Hobbyist Forums banner
1 - 20 of 29 Posts

·
Registered
Joined
·
3,662 Posts
Discussion Starter · #1 ·
Okay guys, I may not be the best T-Jet tuner, and I think I've come along way in the past year, and pretty well figured out how to bring dead ones back to life, and tune some cars to be pretty darn fast. But one gremlin keeps bugging me, and I cannot seem to figure it out. And that is, Rear kick-out when letting off full power, the rear end kicks out to the side-usually to the left. This mainly happens with my fastest Tuff Ones cars, both original Aurora and some JL/AW versions. I have a 1/64 scale full 1/4mi length Dragstrip, and this kick-out occurs especially hard, when the cars go thru the dead strip and hit the dynamic braking -slow down area. I also note that these kick out cars have very little coast- just rear wheel lockup.
What is going on with these cars ? Can I tune this out ? I'm using DASH, AW, or Super II magnets in most of my Tuffy's, and brush tension varies from light to heavy. BTW- did I say these were my fastest Tuffy's.... is this common ? PLEASE HELP !?
 

·
Premium Member
Joined
·
2,145 Posts
Strong mags,are gonna lock everything up on full brake as you've noticed.
Try putting a pot or rheostat into your brake system so you dial the amount of brakes you want into the track,take the tire skidding factor out of the cars
 

·
Registered
Joined
·
1,272 Posts
In addition to Hornet's points, high tension on the comm springs is another contributor. While more increases torque, it also adds drag. Throw that in with the strong magnets and any gear or shaft drag in the system, and it's like yanking the e-brake in your full-sized car. Try backing them down a little at a time to see if it helps. You may also gain some top-end speed in the process. I have also found that substituting a weaker set of mags can help. Especially with JL/AW cars, they are still plenty fast but much easier to drive consistently.
 

·
Registered
Joined
·
3,662 Posts
Discussion Starter · #4 ·
Thanks guys - I look into those ideas :)
Although I use simple set controllers with no brakes, I don't even have a simple Parma Economy controller, but I'll upgrade to better someday, when the slot budget allows.
And I was wondering about the magnets and comm brush tension as a possible source of the gremlin. And I have experimented with weaker magnets in JL/AW cars and have found them soooo much easier to drive. But I think you guys have narrowed it down, and magnets and comm brush tension are probably the cause, and if I can't tune it by changing those to suit, I guess another alternative would be a controller switch to one with a pot or rheostat .
Thanks for the tips guys :thumbsup:
 

·
Registered
Joined
·
1,272 Posts
Ralph, if your track is not wired for brakes the pot won't do anything for that problem. It would have to be wired into a brake circuit that you don't have at this time. The source of the problem has to be in the car in your case. Let us know how it works out. Since the JL/AW cars have such sloppy rear axle holes, the issue is even worse because the rear end 'steers' randomly on deceleration. Try driving one slowly down a straight while watching from behind at track level. Looks like the driver's had a few too many as the car weaves back and forth, 'hunting' in the slot.
 

·
Registered
Joined
·
6,355 Posts
Doesn't this have something to do with the fact that the armature stops rotating quickly and the rest of the chassis tries to keep rotating? (or something like that involving inertia)

Here's the only simple ******* physics experiment my feeble mind could come up with to explain my thinking...

Bolt a Sit N Spin (remember them?) to one of those big flatbed carts like they have at Lowes. Get spinning on it at a good clip. Have someone push the cart while you are spinning. If you suddenly grab the middle handle of the sit n spin hard and stop spinning immediately while the cart is rolling, won't it change the direction of the cart? (I mean, aside from the terrible case of motion sickness you are getting...)

Did any of that make sense? I'm thinking you can't tune that away, it's inherent in the physics of a pancake chassis. Doesn't happen with inlines, does it?

(although it makes sense that if you introduce more coast or otherwise dial back braking power with caps or rheostats or whatever the way others have mentioned, you can lessen it...)

