I had three experiments running on the JS Pro 10 wide pan which is based on the CRC Gen X 10.
New motor Tekin 3.5
Cut down Top plate for increased torsional flex
Forward weight balance. Speed control in fron ot side links.
New motor, Tekin 3.5 -I started with a fairly tall for a 3.5 pan car gear of 13/93. The motor peformed with the Tekin RX8 but it was very sluggish and had slow top speed. It returned after a few minute run at 98F. Not really working yet. I went up to 14/93. Still slow and sluggish. Then 15/93. Now I had good performance, but it was not the equal of the LRP X12. I left it here. More like a 4.5 as far as RPM goes. Kv's are not published so you buy in the dark. Now the car had too much short mid straight punch and not enough rip out of the corners.
New weight distribution. I have slowly moved weight back on this track with powerful motors and received better forward traction in return. Time to retest the theory and see if I was killing any cornering traction. During the three tests above the speed control was forward. I lost huge buckets of traction. There was less rotational inertia on the vertical axis, though. The car did go through a chicane slightly better but every where else including the sweeper the car was worse. On the sweeper the car developed a push as the front tires were overloaded compared to my normal settings. I put the weight back on the nerfwings. The speed control was a good fit there. My forward traction and performance on the sweeper returned. I could hug the inside line on the sweeper now.
Increased torsional flex top plate.
With the Tekin 3.5 geared 15/93, I had huge mid straight punch. a couple of the short straights had a little ripple in the surface. The car developed some axle tramp. This improved with thicker shock oil in the back. I suspect the frame flex or just the top plate flex from not being supported at the front caused the tramp when too much throttle was applied. Anyway, back to the standard top plate. You can see the cutaway top plate in the photo. One of the goals was to get a top loaded battery out of the deal. I did not suceed in that as well. With the top link that far forward. It would not flex and drop in place like it does on the previous pantoura based prototype.
I was making good laps by the end of the session in spite of low-medium traction.
I have obtained a consent to cut my graphite parts from Troy over at Mckunedesign.com. He makes the chassis option for a forward mounted single cell battery that is pictured in a previous post and which is available at Stormerhobbies.com. Look for some motion finally over at StranahanRC.com later in the month. This JS Pro ten kit will become available as suspension kits or a handbuilt complete unit.
Here is another pic of the JS Pro 10 kit on a CRC Gen X 10. The pic shows the fit of the big Tekin RX8 on one of the SRC side Nerf wings. I removed quite a bit of motor wire. I rebalanced left and right side weights. Due to the heavy nature of this speed control and the inability to move the battery to the right on this chassis I ended up adding 2 ounces to the car in ballast on the right side wing. Corner weights are good. The almost full battery top plate is restored to eliminate some axle tramp that I have not experienced before. I split the last gear I used and went with a 14/ 90. Hopefully I will have a little more rip out of the corners and a little less mid short straight punch as a result. This also gave me more clearance on the Panhard bar than a 15/93 which restricted movement a little.
Plans for the future, an LRP X12 3.5 soon. An LRP SPX8 when it becomes available. This is a new speed control from LRP that is supposed to do 1/8 scale and high voltage. The important spec is amps per phase has been increased to 764. This should allow it to work the low turn mods. It looks like it is in the same case as the old LRP TC edition (not the SXX). I look forward to testing this smaller, lighter than Tekin, speed control that should be up to the task of running 3.5 motors on 2S LiPo in the heat. It should remove 2-3 ounces from my car as every excess ounce on the speed control requires and additional ounce on the other side in this position.
Low ET-Thanks for the link. Here is what I think the difference will be. The octawind uses 8 wires wrapped at the same time on each of the three poles of the stator. The standard motor uses 4. I did an induction study on this type of change in the motor. Induction is a measure of how much magnetism is produced by each increment of current. The Octawind packs the wires tighter and will have more induction. The tightest wind would be a square of flat wire single. The power band will shift to higher RPM. You will have more RPM and less bottom end punch. Should work very nice in our wide pans with medium traction. Anyway that is what I predict.
