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-   -   pic: burnt up TETRIX motor (http://www.chiefdelphi.com/forums/showthread.php?t=89848)

colin340 22-01-2011 22:11

pic: burnt up TETRIX motor
 

wilsonmw04 22-01-2011 22:14

Re: pic: burnt up TETRIX motor
 
Thanks for the info. I would advise all teams not to continuously run these motors, at speed, when at the top of the pole. They will burn out. It might be wise to design a cutoff for your minibot when it hit the top. This bit of forethought will save many teams 30 - 60 bucks.

Cyberphil 22-01-2011 22:52

Re: pic: burnt up TETRIX motor
 
Very interesting!

We were just messing around today and thought we burnt out one. But the weird thing was when we plugged it back into the battery without any load, it ran just fine, so much so we mounted it back on and used it for another 5-7 trials.

This is a very good tip though! This will make prototyping much less expensive! :D

colin340 22-01-2011 23:03

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by wilsonmw04 (Post 1006066)
Thanks for the info. I would advise all teams not to continuously run these motors, at speed, when at the top of the pole. They will burn out. It might be wise to design a cutoff for your minibot when it hit the top. This bit of forethought will save many teams 30 - 60 bucks.

yes we are planing on shuting it off but a slip of the hands and boom motor gone

blackiceskier 22-01-2011 23:10

Re: pic: burnt up TETRIX motor
 
Coming from a FTC member before disassembling a DC motor from the kit plug it back in to a power source with no external load. Sometimes the motors smoke and we think they are burnt out but they just smoke and are still usable in 3 years we have gone through 3 motors actually burning out, and that was only from a 1:27 gear ratio on last years shooter for Hot Shot.

Bill_B 22-01-2011 23:21

Re: pic: burnt up TETRIX motor
 
The part that failed is the cylinder-ish one in the back, right? The blue blob is a shunt capacitor I think. It tries to reduce the brush noise on the power input line. If that shorts, you will blow a fuse every time. The smoke some others mention may also be from the part that failed here; just on the verge of failing.

colin340 22-01-2011 23:31

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Bill_B (Post 1006157)
The part that failed is the cylinder-ish one in the back, right? The blue blob is a shunt capacitor I think. It tries to reduce the brush noise on the power input line. If that shorts, you will blow a fuse every time. The smoke some others mention may also be from the part that failed here; just on the verge of failing.

yes the resistor is very burnt up and cracked right in half
the shunt capacitor looks fine

Tristan Lall 23-01-2011 00:20

Re: pic: burnt up TETRIX motor
 
Hypothetically, if one were to install a wire in parallel with the resistor, without making any modifications to the motor, <R47> would not stand in the way.* Since I don't have the motor in front of me, I can't say whether this would actually be possible: in all likelihood it would involve laparoscopic surgery through the vent holes (if any), and wrapping a shunt around the leads.

Perhaps that's not what FIRST intended...but wrapping a wire around a lead is no more a modification than wrapping a chain around a sprocket. Of course, irrespective of what the rule says, it's unlikely that FIRST would give its blessing to this technique if you inquired about it in the Q&A.

In any event, I wouldn't recommend doing this. In fact, I only bring it up because it would be a plausible explanation to give an inspector checking the resistance at the motor terminals. (Not that such checks are common practice.)

*Sometimes you just need to think like a criminal....

vincentkee 23-01-2011 00:27

Re: pic: burnt up TETRIX motor
 
Does anyone have problems with the tabs of the motors frequently breaking off?

We have our minibot climb up a steel pole that doesn't have a top so it falls down. We don't always catch it and then the tabs of the motors keep breaking, rendering them useless unless we solder on replacements.

Bill_B 23-01-2011 01:41

Re: pic: burnt up TETRIX motor
 
Zip tie the leads to the motor body to give some strain relief? Solder is not mentioned in <R92> nor are electrical connectors. I hope this is an oversight. I'm not looking forward to trying to get a wire nut onto those tabs. :yikes: :eek:

ayeckley 23-01-2011 08:07

Re: pic: burnt up TETRIX motor
 
Has anyone experimented with the use of a 10A fuse in place of the 20A "default" fuse? Haven't seen it discussed elsewhere.

As long as the fuse survives the inrush current, it appears that it should hold during a "normal" climb using two motors near the max power operating point, yet still open reasonably quickly once a locked rotor condition occurs. Perhaps this would have prevented the OP's issue altogether - or maybe not.

