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cheesinglee
07-01-2003, 01:15 PM
This problem popped up after we returned from the Seattle regionals.

Anytime the joystick is moved to move the drive motors, the robot controller will reset itself, often before the wheels even start turning, so I'm quite certain it's not some sort of jarring issue.

Strangely enough, moving the motor for the arm does not present the same problem.

I've tested and swapped breakers, and those seem to be in working order.

Pretty much stumped on this; any help would be greatly appreciated.

FotoPlasma
07-01-2003, 01:39 PM
The first thing I'd check is that the batteries you're using are properly charged. If the voltage supplied drops below +9VDC, approximately, the RC will reset.

Hmm. Other than this, I'm not sure what to think.

sanddrag
07-01-2003, 04:12 PM
Dude, your battery is dead. We had the same thing happen. The drive motors draw much more than the arm motor and will cause a big voltage drop which causes the RC to reset. Leave the battery on an automatic charger overnight or use a manual charger and watch the gauge.:)

Mike Betts
07-01-2003, 04:51 PM
If your battery is good and charged...

Turn off all power. tip the robot on it's side and try and move the wheels by hand. A trashed gear box can give you the same type of response (the controller can reset before the CB trips).

Sully
07-01-2003, 06:10 PM
Assuming you have tried everything mentioned above and still have a problem. I would think about the joystick - it may have a short or a loose connection. Try another joystick. Inspect the port on the OI.

dez250
07-01-2003, 06:18 PM
like everyone else has pretty much said, charge the battery, check the joystick to see if theres a short. And check to make sure the oi pins on the comp port or any port are not damaged, you could have a short also somewheres in your bot thats causing a chrge to build up and create an impulse to the comp port. Also take a voltmeter and make sure you are getting flow to the motor, then you will definitly know if it is an electrical or mechanical problem... Other then that blame the programmer (j/k).
~Mike

P.S.~ the prgramming joke is that if its not mechanical then its got to be programmings issue...

Matt Krass
07-01-2003, 06:47 PM
Originally posted by dez250
....Other then that blame the programmer (j/k).
~Mike

P.S.~ the prgramming joke is that if its not mechanical then its got to be programmings issue...

Don't blame the programmer! It sounds like you're having a short circuit or something similar. Just get the multimeter out and start poking around.

Elgin Clock
07-01-2003, 07:59 PM
MOVE THE RADIO!!!

That was our HUGE problem this year!! We found out where we mounted the radio on the robot caused a huge RF interference problem which led to us doing the same exact thing at NYC this year!!

Move the radio!!

If that doesn't work.... rebuild the robot!! lol

dez250
07-01-2003, 09:33 PM
Originally posted by Matt Krass
Don't blame the programmer! It sounds like you're having a short circuit or something similar. Just get the multimeter out and start poking around.

thats what i was poking fun at...yeah like matt said, just strt probing the bot with a multimeter and see if the readings you get back are normal, if they arent, then you found the problem(s).
~Mike

Rickertsen2
07-02-2003, 01:30 PM
It sounds like you may have a short somewhere after a speed controller. As mentioned earlier, it might be posible that a short in the leads between a motor and a speed controller could draw enough current to drop the system voltage beyond the RC reset point before a breaker has time to trip. What happens if you only push the stick forward slightly? Check the resistance between the motor terminals and the M+ and M- terminals of the speed controlers to the V+ and V- terminals. What are they?

[EDITED TO CORRECT MY DUMBNESS.]

Dave Flowerday
07-02-2003, 03:47 PM
Originally posted by Rickertsen2
Disconnect the motor leads from their speed controller and touch them directly to a battery. This will rule out the motor and drive train.
DON'T DO THIS! If there is a short and if it is in the motor (which is definitely possible), you will be causing a direct short across the battery terminals with no circuit breaker/fuse in between for protection! In addition to probably welding the motor leads to the battery, you can damage the battery, the motor, and even possibly start a fire.

dez250
07-02-2003, 04:09 PM
Originally posted by Rickertsen2
Disconnect the motor leads from their speed controller and touch them directly to a battery. This will rule out the motor and drive train.

