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Post by yellerstang on Jan 1, 2015 9:47:29 GMT -7
Im a little surprised that there isnt much activity here, especially since stock class Tjets are so poplar. Anyone up for some discussion on tuning? PM me, maybe we can generate some new or renewed tech info here?
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Post by pceng on Jan 1, 2015 12:17:59 GMT -7
Im a little surprised that there isnt much activity here, especially since stock class Tjets are so poplar. Anyone up for some discussion on tuning? PM me, maybe we can generate some new or renewed tech info here? Lots & lots of info. can be found in tip section (home page). One thing I don't think is covered is loading & unloading of arm poles. Or current entering and leaving arm. In the 60's before brushes meant much to me. We used to cut out chassis so crown could be reversed. Many cars ran better with arm rotating in opposite direction (reverse mags). What I think my friends and I were doing was compensating for brushes not sitting in perch correctly. T-jet arms rotate clock wise. If viewing open chassis from rear. The left side of top or front brush, as well as the right side on bottem or rear brush will be the first to contact lam as arm rotates. And lams pass over brushes. Don't remember where I saw it. But found it true. If the front edges of the brushes, left/front right/rear are slightly lower than the rear of brush. A larger contact surface will be had as brushes break in. Remember seeing hard or square edge on brush causes bounce. Which amounts to low flow of electric. If wear pattern in brush has leading edge of brush that looks like the top leg of a T. Try reversing m/mags (with no idler). And see if car runs smoother. If so, check how those brushes are sitting. Contacts can be tweaked, to adjust angle. Hope I got what I remember right & it might help......... Peter |
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Post by yellerstang on Jan 1, 2015 15:31:06 GMT -7
Hey Peter, I learned a few years ago to tilt the brush springs a bit. Here is an easy description, no pic... With an empty chassis in hand, hold it front to back... look at the brush spring in the REAR hole.... ever so slightly bend the brush spring in a counter clockwise arc (make the right side corner of the spring slightly higher than the left side.) After the adjustment, rotate the chassic 180* and make the exact same adjustment to the REAR spring. Clean and polish your brushes, score them slightly on the bottoms, replace them and the magnets and test the car. It should be faster in forward than reverse now. Over time, it may diminish some, sometimes you can take an exacto blade and rotate the brush to the next point where it is scored. Yeah... I used to think it was timing too. This is a great speed tip.
If you are getting brush chatter on the comm plate, you could take an exacto knife and remove just a tiny bit of copper from the leading edge of the commutator. Tiny amounts.
Speaking of commutators, I no longer use my Dremel to polish the plates. I do this very gently by hand. If the comm gets too warm, it warps. When it warps, you will never get decent RPM from it again...
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Post by yellerstang on Jan 1, 2015 15:34:51 GMT -7
For those who would check arm balance... my friend just takes an arm and spins it like a top on a formica table top. If you watch for wobble and an early wind down, the arm is poor. If it just keeps spinning and stays stable, the balance is pretty good. No tools, just the arms, the table, and your patience. Pick a winner.
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Post by Deleted on Jan 1, 2015 17:04:34 GMT -7
Another way to remove brush chatter is to take a ball point pen and run the ball down between the segments on the comm plate. Apply light pressure when doing this and the ball will smooth those rough edges!
ALan
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Post by yellerstang on Jan 2, 2015 14:37:53 GMT -7
*** Cleaning the commutators *** I often use a soft pencil or ink eraser. Works good. I have used Brasso and a soft rag. This takes the carbon off, but you dont want any residue left on the shaft, it will work itself into the plastic and could wear the bottom hole in the chassis a bit.
I use Brasso, cut it with oil to lap in the gear train.
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Post by yellerstang on Jan 2, 2015 14:39:18 GMT -7
*** Armature runout *** I still have not found an easy way to check this. Dremels and drills wobble too much. Anyone care to input on this??
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Post by pceng on Jan 2, 2015 15:35:48 GMT -7
Found ink eraser in pencil form to be quickest. Pointed end gets between lams. Had brand new arm short out after buildup from one proxy race. Probably shoddy too soft brushes. Can happen quick !
Not sure what you mean by armature runout......... are you referring to how long it keeps turning after power shut down. Or maybe making everything equally distant from shaft (com & poles).
