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Old 06-05-2008, 11:17 AM   #136
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Yesterday we tried several different servos (airtronics 94357, 94358, jr z270, futaba s9451). we had the same results with all execpt the futaba. Now the system runs but the speed isn't consistent it goes fast for a lap or so then it slows down for a short distance then the speed will pick back up. But it never completely stops it just acts as if the truck is dragging dead weight. Maybe we're getting closer least we can get lap or so before it slows.
What your describing here is the Low Voltage Cutoff (LVC) coming on. You may want to confirm your settings. When LVC comes into effect the power to the car/truck is significantly reduced - dragging dead weight. While running in this mode the battery is recovering voltage and resetting the LVC and you run fast again, and the cycle repeats.
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Old 06-05-2008, 11:42 AM   #137
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We were hoping that was the problem so we dit into the computer and I get read error 214 and it then won't let you change any settings. So i dont exactly know what to do I tryed different servos, recievers and i still have the same problem.
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Old 06-05-2008, 11:50 AM   #138
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We were hoping that was the problem so we dit into the computer and I get read error 214 and it then won't let you change any settings. So i dont exactly know what to do I tryed different servos, recievers and i still have the same problem.
Alex
Let Matt give you first hand help this weekend. All the servos you mentioned will work fine. If you have an 8800 it too is fine.

changing the servo's or receivers will have no effect on the LVC directly, indirectly one may require more or less power and in that sense it does have some effect.
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Old 06-05-2008, 11:55 AM   #139
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Let Matt give you first hand help this weekend.
Wow, you are going to fly to NE to help him out? I was not aware Losi provided such Customer service, I am impressed!!
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Old 06-05-2008, 11:56 AM   #140
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Wow, you are going to fly to NE to help him out? I was not aware Losi provided such Customer service, I am impressed!!
uh....I'm already here
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Old 06-05-2008, 11:58 AM   #141
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We were hoping that was the problem so we dit into the computer and I get read error 214 and it then won't let you change any settings. So i dont exactly know what to do I tryed different servos, recievers and i still have the same problem.
Alex
Maybe the problem with the LV condition is in the Battery or Motor connections themselves. If you have a connection that is weak on the battery or motor, then resistance will increase, which causes Voltage to Drop, and then Amperage to increase.

Basic Voltage/Amperage: Higher Voltage = Less Amp Draw, Lower Voltage = Higher Amp Draw. So essentially you want to keep the resistance low to maintain the battery voltage. Check the temp of the power and motor wires after a 5-min run. If you find a wire that is hotter than the rest, that is probably the wire with the highest resistance.

Here is a great website that explains and demonstrates electronics, voltage, resistance, etc...

http://www.bcae1.com/

Last edited by kn7671; 06-05-2008 at 12:32 PM.
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Old 06-05-2008, 01:17 PM   #142
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Weird thing is that the quoted on resistance is lower in the novak than the top tekin. Novak has 18 fets and the tekin has 48.

The novak super sport has twin fets which were effectivly 2 fets in one package which might be what tekin have used. I think they are cheaper but take less space.
It gets more interesting than that. We are not sure what new math everyone is using. There are different numbers for current and on resistance on the spec sheets that can be used but are not very real in actual use. We use the numbers that are reasonable in actual use and even those are severly overrated when the units are extremely hot.

In Example We claim the RSpro and R1pro at 208 amps per phase and they both have 48 fets in them. I just opened a LRP TC comp and they are using the exact same fet that we are ( recent change I believe), but there are only 24 of them and they claim 400 amps per phase! So we have double the fets and claim half the amp rating... that is a 4x difference in marketing claims. Perhaps we spend too much time engineering and not enough on marketing

FYI the GTB and I assume the Losi have 18 fets? Kudos to Losi for only claiming a reasonable 100amps and not playing the fluff game.

Careful what you read and how you swallow it. How it performs and the durability is the real issue. Truth be known the pcb has way more resistance than the fet package making that number somewhat meaningless. A good multi layer heavy copper pcb is as or more important and expensive.

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Old 06-05-2008, 08:09 PM   #143
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The lower the C rating and mah, then the higher the voltage drop under load, because the motor you have (a 6.5) pulls a lot of amps, and the only way for the battery to supply enough is to drop the voltage to raise up the amps.

