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  #1  
Old 07-16-2006, 10:48 PM
ccarey75
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GP1100's and a brushless 400

I have a brushless 400-size (Warp4 2-turn) motor in my micro RS4 and i've had a pretty interesting time of it trying to make it run properly.

motor: Warp4 2-turn BL (400 size)
esc: Mamba-25
cells: 9x GP100
pinion: 24T (largest i have so far tried) / 20T (current)

It all looks sweet but I was buggered if i could get it to run right. A friend of mine (adamc) got it going initially and it seemed to run more-or-less ok but it was a bit glitchy and tended to stutter at low-rpm. Stuttering at high (max) rpm was less pronounced but still prevalent.

Many people have kindly offered advice as to what the issue was likely to be (most pointed to either the esc or the cells being unable to supply enough current). The ESC gets pretty damn hot and very quickly so we considered overheating / overgearing might be the issue. The last possibility was a faulty receiver but by the time i got around to testing this I had my answer.

I was a little reluctant (from a sheer cost perspective) to replace either component until I was sure what the deal was so I started conducting a few tests with the equipment I had available. I'm sure there are more scientific ways of going about this but here's what I found.

All the tests below were conducted with the car stationary (wheels free spinning). Each run lasted 10 seconds (on the netball courts where we run the car is out of sight in less time than that anyway)

HEAT
- a 10 second run at max throttle puts the ESC at 60 degrees C (according to my infra-red thermometer). From what information i've been able to find online that's close to the maximum operating temp for the unit but should be safe. This test was done running the 24T pinion and the wheels spinning freely so it will probably get somewhat hotter under real load (but some air flow may compensate a bit).

VOLTAGE DROP
- measuring the voltage drop at max-rpm was a bit of a surprise. A fully charged pack hot off the charger sits at around 11.8V. At full throttle this drops to around 7.5V. I had thought the GP1100's would stand up a little better than this. It's possible that the pack is faulty but I don't know how to test this beyond measuring each cell voltage (all around 1.3V give or take 0.02V).

Either way the ESC has the cutoff set at 5V - that is it shuts down if the voltage dips below 5V. I know I can disable this setting but it seemed irrelevant if the voltage was above that anyway.

CURRENT
- All the equipment to effectively measure this seemed very expensive (ie more expensive than just buying all new components and hoping for the best). I finally settled on a kit clamp-meter from Jaycar which I'm quite happy with for $30.

This is where it got interesting for me - I had a 3S (11.1V) 1800 LiPo pack hanging around so I figured i'd use this as a comparison against the GP1100 pack.

The best measurement I could get from the GP1100 pack was around 15A. I say "the best measurement" because the stuttering caused the current to fluctuate fairly wildly making it difficult to get an accurate reading. The meter was effectively measuring a series of short bursts rather than a continuous figure.

By comparison the LiPo pack managed a steady 27A. Interestingly enough the stuttering was completely eliminated! The thing is as sooth as silk through the whole throttle range.

RPM was a fair bit higher with the LiPo (measured with one of those venom speed meter gadgets) so I assume voltage drop wasn't as extreme but I didn't get a reading on it (time was getting away from me by this stage)

CONCLUSION
I'm going to replace the battery pack and see how that goes - having had such a nice result from the LiPo I'm leaning toward just ditching the NiMH cells altogether but the chassis is nicely cut out for them so I will continue to agonise over that for a while.

There exists the possibility that the GP1100 pack is just dead and that's why it's not working properly. I've read a bunch of reports of people managing very high current draws out of these cells (and the IB1300 equivalents).

If anyone's got some advice on how I can test for this definitively I'm all ears!

-CC
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  #2  
Old 07-16-2006, 11:05 PM
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I really think its the cells.....there not supplying enough current or amps to the motor....try going to bigger cells.....and welcome to the boards man.....
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Last edited by alfred; 07-16-2006 at 11:10 PM.
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  #3  
Old 07-16-2006, 11:32 PM
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Thanks, alfred - this thread is actually a follow-up from this one posted by adamc (same car)

original thread

I originally ruled out the cells as the issue on the basis that Roleof seems to have no trouble getting high current out of them with his ESC but certainly they do seem to be MY problem for whatever reason.

