CristianTabush

iTrader: (13)

LJae, good to hear John's help works. On another note, there seems to be that the TC4 has an inherent problem with corner grip. The car just produces too much of it. I've noticed that from the results the team has gotten at big races and also with talking with one of their engineers on the subject.

I don't get to run on carpet at all, but will hopefully get to do it in about a month at a race in Dallas. I know a lot of people have thrown the towel on the TC4, but I am not prepared to do it yet. My question is, what have you been doing in order to try to get the car to "free up" in the corners. On asphalt, I got particularly good results from raising the rear roll center higher than the front, shortening the front link, increasing the length of rear link (running it on the outside hole on the hub carrier would make my car spin out), And then obviously adjustment of toe in.
Anyways, just trying to pick you brain.

LJae

iTrader: (4)

Cristian, I this weekend was the first time that I got positive results from the TC4 and I feel that is largely due to guided adjustment information that I got from John. When I get a a chance to hit the track again with the proper numbers on the car, I can better inform you of the changes and handling effects. My TC3 feels really nice and balanced so hopefully with the correct numbers on the TC4, it well fell the same. At the moment, the only change to get matching numbers is to remove .025 inches of shims from the front and rear of the car. When is the Dallas race? I'll try to get more testing done and the results to you to, hopeful, better perpare you. I'm not sure if me having BMI chassis on my TC4 will make alot of difference but the the changes and handling effect should coincide(sp) between the cars. I'm working with the guy that let me use his tires so I'll do some testing with his FTTC4 just to verify adjustment results.

John Stranahan

iTrader: (27)

Ljae-Good to hear you are having some posivitive results from tinkering with the roll centers. Please continue to keep us informed.

Trinity Cobalt Flat vs Round wire
I started this discussion on the previous page of this thread. There is a photo of the install in the Losi JRXS with a Novak GTX on the previous page.

I have the two armatures in hand now. Here is a pic. They are wound quite well. The three poles are as close to a pattern wind (each pole exactly the same) as I have seen on a RC car armature. The opposite end is quite a bit more uniform. The comms and silver braze look good. Note that the wires on a pole do not cross at the comm. This gives you a little shorter lower resistance coil than a similar wind with crossed wires. I forget the name for the two patterns. (I used to wind arms). Thanks again to Trinity for supplying the armatures for this test. You can see the epoxy that is applied by hand to balance these armatures after spinning them on a balancer.

CristianTabush

iTrader: (13)

EUREKA!!!!!

I found a setup as close to perfect as I have been able to run on the TC4. I will update on the post and also the link is below.

Anyways changed 3 things. The summation of all 3 things (plus a John Stranahan tuned mod motor) allowed for my avg fast lap to go from around 16.7-16.8 to around a 16.2-16.3. Over a period of 5 minutes it adds up to about half a lap. Note, the fastest lap on the track for myself went from 16.4 previously to a blistering 15.9 ( I don't think anyone else has run anything close to a mid 16, high 16's are blistering laps for other people on this track).

Ok the changes:
1.Lowered the roll center in the front to 1 pin (from 2) on both block carriers. My car no sits at 1 pin in both front blocks and 4 pins under both rear blocks. Effect desired and received: Lowering the roll center in the front by the smallest shim allowed me to achieve the perfect roll stiffness for this track with a blue spring in the front. Car now has sufficient body roll and grip with a spool in the front; that was overtly done with a silver spring and the black swaybar as well as gold spring with no swaybar.

2.Losi XXXS hubs in the rear. I know people had been doing this for a while, but I had not tried it. Using these hubs lengthened the rear link slightly as well as raised my roll center a tad by raising the pivot point on the outside of the link. (I used the inside hole on the hub, centered on the wheelbase) Effect achieved/desired: Car now pivots better in the rear end- it switches directions much quicker with 2.5 deg of rear toe. I had tried 2 degrees in the rear, but had lost the turn in gained by the extra rear toe and car was unpredictable in high-speed sections as well as hairpins.