Our plan was to do this during build season, then revert to the 20A fuse for competition (and even then, replace that fuse every few matches). The worst-case scenario *seems* to be that there might be a lot of nuisance fuse openings, but it would be far less expensive to replace fuses than motors.

Bill_B 23-01-2011 08:29

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by ayeckley (Post 1006281)
Has anyone experimented with the use of a 10A fuse in place of the 20A "default" fuse? Haven't seen it discussed elsewhere.

...

Sounds like a good idea in light of the OP's situation. I've blown one 20a so far but I'm presuming that Colin's failure was with the same fuse in place. Also interesting to note that "fuse" is not mentioned in the minibot rules section.

colin340 23-01-2011 09:26

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by ayeckley (Post 1006281)
Has anyone experimented with the use of a 10A fuse in place of the 20A "default" fuse? Haven't seen it discussed elsewhere.

my electrical people said a fuse would take to long to blow as the resistor or inductor was gone in under 2 sec

Al Skierkiewicz 23-01-2011 10:57

Re: pic: burnt up TETRIX motor
 
The "resistor" is an inductor. Opening the motor is a illegal modification and it pretty much screws up the brush assy if not done carefully.
<R93> Motors may not be modified with exceptions of those in Rule <R47>.
A 5 or 6 amp fuse in line with each motor might be a good protection. If installed properly with insulation, etc., I do not see any rule that would prevent it. The stall current on the motor is listed at 7 amps I believe.

colin340 23-01-2011 11:21

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1006343)
The "resistor" is an inductor.

Al why do u think it is a inductor? just to quiet the brush noise?

also any idea on value of the inductor?

Mark McLeod 23-01-2011 12:23

Re: pic: burnt up TETRIX motor
 
There is this FIRST legal option for development, but not competition:
http://www.legoeducation.us/store/de...2&s=32&ID=2135

Use the promo code FRCT3340 (thanks Travis!) and it's $9.

PhilBot 23-01-2011 12:25

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1006343)
A 5 or 6 amp fuse in line with each motor might be a good protection. If installed properly with insulation, etc., I do not see any rule that would prevent it. The stall current on the motor is listed at 7 amps I believe.

Pitsco sells just such a modified motor power wire:

It's hugely expensive for what it is, but it's clearly 100% legal (since it's a standard TETRIX part) and it's ready to go for those not wanting to do soldering.

http://parts.ftcrobots.com/store/det...&c=1&t=0&l= 0

Chris is me 23-01-2011 12:36

Re: pic: burnt up TETRIX motor
 
Does smoke = no longer competition legal motor?

We failed both our motors this way with less than 1 second of stall, and it's quite disappointing - but if the smoke is just the thermal breaker tripping and it happened to reset, then hey, we don't have to spend $60.

I'm almost certain we will be direct driving our minibot now not because it's fastest but just to avoid stall even though I think it will still happen.

wilsonmw04 23-01-2011 13:06

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Chris is me (Post 1006386)
Does smoke = no longer competition legal motor?

From my experience, no, smoke does not not make the motor illegal. I can also say that smoke does not mean the motor is bad either. We have used every motor we have "smoked" again in competition. In face, I think we still have all the motors we started with 3 years ago. The only real problem we have is that we snapped two posts before they made the new adapters.

Jonathan Norris 23-01-2011 13:55

Re: pic: burnt up TETRIX motor
 
We have had both our motors burn up so far... I opened up one of ours yesterday and shorted the burnt resistor, planning on putting a new resistor on the outside. Does anyone know what resistance the resistor is supposed to be??

If these motors burn out this easily mini bots are going to get expensive very quickly...

billbo911 23-01-2011 14:16

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by colin340 (Post 1006356)
Al why do u think it is a inductor? just to quiet the brush noise?

also any idea on value of the inductor?

I honestly can't prove if it is a resister or an inductor. One thing I can say is it is a series device, not a shunt device. The cap is in fact a shunt.

That being said, it makes perfect sense that it is an inductor. The inductor and cap create an LC low pass filter, thus keeping the higher frequency noise from being radiated or conducted to other components or systems.

Al Skierkiewicz 23-01-2011 16:34

Re: pic: burnt up TETRIX motor
 
I will see if the motor I have open at work can CSI'd.