..... Peter
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Post by pceng on Jan 2, 2015 16:02:29 GMT -7
I use Brasso, cut it with oil to lap in the gear train.[/quote]
Duh , forgot you mentioned lapping......... if you have not already tried, try sanding gears (add one gear at a time while running on low voltage).
I've tried about everything for lapping. After starting with sanding..... have started redoing old lapping jobs. Has made everyone so far smoother than it was. And I find it way faster also, than lapping. 5 - 10 mins when I first did it. No more than 5 mins. after first.
...... Peter
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Post by AJR on Jan 2, 2015 16:54:23 GMT -7
I use CRC contact cleaner on a Q tip for cleaning comms and the pointed end of a reaming tool that I have for the groove between the plates. I also taper the leading edge of each plate with an xacto knife as well as polishing with a homemade comm tool. Works great.
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Post by yellerstang on Jan 2, 2015 19:10:54 GMT -7
Gears.... get some 2000 grit sand paper. You have a choice, you can remove gears, sand and deburr.... or.... you can slip a little sliver of the 2000 grit paper (wet with any thin oil) just slip it under the rotating gears while the motor is running.
Its generally more effective to remove the gears, sand them flat with 2000 grit paper, then buff them on paper card stock. I use an old yellow envelope cut open and laid flat. If you do this right, it will make the gears shine like a mirror. You can also sand each tooth gear valley with just a stroke or two, then polish and clean. Then reassemble. Run the car, break in the gears with oil, then lap them if needed. If you are comfortable removing and replacing gears, this is very effective.
One even easier method... sand the gears like above, slip a tiny piece of 2000 grit (wet it with oil) under and on top of each gear while running the motor. Then, take out the magnets and brushes, put the gear plate back in place. Then with a dremel and a BRASS wire wheel you can spin the entire gear train. You must keep it wet with oil. Buzz up and across all off the gears, the wire wheel will deburr them readily. Keep it oiled. Watch your eyes, this stuff flies off and it will hit you in the face. Clean the car with lighter fluid to get off the crud.
When finished, you can clean the car with a toothbrush and Dow Bathroom Cleaner (eats oil and deep cleans) or put the chassis into an ultrasonic cleaner. Its tough to beat the ultrasonic cleaners, but too much use will weaken copper parts and induce some wear.
I am super careful about spraying the armature, I find that over the long run the chemicals seem to attack the windings and the motors lose power.
An alternate way to clean the chassis up is to run it in a cup of hot water. Wire the car and drop it slowly into the water, an amazing amount of crud will come out of the chassis. Sometimes I do this, then use the bathroom cleaner, rinse it all off, then dry it with a can of compressed air or a hair dryer.
These are all valid methods, but, you have to be GENTLE. If you mess up a wire, the motor is done.
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Post by yellerstang on Jan 2, 2015 19:17:50 GMT -7
Gear Plates... If you make up a few of these like above, pick ONE chassis and swap gear plates until you find the one that spins up the best. You will hear it when you get a good one. I have put together my fastest cars this way. Im new to drag racing at any sanctioned event, so I am still learning too. I have a decent 4 lane track, we have been applying this method to the tjets for a very long time... My best 1/4 mile time at Skippack on a stock car was 1.66 seconds. I was very pleased and Im looking to improve on that.
By the way, I want to say thanks to the guys who gave me some sound advice at that meet. Nice group of racers.
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Post by yellerstang on Jan 2, 2015 19:20:20 GMT -7
Gears..... ok, now someone else tell us... what specifically do you look for in the gear plate gear sets and in the pinion/crown gears? Fit, depth of teeth? Setting depth on plate? This is one area where I need help. Thanks.
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Post by pceng on Jan 3, 2015 8:14:33 GMT -7
To smooth out gears when sanding (while running)......... after doing bottem (sand paper worked under gear until shaft or post is reached). The outside edge or point of teeth is next. This does more to free up gears than anything.
........ Peter
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Post by yellerstang on Jan 3, 2015 10:29:07 GMT -7
To smooth out gears when sanding (while running)......... after doing bottem (sand paper worked under gear until shaft or post is reached). The outside edge or point of teeth is next. This does more to free up gears than anything. ........ Peter Yes it does, I use 2000 grit or finer. I have used card stock after the 2000 grit, all with liberal amounts of oil. You can actually polish the bottom of the gears while in the car. There are lots of ways to free up a car and reduce friction. This method with lapping gears can make a huge difference. |
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