Don't do that at all!!!!! With in doing that, you will not only happen to ruin the motor or battery, but if there is a shirt in the motor, this is the same thing as just placing a solid wire across two battery terminals, that will cause a short. Also with a short circuit on a battery directly, this can cause the battery to have too much current flowing through it and will cause the battery to most likely explode and or ignite on fire... Common physics and electrics never make a direct connection across a battery without a breaker or an output with resistance in series.
~Mike

Adam Y.
07-02-2003, 10:36 PM
Don't do that at all!!!!! With in doing that, you will not only happen to ruin the motor or battery, but if there is a shirt in the motor, this is the same thing as just placing a solid wire across two battery terminals, that will cause a short. Also with a short circuit on a battery directly, this can cause the battery to have too much current flowing through it and will cause the battery to most likely explode and or ignite on fire... Common physics and electrics never make a direct connection across a battery without a breaker or an output with resistance in series.
I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor. Then again stalling the motor is just as likely to destroy the motor before the battery. It seems very hard to make an SLA acid battery explode. I have read horror stories about people abusing there batteries and all the battery would do is stink, and expand a lot.

rbayer
07-02-2003, 10:49 PM
Originally posted by Adam Y.
I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor. Then again stalling the motor is just as likely to destroy the motor before the battery. It seems very hard to make an SLA acid battery explode. I have read horror stories about people abusing there batteries and all the battery would do is stink, and expand a lot.

That's assuming the motor is in good working order. If it's shorted internally (if the brushes shomehow fell off and landed in the wrong place, etc), it's virtually the same as connecting a wire between the two terminals. Yes, the sparks are very pretty, but it really isn't worth it...

Adam Y.
07-02-2003, 10:58 PM
That's assuming the motor is in good working order. If it's shorted internally (if the brushes shomehow fell off and landed in the wrong place, etc), it's virtually the same as connecting a wire between the two terminals. Yes, the sparks are very pretty, but it really isn't worth it...
You really can not blow up a SLA battery. I have read quite a few posts where people have accidently shorted out there SLA's and all the end up doing is expanding.

Rickertsen2
07-02-2003, 11:04 PM
Originally posted by Dave Flowerday
DON'T DO THIS! If there is a short and if it is in the motor (which is definitely possible), you will be causing a direct short across the battery terminals with no circuit breaker/fuse in between for protection! In addition to probably welding the motor leads to the battery, you can damage the battery, the motor, and even possibly start a fire.

Good Point! I TAKE WHAT I SAID BACK. Use an ohmeter or inductance meter instead (im not sure what the readings for these motors should be around, but im sure someone on these forums can tell you. If there is in fact a short BAD THINGS WILL HAPPEN. (I normally test motors with a current limited bench power supply and i guess something didn't click in my head about using a battery instead!:() sorry. I feel really stupid now.

Adam Y.
07-02-2003, 11:13 PM
Good Point! I TAKE WHAT I SAID BACK. Use an ohmeter or inductance meter instead (im not sure what the readings for these motors should be around, but im sure someone on these forums can tell you. If there is in fact a short BAD THINGS WILL HAPPEN. (I normally test motors with a current limited bench power supply and i guess something didn't click in my head about using a battery instead!) sorry.
That is odd my books tell me you can't measure resistance of a motor using an ohmeter. I really do not know why though. Try getting a few D alkaline batteries or a regulated power supply.

dez250
07-02-2003, 11:53 PM
Originally posted by Rickertsen2
I feel really stupid now.

dont, you noticed your mistake and isnt that what first is all about, a learning experience? Well yeah like adam said a regulated power supply should work since normally they have a fuse or a breaker on them so you really cant hurt yourself, but safest thing now is to probe with a multimeter and see if readings are strange.
~Mike

sanddrag
07-02-2003, 11:54 PM
Originally posted by Adam Y.
Try getting a few D alkaline batteries or a regulated power supply. The D battery thing most likely won't work. I've tried runing a window motor all by itself that way and it didn't even budge. Even though it's a D, it just can't supply the current of a 12V SLA.

