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Old 06-20-2008, 12:04 PM   #121
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Sadly enough I'm from Europe so shipping a motor to you would be somewhat costly.. GM has both types of winds in their line-up and they're all sensored.

If I was from your neighbourhood, I'd give you my 9T delta to test maybe someone else can provide you with something??
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Old 06-20-2008, 01:24 PM   #122
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John, From the Start menu, choose Run, then type in cmd and hit enter. This should bring up a black window with a dos prompt. Type in - cd c:\facts. Your prompt should now read - C:\FACTS.

Type in - Facts.exe.

The software should now be running. Once you're done playing around and end up back at the dos prompt, you can either type exit or hit the X in the upper right hand of the window to close it.
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Old 06-20-2008, 02:38 PM   #123
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Will do

Run Line, Average RPM
One of the benefits of the latest Facts Machine Software is some help with gearing. I ran some numbers through the calculator that were of interest rather than using the software which I do not have.

Our run line is just short of 175 feet by a couple of feet. Average laps are 4.4 s. Average speed is 173ft/4.4s = 39.3 (ft/s) (27 mph) or 471.6 in/s.
If I divide by rollout I will get my average RPM.

(471.6 in/s)/3.2 in/rev) = 147.3 rev/sec

change to RPM

147.3 rev/s x 60 s/m = 88425 RPM or 8.8 kRPM

So where is that in relation to my power peak with the fat rotor (8.9 kRPM).
About as close as possible. I am getting the most out of the motor. If I change to the small rotor I am going to gear lower as calculated in a previous post above. Note I am also coming off the track at 175F but on a 140F track. Motor temperature is somewhat useful for gearing but only if your track temp is the same as that other guy that is giving you temp advice.

John

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Old 06-20-2008, 11:52 PM   #124
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Gearing an Electric Motor
I thought I would try to explain why it's important to get the gears at the right ratio, on road, or on the oval. First take a look at the left side graph. This is output from the Fantom Dyno, through the Fantom power supply, for a Novak EBX 13.5 brushless motor. The graph plots Amp draw vs RPM. All I want you to notice is the shape. The graph is highest on the left at low RPM. If the motor stays in this range it overheats. At the right the line is low. The motor pulls few amps at high RPM. It therefore runs cool at high RPM. Amp draw is highest with the motor stopped (right at the start of a race).

Next take a look at the right hand graph which plots power vs RPM for the same dyno run. Notice we have a hump shaped curve. Power peaks at mid RPM. The point of carefully gearing a motor is to try and keep it near its power peak a greater percentage of the time. There are sometimes heat considerations that will foil our attempt but you see my point.

If we gear the oval motor to a higher rollout. It is going to run at fewer RPMs. It is going to draw more current. If we are to the right, of the humps top, this is a good move. If we are too the left of the top you will just heat the motor more and produce less effective power.

I was interested to see these brushless motor curves to see if they were dramatically different than brushed. Maybe the hump was broader or something like that, but no, they are remarkably similar. The proper gearing is still going to give you an edge.

The numbers on these graphs are low for reasons I stated previously having to do with the LRP speed control.

Eventually you just develop a gut feel for what a good ratio is by looking at the car accelerate out of the slow corners of the track and onto the straight. For the beginner there is no substitute for advice from someone experienced with their particular combination as a starting point and then lap times after that. A dyno is not needed just a nice thing to toy with.
Attached Thumbnails
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-amps-vs-vs-rpm-ebx-13-5001.jpg   CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-power-vs-rpm-ebx-13-5002.jpg  

Last edited by John Stranahan; 06-21-2008 at 01:09 PM.
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Old 06-21-2008, 04:36 AM   #125
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Hi John

I remember reading some time ago re voltage of a lipo pack when fully charged, i have 3 chargers, after the pack is charged i am left with different resting voltages.

8.32
8.36
8.43

Is it meant to peak at 8.40? and will there be any damage to the packs charging them to 8.43? I wonder if there is any performance advantage.
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Old 06-21-2008, 08:22 AM   #126
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One thing we found using the Facts Oval Gearing facility through the years was that you couldn't use the actual runline to achieve accurate/realistic gearing from the program. The reasoning for this was that your rear tires slip from time to time, so in reality they may have to turn the equivalent of 181 ft, to carry your car around the optimum 175 ft runline.

