John Stranahan

iTrader: (27)

Greasemonkey-Here is the last pic of Mathjis X10 posted on this thread in case that was what you are looking for.

GreaseMonkey

iTrader: (4)

Thanks Jon, that's exactly what I was looking for.

John Stranahan

iTrader: (27)

Track Report 50 F Vacuumed water off. Track green but clean-


The car is hooked up well. The new porsche body was planted on the straight and the sweeper. I have increased front shock oil to 37.5 weight from 35. I increased the rear to 35 weight from 30. The car was a bit twitchy. Increasing the shock oil weight took some of it out, but it is still just a bit twitchy. I may play with the droop next. I can adjust it with spacers inside the shock under the piston. No breakage yet.

Spring Rate
I have a collection of VCS Microshock springs which are about 10 mm Id and 12 mm OD from two sources. Associated and MurdockRC. The spring rates don't match the labels very closely and in the case of the Associated springs are way off. Here is a formula that you can use to calculate the spring rate using measurments from your dial caliper. All of my springs have 6 active coils to start with. I have cut my red and blue one down to about 3.5 coils.

Spring Rate = (G x d^4)/(8 x N x D^3)

G = Torsional modulus for steel = 11.25 x 10^6
d = the diameter of the spring wire in inches
N = the number of active coils (full coils)
D = the mean coil diameter (the average of the spring OD and spring ID
8 = a geometric constant for all coil springs

This formula works for full size cars also.

So here are the results it may help you if you use this type of spring or if you are Marty and need a spring for your prototype front end.

Associated Blue = 13.5 lb
Associated Copper = 13.7 lb (this was supposed to be my new 16 lb spring)
Murdoch RC Gold 14.1 lb
Murdock RC Copper 14.6 lb/in
Associated Red 18 lb (this is supposed to be a 14 lb spring)

Note that IRS sells springs for The RC18 as well as shocks for this minitruck.

John

John Stranahan

iTrader: (27)

Friday Practice, Breakage Report

I had two high speed horrible crashes with the pan car yesterday. I had to hire two new drivers due to the fatalities (small ones ). I had no damage on the first crash. On the second crash, at the end of the straight. I clipped the track bumper hard making a tight entry into the sweeper. We were losing daylight. The crash broke the side tabs completely off one side of the servo. I will have to make better mounts. I have the servo taped to a wedge now that I cut out of polypropylene solid stock. It worked well during the race today. The front arms were undamaged during both of these crashes. I think this is why. I have never broken an upper pan car A-arm. This is becuase the lower one will break first and relieve the pressure. (The lower arm is much harder to break than a touring car arm because there is an upper A-arm.) The upper mount has some flex as you push the A-arm back; this also prevents breakage of the upper arm. I now have this same mount for the top and bottom arm. This is a very strong way to mount an A-arm. The single post lower arm is holding up extremely well. I could however use some more steering link clearance at full throw. The rearward screw of my mounts is a tiny bit too far back.

Saturday Race
75F traction medium

This was the first big test of the new front suspension (previously posted pic). I had new 2.40 inch diameter tires front and back for the first time on this suspension. I had raised the suspension up on one #8 Associated washer to correct for the tall tires. The car had very good manners on the straight and the sweeper. I had some understeer (push) in the infield most noticeable on the hairpins.

I removed the washers from under the suspension arms to lower the roll center. I corrected the ride height with the shock collars. This had the effect of lowering the roll center. Steering was much better. I did not have enough steering throw, though. Lap times were improved.

I turned my shocks over to give me a few degrees more travel. The smallish servo saver did not really have enough travel (because the steering link is in the back holes on the steering arm). This was causing one of the tires to quit moving at full throw. The balls in the servo saver were lined up vertically at full throw. I fixed this problem by installing a medium size Kimbrough Servo Saver (#201 I believe). Now I had enough throw and more proper Ackerman at near full throw.

The car ran its fastest laps ever, .4 seconds faster than the previous club race which had similar traction. The major change since then was the new front suspension. Previously I had run the Associated suspension with long kingpins. The car was .1 faster than its best previouly with a sugar water treated track. Tire wear is very even on the front. The rear tire wear averaged about .030 inch for 20 minutes of racing.

