22-01-2011 22:14

wilsonmw04

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.

22-01-2011 22:52

Cyberphil

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!

22-01-2011 23:03

colin340

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by wilsonmw04 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.

22-01-2011 23:10

blackiceskier

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.

22-01-2011 23:21

Bill_B

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.

22-01-2011 23:31

colin340

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Bill_B 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.

23-01-2011 00:20

Tristan Lall

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....

23-01-2011 00:27

vincentkee

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.

23-01-2011 01:41

Bill_B

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.

23-01-2011 08:07

ayeckley

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.

23-01-2011 08:29

Bill_B

Re: pic: burnt up TETRIX motor

Quote:

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

23-01-2011 09:26

colin340

Re: pic: burnt up TETRIX motor

Quote:

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

23-01-2011 10:57

Al Skierkiewicz

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.

23-01-2011 11:21

colin340

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Al Skierkiewicz The "resistor" is an inductor.

23-01-2011 12:23

Mark McLeod

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.

23-01-2011 12:25

PhilBot

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Al Skierkiewicz 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.

23-01-2011 12:36

Chris is me

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.

23-01-2011 13:06

wilsonmw04

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Chris is me Does smoke = no longer competition legal motor?

23-01-2011 13:55

Jonathan Norris

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...

23-01-2011 14:16

billbo911

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by colin340 Al why do u think it is a inductor? just to quiet the brush noise? also any idea on value of the inductor?

23-01-2011 16:34

Al Skierkiewicz

Re: pic: burnt up TETRIX motor

I will see if the motor I have open at work can CSI'd.

23-01-2011 17:07

Teched3

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.

23-01-2011 17:24

billbcc91

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?

23-01-2011 18:34

Al Skierkiewicz

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Mark McLeod 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.

23-01-2011 18:41

artdutra04

Re: pic: burnt up TETRIX motor

Quote:

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

23-01-2011 20:00

Al Skierkiewicz

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.

23-01-2011 22:06

Teched3

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.

23-01-2011 23:26

Al Skierkiewicz

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.

24-01-2011 09:11

caffel

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)

24-01-2011 09:23

Al Skierkiewicz

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...

24-01-2011 09:23

ayeckley

Re: pic: burnt up TETRIX motor, excellent post

Quote:

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

24-01-2011 09:25

Al Skierkiewicz

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.

24-01-2011 21:11

Bill_B

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Al Skierkiewicz 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...

26-01-2011 08:35

Al Skierkiewicz

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.

26-01-2011 08:57

IndySam

Re: pic: burnt up TETRIX motor

I hope they have a lot in stock!

26-01-2011 17:07

DonRotolo

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

26-01-2011 17:43

U5ER NAM3

Re: pic: burnt up TETRIX motor

how do i post my own post? i need help please help me

26-01-2011 23:10

Nishant

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?

30-01-2011 14:14

Tom Line

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.

04-02-2011 10:06

WarehouseCrew

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.

04-02-2011 12:25

MechJim

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.

06-02-2011 11:07

elbuo

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by billbcc91 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?

06-02-2011 12:32

Al Skierkiewicz

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.

06-02-2011 14:41

Tristan Lall

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by Tristan Lall 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.

07-02-2011 18:22

davidthefat

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

13-03-2011 18:02

chapman1

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!

27-03-2011 17:01

SuperBK

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

27-03-2011 17:44

colin340

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by SuperBK 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

28-03-2011 04:56

Al Skierkiewicz

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.

28-03-2011 09:14

SuperBK

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.

25-04-2011 15:17

lonski

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by vincentkee 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.

25-04-2011 15:39

Jeffy

Re: pic: burnt up TETRIX motor

Quote:

Originally Posted by lonski 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

26-04-2011 08:48

Ninja_Bait

Re: pic: burnt up TETRIX motor

Quote:

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