To compensate for this, we would take a well tuned car with a specific motor and keep on adjusting the runline in the program, until it gave us the proper gearing/rollout we had already predeterrmined through trial and error. Once this was established, the results from the Facts program were much more reliable/accurate.

You may wish to apply this theory in your manual calculations as well.
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Old 06-21-2008, 01:19 PM   #127
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Besercoe- I find little performance difference between a fully charged and a 95% charged pack. I can't tell the difference in the car. I doubt you would see a peformance difference on your fully charged packs. There is another post that noted a high finish charge with a Scorpion Charger. I imagine these differences are the result of normal variation between electronic components that are used to hold that final 8.40 Voltage. Your results are exact enough. That finish Voltage should more properly be stated 8.40 + .05 V or something similar.

The LiPo packs stay like new longer if you charge at 1C rather than faster.

John


Barry-I noticed that fudge factor in the gearing routine of the Fantom Dyno. I did put some numbers in it for a look see. My gearing is more determined by seat of the pants, so I imagine that a fudge factor is built in. I did not exactly measure the run line. I do notice that my car starts being better able to chase down and pass the competition later in the run. If I add one more tooth to the pinion, I notice the car slows later in the run.

Racing tomorrow!

John

Last edited by John Stranahan; 06-21-2008 at 10:09 PM.
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Old 06-23-2008, 12:17 AM   #128
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I did not finish the race. It was 97F and we were racing with four to Five Nitro heats which overly extended my health. Anyway. I did run two heats. The first heat with GRP's I did not have enough traction. I had not prepped the track myself so it was a little different. I was actually spinning the back tires on corner exit. Once in a while I would roll the throttle on right and the car would scoot forward more rapidly than usual. I was using the small rotor geared lower in the 13.5. I had a bad crash where I spun and then a car hit me head on. It sheared the three aluminum bumper screws. These are now steel. This also damaged my spur which went unoticed so I thermalled in the second heat followed by thermalling myself. The new top plate sans hole held up well.


Here is Ricks Car with his electronics ready for a return trip. I thought you might want to see the electronics install which ended up fairly neat.

Also note the JR servo with a small servo saver. My medium Kimbrough servo saver had the incorrect spline. It is better suited. I did reinforce this servo saver with a nice graphite piece that CRC sells for the arm. Also I found some nice Blue decorative washers as this servo needed some washers. The holes were larger than the other two servos that had been on the car.

Here is a list of upgrades we made to the car. Most of these are to increase the ruggedness outdoors.


3344 Titanium Pivot Ball
3317 Ti Steering Tie Rod Gen X
1251 steering block front end (I think these are the little graphite arms)
Servo Saver reinforcement
Carbide diff balls
lightweight diff washers
Blue Aluminum Diff Nylock nut
Steel Center pivot ball from RC10L2 Tplate pivots
1/4 inch red Aluminum Axle Spacer from a KSG set

https://www.ssl-stormerhobbies.com/cgi-bin/seekpart.pl?src=ns&pn=LOSA3078
thin Belleville washers
https://www.ssl-stormerhobbies.com/cgi-bin/seekpart.pl?src=ns&pn=LOSA6009
Steel ball nuts
https://www.ssl-stormerhobbies.com/cgi-bin/seekpart.pl?src=ns&pn=ASC3858
Steel ball studs

Rick-Thanks a lot. I appreciated the loan. I'll send you a PM with details. Very nice car!
John
Attached Thumbnails
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-crc-battle-axe-return-001.jpg   CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-crc-battle-axe-jr-servo-resized.jpg  

Last edited by John Stranahan; 06-23-2008 at 12:16 PM.
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Old 06-23-2008, 03:44 AM   #129
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John,

It's been my pleasure.

Still waiting for the setup sheets from Frank at CRC. At lease I have good starting point now since I can't get it from CRC. And I was thinking about buying the Gen 10??????????

If there is anything else I can do for you, let me know.

You have a PM.

Rick


Quote:
Originally Posted by John Stranahan View Post
I did not finish the race. It was 97F and we were racing with four to Five Nitro heats which overly extended my health. Anyway. I did run two heats. The first heat with GRP's I did not have enough traction. I had not prepped the track myself so it was a little different. I was actually spinning the back tires on corner exit. Once in a while I would roll the throttle on right and the car would scoot forward more rapidly than usual. I was using the small rotor geared lower in the 13.5. I had a bad crash where I spun and then a car hit me head on. It sheared the three aluminum bumper screws. These are now steel. This also damaged my spur which went unoticed so I thermalled in the second heat followed by thermalling myself. The new top plate sans hole held up well.