Teched3 23-01-2011 17:07

Re: pic: burnt up TETRIX motor
 
Now that you see there is a problem, time to engineer a solution. Shouldn't be too difficult to design a way to turn off motor power when you strike the target.:) :)

billbcc91 23-01-2011 17:24

Re: pic: burnt up TETRIX motor
 
Al says that is an inductor and he is usually right. But it does look like a resistor to this mechanical engineer who remembers just about nothing from my EE courses 20 years ago. So I could very easily be mistaken.

Somebody asked about the value of part. If it is a resistor, you can tell by the color of the bands. I can't tell what the inner 2 bands are from the photo due to the crispiness. Maybe somebody who has cracked a motor open can post what the band colors are. Here is a link about how to decode the color bands to a value.

http://www.electronicsteacher.com/tu...a-resistor.php

I would expect there may be an equivalent code for inductors?

Al Skierkiewicz 23-01-2011 18:34

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Mark McLeod (Post 1006373)
There is this FIRST legal option
http://www.legoeducation.us/store/de...2&s=32&ID=2135

Use the promo code FRCT3340 (thanks Travis!) and it's $9.

Mark,
Thanks for the link unfortunately it is not currently part of the allowed list of Tetrix parts. Please standby...

artdutra04 23-01-2011 18:41

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1006664)
Mark,
Thanks for the link unfortunately it is not currently part of the allowed list of Tetrix parts. Please standby...

They are listed on the third page of the TETRIX product catalog linked to in Minibot section of The Robot rules.

http://www.tetrixrobotics.com/Buildi....aspx?moid=533.

Al Skierkiewicz 23-01-2011 20:00

Re: pic: burnt up TETRIX motor
 
OK,
I will check on this. I have a doc that is the allowed parts for inspectors. I cannot load the Tetrix page, it appears to be having an issue. My doc does not list the thermal protectors.

Teched3 23-01-2011 22:06

Re: pic: burnt up TETRIX motor
 
In Team Update 3, FIRST gives a 2nd link to Lego Education, FRC Tetrix parts, which is notably expanded over the Pitsco catalogue in the original manual.

www.legoeducation.us/FRC

That link should take you to a 9 page catalogue of additional Tetrix acceptable parts.:) :)

Al Skierkiewicz 23-01-2011 23:26

Re: pic: burnt up TETRIX motor
 
TecheD,
There in lies some of the confusion. The lego link is not in the Team Update. It is a place that can be used to obtain parts. From TU#3
Please note that the Rule <R92> only allows Tetrix components. While Tetrix components are a subset of FTC components, it is essential to realize that not all FTC parts are Tetrix parts. As such, not all FTC parts are permitted on the MINIBOT. Please be sure to vet your components against the above list before constructing your MINIBOT.
I am receiving a corrupt file error when trying to access the Tetrix page. Therefore, I cannot compare it to my file.

caffel 24-01-2011 09:11

Re: pic: burnt up TETRIX motor, excellent post
 
Thanks for the G2 on this motor and the implication that we must have a limit switch.
Hopefully someone, perhaps you yourself, will put this up in the Q&A so we can get a clarification.
Have you seen the resister stripes of a new one ?
Like what is the resistor rated at ?
Maybe we could use a small cricuit braker in series (they go down to 3 Amps, although hard to source in that rated size)

Al Skierkiewicz 24-01-2011 09:23

Re: pic: burnt up TETRIX motor
 
The motor I have here at work failed in a way that it opened the case and exposed the interior of the inductor. It is a 3.9 microhenry RF choke in series with the motor. The shunt cap is .039 microfarad. The motor interior looks OK but the choke is open circuit. It would appear that the thermal protection is a good fix. Please stand by...

ayeckley 24-01-2011 09:23

Re: pic: burnt up TETRIX motor, excellent post
 
Quote:

Originally Posted by caffel (Post 1007085)
Maybe we could use a small cricuit braker in series (they go down to 3 Amps, although hard to source in that rated size)

The response times for circuit breakers are typically much longer than for equivalent-value fuses. If you go this route (and if it's determined to be FRC2011-legal), make sure to check that the response time of the device is within whatever time you decide is acceptable. Based on what I'm reading, it sounds like it would need to trip within 1 sec @ 7A (assuming one per motor) to prevent the "smoking" issue.

Al Skierkiewicz 24-01-2011 09:25

Re: pic: burnt up TETRIX motor
 
Alex,
The trip characteristic for the snap action breakers would likely require something like the 1 amp type. A 3 amp breaker may never trip on 7 amps.