OVAL NEWS: Battle Axe Offset Pod Just Released
I can't believe but that we did some pioneering work here on this thread on the offset pod. CRC has their on version now part number 190 offset Pod Kit. This includes the offset pod hubs as well as three graphite parts necessary for the conversion at a great price. $80. I will have this version available in my store in a couple weeks very slightly cheaper. I will also have my own version that was pictured earlier in the thread available in about 2-3 weeks. It will have a Heavy duty pod bottom and top plate and will be upgradable to a 3-link if you decide to do so later. These are both brand new products, The CRC offset Pod kit and my own SRC offset pod kit.
Wide Pan, Speed Control Location, Lightening, Diffuser
Work continues on the wide pan. First I have lightened it a little as it was getting porky with the Heavy Tekin. I have removed the very fine Red Aluminum GFR body posts and replaced them with plastic. I have used a very light bumper from CRC for their 1/12 scales. I am going to leave the body unreinforced for a while to reduce body weight. I am going to use a ligher weight diffuser which will be the subject of my next post.
Traction wise on medium traction outdoor asphalt I have found there is an optimum weight for a wide pan. I have found this to be about 43-44 ounces. If you run them heavier they tend to start sliding in the corners more than usual. They feel heavy. If you run them lighter though, the foams don't seem to get trough the layer of dust present as well. The car starts sliding more. This is peculiar to foam tires as my rubber tired Touring cars work better and better the lighter they are.
Second I have moved the chunky R8 Tekin speed control to a third position. I moved my center link back a little. The rear attaches to the pod center post now. I mounted the speed control center high. This allowed me to remove all ballast. Receiver is right rear on the inner wing on the edge. The transponder is left rear. Corner weights are good. Handling is good. No body holes are needed.
The position I liked best was mounted over the left rear side plate with a homemade graphite extension, It pokes through the body there which may disturb some people. It is surely cooled better there; no fan is needed. I am running the stock fan in its current location now. The LRP X12 3.5 is in for further testing on this car.
I am going to try leaving the side dams off to save weight. I left extra material behind the wheels that will have the same effect. I left a little extra width on the rear wing, a whale tail so to speak, as I had the extra material and I believe it will conform to the rules. We have a generous width spec. The wing is made from excess body material at the rear.
Front Diffuser Construction and Theory next.
Diffusers are under car devices that increase downforce. They are used in the front and the back of the newest GTP style or Lemans style cars. What a diffuser requires is a good stream of air in Laminar flow. The diffuser expands this air in a venturi or V shaped tunnel. The expansion reduces the pressure and causes the increased downforce.
Now how to get some decent front downforce on 1/10 pan. The peugeout 905 b HD body from protoform is a start. Some minor changes to the body would have astonishingly better front downforce. I have run some 1/10 pan bodies in a homemade air tunnel. Suprisingly only ounces are developed at the front. We can get pounds off the back.
Look at the figure. A is the typical Sendan body. Air passes under the front dam. The edge creates much turbulence (the round flow). This prevents maximum effectiveness.
B is a sedan body with belly pan. This is just to show you the laminar flow required of a diffuser. This would be more streamlined, have less drag than A.
C The peugeot 905 B showing the problems that it encounters. The front wing shape is nice and produces downforce. It also creates turbulence at its trailing edge that probably spoils a lot of downforce. Underneath the same problem the lip of the dam causes turbulence and spoils the laminar flow underneatch.
D My solution Add a wing under the Peugeot to eliminate the lip. Acts like the belly pan, produces laminar flow. Now curve the flow up smoothly to the part of the body aft of the built in wing. A strip of tape will help smooth the back area.
the effect on the track is large. Like adding a rear wing. A car that dances on the straight at 65 mph over the bumps is now glued down. Grip on the sweeper is much improved. It seems to even help both ends of the car as that laminar flow follows the body upward.