The power supply might work but it's got to be good enough to supply the current needed.

dez250
07-03-2003, 02:48 AM
Originally posted by Adam Y.
You really can not blow up a SLA battery. I have read quite a few posts where people have accidentally shorted out there SLA's and all the end up doing is expanding.

yes the smell that is present there is the chemical reaction that shouldn't happen inside most likely eating the plastic shell, its a reduction reaction... that can be very bad. also the expansion is the force created by the extra reactions that is the same thing as an explosion, just not as much force, which causes the expansion. and if it did crack you could have a caustic mess in the area where it leaked. Don't short out any battery, electricity may be fun to mess with, until you get zapped and/or injured.
~Mike

Adam Y.
07-03-2003, 01:07 PM
yes the smell that is present there is the chemical reaction that shouldn't happen inside most likely eating the plastic shell, its a reduction reaction... that can be very bad. also the expansion is the force created by the extra reactions that is the same thing as an explosion, just not as much force, which causes the expansion. and if it did crack you could have a caustic mess in the area where it leaked.
I always thought SLA batteries will not leak acid like reagular lead acid batteries which is the reason why combat robots are only allowed to use them. Besides I also read horror stories where a piece of molten metal went through a SLA and it still worked. In reality those people are dumb but it really shows how safe the battery is. There are ways to make them explode but that would be assinine. Anyway here are some more safety tips do not pot the battery or encase it to protect it. The battery will explode since gasses build up in all batteries and will have no way to vent. Always use the right charger for the batteries. Do not think all batteries will use the same charger. Some batteries like lithium-ion do need special chargers.

Rickertsen2
07-03-2003, 02:34 PM
Originally posted by Adam Y.
That is odd my books tell me you can't measure resistance of a motor using an ohmeter. I really do not know why though. Try getting a few D alkaline batteries or a regulated power supply.


Your books probably say that bacause motors have a very high inductace and will have dirrerent resistances depending on a number of conditions such as mechanical load, frequency, etc. At the very low DC voltages used by most ohmeters, the inductance is negledgable and an ohmeter can be used to test for shorts if you know the resistance of a good motor of the same type. And by the way i use an variable current limited bench power supply to test motors.

Adam Y.
07-03-2003, 02:49 PM
Your books probably say that bacause motors have a very high inductace and will have dirrerent resistances depending on a number of conditions such as mechanical load, frequency, etc. At the very low DC voltages used by most ohmeters, the inductance is negledgable and an ohmeter can be used to test for shorts if you know the resistance of a good motor of the same type.
Ackkk I figured it out.:) The resistance may be too small for the ohmeter to work. That is the reason why my books say that.

Rickertsen2
07-03-2003, 03:19 PM
Ahh! Didn't think of that. It is true many ohmeters don't perform too well or at all when measuring very low resistances. Just out of curiosity what book is it? I might want to read it.

Adam Y.
07-03-2003, 03:28 PM
Ahh! Didn't think of that. It is true many ohmeters don't perform too well or at all when measuring very low resistances. Just out of curiosity what book is it? I might want to read it.
Well I did not find the answer in the books but there is a pretty cool website I found that had the answer.
http://homepages.which.net/~paul.hills/

Al Skierkiewicz
07-03-2003, 05:00 PM
Originally posted by Adam Y.
I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor.