3.An old trick we used to do with my dad on the old MR4tc's was to run plastic front suspension components. So I installed associated TC4 plastic a-arms. Effect achieved/desired: I wanted more Front grip. The TC4 plows, this allowed the front end to probably flex a microscopic amount, but with the summation of the other changes it did the trick, a little more flex in the front of the car and BAM! 1/2 a sec a lap!

Overall I am so happy with the FTTC4, I was ready to give up on it, because I knew that there was 1/2 sec per lap left in it and I could not get it to turn, but now I am very pleased with the car, there is nothing to be desired from other cars. The efficient drive train makes it trickier to put the power down, but with a silky smooth throttle finger and all the steering in the world this car now is up to par with any of the other ones. The TC4 turns now, with plenty of corner speed: MISSION ACCOMPLISHED.

Now all I need is for John to build my motors (good for another .2 tenths/sec lap over my motors).

CristianTabush

iTrader: (13)

http://rctech.net/forum/showthread.p...40#post2068840

John Stranahan

iTrader: (27)

Flat vs Round Wire (Round 1)
We ran the Trinity 10 x 1s with stock (not the custom wound arms)flat wire and round wire arms in both the FTTC4 (you can guess who) and the Losi JRXS. There is no doubt about it, the 10 x 1 round wire was ballistic when geared at 7.5 in the FTTC4 (track record fast lap) and geared at 7.56 in the Losi JRXS at GulfCoastRCracetrack. This round wire arm has good sized 16 gauge wire and has very nice punch and huge top speed.
The stock flat wire arm has about 18 gauge wire which is quite a bit smaller than the round wire arm. This limits the punch a bit. It is also on a lighter D1 arm blank. It has to be geared at about 7.42 JRXS or 7.35 FTTC4 to have adequate top speed for our long straight.

The custom arms are both 17 gauge so they are in between these two.

Differences
The round wire (big wire) arm gives awsome acceleration from a rolling start like coming onto our straight, or on the shorter straight approching the first hairpin. You need a gentle touch of the trigger to stay hooked up. Truly a delightful motor on our track.

The flat wire arm shines coming off the hairpins from a slow speed. Top speed is adequate when geared like I suggested. The motor feels like a quint or hex wind and is very smooth on the throttle. You can drive the motor very hard without losing forward traction. This gives pretty consistent lap times althought the best lap might not be as good as the round wire. This is pretty much as advertized.

Drag Brake Feel with Flat Wire
We both noticed that the flat wire has a bit more drag brake tendency. I think that this is because of eddy currents created in the flat wire on coast. These are circular currents in flat metal that are often used to dampen balance beams and such. This makes the motor coast a little more like a stock motor which is good. You can use quite a bit less brakes. The sound of the motor is completely different. A lot more whine with this motor.

The Ballistic Motor Setup
I set up both motors at the recommended 20 degrees of timing (that's a lot for a 10 turn). I used the high silver brushes the motors came with. I tweaked the motor springs to read 4 on the Trinity brush tension gauge. Run the motor in for 5 minutes on the power supply. No fan. This setup, with the gearing we use, is a balls to the wall setup. You only get two runs. Then you need to cut the comm and reseat the brushes. If you start the third run you will fry the comm. The brushes are not burnt. They are holding up very well. Using a lower gear does not help matters much, it just makes the motor feel slow.

John Stranahan

iTrader: (27)

Flexures

I discussed flexures a bit on the Chassis Stiffness thread. It has cropped up here again in Christians post in a round about way. First the history. In Formula I, the bodies and wings can develop 3.5 g's of down force. This means that coming around a high speed corner, the approximately 1,700 pound car has a supsension loading of 5100 pounds. This means the springs have to support this much weight and keep it off the ground. You don't want huge changes in ride height, so hugely stiff springing is needed. With these kind of forces suspension friction (stiction) becomes a limiting factor in developing good cornering grip. The F1 cars are starting to include flexures to support the majority of the load. The lower A-arm can consist of a solid aerodynamic carbon fibre blade that flexes rather than pivots on the chassis side. This is supplemented with longitudinal coil over shocks to allow tuning.