E The ideal solution; Reshape the pan car nose to eliminate the turbulence.
the picture shows a Lexan touring car wing trimmed to fit underneath the nose. It is mount with 5- 2 x 56 screws. I used a 4-40 mini nut for a spacer and a 2x56 nut also. I then attached it to the lip with 2 x56 nuts.
Is it worth the trouble. Hell yes. I found on a 200 mm pan that this prevented blowovers at its max speed of 57 mph on a rough track with primitive sliding kingpin front suspension. My diffuser equipped wide pan can hit 65 mph on the straight of our track.
Hey John - what about taking some ShoeGoo or something and using that to fill in the gap you are talking about on top where the front "splitter" meets the regular body. That would smooth out the turbulence creator, no? Not sure how heavy it would be. . .but it would add strength, and the 905b I had like that cracked at that spot. . .
Boomer-Thanks for the reply. I think shoe goo would add over an ounce. A filler containing a high proportion of hollow glass beads may be lighter if it would stick. Then you could work it smooth. A piece of tape would work. What would also work is to reshape the mold.
I set the track grip to medium high with sugar water. 24 lbs of sugar on the 275 x 75 foot track.
The lightening measures were effective. The wide pan worked great this Sunday. I could enter the sweeper now at high speed with no brakes. The wide pan was a few tenths faster than my electric TC which won last weeks club race. It was faster than almost all the 1/10 Nitros on the track. I need more practice with the wide pan now and it is sure to improve. The speed control in the center but up high worked well. Weight transfers well to the back for great forward traction. The rotational inertial on the vertical axis is low for good performance in the chicane. Cooling was adequate for the big Tekin R8.
The New X12 3.5 did not run like the old X12. I ended up gearing it like the Tekin at 14/90. Then it worked well and developed a little temperature to 150F after a long run. I suspect they have made changes to the motor to detune it. I still have the old can and plan to rebuild it now that I was able to remove the outer race on the inner bearing.
Just a new X12 with the original tetra wind. I suspect they have made the wire a tiny bit smaller or tinkered with base timing. Same thing happened with the original Novak 3.5. The original Novak 3.5 is truly a powerful beast at 820 W. More than one horsepower. Unfortunately I have not been able to get it to run with the Tekin RX8. Later models were detuned.
The X12 was the most powerful of my recent batch of 3.5's that I dynoed. Now this new X12, I think, is more like the Novak Ballistic 3.5 in power and RPM. 100 Watts less than the original Novaks. I needed a 14\90 gear to get some zip into it.
The new wide pan just keeps getting better as I tune it better to the track.
Roll Center Adjustment
The roll center on a dual A-arm suspension can be changed at any of the four A-arm pivots. The easiest one to tinker with on this suspension is the lower outer A-arm pivots. I moved one spacer (.075 inch) from above the A-arm to below the A-arm. Outer pivot is moved up. This lowers the roll center. On the track the front steering grip changed very predictably. It was increased. On a sliding kingpin strut this is a difficult change to make for as it turns out, changing wheel camber has a big effect on roll center. Not so on a dual A-arm suspension.
This front suspension uses the very familiar Associated system to change caster. Reactive caster blocks can even be used though I have not found a need too. All the washers in the back tilts the kingpin back and adds 6 degrees of caster. A quick measure with a gauge agreed. Camber is also adjusted with the familiar associated turnbuckle on the upper arm. In this case the roll center is not changed with this camber adjustment.
Rear Axle Width
I have made optional front A-arm extensions to give a wider front width. I have not found this necessary on a road coarse. The 216 mm width selected fits the standard wide pan car bodies extremely well. At the rear you can add a couple spacers to bring the width out from about 225 mm stock to 235 mm. This should cut a little rear cornering grip.
The car is driving extremely well now. I geared it 13/90 for softer out of corner punch. I drove the last pack without any incidents of poor driving. I should get some lap times in the next week or so.