Here is Ricks Car with his electronics ready for a return trip. I thought you might want to see the electronics install which ended up fairly neat.

Also note the JR servo with a small servo saver. My medium Kimbrough servo saver had the incorrect spline. It is better suited. I did reinforce this servo saver with a nice graphite piece that CRC sells for the arm. Also I found some nice Blue decorative washers as this servo needed some washers. The holes were larger than the other two servos that been on the car.

Here is a list of upgrades we made to the car. Most of these are to increase the ruggedness outdoors.


3344 Titanium Pivot Ball
3317 Ti Steering Tie Rod Gen X
1251 steering block front end (I think these are the little graphite arms)
Servo Saver reinforcement
Carbide diff balls
lightweight diff washers
Blue Aluminum Diff Nylock nut
Steel Center pivot ball from RC10L2 Tplate pivots
1/4 inch red Aluminum Axle Spacer from a KSG set

https://www.ssl-stormerhobbies.com/cgi-bin/seekpart.pl?src=ns&pn=LOSA3078
thin Belleville washers
https://www.ssl-stormerhobbies.com/cgi-bin/seekpart.pl?src=ns&pn=LOSA6009
Steel ball nuts
https://www.ssl-stormerhobbies.com/cgi-bin/seekpart.pl?src=ns&pn=ASC3858
Steel ball studs

Rick-Thanks a lot. I appreciated the loan. I'll send you a PM with details. Very nice car!
John
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Old 06-23-2008, 03:30 PM   #130
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Hi John

I was wondering is it possible to test the different efficiencies of the different rotors. I know it's no so important for stock but could be useful for mod?.

Cheers
Tim
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Old 06-23-2008, 05:25 PM   #131
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Tim-I'll take a look through my data. Your answer may be there.


3-Link Oval Car
Let me give you a little history of this car. My experience just previous to oval was on-road pan car with 6 cells and powerful motors. I found through a long series of experiments some weaknesses of typical pan cars that could be overcome with different style of supension or in some cases slight mods of the current suspension.

Flying on the straight
Some of the newer pan car guys have already experienced this. One solution is not to run powerful motors. Even 6 cell super stock with a 10.5 apparently has this problem with a GT body on a long enough outdoor track. Another solution I found after a long series of steps trying to get a strut suspension to work on a bumpy straight is a double front A-arm suspension with a front shock. My 3-link cars both have this. Even just tacking RC18T shocks onto the front of the associated suspension worked up to a 4.5 six cell on our straight. That's about 47 mph. I am hitting 53 mph with the 3.5 motor. The guys in Europe solve this problem by having smooth tracks, I believe. Some other things that are helpful are generous front suspension travel. At least 6 mm. Goo, that becomes nasty outdoors, on the front kingpins. A soft air dam made from electrical tape that can drag the track on the worst bumps. A high downforce body. Believe it or not the Wide Pan Nissan 300z GT body from McAllister is probably best at preventing blowovers. This weakness was responsible for elimination of pan car Nats. It was thought a safety issue.

Rear End Patter and loss of forward traction
Another problem I had on a bumpy track is rear end patter. This happens when the car hits bumps that only affect one side of the car. When this happens the rear tires are slow to return to ground. You can hear the car patter, the motor is at top speed, but the cars speed does not match. I solved this problem on the car by using a 3 link rear suspension which is a bit more modern type of rear solid axle suspension. Each rear tire has its own shock and spring to quickly direct it back to ground. Top speeds are about 5 mph greater on our straight compared to a normal pan car. Again if the track is very smooth you don't have this problem.

Left Down Tweak adjustment.
Now I am on the oval. I did not intend this design to be good on the oval but it was. Not better on the oval than current oval cars, but as good. One piece that was missing is a way to get sufficient left down tweak on the car. After a few months experience this seems to be a critical adjustment. What I did is added the third horizontal shock in the photo. I can easily get my 10 ounces of left down tweak. Note my two rear vertical shocks now have similar preload. Previously the right rear shock was completely unloaded with the body off. That limited the amount of adjustment available. I'll test the new arrangement over the next few weeks. This new shock could be placed lower with a different top plate in the standard configuration. It should work well enough where I placed it.

I also have a test planned on the wide pan on-road car if the weather cooperates Tuesday.