Now our cars don't have huge aero loads, but we have primitive suspension joints with plenty of stiction. Reducing this to a minimum has alway created more cornering traction for me. That's why I removed the sway bar attachments on the A-arms of the JRXS and prefer not to use sway bars on 1/10 scale.

When Cristian went to plastic arms on the front instead of graphite, he created a flexure outboard of the lower shock mount. He found a lot more steering traction.

Well, not to be outdone, I have created my own flexures on the JRXS by reducing the depth of the arms ouboard of my front shocks with the large drum sander on the Dremel. No plastic arms are available. These short arms are super stiff, just because they are so short. I removed about 1/2 the material. I indeed got more steering traction. I had to move the top of the front shock 1 hole and the rear shock 2 holes to get my balance back. The car is a bit twitchy this way. If you lose concetration and go off throttle too much while turning you can spin out. Cristian noticed this a couple of times. You can drive it fast if you are smooth. I'll test it some more and post a pic if it holds up. The greatest benefit was off power steering came up.

I abandoned these arms. Too twitchy. Maybe they were too thin.

John Stranahan

iTrader: (27)

Orion Top based Mod Motor Internal Damage.

I have inspected the interior of two Orion Top based mod motors now, 1 Peak and 1 Fantom, that had similar damage to the wires on the endbell side of the arm. Too similar to be a coincidence from track debris. So this is what happens. You bump the car on the endbell side. The bearing in the endbell is secured in place with a silly O-ring. How about a nice snap ring instead. The bearing moves-the commutator tabs start chewing on the angled brush hood tips. They create metal chaff which damages the wires. This chaff is ejected before you pit. The damage to the brush hoods is plainly visible. The peak motor, that I inspected had enough damage to the hoods that a burr was created preventing the brushes from extending beyond the hood.

Here is the fix. Remove the brushes. File or cut away the burr in the brush hoods with a tiny file or X-acto knife. Throw away this bad use for an O-ring. Clean the bearing channel and outer part of the outer bearing race with alcohol. Use red loctite to secure the bearing in place properly. This bearing usually outlasts the motor. If you do need to replace the bearing, just heat it up with your soldering iron. The Loctite will liquify and you can press the bearing out. They do make a high temperature resistant red loctite that you can get at an autoparts store.

While the loctite dries overnight, you can use a standard endbell from a motor in your dead motor drawer. The Cobalt endbell will fit this motor. Then you can use standard easy to tune springs and standard sized brushes.

Re-oil and you are ready to go.

John Stranahan

iTrader: (27)

First 2 Cool Racing Team Charity Race

We just finished the First Annual 2 Cool Racing Team Charity race at Mikes-hobbyshop.com. Many thanks to Paul and Gary for putting on a good show. There was good food and a good time had by all. Proceeds benefitted the Shriners Hospital.
I qualified 3rd but had troubles in the mod main. We had a good 19 turn class which we may add in the future if there is enough interest. The 19 turn motors looked good even on this long track.

10 turn vs Lower turn
We had both 10 turn motors and lower turn motors in this race. Our straight is about 140 ft long. My Trinity Cobalt 10 x 1 actually had top speed honors which were recorded by radar gun on the straight. I reached 45 mph. The lower turn motors with a different body were running about 44 mph. None of the motors are geared for top speed but rather a combination of good performance out of the corners, lowest lap time, and to some extent top speed in that it affects lap times on this track due to its length.

I have always suspected from my experience with mod motors and having dynoed many of them that the most powerful motors are in the 10 to 11 turn range. This race did nothing to alter that opinion. The seven single had the fast lap during the race but it was only equal to the fast lap in the same car with my 10 x 1. The 8 x 2 was fast but not faster than the 10 x 1 on the straight or out of the corners. The seven single had a little more smoothness to the power band, more like the flat wire.

Problems with the lower turn motors
We had a generous number of mod motor problems at this race. The primary one was keeping the brush in good contact for the entire race. I think we will move to the Trinity silver spring (14 ounce) in the future to help with this, especially when the comm gets small. Another problem is the Orion top based motors are difficult to solder leads to with the low AC voltage typical at a track. It really needs some motor solder tabs like at least one other brand with aluminum endbell is using.