BTW, higher voltage means higher amps, but usually when you have more voltage you use a motor that pulls less amps (lower kv), to get the same power output (watts = volts x amps). Also higher resistance causes the amps to go down because their less current flow, and I'm not so sure about this part, but I think that's what causes the voltage to go down also.
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Old 06-06-2008, 08:28 AM   #144
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We claim the RSpro and R1pro at 208 amps per phase and they both have 48 fets in them. I just opened a LRP TC comp and they are using the exact same fet that we are ( recent change I believe), but there are only 24 of them and they claim 400 amps per phase! So we have double the fets and claim half the amp rating... that is a 4x difference in marketing claims. Perhaps we spend too much time engineering and not enough on marketing

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But what is the point in coming onto the Losi Xcelorin thread and posting how the Tekin ESC will handle 208 amps when most Batteries can hardly even supply a 100 amp load when called on? This is like saying that just because a car has Z-Rated tires on it, that it can go over 149+ mph.
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Old 06-06-2008, 08:56 AM   #145
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higher voltage means higher amps, but usually when you have more voltage you use a motor that pulls less amps (lower kv), to get the same power output (watts = volts x amps). Also higher resistance causes the amps to go down because their less current flow, and I'm not so sure about this part, but I think that's what causes the voltage to go down also.
You are right, Higher Voltage = Higher amperage, but we aren't dealing with a power supply, but a battery whose Voltage will fluctuate based on the amperage load placed upon it.

In the case of 6-cell NiMH or LiPo's, the nominal voltage is 7.2V or 7.4V for LiPo. Fully charged a LiPo will be at 8.4V, but place a 30amp load on the 8.4V battery and the voltage will drop to 7.7V or lower, depending on the internal resistance. As the nominal voltage drops. To produce the same power at 7.7V increases the amp draw.

Electric/Hybrid cars like the Prius run at 48V, not 12V. The reason is that higher voltage systems require less amps to provide the same amount of power to the circuits. As such, with higher voltage you can utilize wire of a smaller gauge, which helps reduce weight in a car.

The whole point I was trying to get at here is that the entire state of the electrical system on our RC Cars has to be in top shape to provide a stable flow of electricity under high demands.
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Old 06-06-2008, 09:08 AM   #146
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Funny thing is, people have had problems with the tekins overheating .

I'm sure the tekins have low on resitance than most because they don't run a heatsink, but I think you made a mistake by not making provision for one. Now we have people who run mod having to come up with DIY cooling solutions .

A lot of lipos can peak over 100 amps but then voltage drops a lot. It's contrinous rating that is important anyway.

To back on topic. A friend of mine has been having problem with his exelorin esc cutting out. He said he totaly loses his brakes every once in a while. I suspect it is to do with the bec not handling >6v very well, ie when he accellerates it cuts out just before he presses brake and only then realises it has cut out. He tried a capacitor on the receiver and I think it helped. I will report back if it was a total success or not.
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Old 06-06-2008, 09:35 AM   #147
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But what is the point in coming onto the Losi Xcelorin thread and posting how the Tekin ESC will handle 208 amps when most Batteries can hardly even supply a 100 amp load when called on? This is like saying that just because a car has Z-Rated tires on it, that it can go over 149+ mph.

The point was simply that people are using different numbers off the spec sheets to claim on resistance and amps. I thought I was very careful not to be bashing and just supplying information for people to make there own conclusions.

Some products have less fets and rely on a lot of external cooling with heatsinks and fans. We went with a lot of fets so that we did not need any cooling except in extreme situations and could keep the size small. A big V8 idling along or a little import operating at max ability.

100 amps is an average current type number. We drive these motors with a pulse and see much larger currents than you realize. A mod motor will pull over 120amps average just looking at it with a slow sampling data logger like a Eagle tree. On a scope looking at real time the currents are much larger for very short pulses. Every time we turn on the fets it is a direct short from the battery to the motor. Basic V/R=I says the currents are massive during the initial pulses.
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Old 06-06-2008, 09:37 AM   #148
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Curious, has anyone that has the LV or cutout issue tried lowering the Initial Punch setting to Normal or Low?
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Old 06-06-2008, 02:31 PM   #149
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It gets more interesting than that. We are not sure what new math everyone is using. There are different numbers for current and on resistance on the spec sheets that can be used but are not very real in actual use.
Nothing new same as always called 'marketing hype'
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Old 06-10-2008, 03:41 AM   #150
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Anyone tried the Losi Xcelorin 10.5? If so how does it compare with the Novak, LRP, Orion, Nosram etc 10.5's?

The Losi ESC and Motor combo can be had for a lot less than other sensored brushless ESC's - almost seems too good to be true....
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