Team Update #11

[EricH]

http://usfirst.org/uploadedFiles/Rob..._Update_11.pdf

Updated manual to follow tomorrow. Burned out Tetrix motor inductors may be replaced, and parts may be repaired (keep the performance the same, though)--though teams are encouraged to use caution when doing to, and assume voided warranties.

[DarrinMunter]

Does anyone know what the value of the inductor is? I've only taken them apart after they burned up.

If you have taken apart a good motor and know the color bands please let us know, so I can put up a part number and a vendor so we can have spares.

We're up to 5 additional motors now for the one mini-bot.

[VKP]

Thanks for posting this =D

[Justin Montois]

Does anyone have a supplier for the inductors?

This opens up a situation where gracious professionalism is going to be paramount. Even in an instance where a team makes an honest mistake an thinks they have replaced the inductor with an identical part, the performance difference can be huge.

[Trying to Help]

Thank you for posting this. How does FIRST know that today I ordered both mini-bot and pneumatic parts?

[Mike Betts]

I would hope that FIRST publishes the recommended inductive component part number so that teams with limited technical resources can take advantage of this change.

[Bill_B]

Originally Posted by Munter2081

Does anyone know what the value of the inductor is? I've only taken them apart after they burned up.

If you have taken apart a good motor and know the color bands please let us know, so I can put up a part number and a vendor so we can have spares.

We're up to 5 additional motors now for the one mini-bot.

This post has the only mention of inductance value that I remember seeing. It's a tiny part, so I expect a small current rating would apply based on its size. The thermal protector is rated at 2.5A. I'm off to search for an inductor with those specs.

Let's carry on further discussion in the topic above, OK?

Oh, and thanks to the GDC for injecting some rationality into the meeting of component fragility with somewhat freewheeling experimentation.

[Justin Montois]

Originally Posted by Bill_B

Let's carry on further discussion in the topic above, OK?

I understand your desire to keep the discussion in that thread, but due to the fact that this Update specifically says that you can replace the inductor, I feel more people will access the information in this thread.

Below are links that may be an identical part to the inductor that comes stock on the Tetrix motor.

Picture of the Inductor on the motor:
http://www.chiefdelphi.com/forums/sh...62&postcount=1

A PDF listing the specs, also in the upper left hand corner a picture that appears to show a similar inductor as the stock component:
http://www.bourns.com/data/global/pdfs/9310_series.pdf

And a link where you can but the above product:
http://www.mouser.com/ProductDetail/...7kb9bpww%3d%3d

At $0.86, if this is an identical part it sure beats the heck out of having to buy a brand new motor.

Can anyone confirm/deny this part as being identical?

[martin417]

Originally Posted by 340x4xLife

Does anyone have a supplier for the inductors?

This opens up a situation where gracious professionalism is going to be paramount. Even in an instance where a team makes an honest mistake an thinks they have replaced the inductor with an identical part, the performance difference can be huge.

My Electric Circuits theory is a bit rusty, but I am pretty sure that an inductor appears the same as a wire to a DC current. I don't think there can be any advantage gained by using different components in place of the inductor. The purpose of the inductor is to work with the shunt capacitor to make the motor less electrically "noisy". Unless the inductor has a resistive component as well (more than an equivalent length of wire) the only effect of substituting the component will be more electrical noise in your system.

___pause to check the specs____

I just looked at the specs for the 3.9 microhenry inductor listed, and it shows a 2.3 ohm DC resistance. It also lists a max current of 280 mA. at the max listed current, the inductor would drop 0.65 volts. I doubt that .65 volt drop would account for a "significant" difference in pole climb time, but it could make a small difference.

[ratdude747]

4.4.1 Robot Wireless Control
 Robots may be operated via wireless control only on the competition fields and the
practice field with the FIRST supplied radio; and
 Teams are not allowed to set up their own 802.11a/b/g/n (2.4GHz or 5GHz) wireless
communication (access points or ad-hoc networks) in the venue

sounds like scouting may be more of a challenge this year...

[IndySam]

My first ever Q&A question was used for an update!