When the comm gets below about 2.75-2.78 inch, or so, my two run setup becomes a one run setup. It is helpfull now to narrow the brush a bit to reduce dwell on the comm segment and to keep timing the same. I did this with the cuttoff wheel on the dremmel by hand and narrowed the brush about half the width of the hard Dremmel wheel. The motor was fast again. Lin prefered a small file. I was running the stock flat wire 10 x 1 having used up the very fast Cobalt round wire 10 x 1.

On the 7 turn we tried a very good cooling fan arrangement which ducted cool air from under the chassis onto the endbell. The motor still tended to die by arcing and then desoldering its leads!!. We think maybe our track is too long for these low turn mods. An 8 turn reedy Worlds edition (medium sized comm) repeated this performance even with light application of throttle and no full throttle! Suggestions would be appreciated. Tol suggested not using brakes as this adds additional heat to the motor.

John Stranahan

iTrader: (27)

Mod Motor Durability.

We made a little progress on our Mod Motor Durabiltiy at Mikes GulfCoast RC Race Track. We went up from purple springs (about 13 ounce) to silver (14 ounces). On a Trinity cobalt motor, I can get a good reading on the Trinity Spring Tension gauge. About 4.5 is good for durabilty on this track. 4.0 is ballistic but short lived. We tried the gauge on the new Aluminum Endbell Trinity Motor (Epic Shock) and it did not work as well as the spring wire arm tends to stick in the Aluminum recess. The gauge also has less leverage on the spring with this endbell so the numbers do not cross over from one motor to the other. Lin ran purple on negative and silver on positive. Usually the positive brush tends to burn more.

Results- With a new comm, I ran two heats with the silver silver combination. the comm looked good. It was copper colored and still shiny. I made only one .001 inch pass to clean it up. Lin's motor was improved, but there was still too much wear. He has to order up some more silver springs for his motors which do not have overhead springs (overhead springs have two different types of springs on positive and negative, both solder tabs are on top or overhead)

Plasma Sprayed Comm
There is a process to add metal to an object called sputtering (in a vacuum) or plasma spray (in air). This process vaporizes metal at high temperature and then the hot metal plasma deposits on the cooler object. If your comm on which you are running high silver brushes, comes out silver colored and all eaten up then you have arcing that has actually plasma sprayed the comm with a coating of silver from the brushes. Things have gotten really hot. The arcing is responsible for most of the comm damage. Heavier springs or a lower gear ratio is usually the cure.

Another problem- My motor was running well in the main and then I heard a snap at the end of one of our long straights (about 45 mph). One wire actually came loose from the comm tab, from centrifugal force, I believe, as there is no evidence of overheating. The comm and brushes looked very good. It is possible that a Hemi wind, where the wires don't cross at the comm end of the arm, is not suitable for a high speed track, unless it has an extra thread securing the wires. I found this extra wrap of high tensile thread on one of my flat wire arms. The 10 x 1, that snapped, also had larger gauge wire (15 gauge) than my previous 10 x 1 (16 gauge-same manufacturer) which was very succesful on this track. The larger wire being heavier may have caused the problem. They never tell us the gauge or type of wind. I wish they would.

This problem could also have been caused by a piece of epoxy balance material that was ejected from centrifugal force, and then collided with the comm tab. There is a bare spot on the end of the arm. Since the com tab is the one with two ends of wire, I suspect the wire broke first. I found no bits of epoxy in the frozen motor.

The photo shows a Trinity Flat wire 10 x 1 with a Hemi Wind and Thread Reinforcement. Some damage from Arcing, but only a hint of the silver plasma sprayed color.

AdrianM

iTrader: (4)

We find that at our local 140x70 outdoor track of you gear a basic 7 turn lower than 9.00:1 you can count on throwing a wind at the end of the straight. The RPM is just too much for the motor to hold toghter.

