# Need help taking my tjet tuning to the next level



## gotmark73 (Sep 10, 2007)

I have read and I think followed many of the tuning tips on here and also Tom Bowmans "How to build a Fray car". I have managed to turn my 8th place cars into 6th place :hat:. After looking at the thread about t-jet tools that looks like a NASA/NASCAR group effort I want to take my cars to the next level. I match the magnets, find a com with equal poles and that is prettty close to balanced, (I have even balanced one to no avail). I wire brush the gears and then break them in with rubbing compound. I boil the chassis and make sure the axles turn smooth. The cars are better but I know I am missing something. What Amps should I have at what Volts when the car is hooked up to a power supply eg .15a at 12V? Are there other tips any of you are willing to share. Everytime I think "this is a great car", it's sounds smooth and seems fast in practice it turns out to be a strong 6th. I am sure I am not alone in wondering this, thank you in advance for any help.


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## SwamperGene (Dec 1, 2003)

You need this:


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## Brixmix (Dec 2, 2007)

As far as Amp draw I try to get mine in the .11-.15 at 20volts. I would say make sure that your shoes are set up really well. they should have no burn marks and show wear the whole length of the shoes. Also make sure the rear hanger is clean and free of oil and grim. Sometimes a better handling car will finish better than the car with the best arm. There is a mass amount of little things that can be done to get more out of the car. The most important are with the shoes. You should tungsten Carbide axles this will help your handling also. How the Body sits on the car is also important in handling. it need to be kinda of loose and have float.


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## neorules (Oct 20, 2006)

Get some of those pick-up shoes coated with neo dust on top. Rumor has it some of the not as slow as you are guys have had great success going that route.


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## gotmark73 (Sep 10, 2007)

neorules said:


> Get some of those pick-up shoes coated with neo dust on top. Rumor has it some of the not as slow as you are guys have had great success going that route.


We run multiple classes, I just would rather spend time making a tjet fast, for the same reason I raced non-wing midgets, I like racing to be about the driver more than "aids" weather it be huge wings or traction magnets. Down the road I will work on tuning my magnet cars.


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## gotmark73 (Sep 10, 2007)

Brixmix said:


> As far as Amp draw I try to get mine in the .11-.15 at 20volts. I would say make sure that your shoes are set up really well. they should have no burn marks and show wear the whole length of the shoes. Also make sure the rear hanger is clean and free of oil and grim. Sometimes a better handling car will finish better than the car with the best arm. There is a mass amount of little things that can be done to get more out of the car. The most important are with the shoes. You should tungsten Carbide axles this will help your handling also. How the Body sits on the car is also important in handling. it need to be kinda of loose and have float.


Thank you for the heads up about the shoes, I have spent a little time on tweaking them but did not know how critical they were, gonna work on that this weekend


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## Bill Hall (Jan 6, 2007)

SwamperGene said:


> You need this:


Hahahahahahahaha!

Ya finally put the "Gene-ee" in the bottle?


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## martybauer31 (Jan 27, 2004)

I would also be asking what the guys placing 1st through 5th are doing to their cars as well...


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## smalltime (Jun 3, 2006)

gotmark73 said:


> Thank you for the heads up about the shoes, I have spent a little time on tweaking them but did not know how critical they were, gonna work on that this weekend


Listen to Travis, He's got the MOJO right now.

It is hard to overestimate the importance of up pickup shoe settings on a T-Jet. First, I would try ALL of the available brands. Learn to adjust them. Mix and match them. And Keep coming back for question and answer time.:wave:


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## martybauer31 (Jan 27, 2004)

Oh yeah, Tim's post just reminded me of a great one he started that SHOULD be stickied....

http://www.hobbytalk.com/bbs1/showthread.php?t=197364


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## Brixmix (Dec 2, 2007)

I totally agree with Marty Tims article is VERY well written. He has in writing a ton of the things that make T-jet's go good. There are alot of small things that could be done to get that little bit extra but they are hard to put in writing, I have learned so much over the last 2yrs with t-jets not just the Fray style car. The thing is that there is alot that carries over to make really good stockers with way more restricted rules. Don't be afraid to ask how this or that is do at a race. The more you work on these cars when someone tells you or shows you something it will be easier to apply or if your showed a certain technique it will be like why didn't think of that seems so easy.