The 2011 Kit of Parts Checklist, Rev E has been updated to include VUVG-L10-B52-T-M7 as an alternate part number for the FESTO valves delivered in the Kit of Parts. There were two part numbers shipped for use in kitting and this revision allows teams to use either or both valves on the ROBOT.

[martin417]

Originally Posted by martin417

My Electric Circuits theory is a bit rusty, but I am pretty sure that an inductor appears the same as a wire to a DC current. I don't think there can be any advantage gained by using different components in place of the inductor. The purpose of the inductor is to work with the shunt capacitor to make the motor less electrically "noisy". Unless the inductor has a resistive component as well (more than an equivalent length of wire) the only effect of substituting the component will be more electrical noise in your system.

___pause to check the specs____

I just looked at the specs for the 3.9 microhenry inductor listed, and it shows a 2.3 ohm DC resistance. It also lists a max current of 280 mA. at the max listed current, the inductor would drop 0.65 volts. I doubt that .65 volt drop would account for a "significant" difference in pole climb time, but it could make a small difference.

After talking with an EE, I have been informed that there COULD be significant gains by replacing the inductor with a wire. Possibly as much as a 10% power boost. has anyone tried this? An easy test for this is a resistance check across the motor windings. The motor winding resistance is normally quite low, so a quick check could show that someone has "mistakenly" replaced the inductor with a non-complying part.

[Bill_B]

Originally Posted by martin417

My Electric Circuits theory is a bit rusty, but I am pretty sure that an inductor appears the same as a wire to a DC current. I don't think there can be any advantage gained by using different components in place of the inductor. The purpose of the inductor is to work with the shunt capacitor to make the motor less electrically "noisy". Unless the inductor has a resistive component as well (more than an equivalent length of wire) the only effect of substituting the component will be more electrical noise in your system.

___pause to check the specs____

I just looked at the specs for the 3.9 microhenry inductor listed, and it shows a 2.3 ohm DC resistance. It also lists a max current of 280 mA. at the max listed current, the inductor would drop 0.65 volts. I doubt that .65 volt drop would account for a "significant" difference in pole climb time, but it could make a small difference.

Your circuit theory cannot be much rustier than mine, however, the current to a brushed DC motor, direct as it is, still varies as the commutator redirects the current to the armature coils. This motor has a three coil armature, so two coils are powered at a time. The coils are inductors themselves, although they are not usually rated that way. One way to think of an inductor is a current sustainer. That is, it tries to maintain the same current flow across voltage fluctuation. (contrast to a capacitor that tries to maintain voltage in current fluctuations) A collapsing field in a 3.9 micro henry inductor will not be able to generate much current flow for this motor. The capacitor will be equally inadequate to maintain much voltage. The result is called a low-pass filter, because only the very high frequency parts of the direct voltage variation will be absorbed by this LC filter. Well into the radio range I'd guess without doing any math.

This brings me to the current rating of the inductor. Based on various other observations, we can be pretty sure that more than 280mA is being drawn by this motor in minibot operation. Probably more than that in FTC robot operation as well. So the mystery becomes, how can such a relatively low-rated component expect to survive these over-current excursions? by duty cycle? by conservative rating spec.? Another spec. I read mentioned a 40 degree C rise for their inductor at rated current. This setup won't allow for very much heat dissipation, especially being enclosed and in as close proximity to a plastic mounting as it is.

The one thing I do know is that replacement by a wire in one case allowed way too much current for the fuse I was using. There may be something else wrong with that motor, but it wasn't obvious visually. Meanwhile, I have replacement motors to use for testing using the thermal limiter device. I will postpone further repair attempts until time allows or more learned commentary here convinces me to have another shot at it.

Thanks for your consideration.

[AllenGregoryIV]

Does anyone know why they changed the rules about the floor protector for the tower? They removed the sentence about it only having a 1/4in ridge in the field but did not replace it with anything else. Does anyone know if this means the bump will be larger or smaller?

[Mr.G]

Originally Posted by AllenGregoryIV

Does anyone know why they changed the rules about the floor protector for the tower? They removed the sentence about it only having a 1/4in ridge in the field but did not replace it with anything else. Does anyone know if this means the bump will be larger or smaller?

Now we are going to get stuck on it and not be able to reach the tower with our 1 inch off the ground bumpers.......j/k