I installed an approximately 2 lb/inch spring. Same as on the front now. This kept the chassis from rubbing a Nerf wing in roll on the sweeper and from squatting and rubbing on the bumps from the large down pressure at 65 mph on the straight. It drove better with these heavy springs. .047 inch diameter, .375 inch ID, and 5 coils.
Long Right Hand Hubs
I measured some common right side long hubs. The standard CRC hub with adapter is the longest at 40 mm, Hyperdrive (offset hub) 36 mm, the just released CRC offset Hub 36 mm. This makes the adapter the best for this 235 mm application and keeps you from having to buy a wide pan axle. The extra hub width keeps the pinion closer to the motor when running 235 mm at the rear.
I noted a recent X 12 3.5 was slightly low on power and it had become more punchy when compared to a early model of the same motor. I measured the rotor and it's a 12.5 mm. (medium). I have a 12.0 replacement rotor installed in the older motor now. The rotor difference may have been the change with the new motor as a new 3.0 on the box noted a change from 12.0 mm to the 12.5 rotor. The bigger rotor gives a few thousand less RPM, less max power, but more bottom end power and punch. Another track test and I will know more about the old (early) X12 motor which I liked a lot in the wide pan.
The Dual A-arm Front end in the photos will be an alternative to the graphite extensions that CRC makes to move the sliding kingpin strut suspension out to make a wide pan. I have done some more modifications to my prototype so you will have a couple of choices. This suspension can be mounted to the original mounting holes. A small trim of the "chassis ears" will be required for clearance. The PDF file shows the trim line. In this case any stock bumper for the battle Axe or Gen X 10 will fit.
I have lengthened my prototype by 1/4 inch over stock which is really more suitable to a long track. With the bit of "chassis ear" that remains a droop screw that is incorporated into my chassis extension will work. Easy droop adjustment by the turn of a screw. Easy ride height adjustment at the shock collar (or by shimming four screws).
Dual A-arm Roll center
The photo shows the setup that I used to measure the roll center at the front and put it at the ground. This required moving my outer upper arms down, and outer lower arms up giving me an outboard instant center. Measurement of each pivot from the metal blocks supporting the axles are taken with a dial caliper. The roll center is then calculated by a spreadsheet that I wrote for dual A arm suspension. I have it available for the touring car. Send a request to JohnStranahan@aol.com. Steering improved markedly with the low roll center. I was pleased and will ship the front end like this. The roll center is easy to raise at either upper or lower arm end by moving shims.
Outer Upper A-arm, up, down
roll center, higher, lower
Outer Lower A-arm, Up, down
roll center, lower, higher
Inner Upper (upper deck), Up, down
Roll center, Lower, Higher
Roll center lower give a softer front end with more grip.
A higher roll center stiffens the front end and reduces grip.
The second photo shows the new chassis format. I have removed the delicate front ears off the chassis and use a center screw and the center body post to hold the bumper. This RPM bumper with a few mods fits nicely.
Drill and Trim Template JS Pro 10 conversion to CRC Gen X 10
Finally the drill and trim template in a .PDF file that will come with the car. Note again you do not need to drill, only if you want the long chassis option. You do need to make a small trim of the middle ears off the chassis for clearance to the lower A-arm. Note the low center of gravity to the bulk of the lower A-arms.
I provide this drill and trim option for $5.00 on your chassis or you can buy a modified chassis from me at a reasonable price.
Battle Axe News
I ordered in a few Battle Axe chassis to have them available for those wanting 3-link or dual A-arms on their battle Axe with a predrilled chassis.
Lo and behold a side slot exists now for a cross wrap of battery tape. That is a great thing! I suggested same a while back in this thread. My Battle Axe already has a home made one. You can slot your own. Drill a couple of holes and then cut the slot in between with the Dremmel cutoff wheel.
The beauty of the customized JS Pro 200 Battle Axe will be that it has more mechanical traction allowing you to use harder than normal tires for lower rolling friction. This is important in 1 cell racing.