John Stranahan

iTrader: (27)

Gearing
The best way to gear your car is to start with a fast guys gearing. Some other things to note. An electric motor has its peak power at about 1/2 of its maxium amp draw. Amp draw at peak power is usually a big number and results in a lot of motor heating as we strive to gear the motor for peak power. So another trick we use is a temp gun and gear for 160-180 F. This should not be an absolute as on some tiny tracks you may just have to gear lower and not develop so much heat. In low traction you will not develop as much heat either.

Gearing Maximum Power at the Average Speed
I have used this method on the oval to good success. I thought I would explain it here as it turns out my TC4 is geared pretty close to this after some trial and error gear testing on the track and in my driveway.

I paced out my runline on the track with a 3 foot pace, 82 paces, 246 ft run line. A good lap is 10.4 seconds. Dividing gives my average speed of 23.6 ft/s (16 miles per hour). I will change this to inches per min for convenience

23.6 ft/s x 12in/1ft x 60s/1min = 16992 in/min

If I divide this by the wheels circumference I will get average wheel RPM

wheel circumference = (diameter x pi)
16992 in/min / (2.375 x 3.14) = 2280 RPM

Now to see what my wheel RPM is at Maximum Power. I look at the dyno sheet at the Red line. It peaks pretty close to 10,000 RPM, Maybe just a little past. If I divide this by my gear ratioI will get my wheel RPM at max power.
10,000 / 4.72

2118 RPM

My average wheel RPM is 2280 That is within 7% of my Wheel RPM at max power. To get closer I should gear up.

10,000/2280 = 4.38

Anyway the concept would work to gear maximum power at the average speed even on this small touring car track. Note that this dyno run came from my homemade novak Sentry dyno that we developed on a thread by the same name. Most 13.5 motors are going to be very similar to this one where they develop maximum power. I am running a speed passion 13.5. It would be interesting to get a dyno run. I stole the dynos speed control for this car, though, so its not so convenient.

Maximum Amp Draw
Check out that green line, amp draw. Our sentrys were specifically modified to get good number here up to 220 amps or so. This motor is pulling 110 amps soon after startup. You need good connectors and fat wire to get this to the motor. You only achieve this on the track with good traction.

John

John Stranahan

iTrader: (27)

That 4.38 gear came out to a 66/37.7, I had a 38. I installed it and the car felt better on the driveway. It accelerated with more zip. I will try in in the race tomorrow. This gear might overheat the motor on a track with really good traction so use the temp gun also.

John Stranahan

iTrader: (27)

Race Report
We had an eventual rainout, but I arrived early and got some tire testing done and tested the new 4.38 gear ratio.
Firstly the car had more punch and more speed on the straight than ever before. I reccomend the method of gearing the average speed right at maximum motor power, on a tiny track, where speeds are low. The motor may overheat on a bigger track at 4.38. It also works good on the oval.

I tested, Takeoff CS 27, Sorex 32, against Sweep 36. I had no timed laps but the sweeps felt a little more hooked up. I used 5 minutes soak of Jack the Gripper on the tires. Next time I will test against Sorex 36.

I reset the GTB to Profile 4 which gave me 20 % drag brake. This helped slow the car for the very tight corners on corners where I did not want to use trigger brake. I set trigger brakes to about 60%.

It rained 2.5 inches right over the track. The rest of the city was dry. Back in the Losi XXXS now for a weekend mod race.
John

rich67

Great thread I just started to run a TC4 FT indoors on carpet, my first touring car for about 10 years, so am starting to try and improve the setup. Like the slipper spool idea so may try that. Have now got hold of a used rtr for my daughter to start racing with. Keep us updated with your progress.

SVODude

iTrader: (13)

Great Thread! I have been working on a competitive RCGT Setup and weight has been my first priority (Before the recent rule change that is <-- Not happy about that).

I have been working on Carbon Fiber Driveshaft design and finally made a prototype. I have managed to cut the weight in half and so far have had no reliability issues. I have not had a chance to race the car with this new drive shaft (next race on July 11th), but so far I seem to be off to a good start. The Stock driveshaft weighs in at 13.4g (0.47oz) and my carbon driveshaft weighs 6.5g
(.23oz).

All parts were precision machined and a high quality industrial epoxy was used to bond the parts together.

John Stranahan

iTrader: (27)

Thanks for the post guys.

