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Tamiya mini cooper

Old 02-27-2013, 05:13 PM
  #18496  
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I'm pretty sure my servo is crap... I adjust the trim to get it to track straight then it'll pull the other way and I'll have to adjust the trim again. This keeps happening. What servo are some of you guys running?
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Old 02-27-2013, 06:47 PM
  #18497  
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Originally Posted by monkeyracing
Well, never allow them discharge below the recommended level, at least. My packs are generally around 7.8v when I finish a 6 minute heat, or 7.6v after 10 minutes, so they're darn close to storage voltage. If I'm using them again that day, they get balance charged at 1C. If they're getting put away for the week, they get balanced to storage voltage (7.6-7.8v) and stored in a nice cool ammo box. It helps them last a long time with a minimum of internal resistance.
That is surprising.

A battery off the charger is at 8.4 volts, but as soon as you plug it in and drive away drops to about 7.4 and stays there or drops slightly depending how much you use it before recharging. I would suggest you measure your battery with a small load (plugged in the car is fine, the receiver draws about 20mA or thereabouts) to get a more reliable value. At no load the voltage doesn't mean much. Intelligent chargers such as the Supernova (which is pretty much standard around here) place a small load when measuring the voltage they display. You need the same load applied to give you a comparison.
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Old 02-27-2013, 07:28 PM
  #18498  
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Originally Posted by ewashburnaf
I'm pretty sure my servo is crap... I adjust the trim to get it to track straight then it'll pull the other way and I'll have to adjust the trim again. This keeps happening. What servo are some of you guys running?
If you have a saver check that first before blaming the servo. Most servos including crap ones centralise fine, but a crap saver doesn't (that is why it is called crap). Weaker servos might not centralise under load, but check first and make sure the saver is tip top.
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Old 02-27-2013, 07:46 PM
  #18499  
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Originally Posted by Granpa
Yeah, most are 3X10mm. Since they have used the self tapping screws already, you shouldn't have to use a tap. I routinely use machine screws to build from the start, but do have to tap the holes part way or they become to difficult to tighten. I use 3X6 on the bumpers and a 3X16 or 18 on the servo mount.

You can replace the shoulder screws in the camber links by using 4X6 flanged tubes. Can't remember the exact length of the screw, but 3X14 or 16 seems right. Part # for the tubes is 50593. I got mine from Tower Hobbies.
Thank you for the help Granpa!
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Old 02-27-2013, 11:36 PM
  #18500  
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Originally Posted by niznai
That is surprising.

A battery off the charger is at 8.4 volts, but as soon as you plug it in and drive away drops to about 7.4 and stays there or drops slightly depending how much you use it before recharging. I would suggest you measure your battery with a small load (plugged in the car is fine, the receiver draws about 20mA or thereabouts) to get a more reliable value. At no load the voltage doesn't mean much. Intelligent chargers such as the Supernova (which is pretty much standard around here) place a small load when measuring the voltage they display. You need the same load applied to give you a comparison.
Alright, you got my attention. I charged up a pack and did some testing. Used my charger, multimeter and a pocket voltage checker to verify at various stages. Here's what I found:

Charged to 8.4v
Hooked up to car 8.4v
Powered on 8.4v
Running at part throttle 8.3v
Running almost wide open, heavy load (stiff diff, wheel held) 7.8v
Immediately after running for about 1 minute 8.15v
Resting, rose to 8.3v after 1 minute

I generally check my voltage immediately when I get to my pit table, so we'll call that about a minute.

Not sure why a battery would drop to 7.4v and stay there unless it's been run hard for more than a couple of minutes. Testing with a load tests ability of the battery to deliver power only while under said load, not at rest. I agree that a battery can show lower numbers while stressed, but when we check voltage, we're generally not chasing the car around the track.
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Old 02-27-2013, 11:48 PM
  #18501  
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No, but you can use a data logger that will tell you what happens with the voltage and the current being drawn at the same time.

Just like a car battery that can show a higher voltage right after charging, when under it's intended load, it will revert to just under 12V, not above. If your batteries show more than 7.4V, then perhaps the load is not as high as intended by design. Try a touring car with a serious steering servo (mine draws about 6-10A under load) and see what happens.
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Old 02-28-2013, 12:03 AM
  #18502  
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I race minis. TC is for chumps!