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## gotmark73 (Sep 10, 2007)

I just built a car, went through all the smoothing tricks and the gear plate felt really smooth, put in a set of new matched JL magnets, on my poor mans dyno it made .5volts, my "best" car (the one I have been happiest with) made .9 volts. I changed my car back to a magnet that is black and one that has a white stripe (matched) and the car makes .85 volts. So the car is spinning almost twice as fast with the weaker magnets. I am not sure what I proved or dis-proved other than bigger is not always better. Any thoughts?


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## martybauer31 (Jan 27, 2004)

gotmark73 said:


> I just built a car, went through all the smoothing tricks and the gear plate felt really smooth, put in a set of new matched JL magnets, on my poor mans dyno it made .5volts, my "best" car (the one I have been happiest with) made .9 volts. I changed my car back to a magnet that is black and one that has a white stripe (matched) and the car makes .85 volts. So the car is spinning almost twice as fast with the weaker magnets. I am not sure what I proved or dis-proved other than bigger is not always better. Any thoughts?


My thought is that a lot of that stuff does have some value, I'm just not sure how much. Unfortunately running well on a dyno does not always equal a great car, much like having an arm ohm at 16.0/16.0/16.0....

Some of my best cars have sounded like a dump truck driving over a field of scrap metal and have had arms that ohm out at 18.5/17.9/17.5

Really the best thing you can do is make sure parts mesh well, smooth out the rough edges, make sure your shoes are FLAT on that rail and go run it on the track and see.


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## smalltime (Jun 3, 2006)

What I do when tuning a new chassis is:

first off, make shure you test with a body on the chassis. This takes care of the weight thing.

Be shure to check for bent axles/out of round tires.

Make shure the guide pin is not moving. (glue it in)

Use a sharpy to mark the screw, the tags of the shoes and the bottom edge of the body, to be shure it is not hitting the track.

If all this passes muster, then we move on to diagnosis of the problem.

Were is the problem?

"My car comes out as I enter the corner."
There are two possible situations here. The first is that you're entering too fast (driver error) or that the car does not like to change direction. If you are entering the corner at roughly the same speed as the other competitors, then we should move on to the direction change thing.

Limit travel in you shoes. On the settup plate, you should just barely see movment of the shoes as you lift the chassis and replace it.

Lighten up on the pickup shoe tension. Do this by feel for now. I remove the shoe and bend the hook to give the spring less preload. if you do this and there is improvment, then you can get more technical and cut springs, or tweek shoes. whatever makes you more comfortable.
When you get these close, and you feel like you want more HP, try to flatten the shoes out first before adding tension back in.

If it is still having a problem changing direction, try paying attention to if this happens in both directions.
Many times a chassis can get bent during an off. use you settup plate to be shure that all four tires are touching.

Let us know how these tweeks helped, if at all.


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## brownie374 (Nov 21, 2007)

I have arms that are faster with weaker magnets.


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## smalltime (Jun 3, 2006)

brownie374 said:


> I have arms that are faster with weaker magnets.


Are they faster in RPM or do they turn faster lap times?


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## gotmark73 (Sep 10, 2007)

I took one of my skinny tire tjets and put it on the plate, without a body the shoes were picking the front tires off the plate. I took the springs out and smashed them with needle nose pliers, the tires now touch but there is still a lot of pressure. I am trying to figure out how to bend the shoes to take away spring pressure, in my mind it makes sense but looking at the car I can not figure it out.

Dennis and Rick after the first of the year I would love to find a sat or sun that we can get together either at park lane or somewhere else and have a seminar. I would be glad to help someone drill and tap bodies and I would love to learn how to further refine the cars. I think we all have things we are good at and if we pay it forward we can make the local racing grow.


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## bearsox (Apr 22, 2006)

gotmark73 said:


> I took one of my skinny tire tjets and put it on the plate, without a body the shoes were picking the front tires off the plate. I took the springs out and smashed them with needle nose pliers, the tires now touch but there is still a lot of pressure. I am trying to figure out how to bend the shoes to take away spring pressure, in my mind it makes sense but looking at the car I can not figure it out.
> 
> Dennis and Rick after the first of the year I would love to find a sat or sun that we can get together either at park lane or somewhere else and have a seminar. I would be glad to help someone drill and tap bodies and I would love to learn how to further refine the cars. I think we all have things we are good at and if we pay it forward we can make the local racing grow.


