drive train wearing out?

[Qbranch]

Our robot's odometer reads a little under 75,000ft on it's drivetrian now (about 14.2mi ) and the chains have started to gum up from carpet fuzz (among other things).

Our (currently tired) robot is due for an overhaul that we'll be doing thursday morning in Atlanta. It'll be back up to it's old midwest-regional-speed self first thing Thursday.

But yeah, you are not alone in your robot's symptoms gurellia53, they aren't much different from the ones ours developed.

Good luck finding your problem,

-q

[imdunne8]

Well if it helps at all, we were seeing temperatures of around 150 degrees farenheit using a non-contact thermometer after a decent amount of use. This was the temperature of the casing of the motor, so it could have been hotter in the center.

Thanks so much for all of the replies so far. We will definitely be putting a lot of effort into the robot on the practice day in Atlanta. I'll be sure to check everything you guys have recommended. The only reason I am thinking that it is not a loose connection is that we have noticed a significant difference in the drive motors, a smaller difference in the launcher motors, and no difference in the lifter. As some have said though, the lifter gets very little use.

[Jim E]

W are experiencing similar issues too. The Electrical paths is one of the items we will address at Atlanta before anything else.

I want to add that the Ground returns are just as important to check along with the power side.

All of those return molecules have to go somewhere. Think of a Dam.

If the water leaving the dam is restrained, it backs up behind it. If the dam is wide open and the water to the dam is a trickle, the same amount of water is still leaving the dam. The trick is figuring out what scenario is happening. Sometime heated wires can pinpoint where the problem is occurring.

At the Florida Regional, we must have redone connections on the battery terminals at least 5-6 times. Those screws would work loose and then you would have a resistance build up or intermittent connection. That surprised me the most. If you think a connection is tight enough, give it another 1/4 turn for safe measure.

The yellow jumper may also be an issue on the distribution block. Move your wires around so the maxi-block is fed by the same block as the power coming in without the yellow jumper being a factor.

All of our other wire connections are soldered to minimize resistance, so the focus will be from the maxi-block back to the battery.

[Mr.G]

Originally Posted by gurellia53

We have kitbot 6wd with center wheel lowered. All IFI high traction wheels. Each side is powered by 1 CIM through an AM supershifter and a 1:1 sprocket ratio.

I think the drivetrain is way under powered. We have 2 CIM's per side and a AM Shifter and a ~3:1 sprocket ratio, and we have a hard time turning sometimes with this setup.

You have one CIM and a 1:1 sprocket ratio. It is geared for speed and not for turning. I think like "Alan Anderson" said the surface you were on at your school made you able to turn and now you are on a surface with more traction and can't turn.

[dtengineering]

I'm with Kevin on this one... we built a six wheel drive kitbot with the centre wheels lowered and 6" IFI traction wheels on each corner for the Aim High game a couple years ago. Even with two CIMs per side and a slight reduction in the sprockets the robot had difficultly turning on carpet. It may be that the carpet you tested on was lower friction than the carpet at the tournaments. (Edit: or that your robot was lighter at the time or had a different weight distribution.)

If you can try slapping a pair of omni wheels on the heavier end of your robot, I am willing to bet that all your turning issues will suddenly disappear. Yeah, your traction will drop a bit, but given the nature of this year's game and the gear ratios that you have that should have little effect on your machine's performance.

Good luck with it!

Jason

[Al Skierkiewicz]

Andrew,
Come and find me early in Atlanta. I will be one of the Lead Inspectors so I should be easy to find. There is a lot of evidence that points to an electrical problem but the drive motors sound like they have been stressed. 150 degrees is likely 30-50 degrees cooler than the armature temp. These motors do start to short windings which limits output power with extreme temperatures. Be ready to replace in Atlanta. If they are shorted, they will be putting an increased load on the battery that was not there during practice. However, if all problem motors are driven from the 40 amp block, that is the first place to look.

[imdunne8]

Well, the carpet may have been slightly different between the practice field and competition field, but there was such a small difference that it would not have as drastic of an effect as we are seeing. It performed very well on the practice field and now with the same robot and an almost equal field. it seems to us that our drive and launch systems are far less effective. We are thinking that it is either a mechanical or electrical problem somewhere between the battery and the transmissions.

Al, thanks so much for your offer for help. We will be sure to find you in Atlanta!

[M4 Sherman]

This is from my RC Car racing days, But could you have thrown the Solder?

No doubt that the motors got hot from doing turns in high gear. I've seen it when motors lose all power and efficiency from throwin the solder.

[KF987]

Try changing the chain's on your DT. The chain on our comp. bot is really tight, and the bot is a little slower as well , while our practice bot's chain is fairly loose... we are going to change out the chains thursday for the first match and see how we do...