The thing is that most people aren't using data loggers. They're checking voltage after a battery is charged and after it's been run. Voltage under load is meaningless to most - even nerds like me.
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Old 02-28-2013, 12:13 AM
  #18503  
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Voltage under load shows the real state of health of your battery. If voltage drops rapidly (not your case, I suppose) or dramatically, then your battery has lost some its capacity. What you describe is serious underuse of the battery, long term it is believed it's not beneficial because you're basically cycling the battery around nominal full charged level. I know some people initially believed Lipos did not show memory effects like NiCd/NiMH but after they became common in laptops it turned out it only took a bit longer to develop. I think you would need to use more than that out of your batteries between charges for a longer life.
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Old 02-28-2013, 01:17 AM
  #18504  
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i always discharge my lipos to 6.6v then charge , i needed to charge at 7a because of time between runs and only having 1 lipo that was any good

i have run my TC lipos for 2 years discharging and charging at 20a and they are still good

had this discussion many times before and there seems to be various differant opinions
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Old 02-28-2013, 06:41 AM
  #18505  
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Originally Posted by sidecarphil1
i always discharge my lipos to 6.6v then charge , i needed to charge at 7a because of time between runs and only having 1 lipo that was any good

i have run my TC lipos for 2 years discharging and charging at 20a and they are still good

had this discussion many times before and there seems to be various differant opinions
Sure, I understand. You've had this discussion many times before and there's nothing that's going to change your mind.

So just out of curiosity, where did you hear that you should charge at 20amps and discharge to 6.6v?????? None of the major manufacturers recommend that.

Also, when you go to "gas" your car, you don't empty all but precisely one gallon of gas before refilling the tank as fast as possible without "blowing" up the fuel system, do you????? That makes about as much sense as what ypu're doing with your lipos.

Last edited by Granpa; 02-28-2013 at 07:36 AM. Reason: addition
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Old 02-28-2013, 07:05 AM
  #18506  
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Originally Posted by sidecarphil1
i always discharge my lipos to 6.6v then charge , i needed to charge at 7a because of time between runs and only having 1 lipo that was any good

i have run my TC lipos for 2 years discharging and charging at 20a and they are still good

had this discussion many times before and there seems to be various differant opinions
even so, there is no need to discharge the pack any lower then when it came off the track. just go from the track to the charger and top off.
you are wasting time bothering with an additional discharge process.

without trying to be a know it all, your logic is flawed. but in the end they are your batteries to do what you want with.
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Old 02-28-2013, 07:28 AM
  #18507  
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Originally Posted by niznai
That is surprising.

A battery off the charger is at 8.4 volts, but as soon as you plug it in and drive away drops to about 7.4 and stays there or drops slightly depending how much you use it before recharging. I would suggest you measure your battery with a small load (plugged in the car is fine, the receiver draws about 20mA or thereabouts) to get a more reliable value. At no load the voltage doesn't mean much. Intelligent chargers such as the Supernova (which is pretty much standard around here) place a small load when measuring the voltage they display. You need the same load applied to give you a comparison.
I posses a very technology deprived intellect so think in much simpler terms. Hell, I don't even know what an intelligent charger is. I bought a voltage meter, but found very little use for it after switching to lipos.

Now, keeping the above fact in mind, is there a simple explanation for why my cars just seem faster with a freshly charged battery. They also seem to turn their fastest laps near the beginning of the run. Maybe my experience is unique and no one else has seen this phenomenon occur, though I don't believe so.

Why does a no load value of a battery not mean much?????? Why does placing a load as small as 20ma suddenly make this value so much more relevant??? What makes an intelligent charger so intelligent??? All I ever wanted from a charger was for it to charge a battery.
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Old 02-28-2013, 10:06 AM
  #18508  
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over here we run 13.5 0 timing stock TC , i have back to back tested discharging and charging at 20a and the differance one the track was noticable and the times were quicker

and i copied this with the mini.

but we are going off topic a bit with my battery charging antics
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Old 02-28-2013, 10:46 AM
  #18509  
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Well... strongly cycling a lipo can help bring its IR (internal resistance) numbers down, so I can see merit in the discharging and then charging thing. And I don't think it is so much the discharge but more of the 'long and strong' charge that can slightly warm the battery, juice the chemistry, and help with IR. Some of the fast local guys swear by it, saying to charge your lipos as fast as your charger can.
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Old 02-28-2013, 10:51 AM
  #18510  
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Originally Posted by niznai
If you have a saver check that first before blaming the servo. Most servos including crap ones centralise fine, but a crap saver doesn't (that is why it is called crap). Weaker servos might not centralise under load, but check first and make sure the saver is tip top.
Yeah.. I'm pretty sure it's the servo. What are you guys running just so I can make a comparison to what's in mine.
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