--rick
 

·
Model Murdering
Joined
·
7,331 Posts
In addition to Hornet's points, high tension on the comm springs is another contributor. While more increases torque, it also adds drag. Throw that in with the strong magnets and any gear or shaft drag in the system, and it's like yanking the e-brake in your full-sized car. Try backing them down a little at a time to see if it helps. You may also gain some top-end speed in the process. I have also found that substituting a weaker set of mags can help. Especially with JL/AW cars, they are still plenty fast but much easier to drive consistently.
Well Ralph,

Eventually we all reach this point. Circling the comm pit in frustration. By tuning to the very ragged edge using only the supposed "be all/do all" parts; and falling into the pedal to the metal mentality, we chop the ends off of a motor's response.

It's that place in slotcar tuning (especially T-jets) that I call "point no point". I see it as the final fork in the road of slotcar tuning, at which; you have to decide if the chassis gonna be a drag racer, a road racer, a giant oval contender, or a short track car.

Although common knowledge in the 1:1 world; a concept that is frequently lost in the hobby. Shortly after coming back to the hobby, I wasted some time trying to tune my way around "point no point" because I forgot a well documented, and very basic rule. Straight-line speed is not the fastest way around the track.

If you increase the brush pressure beyond what the armature can comfortably accommodate in the way of preload, it will incrementally compromise on and off throttle response. Adding high gauss magnets, only increases the load.

For me, the trick became recognizing what a set up has to offer...and what it doesnt; then accept it for what it is. More often then not, the optimum setting (sweet spot) is one notch below the ragged edge, which is kinda what AJ implies above. Put a little USEABLE end float back in the armature and shuffle some other magnets in and out.
 

·
Registered
Joined
·
2,530 Posts
I'm thinking you can't tune that away, it's inherent in the physics of a pancake chassis.
--rick
I would agree it is inherent with pancake chassis. I see it more on startup - a kick to one side. It makes sense the car will "jerk" to one side as the armature starts to spin from a dead stop. There may also be a little pulling because the crown gear is not in the center of the rear axle, but off to one side. You will no doubt see this more on cars without traction magnets.

Might be some useful hints in this thread...

http://www.hobbytalk.com/bbs1/showthread.php?t=358329

Joe
 

·
Registered
Joined
·
998 Posts
Someone may have said this already, but I have had issues with front wheels and axles that I totally missed until I eliminated all other options. Sometimes a wheel can catch on the shoe or with an independent front setup there is more resistance from one side than the other. This can show up from initial start but then be gone when the car is circling the track.

Also make sure your guidepin is straight.

Just the basics,
Old Blue
 

·
Registered
Joined
·
3,662 Posts
Discussion Starter · #10 ·
Well guys, I think I figured out the problem and solved it. And together with Bill Hall's *sage advice, I'm starting to re-evaluate my tuning strategies.
Ok, I noted that ALL my Tuff Ones super Fast cars- were the ones that kicked out, almost all were original Aurora TO's -tho one was an old JL(black chassis) Tuffy. The JL was pretty much stock, and merely a rocket ship when it's rear tires weren't spinning. But I had upgraded all the Aurora TO's to DASH magnets or NOS Super II's or AW magnets. I just hunted up all the original Magnets that came with the chassis, and reinstalled them, and also used some less powerful magnets in the JL chassis. And BINGO, the rear end decel kickout(lock-up) was reduced 95% and this also increased their coasting ability ! I also played with brush tension, merely by swapping out various height brushes, but did not see much difference after doing that.
But one negative side effect I saw on a couple of the "re-magged" Tuffies, was that the arm temp when up pretty high after running a few *BALLS OUT Hot laps !....which is something I noted when I first got the cars used, but found that installing the Dash or Super II mags -not only increased power, but also lowered running temps. Can't I have my cake and eat it too ?
 

·
Registered
Joined
·
998 Posts
What is the downside to the kick-out? It reminds me of the old school burnouts that we used to do before the front wheel drive cars came along. I say embrace the kick-out and make it your signature move.


OB
 

·
Registered
Joined
·
2,024 Posts
the same thing will happen with inlines!

with circle racing this can be an issue, with drag cars, it should not matter.
you try to play with brush tension and see if there is a spot to maintain the speed and reduce brake????????

but for drag car, I would focus on top end
 

·
Registered
Joined
·
592 Posts
Sir Isaac says...