Adam tried his SC1700's (sub-c) and still had a bit of a glitch happening but that was before we tried upgrading the firmware on the mamba etc. I haven't tried sub-c's since (that would be an interesting test)

Do you happen to know of a reliable test for determining whether a pack is dead? I think that's the last piece of mind I need to give up and go LiPo
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Old 07-16-2006, 11:34 PM
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what kind of charger do you have.....you can check out the charge rate and voltage on the charger read out....cells do go bad if the load on them is just too high......and i think the motor Roelof uses is a 300bl motor.......but then again could be wrong. At what amps and mv are you charging the batts at. Usually a dead pack will hold a charge for a short time or not at all......the best way for me to test this is too run it in your model, and see how long or short the runtimes are. And as for the glitching problem what radio gear are you using....Am or Fm.....try changing out the crystal to a different freq and see if that helps.
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Last edited by alfred; 07-16-2006 at 11:43 PM.
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Old 07-16-2006, 11:58 PM
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I have a "Swallow Advance" charger - I usually set the charge rate to 2C (2.2A - not sure about voltage but it's automatically sensed by the device i think) which I'm lead to believe is fine for those cells. They don't even get warm when charged at that current.

Runtime *was* ok a few weeks ago but i snapped one of the battery bars off in a crash and in repairing it i may have buggered a cell (runtime seems a lot shorter now so if that's a good indicator as you suggest then it would seem to fit)

glitchy symptoms pre-date damage to the pack though.

As I mentioned in the post I haven't messed around with the radio gear as yet (beyond ensuring that the antenna and signal cables are well away from the power source and the motor) since the thing doesn't glitch *at all* with a LiPo power source. (for reference, though it's a 27MHz AM radio).
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  #6  
Old 07-17-2006, 12:03 AM
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You should charge GP's at 1,1.5, and 2amps, you should never really go over 2 though......and i use 40mv for a 6cell pack.......you might want to try another battery pack and see where that takes you......I know lipos are expensive but you should try to get your system up and running on nimh batts first....since you now know that its the battery causing your problem, ask your buddy Adam to loan you a batt and see if that helps.
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Old 07-17-2006, 12:09 AM
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So you reckon it's worth the investment on alternate NiMH batts? I haven't been able to find a definitive answer to "can the GP1100 supply 30A continuous"...

Perhaps the IB1300 is a better bet?
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Old 07-17-2006, 12:11 AM
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Hi Alfred,

We've tried the pack from my sleeper in the car already

havent tried with the cp1700 pack since the firmware change though.

Chris, gimme the 9 cell pack when i see you next and i'll try it in DA's sleeper, that'll tell us if the pack is toast. gotta get a pinion for it 1st tho

mount up the back end of the sleeper to your x3 and see how it goes too.

From what Chris told me about the testing between the 2 and my experiences with the car, it sounds like he's had major difference with the lipo pack in there. It came out of a heli that had similar spec / sized motor and esc combo.

Soooo, I guess the easiest way to get it going properly is to find a 3s lipo that can supply enough current (similar spec to the heli one) that will fit the sleeper chassis best.
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  #9  
Old 07-17-2006, 12:12 AM
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The gp's are a high current cell.....they can do 30amps but not continuously..... you might want to go with a couple of sub c cells.....they might just do the trick to get your ride on the road with no problems.
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Last edited by alfred; 07-17-2006 at 12:16 AM.
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  #10  
Old 07-17-2006, 12:17 AM
ccarey75
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I'll run a quick test tonight and see what the voltage drop on the lipo pack is under load. I'll try the SC1700 pack as well and see if it makes any difference with the current firmware. As for the current GP1100 pack I fear it may be time to sent it to Jeebers

Adam - IOU one 24T pinion - (unless you happen to have time to comb that entire netball court with a metal detector for the one that got thrown at 30,000 rpm (i'd start looking in adjacent suburbs)

i'll send it up with the pack sometime this week and u can have a play with it
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  #11  
Old 07-17-2006, 12:20 AM
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did you by any chance put a flat spot on the pinion shaft......lol.
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  #12  
Old 07-17-2006, 12:26 AM
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yeah spent about 30 mins with the dremel, it was such a nice motor i didnt want to be the one to ruin it.
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Old 07-17-2006, 12:28 AM
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The car didnt have a shell at that stage so the pinion is lost to us forever

Hey chris, upload a couple of pics here with its pants on and off. I'm sure it will get a good reception
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Old 07-17-2006, 12:28 AM
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And you might also want to put a small heatsink on the esc.....heat and electronics dont mix.....in fact they hate each other..lol....And adam why did it take you so long to put a flat spot on the shaft...lol.....And do the both of you have aim.....if not you should download it at aim.com this makes it easier and faster to talk about rc problems......
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Last edited by alfred; 07-17-2006 at 12:31 AM.
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  #15  
Old 07-17-2006, 12:31 AM
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my nerves arent what they used to be

jk. i spent ages putting the car together, i wanted it to be the best mrs4 i'd built. It still might be.
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