Mark ,
i can show you alot more but quickly here's a couple of things to play around with till we can get together. 1st shoes are generally restricted in 2 ways . Either at the rear ( where you change the radius of the last 1/2 of the bend ) where the shoe hooks under the copper plate. If you look at the shoe from the side the rear looks like a 1/2 circle and all you do is to raise a tiny bit the end in effect opening the radius . 2nd way to restrict travel is in the front where the shoe mounts on the hanger . Again looking from the side this end looks like an reverse L shape. Now spin the shoe to look from the front and you see the slot that travels up and down . To limit the travel there are several folds you can attempt but 1st lets do the easy one. Using a pair of flat faced pliers fold the small top solid patch of the shoe ( top of open slot ) forward towards you. Now take that same piece you folded and fold again till it is flat against the shoe. Now look at it from the front and you should see that the slot is reduced which in turn limits the travel of the shoe. I would practice this simple version on your old beat up shoes or old original shoes till you figure out how to get it right . Then move to the good stuff. There are better ways to fold em but we can go over that later. A quick note here is that you want to match pairs of shoes and different window openings after doing your limiting will equate to using different tire heights to get the shoes in the correct positions for optimal performance so look to swap in a few tires especially in the front. When we get together we will make you a PU shoe adjustment tool and i will show you how to use it. We will also go over cutting , squashing and stretching springs the good the bad and ugly ! LOL

Bear :wave:


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## gotmark73 (Sep 10, 2007)

took a few cars to the hobby shop, one car that sounds like there are loose ball bearings in the driveline is fast. one car kinda sounded like it was draging a metal plate, I took the stock limited shoes off and put new wizzard shoes on and it was way better. I slowly worked on tweaking the shoes til they laid flat, did not notice a HP increase but car smother especally on corner entry.


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## NTxSlotCars (May 27, 2008)

gotmark73 said:


> I just built a car, went through all the smoothing tricks and the gear plate felt really smooth, put in a set of new matched JL magnets, on my poor mans dyno it made .5volts, my "best" car (the one I have been happiest with) made .9 volts. I changed my car back to a magnet that is black and one that has a white stripe (matched) and the car makes .85 volts. So the car is spinning almost twice as fast with the weaker magnets. I am not sure what I proved or dis-proved other than bigger is not always better. Any thoughts?





brownie374 said:


> I have arms that are faster with weaker magnets.


This is true. When you run your car in the forward direction with current, a charge is also produced in the reverse direction.(wound copper passing over a magnet) This is exactly why a car will run hotter with stronger magnets and a stock arm will burn up with neos. How do you over come this 

In electric forklifts, an electromagnet is used in the drive motors to "pulse" current on and off without having a continuous magnetic field. The forklift can maintain speed without the reverse current. This is called "field weakening". It reduces heat and the forklift can actually run faster.

In slot cars, you have a static magnetic field. If you use weaker motor magnets, you can accomplish similar results. It goes against most high performance practices to use weaker motor magnets, but I have used this technic with great success. I depends largely on your driving style, and the track layout, for these reasons. Weak motor magnets mean less brake, more coast, on a 2 terminal controller set up. It also means less torque off the corner. But the trade off can be worth it, both of these characteristics do not translate to less performance, and can actually mean more consistant, better lap times. 

Example, we raced 440x2 Tycos on 2 long tracks with at least 2 long staightaways per track. The tables were 17' and 22'. Box stock, with no tire restrictions. I had 2 motor magnets on the fridge for about 6 months. Most guys set their cars up with strong motor magnets and .438 wizzard tires. I set my car up with weak motor magnets and .460 tires. Sure, I lost some to them in the corners, but flew past on the straights. With more straights than corners, this was an advantage. Because the table was so big, having a car with touchy brakes wasn't a good idea. One misjudged corner, and you're off. Don't get me wrong, some guys prefer stop and go racing, but for me, coasting into a turn, and not spinning the tires on exit works best. This technic helped me be dominant until a ran into a group of guys using magnet zappers to 'blow off' parts of the magnet's field to alter the timing of the motor.

In Tjets, and AFX-Magnatrax it's my understanding that matching the magnets is way more important than the strength of the magnets. More so than in line motors, but strength is still important.

