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Old 06-17-2007, 02:09 PM   #1456
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The Mamba would only run two packs in series for 30 seconds with a Novak 6.5 R motor; it is rated for 3s LiPo. The GTB is only rated for 2S LiPo, so I suspect the run time would be less. I would not try it. I was already getting some short duration shutdowns yesterday at the track of some type with only one battery. I added the Spectrum capacitor to see if that was it. I will need another test at the track. My speed runs are only for entertainment to test the surface for Nick. I think I can get up to 100mph without too many changes. We will see. It looked fast. I had no trouble with the bigger gear. No times yet.
Nick has an onboard speed sensor now but it rained before we spooled his chassis up very fast.
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Old 06-17-2007, 03:35 PM   #1457
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wouldn't two of your packs in series be 4S?
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Old 06-17-2007, 04:16 PM   #1458
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TallyRC-yes. I overdrove The Mamba on a suggestion. 4s had worked out on some T-max type vehicles even though its only rated 3S. 4s did not work out on my pan with a 6.5 R. It may have with a 7.5 or 8.5. The castle creations speed control that Nick is using Courtesy of Castle Creations will handle the higher voltage (12s, 44.4 Volts) and about 100 amps. He will be running 12s soon.

I'll have a radar gun for our next test. We should be able to get some numbers.

John

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Old 06-18-2007, 11:00 PM   #1459
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Power Capacitor on Novak GTB
Here is an interesting link at Novak that answers some questions that I had like what is on the little printed circuit board attached to the main power capacitor. Well there are two additional types of devices. One protects the GTB from voltage spikes (I imagine quite a spike is created when you plug in a LiPo; this often shuts down my Astroflight charger and requires a shut down to reboot it). The second type are just small capacitors to filter out radio interference.

I have this huge 8200uF Novak Power Capacitor looking for a home. After reading the link it appears that more capacitance would help things out; Lower ripple, lower GTB temp. Since my unit cut out twice last road race session I have made several changes. I have added a spectrum capacitor (low voltage here can shut things down). I have turned off the low voltage LiPo cutoff in the GTB program. Tempory low voltage at the GTB which may not exist at the batteries due to the 14 gauge wires may shut things down. Note that 12 gauge will just make the speed control run hotter and shut down more often. I have added the bigger 8200 uFpower capacitor in tandem with the factory 5600uF. I put some big shrink wrap over the pair.

You can also see that the blue motor temp sensor wire is unplugged at the GTB. The motor was only 140F so I don't know why things were cutting out yet.
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-power-cap-resized.jpg  

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Old 06-19-2007, 09:10 AM   #1460
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When I was struggling with thermal shutdowns I also tried cutting the blue sensor wire. This caused runaways at the end of the straight at the moment the unit would normally thermally shut down. NOT GOOD!
I later found my thermal problems came from a busted motor bearing and habe placed the blue wire back.
Since then, no thermal issues.
I'm running a 12T pinion with a 90T spur all the time.
Also with 13/90 I had no thermal issues with proper bearings.

Edit:
I am also looking into alternative capacitor solutions, since my cap now has a large flat spot after it poking through a chassis opening for 1 run LOL.
I'm going to use 10 regular 10V 470 uF Elco's in paralel along with the stock novak surge supressors and high frequency decoupling caps.

I already found that always when a brushless thermals, the Cap is very very hot. The temperatures are probably related.
Perhaps that when the cap becomes hot it functions less ideal, and therefore the motor receives a less "clean" signal to the stator (e.g. triangle instead of sinus). Such a signal could make the motor run at lower efficiency and therefore warm up more.
It's all speculation though. I have no way to measure the power signals, especially not during a run.

More capacity could improve this situation though.
Also more capacity with the right "speed" (of charging and discharging) -> more smaller capacitors instead of one larger capacitor could help.
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Old 06-19-2007, 10:23 AM   #1461
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Mathijs-There is some discussion of capacitors on the New Novak Brushless thread. The Novak rep notes that they choose only capacitors with very low ESR (internal resistance). In other words not all capacitors of the same microfarad rating are suitable. Keep this in mind. They also suggest that the capacitors might need to be cooled.
I have removed the blue wire before with no runaway problem. Nor did did I have one this time. I have even seen Novak reccomend this in some situations. Runaway is a very odd behavior. I can see where it would cause a lot of damage.
My car does tend to runaway when it is out of radio range or when I turn the radio off first. I wonder if this is what you experienced; a low voltage situation that caused loss of reception.

I am using a new sealed front bearing. The seal may be the cause of overheating. Too soon to tell.

