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Ohming out arms and stuff


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#1 Lone Wolf

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Posted 17 March 2009 - 12:59 PM

Can someone tell me how to ohm out a T-jet or A/FX arm with a DVOM ? Also, in values, what is a good arm? And one more thing, I see lots of ebay listings stating green tip , green wire arm etc. What is the best and does it really matter? I am just starting to sort out 35 years of collecting H.O. stuff and I think I have my work cut out for me :blink: Thanks in advance for the info.

Some of the offending junk:

ebay_614.jpg

Joe Lupo





#2 Hworth08

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Posted 17 March 2009 - 02:03 PM

Omhing a T-jet arm is very simple. First clean the comm with Bar Keeper's Friend, a regular cleaning powder that Wal Mart sells, it'll be close to Comet, ect. After cleaning, spin the arm in a "slow" Dremel or a regular hand drill to spin any water out.

Set the multi-meter on the highest ohm setting. Touch either probe to any of the copper comm plates, then the other probe to either of the other 2 plates. The reading on the m/m will be ohm reading. Continue to different plates, or segments, till you check the arm a couple times.

The original T-jet arms measure from 16 ( yea, sixteen!) to 18.5. The Magna Traction average 14 to 15. Most all the rest are in the 6 range except the famous quad lam Super II arm that is around 4.5.

Try to find Neil's Wheels tech tips if it's still on the web. That gives a detailed rundown on each Aurora arm.
Neil had so many e-mails that he had to take the tips off the web when he quit selling HO parts. I'll see if I can find my link to the tips but I doubt it.

Ohming is very easy on a clean comm and very important! About 20% of the arms will be bad and about 1 in a 100 will be "racing quality"!
Don Hollingsworth

#3 Lone Wolf

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Posted 17 March 2009 - 04:17 PM

Don, Thanks for the detailed info. One thing I'm not clear on. You say to move to different com segments. Do I average the value out from all three or do I just take the lowest reading. Or is there another way. You also say some will be bad. Does this mean I will have an open between segments? Joe

Joe Lupo


#4 Hworth08

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Posted 17 March 2009 - 05:54 PM

Hi Joe,

Agh, more or less just take the average. A typical early T-jet arm with gray stacks and green wire will likely read 16.8, 16.9, and then 16.8 on each different segment of the comm.

I don't remember exactly but Aurora used something like 400 turns of close to 40 gage wire on their first arms. It's not at all unusal to find an arm with 15 more turns on one stack, thus the varying ohm readings.

If the arm is "dead" there will be NO ohms at all. Meters vary but the meter will either remain blank or read zero.

I checked my favorites and google but couldn't find Neil's Wheels nice tips, printed it's about 10 pages and covers all the early Aurora chassis. HO cars aren't real popular here, you may try Yahoo Groups for HO World. There are close to a 1000 members. Also try HO World. net (I think it's net). Check the archivies section. Someone has the tech tips on their site, I just can't remember who. There's a lot of HO sites!
Don Hollingsworth

#5 chaparrAL

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Posted 17 March 2009 - 06:44 PM

Ohming tjet arms will only tell if its legal of if it has a bad wire or short. When i raced them i found that first rev testing to find ones ,a dozen or so ,to track test , worked best. Seek the ones that accelerate fast to the highest revs obviously but also take into cosideration the vibrations . Then put them in the chassis you plan to use and track test till you find the best one. NOTE there is huge performance gains to be had with these cars just by reducing friction and inertia and the boys on the Frontrange HO site have this covered nicely .Good luck. Al
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#6 Hworth08

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Posted 17 March 2009 - 07:27 PM

I scanned the Front Range site and it did look good.

Joe, I believe you are the same person that was looking for springs last week. While looking for Neil's store on ebay, I ran across this:

http://cgi.ebay.com/...O...A1|240:1318

Might be a good sourse for springs and the prices look better.
Don Hollingsworth

#7 tjetcar

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Posted 18 March 2009 - 07:14 AM

I scanned the Front Range site and it did look good.

Joe, I believe you are the same person that was looking for springs last week. While looking for Neil's store on ebay, I ran across this:

http://cgi.ebay.com/...O...A1|240:1318

Might be a good sourse for springs and the prices look better.


GO TO SLOTCARMONSTER.COM TONY V. POSTED A STEP BY STEP, ON ARMS AND BUILDING TJETS,ARMS ETC. HE DOES BUILD SOME VERY FAST ONES
Sheldon Brunn

#8 sidejobjon

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Posted 15 June 2012 - 05:07 PM

Can someone tell me how to ohm out a T-jet or A/FX arm with a DVOM ? Also, in values, what is a good arm? And one more thing, I see lots of ebay listings stating green tip , green wire arm etc. What is the best and does it really matter? I am just starting to sort out 35 years of collecting H.O. stuff and I think I have my work cut out for me Posted Image Thanks in advance for the info.

Some of the offending junk:

ebay_614.jpg

Joe,
Now i see when you say it will take some time. WOW your collection is endless.
Keep photos coming
Thanks John F
John Falzarano





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