I can go into the straight very fast and hard now. I'll add a bit more steering for the next race. It is nice to have plenty in reserve. I very much like the adjustability and responsiveness to tuning of this front suspension.

John

Pro ten Holland

iTrader: (1)

move the servo mounts closer to the sides of the servo to prevent breakage of the mounting tabs.
I ususally lenghten the mounting holes towards the servo itself to have the servo sandwiched firmly between the servo mounts.

You might also want to consider other brands of servo's. Hitec's are notorious for their frail plastic.
Best go for Futaba, airtronics, JR or KO.

How did the race itself go?

I can't wait to test your front end. My car could really use some extra steering! I have the rear planted so much it's always difficult to get the front to hook up!

John Stranahan

iTrader: (27)

Mathijs-I don' really have proper servo mounts where I can move it closer. Thanks for the tip, though. I will have to machine some at the angle I need. I have the side tilted up instead of the front. This gives me better motion on the steering links so they don't rub. For now the servo is mounted with a large square of servo tape on a plastic wedge. This is working out OK. Bumpsteer is now 0.

I'll send you this front end when Marty sends me his to test. I'll send a Wedge also. The front to back spacing of the servo is a bit tedious otherwise. Then we can swap after we test them. If you would like to build your own front suspension I can trace the Aluminum upright for you.

I put the Murdock RC Copper spring on for a test today. It is the next lower tension spring below the red. I should have race day traction after I run a couple of packs today.

I gualified fourth, I had several undesired contacts with other cars in my fastest heat the third qualifier. (We had a new national champion (in a different class) racing this time also). I was running 3rd with about 1.5 second lead on fourth in the main. We only had 2 heats and the main started early due to the superbowl. I did not have a full charge. I pulled out after the car slowed 2 laps before the end. Nitro guys don't really keep to much of a shedule that electric guys need to get charged on time. I had a small deficit each heat that accumulated and caused a DNF. I should have used two packs and alternated them.

Lunsford Punisher Rod Ends On Panhard Bar
I bought a set of these mostly because Tower does not sell Losi Rod ends which are my favorites. It turns out these Lunsford rod ends are beefy and round. This let me use them on my Panhard Bar instead of the Traxxas Rod ends which are huge for the T-max. This gives me a little more ground clearance and clearance from my mounts. I drilled the Lunsford rod end out with the proper tap drill for the thread. In the pic you can see the Lunsford end on the lower left on the Panhard bar. The Traxxas end is visible on the top link at the back end of it.

Later after one session I decided these Lunsford ends had too much play for use on the Panhard bar. I replaced them with the original Traxxas Rod ends which are much stronger and have less play.

John Stranahan

iTrader: (27)

I had a short practice today. I replaced the Red Associated Spring with a weaker copper Murdock spring. This seemed to work better on the medium traction track. I had more steering traction. At six coils the copper spring is a 14.6 lb/in spring. I cut it to 3.5 coils to fit the shocks, same as my red spring; this increases the tension to 25 lb/in (calculated using the posted formula). I increased the ride height at the kingpin to compensate for the lower tension. I was using a red spring previously. The car is planted. No scraping of the front end on the bumps at the new ride height. Front and rear shock oil is now 35 weight.
John

Pro ten Holland

iTrader: (1)

Your front end doesn't use te wide car's stock mounting holes right? How far apart (left to right) should I space them? I'll incorporate them on my new chassis design.

John Stranahan

iTrader: (27)

My current dual A-arm front end uses the stock holes on a narrow pan car chassis to make it a wide pan car. If you have a narrow chassis at hand you could measure off of it. I measure 76mm accross from bolt center to bolt center.