I thought I would repeat this from a private message about the Aero car gear lube.

AC-1001 I have not purchased it recently. I am pretty sure its this one from the description. I bought the LGB gear lube in the train section which is the product I like for sure. LGB is a brand of a deluxe model train.

I did find the tooth pick sized brush the original gear lube came with. It has a tiny ball of foam on the end.


SVO dude -Nice drive shaft. There used to be an Associated TC3 composite shaft but usually it was not that straight so I guess they have eliminated it. If it runs true it should help a lot with acceleration as well as overall weight reduction. So how is the joint made. Graphite tube inside of AE aluminum drive shaft, glue?

John

John Stranahan

iTrader: (27)

Driveline Friction
My car, though much freer than new, had excess driveline friction. First move the motor out of position so the driveline freewheels. Now spin up the (locked diff equipped) front wheel by hand. Let the car coast. You should get around 2-3 extra wheel revolutions with rubber sealed bearings, which I like for durability. I was only getting maybe a half revolution of free spin. (With all oil filled, non contact seal, bearings for a special event the wheels can go up to 10 seconds by count. I'll note they quickly deteriorate with each session as grit gets in.) I popped the upper camber links off the inside ball studs. This allows you to spin the wheels individually to check the wheel bearings. I noted previously that I use an extra thin axle spacer inside the outside wheel bearing to insure they are not getting axial loads from the wheel nut. I noticed in my last race the wheel nuts need to be quite tight or they fall off. I don't like the plastic hexes much. When you test the wheels the drive axles will flop around but it is easy to tell if one has extra friction. All were OK.

I took off the diff tops. I used some fine sandpaper on the 1/2 inch Dremmel drum by hand to just take off any high spots from the seams and outer bearing seat of the top and bottom of the gear case. I cleaned bearing outer races well and bearing seats well to make sure that no grit was pushing on the races and making the bearing races out of round. Don't go crazy here with the sandpaper, you don't want to change dimensions and make a sloppy vibrating driveline. On assembly spin the outdrives before and after you tighten the six screws to make sure things have not gone into a bind on tightening. I get about 3 extra revolutions now with the hand coast test after a short breakin at full speed with the motor.
John

John Stranahan

iTrader: (27)

Side to Side Balance and More weight reduction

I used the setup in the photo with two beams on two scales to get the side to side weight. I was about 1 ounce heavy on the motor side. I took off the motor support and cut the long leg that goes forward down quite a bit. The front end is now about 1/4 inch height. It tapers to about 3/8 inch high at the back. The section under the motor clamp is stock. This lowered the weight of the car to 51.6 ounces which is close enough now to the 51.3 ounces. Your car must weight this with worn tires as well.
this improved side to side weight to within about .5 ounces. That's about close enough for this tiny track. I can move electronics a bit to correct this some.
You can also test this by lifting the car on center with two X-acto knives, one front and one back. Get the car to lift evenly from the ground.

Battery tray mod
I noticed my battery had been rubbing the rear of the drive shaft just a tiny bit. The ribs on the side of the battery tray was not allowing the LiPo to sit flat. I removed the ribs on the far left side to let the battery sit more near the frame rail. I also removed just enough of the inner ribs to let the battery sit down low in the frame. I was able to lower my battery hold down screws about 3 full turns.

John

Conrad

iTrader: (3)

SVOdude, John. There is a forum member on here who already makes, well used to make c/f shafts for different cars. I think he still does custom ones for a fair price. [here]

John Stranahan

iTrader: (27)

Note that I have for sale the entire electronics that came with my TC4 RTR. This includes radio speed control (brushed) motor, servo and receiver.
John

Here is a link for the exact train gear lube that I like. The small container lasts a long time.

http://www.discounttrainsonline.com/...160-99982.html

SVODude

iTrader: (13)

Thanks for link John!

As far as the Carbon DriveShaft, I already made it and I already invested in the tooling to make it. I am currently working on my own design (not using a stock driveshaft donor) that I could sell for around $25 a unit shipped if the demand is still there and I am pleased with the durability.
Thanks for the info.

John Stranahan

iTrader: (27)

Track Report
100 F air temp
after sweeping and blowing off the track the traction was low. It improved to medium-low after a couple of long runs. The only problem I had was oversteer off throttle. When you are off throttle torque steer from the front diff is not a big issue. I used standard tuning and made the front roll stiffness a little stiffer. I moved the top of the shocks out 2 holes and then 3 holes. The car responded well. Additionally I added some on power steering at the same time. I had one sweep 36 tire tear out a small section of bead and rip up all the way to the tread. I have a spare that I can use.