OK guys, We have talked about this before. If you stall the motor you are putting one or two windings in parallel across the power source. There is still some resistance in the windings and therefore the resistance will limit the current.( It will be high but not maximum.) This IS NOT the same as a short of zero resistance. Maximum current will be drawn from the power source. In our case the battery is capable of more than four hundred (400) amps. That is more than enough to weld wire to the terminals, create a shower of sparks (both fire hazard and burning hazard), may cause bright flashes (retinal burns) and ultimately could cause battery explosion. Just because you have never witnessed a battery exploding doesn't meant it can't happen. Some of you have seen a battery that was stressed, swell and deform the case. That should be evidence enough that catastrophic failure is possible.
Sealed Lead Acid batteries are still lead acid batteries. The electrolyte is a sulphuric acid compound and the plates are lead. When batteries are stressed the electrolyte heats up and the lead deforms both of which contribute to the swelling case. You can interpolate the result if the deformation was rapid, an explosion would be the result. Hot, gelled sulphuric acid and plastic shrapnel are not my idea of fun.
I would try this, start by removing all of the circuit breakers that feed motors. If the controller still shuts down, it is not the motors or controllers. (assuming you have wired them according to electrical rules.) If all is OK, then insert one breaker and try again. Continue until you find the offending device. My suspicion is a wayward connector that will be obvious under visual inspection, or a damaged drill motor. Please let us know what you find.

Al Skierkiewicz
07-03-2003, 10:32 PM
Originally posted by Adam Y.
I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor.


OK, we have discussed this before but to prevent any further confusion...

When a motor is in stall, one or two windings are in contact with the brush assembly. Each winding has some resistance which limits the amount of current flowing. For the drill motor this year, stall current was rated at 129 amps. However, the SLA battery is capable of supplying in excess of 400 amps in short circuit! That is sufficient to weld wire, sending sparks (fire and skin burning hazard) bright arcing light (retinal burns) high temperature on the conductor (creating poisonous gasses) and the possible explosion of the battery. High temperatures are not only generated in the wire you use. Remember that the circuit is a series one. Current, everywhere in a series circuit, is the same. 400 amps flowing through a wire is also flowing through the battery. That amount of current will rapidly raise the internal temperature of the battery, resulting in damage to the case if you are lucky. When high currents are flowing in the battery, you boil the electrolyte and deform the lead plates. Use circuit protection when testing motors! Hot sulphuric acid and plastic shrapnel is not my idea of a fun time.

Now back to the problem. Something is drawing the power supply down below reset on the RC. Remove all the circuit breakers that feed motors and repower the robot. If moving the joystick still causes reset, then suspect a bad PWM cable or a bad PWM input on a controller. You can isolate this by removing PWM cables one at a time and repeating the joystick test.
If the RC does not reset with all the breakers removed, then add the breakers back one at a time until you isolate the bad circuit. I think you will find a wire or connector has come loose and/or is touching another contact. There has been trouble with the drill motor brush assembly and it is possible to cause a short in this area if the plastic at the brush end of the motor is damaged or out of alignment.

Adam Y.
07-04-2003, 12:46 PM
However, the SLA battery is capable of supplying in excess of 400 amps in short circuit!
The spec sheet says 230 amps and for five seconds. Is there overcurrent protection on these batteries?? By the way I never said I stalled the motor. Your right that is dumb and will destroy everything.
There has been trouble with the drill motor brush assembly and it is possible to cause a short in this area if the plastic at the brush end of the motor is damaged or out of alignment.
That is usually easy to tell if the motor is damaged. The brushes should pop right out.

Al Skierkiewicz
07-04-2003, 09:59 PM
Adam,
Read carefully when you are checking the spec sheets. A fully charged battery has an internal resistance of 10 milliohm. By Ohm's Law I=V/R=12/.01=1200 Amps. Now asume some variables creep into the calculations like not fully charged battery, some resistance in the wire (#10 is .001 ohm/foot) and a high resistance connection on the wire doing the short and 400 amps is pretty easy to get. Let us remember that the current through the internal resistance causes a voltage drop and that lowers the terminal voltage at the outside of the battery. A stalled motor is still a higher resistance than a dead short and therefore lower current when at stall. Teams stall motors all the time during competition and do not damage batteries or motors unless the stall condition continues for a great length of time.

The brush assembly on the drill motor can easily be damaged and the brushes can be out of alignment without any obvious damage. I came across several in Houston where the brushes were not touching the commutator or were severely misaligned enough to be be damaged by the wire contact at the edge of the commutator.
Sorry for the double post, it had something to do with the spell checker and I am still trying to work that out.