Bill_B 24-01-2011 21:11

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Al Skierkiewicz (Post 1007092)
The motor I have here at work failed in a way that it opened the case and exposed the interior of the inductor. It is a 3.9 microhenry RF choke in series with the motor. The shunt cap is .039 microfarad. The motor interior looks OK but the choke is open circuit. It would appear that the thermal protection is a good fix. Please stand by...

Cursory search for a choke like that with a suitable current rating for this motor is perplexing. The ones I found are all too big to fit inside the motor. The common factor is a resistance so low as to be practically undetectable at .013 .024 ohms for instance. This would sorely test my FIRST Jiminy Cricket if I had two dead motors and less than a week to competition.:yikes:

Al Skierkiewicz 26-01-2011 08:35

Re: pic: burnt up TETRIX motor
 
By now, everyone should have read Team Update #5 where the thermal protected wire for the Tetrix motors is now approved for your use. Enjoy.

IndySam 26-01-2011 08:57

Re: pic: burnt up TETRIX motor
 
I hope they have a lot in stock!

DonRotolo 26-01-2011 17:07

Re: pic: burnt up TETRIX motor
 
Go look up the MINI Blade fuse performance curves here to get an idea of how long a, say, 2A fuse can carry 10A

U5ER NAM3 26-01-2011 17:43

Re: pic: burnt up TETRIX motor
 
how do i post my own post? i need help:confused: please help me

Nishant 26-01-2011 23:10

Re: pic: burnt up TETRIX motor
 
I burnt a motor today using a 3:1 gear ratio (not counting gearbox). The smoke came from the gearbox, but both the gearbox and motor smelled. By my calculations, our robot's fastest speed would occur at a 6.48:1 gear ratio (not counting gearbox). I checked my calculations, but why does the tetrix motor smoke like this?

Tom Line 30-01-2011 14:14

Re: pic: burnt up TETRIX motor
 
Your motor is smoking because you are stalling it and drawing too much current. Don't expect it last long - and have someone else check your calculations.

WarehouseCrew 04-02-2011 10:06

Re: pic: burnt up TETRIX motor
 
Could anyone using the Tetrix fuse protected motor power cable answer a couple questions:

1. Does it prevent burning up the Tetrix motors (eg. live up to its promise)?
2. Does the fuse act like a circuit breaker (eg. when it cools down it works again) or do you need to replace the fuse/power cable once it has prevented a motor stall ($9 vs. $30 for motor)?
3. If it is a "fuse" that is destroyed while preventing damage to the motor; can just the fuse (hopefully less that $9) be replaced on this cable without violating the FIRST rules?
4. Is this the cable people are referring to regarding thermal protection?

Thanks.

MechJim 04-02-2011 12:25

Re: pic: burnt up TETRIX motor
 
We recieved our fuse protected power cable and it has so far worked very well. It does not use a fuse, it uses some sort of solid state circuit that inturrupts the power. The circuit then resets after a short time.

Very good investment.

elbuo 06-02-2011 11:07

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by billbcc91 (Post 1006603)
Al says that is an inductor and he is usually right. But it does look like a resistor to this mechanical engineer who remembers just about nothing from my EE courses 20 years ago. So I could very easily be mistaken.

Somebody asked about the value of part. If it is a resistor, you can tell by the color of the bands. I can't tell what the inner 2 bands are from the photo due to the crispiness. Maybe somebody who has cracked a motor open can post what the band colors are. Here is a link about how to decode the color bands to a value.

http://www.electronicsteacher.com/tu...a-resistor.php

I would expect there may be an equivalent code for inductors?

Can someone provide the resistor value? I'm experiencing the same issue

Al Skierkiewicz 06-02-2011 12:32

Re: pic: burnt up TETRIX motor
 
Yamil,
It is an inductor. Search for my other post on this subject. I give the values and a method for repairing a motor with an open inductor. This is not a competition legal fix, but one that will give you motors to use for prototyping and practice.

Tristan Lall 06-02-2011 14:41

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by Tristan Lall (Post 1006206)
Hypothetically, if one were to install a wire in parallel with the resistor, without making any modifications to the motor, <R47> would not stand in the way.

While my previous comment was true, and at least a plausible interpretation absent a direct ruling, I neglected to consider <R03>. So just in case anyone was considering implementing that: don't. <R03> prohibits custom circuits affecting motor outputs on the entire robot, not just the hostbot.