Rear kick-out when letting off full power, the rear end kicks out to the side-usually to the left. PLEASE HELP !?
This is simple physics - for every action there is an equal and opposite reaction. When the arm quickly slows down under braking, it creates a torque in the opposite direction. The guide pin keeps the front anchored so the rear end hangs out. And Tuffys are the worst because of their gearing. Remedies (at least partial ones) are many. Go through the complete drivetrain AGAIN and lap all the gears AGAIN. Check each and every part that spins and be sure it is the absolute least friction of any car you have. Brush arms are an obvious point to address. Which is more important for the kind of racing you do - blind speed or handling? If it is blind speed, you want all the brush compression those little arms can provide. But if you are in some serious need of handling, back off the brush arms a bit. Make darn sure the car is sitting flat, not just has all four tires touching the track - big difference. You have to get the maximum traction out of those rear tires. And if you don't need the blinding speed, you might consider changing the final drive ration away from the 14T drive pinion. A 12T is an improvement and the 9T is a major step to better handling.
 

·
Registered
Joined
·
3,662 Posts
Discussion Starter · #14 ·
Signature move

LOL- "Signature move" ...I like that :thumbsup:
But seriously, there are some downsides, and I'll give two examples. #1) On my Dragstrip, if I'm in the right side lane, and hit the dynamic braking section and the car kicks to the left, the tail usually ends up getting smacked pretty DAMN HARD by the car in the opposite lane, if it has more coasting than my car, And some of my cars(and opponents) reach some pretty fast trap speeds, hence some body damage can occur from a high speed tail clip ! #2) And this is similar to #1, but if I'm braking on an oval track or road course, and the rear kicks out into the lane to the left, I'm likely to get nerf'd if there is a car closing on me in that lane. so again, I get my tail clipped, but not near as bad as a 20+mph Top end Dragstrip clip !

What is the downside to the kick-out? It reminds me of the old school burnouts that we used to do before the front wheel drive cars came along. I say embrace the kick-out and make it your signature move.


OB
 

·
Registered
Joined
·
3,662 Posts
Discussion Starter · #15 · (Edited)
Ahhhh...this was a GREAT reply also, as it made me start thinking about other things. And you were right, the brush tension does also have an effect of matters including coasting. Also, I'd like to address your point on gearing, as I have lots of fast T-Jets, but ONLY some of the Tuffy geared ones kick out. This puzzled me, as I have some very fast Wild Ones cars - but they are lowered geared with the 9 tooth pinion and they have no kick-out problems at all. BTW- Half of my lower geared Wild Ones are just as fast if not faster on road courses and oval tracks as the Tuffies are, it's only on long straight always that the Tuffies start pulling away. :thumbsup:
Thanks for replying, and getting me thinking again.
This is simple physics - for every action there is an equal and opposite reaction. When the arm quickly slows down under braking, it creates a torque in the opposite direction. The guide pin keeps the front anchored so the rear end hangs out. And Tuffys are the worst because of their gearing. Remedies (at least partial ones) are many. Go through the complete drivetrain AGAIN and lap all the gears AGAIN. Check each and every part that spins and be sure it is the absolute least friction of any car you have. Brush arms are an obvious point to address. Which is more important for the kind of racing you do - blind speed or handling? If it is blind speed, you want all the brush compression those little arms can provide. But if you are in some serious need of handling, back off the brush arms a bit. Make darn sure the car is sitting flat, not just has all four tires touching the track - big difference. You have to get the maximum traction out of those rear tires. And if you don't need the blinding speed, you might consider changing the final drive ration away from the 14T drive pinion. A 12T is an improvement and the 9T is a major step to better handling.
 

·
Registered
Joined
·
3,662 Posts
Discussion Starter · #19 ·
Ummm....not good idea

Try disconnecting the dynamic brakes.
FYI- I have a 20' dragstrip with an additional 6' shutdown/dynamic braking section. An even with that much shutdown- some cars still hit the bubblewrap box at the end ! I cannot imagine what it would be like WITHOUT the Dynamic braking !
BTW- I've had to add straight track borders on Both sides of the last 4' of my shut down area. As some of the cars kicked out so bad, that their tails would be off the track and sometimes tumble. Funny side note, I found I needed to add a border to the right side as well, because one or two cars actually kick out to the right ?! And my one and only, Original Speciality(4 gear) Dodge Fever Dragster, also kicks to the right in the tail in the shutdown- but ironically also ends up with it's long nose pointed into the left lane ! LOL- I save that car for Exhibition USE Only :D
 
1 - 20 of 29 Posts
Top