-Keaton

[adman]

Hi guys,

I have been working with DC motors for a very long time. The ones I work
with are called starter motors on very big diesels. These have lifetimes
like all DC motors. The big problem on small motors that aren't heat sinked
is breakdown of the varnish that is on the armature windings.
A bigger problem is the commutator surface. Normally it is an even surface of copper
that the brushes contact. Over time this surface gets hit with constant
current spikes. If brush wear is even then the current is distibuted evenly.
If hot spots occur then the surface starts getting burned. The more
burning the more nonconduction of the surface and the motor starts losing
performance. Take an old DC (or AC) brushed motor apart and look at the
commutator. I have been amazed at some of these still working despite their
appearance. If your motor doesn't turn and some one moves the drive
wheel ( do this with an object not your hand) and all of a sudden the motor
starts moving then you may have commutator brush problems. When you
move the motor it goes to a different spot on the commutator that isn't
burned then it starts to spin.

HOT Cims also can affect brush springs. As they get softer they don't exert
as much force on the commutator. Less force less contact less current. The
dust from the brushes also gets in the brush retainers thus they don't slide.

The problem with CIMs is like all DC motors they will spin like crazy with
no load and sound just fine. You must load the motor to test it. A little
Dyno would be perfect.

I advocate what many of you already said. Run your bot for a test run
on the carpeted practice area. Then feel all the connections. Any heat
is lost voltage. Its that simple. A simple thing to do is carefully place
a voltmeter in the Robot where you can easily see it. Make leads that
attach from the battery lead to the input side of your motor controller.
When the robot is running it should not drop more than a few tenths of
a volt. If it is you are losing voltage thats a bad thing. If you are then
just start probing from the battery to the next thing and so on until you
find out who is dropping all the voltage. A loose connection can get so
hot it will burn your fingers so be careful.

If you find you are delivering full voltage to the controller then you need to
see what voltage is being applied to your motor at full throttle. It should
be at least 95% of the applied voltage. (Your motor control uses parallel
MosFets that act as switches that turn on and off very fast, the motor
armature is an inductor so this integrates an RMS current through the
winding and produces Electro motive Force to spin the motor ) As you
approach full signal the mosfets turn on for such a long time verus off
that it will appear as the MosFets are fully on. (they still have Rds on though)

I put a lot of buzz words in here so you guys can hit Wikipedia to learn
more.

The summary is Check your system for voltage drops, (heat or voltmeter)
You need to have the robot under load to do this so
DO IT SAFELY, have a mentor around to observe
If you have full voltage then clean out your drive line
of carpet fuzz, check bearings (for string,hair), clean chains
If you still seem to not have the power it may be prudent
to change out the CIMS. If you have two maybe you can
change one at a time to see if only one is bad.

Sorry for the long post but knowledge is Power (ha-ha)

[bobdahaxor]

We had that SAME EXACT problem with our drive train. We used a direct front wheel drive 1 CIM per side configuration with traction wheels. (We had omni's in the back) Our issue was we would test on our hard linoleum surface and be fine. We also tested at the play date. We were fine (but we only ran one match per trial). We got to Chesapeake and nothing worked. If you use a Gyro, disable the gyro code and any other sensors that would affect your drivetrain. These could be hindering your turning ability because they attempt to control the spin and causing you to be unable to turn. When the motors are cool, I bet you have decent performance. As motors heat up, the become less efficient causing more power to be drawn. Did you ever notice a "stuttering"? This would be caused by circuit breakers popping and resetting. If possible, I would strongly consider changing your gear ratio or between matches putting ice packs on all of your motors. We did this with great success at Philly and I think it can work for your team too!

[gurellia53]

Thank you everyone!

I think we'll plan on changing the motors (we have to open the transmissions anyways) and check for loose wires. We also have some sort of a thermometer on our multimeters (how awesome is that ) so we'll probe around for hot spots. Also, not mentioned in this thread, some people on our team think that we may have bad victors. And since we have 2 empty victors on our robot, we'll switch the drive motor victors.

Al, thanks for your offer! I'll definitely look for you in Atlanta.

-Andrew

[RyanN]

I haven't seen anyone throw this out yet, but you should also check your Victors. A few years ago, our robot had a weird issue of driving very weird in forward, but perfectly in reverse. When I took the fan off the victor, I saw that one of the transistors was blown, causing less power to go to the motor. With the stress of one motor driving the robot, the Victors take more abuse, which may cause them to fail.

To check this, just pop off the fan, get a small flash light, and look at each transistor and see if there are any pieces missing from them. Also check for melted plastic where the transistor enters the case. This is also a sign of something wrong.

[Al Skierkiewicz]

Originally Posted by RyanN

When I took the fan off the victor, I saw that one of the transistors was blown, causing less power to go to the motor.
To check this, just pop off the fan, get a small flash light, and look at each transistor and see if there are any pieces missing from them.

A much easier way is to use your nose. When Victors pop the FETs they give off an very unique odor. Please remember that in my experience, about 90% of all Victor failures are due to metal dust and shavings.

[JesseK]

Another tip to remember: nothing is EVER maintenance-free. Check for loose bolts and for pieces of the bot that may have shifted or come undone. This may be causing a not-so-obvious mechanical interference that causes an inefficiency.