And besides, now that it's been identified as an inductor and not a current-limiting resistor, there's a pretty good practical reason to retain it (over and above what the rules dictate).

davidthefat 07-02-2011 18:22

Re: pic: burnt up TETRIX motor
 
We had the same problem, a burned out motor. I assume that it is a blown inductor. How many amps will blow out the inductor? And is there an acceptable fuse that will prevent this from happening, preferably one that fits in the battery's fuse clip?

Thanks,
David

chapman1 13-03-2011 18:02

repairing burnt up TETRIX motor
 
In order to resore our blown Tetrix motor for "development" use (working on them is an "illegal" mod), I took it apart as follows:

- remove from gearcase
- mark the orientation of the brush plate relative to the case
-file away the areas where the case is "lipped over" to hold the brush plate. I used a small triangular file.
- carefully tap the opposite end (the gear) on a hard surface to pop the brush plate up.
- do not pull up on the brush plate! This will damage the brushes. Instead, slide it sideways off the commutator.

Once I had it apart, I could see that the inductor was obviously smoked. I unsoldered it, and in its place, soldered a solid wire (don't worry, it will still work!)

To reassemble:

- create 2 loops using fine thread. Hook one loop around each of the brushes.
- with the loops, carefully pull the brushes far enough apart to clear the commutator.
- pinch the threads around the circumference in a way that will hold the brushes while you reinstall the brush plate on the shaft.
- when it's in place, snip each thread loop and pull one end to remove them.
- place the motor on its side and using a small hammer, gently "tab over" the housing adjacent to the notches you filed away to remove the brush plate.

If you are as lucky as me, the motor will run like new! Granted, it doesn't have the "inductor", but it seems to work just fine for testing and development. It pains me to have to spend $30 each time a motor blows!

SuperBK 27-03-2011 17:01

Re: pic: burnt up TETRIX motor
 
What current should the inductor be rated for?

I see its legal to repair it as per <R93>
b) a burned out motor may be repaired by replacement of the burned-out inductor with an identical part

colin340 27-03-2011 17:44

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by SuperBK (Post 1045857)
What current should the inductor be rated for?

I see its legal to repair it as per <R93>
b) a burned out motor may be repaired by replacement of the burned-out inductor with an identical part


I believe that the very has been stated somewhere but no one can find a replacement part

Al Skierkiewicz 28-03-2011 04:56

Re: pic: burnt up TETRIX motor
 
Brian,
The highest current device I have found thus far for this size package is 900ma. Unfortunately, those are non-stock at Mouser.

SuperBK 28-03-2011 09:14

Re: pic: burnt up TETRIX motor
 
Thanks Al, what size package is it? (length, width)? Ours is locked away in our trailer since we got home Saturday night from Palmetto. We have a week and a half to get ready for our next regional.

lonski 25-04-2011 15:17

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by vincentkee (Post 1006211)
Does anyone have problems with the tabs of the motors frequently breaking off?

We have our minibot climb up a steel pole that doesn't have a top so it falls down. We don't always catch it and then the tabs of the motors keep breaking, rendering them useless unless we solder on replacements.

we have had troubles with the connectors and we soldered the wires to the connector and never had any more issues with them beraking. we just have an issue with a brand new motor that we bought just burnt out. we broke in the motor before we put preassure on the motor and then we climed the pole and the tird time and the motor just randomly stoped. the shaft spins nicely the motor didnt heat up or smoke. anyone know how to open the motor

Jeffy 25-04-2011 15:39

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by lonski (Post 1056405)
we have had troubles with the connectors and we soldered the wires to the connector and never had any more issues with them beraking. we just have an issue with a brand new motor that we bought just burnt out. we broke in the motor before we put preassure on the motor and then we climed the pole and the tird time and the motor just randomly stoped. the shaft spins nicely the motor didnt heat up or smoke. anyone know how to open the motor

Easiest way is to lightly tap on the end of the motor shaft without the back end of the motor supported. The back piece pops right off.

Ninja_Bait 26-04-2011 08:48

Re: pic: burnt up TETRIX motor
 
Quote:

Originally Posted by colin340 (Post 1006291)
my electrical people said a fuse would take to long to blow as the resistor or inductor was gone in under 2 sec

15- and 10-amp fuses saved our motors more often than 20's did. Once we had a design that worked, we switched back to 20-amp fuses because we had more of them, but the lower amperage was helpful.


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