/positive black/negative, but somehow our cable’s flipped.

All is good.

Whoa!! I thought the plug could not physically be switched around in the outlet. I guess I was wrong. Or did you guys damage something??

The battery’s connected through a plug on the electronics board, which goes to spade connecters on the RC. These connecters were switched.

Thanks for letting us know what the problem was. Just one more “obvious” thing to look for in helping other teams!