The kevlar cord wrap seems to stop this from happening. All the Reedy Ti3 7 and 8 turns I have gotten lately come kevlar wrapped.

John Stranahan

iTrader: (27)

Adrian-Thanks for the post. We had a 7 turn throw a turn the previous weekend. Our 10 x 1s are geared right about 7.5. You would not think it was turning too fast, but I guess the extra weight of the 15 gauge coupled with the attraction of the magnetized coil to the magnets caused the problem. Wish this arm had had the Kevlar Wrap. The car was hooked up pretty well in the main.

Note that I added a picture of this Kevlar wrap to my previous post.

John Stranahan

iTrader: (27)

Flexures Revisited

The last time I ran more flexible A-arms in the JRXS my car got twitchy. I did have more turn in. I discovered later that my ball diff was coming loose. I used loctite on the nut to resecure it as it has come loose before. I think the screw is a bit short to fully engage the nylon in the locknut. This might have been the reason for the twitchyness.

I made some flexible A-arms from 1/16 inch piano wire and #6 brass nuts and brass tubing. the goal was to have a flexible section ouboard of the lower shock mount to make a Flexure. The stock arms being very short have a tendency to be on the stiff side perhaps. Track was closed for repairs anyway. the flexure is damped by the shock and can be fine tuned with the regular coil spring as normal.

I made three changes. the arms are more flexible than stock. I moved the shock mount inward a tad to provide more arm flex. I moved the arm forward 1/8 inch to straighten the drive axles a little. The arms should be strong enough to run with. Probably not strong enough to crash with, but neither are the stock arms. I am not crashing as much now. I have a jig that supports the various brass pieces in place so the arm can be straightened and resoldered into aligment quickly. Here is a pic.

I can add pianno wire in parallel to the one piece, use a cross brace, or use gussets or a partial web, to stiffen and strengthen the A-arm if need be. I can add a droop screw later, but the droop ended up in a good place to test. The spring is not loose at full droop. You can also adjust droop with spacers under the shock piston. I used one silcone shock O-ring under the shock piston to set the car up with less droop for the moment.

I can tell that stiction is much reduced already from the brass on steel pivots.

John Stranahan

iTrader: (27)

Here is a company that could build a flexible arm out of sheet titanium or milled from solid stock. They build parts for T-max etc. at present.

http://www.flextekrc.com/about/index.shtml#

I believe I saw another company that had a combination sheet titanium and bonded aluminum arm. Could not find the link again.

John Stranahan

iTrader: (27)

Homemade Flexure Report

The homemade front A-arms that I made from flexible piano wire worked well. There is a photo 2 posts up. I did indeed get more turn in (initial cornering traction on coast). The car ended up a little loose (oversteered). The rear end lacked cornering grip to match the front. This was hard to adjust out. At home I discovere a rear inner hinge pin was slightly bent causing some suspension friction. It is nothing short of amazing how a little problem like this will take away traction. Anyway I will need to test the arms again and the car will probably be more responsive to tuning. I may make make mathching rear arms.
If the arms work out, better than stock, I will contact a manufacturer to see if they can produce some flexible arms. I see some potential gain here for this short armed car on tracks with less than optimum traction. There was no twichyness.

I ran 5 packs and the A-arms were sufficiently durable. I tapped one of our corner bumpers quite hard once. There was no apparent damage to the front arms or bending of the wire. They flex instead of shatter.

The 11x1 Trinity Cobalt motor, I purchased to practice with, woke up with a little taller gear of 7.43. It looked good after the change up from 7.56. At this point after consitently whipping me before the gear change, Lin's motor had a problem so testing stopped.

New Ride Height and Roll Center Adjustment
Jeff had some luck with the bumps on our back straight. He used a wheeled concrete grinder about the size of a tiller. We have good smooth line down the center of the of the back straight at present. I was able to lower my car to 5 mm chassis height from 6.5 without scraping a little chassis off on each lap. This also put the roll center well below the ground. I raised the inner A-arm pivots .040 inch to bring the roll center back up to just below the ground. This will require retuning the spring positions and possibly springs due to the lower center of gravity.