After considerable testing with both wide and narrow chassis (on a wide pan car), I always like the narrow one slightly better on asphalt. I think it has more flex. If I were making a wide chassis, I would make it with a narrow waist and flair it out for the wide mount holes. This may not suit your battery placement preferences.
John

John Stranahan

iTrader: (27)

Here is a pic of the new front end at full left lock. I have moved the rear A-arm mount screw forward. This improved my clearance on the links. Also visible is the larger Kimbrough servo saver. I have enough steering throw for any situation now.
John

Pro ten Holland

iTrader: (1)

The narrow car was originally 190mm wide right?
I'll draw in the mounting holes.
I also like a flexible chassis. That's why I use large cutouts on my chassis.
A little flex increases traction and makes your car more forgiving.
A really stiff chassis is only benificial if you're in the league of Masami Hirosaka.

Boomer

Unless you can create a suspension that is forgiving and works as it should and then you can use the suspension to do the work (making it adjustable, etc.) as opposed to the chassis!

John Stranahan

iTrader: (27)

The front of the narrow car was 185 mm. The rear was wider at 200mm. That 76mm hole spacing is very close to 3 inches. Chances are that it is 3.00 inches.

Boomer-I have had this chassis flex discussion with the touring car guys. There is a little magic in chassis flex that you cannot obtain with the shocks and springs. I think that it is because it can absorb some bumps without stiction. The chassis acts like a flexure. This is not a problem on the full size cars as generally they cannot make a chassis that is too stiff for asphalt without a big weight penalty. A full size car chassis that is too stiff for dirt oval can be made.
John

Boomer

ahh - very cool then. My apologies to Pro10. . .

John Stranahan

iTrader: (27)

The first set of these that I got with the car were a very tight fit in the rod ends. They needed to be pressed in hard with tools. A second set of these CRC pivot balls were a loose fit in new Associated rod ends. I could push them in with my finger. I am using these now. It might be best to match brands of pivot balls to the rod ends on these. I have ordered a set of IRS hardcoated Aluminum pivot balls. I'll see how they fit and wear and report back. I would hate to send Mathijs a sloppy front end.
We had a couple of good practices since my last post. The car is holding up well. Tire wear is good. No complaints. Very fast. Still waiting on the Tekin Speed Control. I am going to try a heavier gold RC18t front spring on the back shocks to help prevent chassis contact and wear. I may have to readust the front.

We are starting some preparations for a couple of big races which include the ROAR on Road Nitro Nats this year. I decided to help a little by developing a method to efficiently removed asphalt bumps on the track. Places where the suspension bottoms. These are clearly marked with scratches from the nitro cars. I made a wood jig 3 feet long by 10 inches wide. This has a 6 inch wide guide for a skill saw screwed onto it long ways. I have 1 x 1 (x 18 long) inch stock screwed to the ends of the 10 inch board to raise it up 1 inch. The 1x1 stock is offset to the left of the board so you don't cut it by accident. The cutting is done with a carbide tipped course wood skill saw blade.

You put the jig on the bump longways to the layout. Start at one side. I cut grooves about every 1/4 inch with the saw. I push the jig over with my hand make a new cut each time. You can make the cut faster than you usually cut wood. I set the saw blade to just skim the asphalt near the 1 inch feet. Then it cuts deeper near the middle of the board where the bump is tallest. Then chip out most of the asphalt with a suitable pick or heavy root cutter. Now recut moving the jig and blade side to side with a slow forward feed. This gets most of the material out very quickly. Now sand or grind it smooth and skim coat. The carbide blade lasted very well with a 1/4 inch cut. I cut through some little rocks in the base asphalt with ease. These blades are available for 5 for $20 at Home Depot. That should do our whole straight and save days of grinding. Most important, be careful, don't cut your left hand off.. Wear safety glasses to cut.

Apparently this is a difficult problem at other tracks. I met and discussed this with Mike Cueller the ROAR president who is at our track for an invitational offroad race this weekend. He found it to be a better method than he has seen tried, so I thought I would make this post. He has 30 years in the RC racing business.

New Pan Car at Our track.
Nick brought his 200 mm pan car (actually setup for oval). We got it up and running in short order. I will enjoy the company. We may do a high speed test with my car once the Tekin comes in. Can you say insane speed run.
John