John

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Old 06-19-2007, 10:27 AM   #1462
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Using 10 smaller powercaps instead of one large powercap in general is a good idea but you have to make sure you are using very good Low-ESR caps. Any standard caps from the electronic store doesnīt work for our purpose. At least they have to meet the extended temperature range of 105°C instead of the usual 85°C what usually means Low-ESR also but you have to look for other data also. Digi-Key sell caps like that, Nichicon and Rubycon are some major brands here. But in the end itīs not the capacity what really matters but high current delivery and low resistance. Also itīs very important using short and thick wire for connecting, the very thin wires of the caps are not working. I think 14-16 AWG wire and up to 1" length is OK.

GM just released a special PCB using seven 470uF Low-ESR caps what can be soldered right to the solderposts of a Genius brushless ESC. I think you can use this also for other ESC.

All of the brushless ESC are generating square wave voltage not sinus. An ESC generating sinus would be way bigger and generating much higher temperature as the current ones.
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Old 06-19-2007, 10:32 AM   #1463
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This is the special PCB with powercaps made by GM Racing
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Old 06-19-2007, 12:29 PM   #1464
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Good input, thanks!
Anyone have a good adress for suitable caps?
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Old 06-19-2007, 07:15 PM   #1465
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Hi guys,
I ran my RC10L last race meeting, I didn't have a brushless system to run in it so i ran a 12 turn with seven cells. The car handled pretty well in the first pratise session but it was a little touchy for my liking so i changed the rear tyres from magenta to pink and the car was then on rails.
I ran a 4.09 FDR (90/22) with the 12x1 and the speed down the straight was phenomenal, the cells were really old IB3800's. The motor came in at about 85 degrees C, pretty good considering how it was running. The quickest time for my touring car was 20.2 seconds and the quickest time for my pan was 20.4 seconds (quickest for the nitro's was mid 18's), keeping in mind the touring car cuts in to a chicane in the middle of the back straight. The pan was still very quick considering it was it's first run and it didn't have the power the touring car did. I imagine the pan would be in the mid to low 18's with a 3.5 some good cells and maybe a better setup. I'll post how the car goes next meeting when i have a brushless system for it. Heres a short vid of the pan and the touring car. http://www.youtube.com/watch?v=j4ein0Jcsac
Thanks, Drew.
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-setup.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-team.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-front-far.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-front.jpg  
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Old 06-19-2007, 07:49 PM   #1466
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Thanks for the report Drew. Great Video. You will only get faster from here on. Tell us about your body and tire prep. Really nice paint!

Mathijs-I have no capacitor source except from Novak. That GM rack of capacitors looks like it might fit our power wires. If someone has one give us a dimension between centers of the two solder terminals. Thanks for telling us your gear ratios with the 3.5R.


I have my GTB 3.5R in hand now. I have plenty of hard coated pinions. I will test it tomorrow weather permitting. My bearings on the 4.5R that gave me some thermal or low voltage cutouts are in very good shape. I am back in the high speed buisiness. It is going to be really hot later this week. I will be a good test the new capacitor setup.
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Old 06-19-2007, 07:57 PM   #1467
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Drew, I've got a beautiful old DA graphite chassis for the 10L I've been wanting to build up and just never got around to it. Seeing yours makes me think about it again Love the Trinity front end you have on it. I was thinking on using a newer rear pod/t-plate on mine and 3 shocks or the old Cheetah rear pod that used 4 pivot balls with 3 shocks. I know where I can get some old Cheetah t-plates but the rear pod plates I'll have to custom make myself.
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Old 06-19-2007, 08:02 PM   #1468
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The body is just a lola body made for 235mm nitro cars http://www2.towerhobbies.com/cgi-bin...&I=LXZY95&P=SM. I don't really have any tire prep (traction compounds if thats what you meant) as most of the clubs I race my touring car at don't allow it. I used tire warmers before each race (they didn't fit the massive back tires properly lol) and that helped a lot with the forward bit.
Thanks, Drew.
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Old 06-19-2007, 09:06 PM   #1469
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Drew-Thanks for the additional info. Nice to gradually discover the history of the bits on the car. I did not recognize that Trinity front end as a 10L piece in your previous pic.
I have one of those bodies on the shelf. I should have recognized it. It is a bit wide in the front for a pan car, but it looks like it handled well from the video. I imagine that your pan car front end is about 212 mm like the almost virgin 10L that I measured. Mine also had a viscous disk in the back instead of side shocks. I wonder if the rear side shocks were added later as well.
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Old 06-19-2007, 09:16 PM   #1470
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Yeah i think so, I have a viscous disk with it but considering how it's handling it would probably be a good idea not to run it.
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