Left pic is my new wedge control shock. Right Pic is a Powell wide pan conversion for a Pantoura with home added front shocks. Note he also sells a very nice wide pan conversion for an RC10 L3T or similar type of pan cars. This does not include rear axle parts which are available from I.R.S.


Tim- Here are the efficiency numbers. I only have one test on each which showed efficiency.

Small Sintered Rotor in a SS13.5 77.3%
Large Sintered Rotor in a SS13.5 78.7 %

That is probably too close to call for sure but is the trend I would expect.

My old P2K2 brushed motor by comparison is 49.0 %
Attached Thumbnails
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-3-link-wedge-control-resized.jpg   CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-powell-chassis-front-006-resized.jpg  

Last edited by John Stranahan; 06-23-2008 at 06:17 PM.
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Old 06-24-2008, 06:26 AM   #132
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Quote:
Tim- Here are the efficiency numbers. I only have one test on each which showed efficiency.

Small Sintered Rotor in a SS13.5 77.3%
Large Sintered Rotor in a SS13.5 78.7 %

That is probably too close to call for sure but is the trend I would expect.

My old P2K2 brushed motor by comparison is 49.0 %
Cheers John

That's what i would have thought too. But it's nice to have numbers to back up the theory.

Cheers
Tim
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Old 06-24-2008, 07:20 AM   #133
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I run 5 cell mod on large, 1/8 tracks. As you probably know runtime is a big issue in these conditions.

Theoretically a big rotor should produce more HP from same current, since the distance between the rotor and can is smaller.

Nevertheless i have found in my limited testing that a smaller rotor usually is more economic. It will have less drag wich means you can let it roll more into corners. This is specially true for big, flowing tracks.


Most of the other mod drivers are doing the same as me: small rotors and less timing for more runtime

Last edited by Itchy; 06-24-2008 at 07:21 AM. Reason: spelling
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Old 06-24-2008, 11:30 AM   #134
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note I have added some red text to my previous post,

Itchy-Thanks for the post.

I have not seen theory that says a big rotor should have more power. It made sense to me though so I used it for a while on the oval. The dyno says otherwise. It says the small rotor has more power in a 13.5. There are a lot of factors that affect motor power. One of these is the reverse voltage produced. It seems that motors and winds with less reverse voltage (3.5s and 3.0s) produce more power. A big rotor acts a lot like putting on an extra wind or 1/2 wind on the motor. There is more reverse voltage, less power, fewer RPM, slightly more efficiency. These are clear from the dyno results. That said I prefer the small rotor in my wide pan on road as well. The power band matches the traction available better. Now if I can hook up that small rotor and gear it properly on the oval, I may be a tad faster.

John
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Old 06-24-2008, 01:36 PM   #135
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Novak 3.5 large vs small rotor
by popular demand. I did some more dyno testing. First order of buisness was the flywheel had about .012 inch side to side wobble from wear. I thought this was too much for a 3.5. Careful application of a prick punch several times near the hole on the worn edges reduced this to about .002 on an dial indicator. This will reduce wobble vibration and stress on the machine. I used the Fantom power supply run by a small 12V gell cell battery. I was getting a good blue full throttle light on the sphere speed control. The power supply by itself will limit the huge amperage that this motor can draw. Fortunately with this motor, efficiency was peaking in the 20,000 RPM range at 5.0 Volts, so I got a good look at peak efficiency. I took 3 runs each on the small and the large rotor. Looking at the raw numbers the small rotor was .186 and the large .183 just averaging the highest readings on the 3 runs. This is inconclusive.

The graphs shows only two of these runs. The first run with the small rotor and the first run with the large rotor.
In the blue are the data points for the small rotor. There are some .18 at the highest point. This is 18% efficiency. Thats why these motors run hot.
The large rotor reached .18 but not quite as long as the small rotor looking at the green data points.
I smoothed the data by adding a polynomial trend line. The green lines peak shows the peak efficiency occuring earlier in the RPM curve but about the same efficiency as the small rotor.

I declare a tie in efficiency, but if you run at lower RPM on a smaller track the big rotor wins.

This motor is really screaming on the dyno. I made a 3/4 inch wood scattershield to place on top in case of a flywheel explosion or motor shaft breakage. The better balance was really appreciated by removing the wobble.

Pic Green large rotor, Blue small rotor both in a Novak 3.5 R, my favorite wide pan motor.

John
Attached Thumbnails
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks-efficiency-vs-rpm-novak-3-5003.jpg  
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