Tire Wear Characteristics
The tire on the Sweep exp 36 is showing good wear characteristics (tiny ripples lined up with the Circumference) and is hooked up pretty good. You can feel these ripple as a fuzz when you run your finger across the thread. Sometimes you can see the tiny ripples with a light wetting from traction compound. I only find these ripples when the tire is hooked up well. If it is too soft it will be smooth with tiny rubber marbles scattered on the surface. It may also get a ripped out look near the center rib as the rubber is torn away. If the tire is too hard it will be scuffed smooth, the car will slide a lot in the corners.
John

John Stranahan

iTrader: (27)

Wedge
Let's say I take a well setup touring car and lower the right rear shock collar. What I have done is add wedge (tweak) to the car. The right rear tire is now heavy. Additionally the car rocks across the diagonal and makes the left front heavy. As a result when the car makes a left turn the right front carries less load; the right front tire carrying the cornering load is more efficient. You get more steering. So you add wedge to get more steering in a left turn. (think oval)

Corner Weights
First correct side to side balance with the setup in a previous post. I made further corrections here by moving the transponder to the battery top strap and moving the capacitor far left. Side to side weight was perfect now.

What we want in a touring car is for the car to turn the same left and right. We want to take out all wedge, or tweak resulting from improper front to rear weight positioning in the car. You do this with scales. It is hard to do any other way. See the pic. I put the the rear of the car on a beam and the two front tires on two separate scales. The front right was light. I added spring shims to the front right and left rear until front weights are even. Now I reversed the car. The rears should be even as well. They were withing .3 ounces. That is about as close as you can get weights due to shock friction. Finished.

Now let's say the left rear was heavy. I would need to move the battery slightly forward by splitting the battery foam spacer into two pieces. For slight errors I can move that transponder but it really should have some empty space under it for best reception.

Here is a pic of the final electronics and battery position.
so now we have the car at minimum weight plus a few tenths ounce at 1450 g
Perfect side to side weights
Perfect corner weights within a few tenths

From now on detweak with a tweak station or X-Acto knife. More on that later.
John

pejota

iTrader: (12)

Quick question about tuning out oversteer.

In that situation you presented, off-throttle oversteer, i'd go up in spring tension. However, you made the shocks more upright, essentially doing the same thing but in a different manner.

What do you see as the major difference between the two approaches? Is one more correct than the other? Or is my approach completely wrong?

Thanks in advance!!

John Stranahan

iTrader: (27)

Pejota-What counts here is called the wheel rate. The spring tension that the wheel feels. You can measure this by pushing on the inverted cars wheel with a known force and measuring deflection. You will get a wheel rate in lbs/in. This rate is of course controlled by the spring rate and its mechanical advantage. When you make the spring more vertical you increase the wheel rate; you increase mechanincal advantage with better geometry. When you go to a higher spring you increase the wheel rate in a bigger jump. So make a course adjustment with spring rate and fine tune with shock position. When there is not another hole to move to you will also need to change the spring. I was only a little off. Here is a relevant section of my online tuning reference.


Spring Rate vs Wheel Rate
The spring rate is how many pounds it takes to compress a spring 1 inch and is measured in pounds/inch (lb/in). If it takes 20 pounds to compress a spring one inch then it is a 20 pound/inch spring. It takes 10 pounds to compress the same spring ½ inch and 5 lbs to compress it 1/4 inch.
Two springs that are popular on the front of a Losi XXXS touring car on an indoor asphalt track with rubber tires are the stock purple spring rated at 20 pound/inch and the blue spring rated at 14.6 pound/inch. I was curious how much of this spring tension actually got to the wheel with the top front shock mount in the various holes. This measurement at the wheel is called the wheel rate. The wheel rate can be calculated but was much easier for me to just measure by putting a weight on the tire with the car upside down and measuring the deflection of the wheel with a dial indicator. The results are found in the table which follows.

• Blue Spring fourth hole out from the inside 6.7 lb/in
• Blue Spring third hole out from the inside 6.4 lb/in
• Blue Spring second hole out from the inside 6.1 lb/in
• Blue Spring first hole on the inside 5.5 lb/in

John