I said all that to say; _It's not your imagination_, weaker motor mags can be faster! (depending on the arm)


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## gotmark73 (Sep 10, 2007)

So we raced sunday, tomy track tighter roadcourse. My car that "seemed" the best to my ear at home and showed best number on dyno was the best. I finished 3rd out of 14 racers. I followed all of the tips from you guys, THANK YOU. The car was not too punchy and seemed smooth on corner entry. The wizzard shoes seemed to make the biggest difference (adjusted ofcourse). Looking forward to a race on a TKO routed to see how the car reacts.


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## smalltime (Jun 3, 2006)

gotmark73 said:


> So we raced sunday, tomy track tighter roadcourse. My car that "seemed" the best to my ear at home and showed best number on dyno was the best. I finished 3rd out of 14 racers. I followed all of the tips from you guys, THANK YOU. The car was not too punchy and seemed smooth on corner entry. The wizzard shoes seemed to make the biggest difference (adjusted ofcourse). Looking forward to a race on a TKO routed to see how the car reacts.



Awsome!
So let's go to the next level:
What kept you from getting second?
Was it too many offs? or car being inconsistent, or maybe tires getting too dirty. 

Try to quantify it and we'll work on the next thing.


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## AfxToo (Aug 29, 2003)

> When you run your car in the forward direction with current, a charge is also produced in the reverse direction.(wound copper passing over a magnet) This is exactly why a car will run hotter with stronger magnets and a stock arm will burn up with neos.


Not exactly but on the right track ... the back emf generated by the armature/rotor has the effect of reducing the current in the arm. The heat generated in the arm is proportional to the current in the arm. The power is current-squared times resistance so even small changes in current have large changes in power, thus heat generation.

What's happening here is that when you run a motor at a fixed voltage and under a fixed load (on the dyno) it will achieve an equilibrium speed which is what you measure on your dyno. The equilibrium speed is essentially the speed that is required to generate enough back emf to completely cancel out the applied voltage. Ideally, in this state the current flow in the arm would be zero and the arm torque would be zero. Realistically, at the equilibrium speed there will still be enough current flow in the arm to maintain the motor speed despite all of the losses in the arm and to generate enough torque to compensate for the load. The load would include all of the drivetrain components and the dyno slave motor for example. 

So why does the motor run faster with weaker magnets? This is because the back emf generated by the motor is directly proportional to the magnetic field flux. Stronger magnets allow the motor to generate more back emf at a given rpm, thus the motor does not have to spin as fast to achieve the equilibrium speed. Basically, it's a more efficient generator so it runs slower at the same applied voltage. If you had a method of reducing the flux while the motor was running, i.e. field weakening, the motor would speed up because its equilibrium speed is now higher. The downside of course to the higher equilibrium speed is the reduction in torque. 

So everything you are seeing makes absolutely perfect sense. In practical racing applications you have to weigh the different options and trade-offs available to you and find the best fit for the specific application.

This also tells us that it would be worthwhile to measure the motor current when testing on a dyno. Taking friction out of the driveline will show up as a reduction in current at the equilibrium speed.


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## LeeRoy98 (Jul 8, 2005)

AfxToo said:


> Not exactly but on the right track ... the back emf generated by the armature/rotor has the effect of reducing the current in the arm. The heat generated in the arm is proportional to the current in the arm. The power is current-squared times resistance so even small changes in current have large changes in power, thus heat generation.
> 
> What's happening here is that when you run a motor at a fixed voltage and under a fixed load (on the dyno) it will achieve an equilibrium speed which is what you measure on your dyno. The equilibrium speed is essentially the speed that is required to generate enough back emf to completely cancel out the applied voltage. Ideally, in this state the current flow in the arm would be zero and the arm torque would be zero. Realistically, at the equilibrium speed there will still be enough current flow in the arm to maintain the motor speed despite all of the losses in the arm and to generate enough torque to compensate for the load. The load would include all of the drivetrain components and the dyno slave motor for example.
> 
> ...


Wow! I actually understood the explanation.
Thanks,
Gary


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## T-Jet Racer (Nov 16, 2006)

SwamperGene said:


> You need this:


NOW THATS FUNNY!!!


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## slotnewbie69 (Dec 3, 2008)

T-Jet Racer said:


> NOW THATS FUNNY!!!


yep.and actually i think boosa's got them for sale!


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## jamie6799588 (Apr 16, 2009)

"No two tjets are created equal" Don't try and make your second car just like your first...It won't work. If your allowed...Dynamicarmatures.com great stuff!!


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