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Just got a used T-Maxx 2.5r

Old 06-03-2014, 03:20 PM
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cumminspower5.9
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Default Just got a used T-Maxx 2.5r

Hey all. I just got a T-Max 2.5r off my cousin for $50 and it's in excellent shape. I've got a few questions and some areas where I need advice.

The Rx battery...obviously 4 AA batteries do not provide enough voltage for all 3 servos. Am I going to have to hard wire leads to the power switch that match the chosen battery pack connector? What cheap battery pack and max voltage is recommended?

The steering is really weak. Is this due to the battery issue, or is the servo not a very high power servo? I have an Axial high torque servo to swap if it's the servo, but I have a feeling it's a battery issue.

Any other issues or mods that I need to make this better? I have had a nitro before so I know that aspect of it, and I had a Traxxas Bandit VXL before, so I know Traxxas kind of well, but the Traxxas MT's I'm not too familiar with.

Thanks for any and all help in advance guys.
Old 06-03-2014, 06:27 PM
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jkdv8
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Are they the factory traxxas servos. If so I doubt they will hold too much. Probably could find a spec sheet somewhere. Often wondered this but wasn't sure how the servos would hold up. Technically I guess you could go as high as you want but would have to make a BEC type circuit for each servo so when only one is running it doesn't burn out receiving all the power(possibly only a problem for long durations.) Maybe add up the max withdrawal on all 3 servos and match the battery to that with the highest mAh possible for run times?!? Then theoretically you could reduce the power supply to the receiver part to save weight or leave it be. Only have to replace/recharge once a year. Also I think they make a 1 in 3 out (or vica versa) servos/power connector then just plug that into the power switch that runs off said battery. Need to dig deeper into this. Got a t-maxx that could use this upgrade. Has a high torque servo but batteries don't last long. From what I noticed the rechargeable ones don't make the power the alkalines do, but rechargeables last longer and obviously are rechargeable. I was just thinking today we need a reliable and powerful solar powered setup for the car radio side of things.

thats a steal btw.
Old 06-04-2014, 07:36 AM
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The stock Tmaxx 2.5 servo is a 2055 with 80 something ounces of torque. If you're going to buy a servo look for something with at least 200oz of torque. I'd also consider replacing the stock servo saver with a stiffer one, the MGT servo saver is a good choice. Either that or you an upgrade to the bellcrank with servo saver built in that comes on the newer Maxx trucks.

As as for the Rx battery the popular choice is a 5cell NiMh hump pack with about 1600mah. The better choice would be a Lipo pack but you'd need a Lipo regulator as the voltage is too high for the Traxxas servos and Rx. Findin the right size Lipo to fit in the box is another challenge and you'd then need a Lipo charger if you don't already have one.
Old 06-04-2014, 08:53 AM
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I replaced the stock steering servo with the one from my Axial SCX10 and it helped a lot. Just needs more voltage to make it steer faster. Have to somehow convince the wife to let me drop $20+ for a new battery. I have a Losi 7 cell I bought for my mini-t, but it's too big.
Old 06-04-2014, 08:57 PM
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Originally Posted by jkdv8 View Post
Are they the factory traxxas servos. If so I doubt they will hold too much. Probably could find a spec sheet somewhere. Often wondered this but wasn't sure how the servos would hold up. Technically I guess you could go as high as you want but would have to make a BEC type circuit for each servo so when only one is running it doesn't burn out receiving all the power(possibly only a problem for long durations.) Maybe add up the max withdrawal on all 3 servos and match the battery to that with the highest mAh possible for run times?!? Then theoretically you could reduce the power supply to the receiver part to save weight or leave it be. Only have to replace/recharge once a year. Also I think they make a 1 in 3 out (or vica versa) servos/power connector then just plug that into the power switch that runs off said battery. Need to dig deeper into this. Got a t-maxx that could use this upgrade. Has a high torque servo but batteries don't last long. From what I noticed the rechargeable ones don't make the power the alkalines do, but rechargeables last longer and obviously are rechargeable. I was just thinking today we need a reliable and powerful solar powered setup for the car radio side of things.

thats a steal btw.
Alkaline batteries are rated at 1.5 volts while rechargeable batteries are 1.2 volts. That's why for rc you don't just install 4 AA rechargeable batteries, you instead go with a 5cell rechargeable pack to maintain the 6.0 volt output.

Now as for the beginning of your post about powering the servos. It doesn't matter how many servos are connected to a power source, you don't need to limit or switch off anything. A servo is a motor, it will draw what it wants to regardless of how much battery there is. When the servo moves or something tries to move it and the servo has to hold it's position, the servo places a load on the battery. While under load the voltage of the battery will drop, doesn't matter what battery or servo voltage drop occurs. If the battery cannot supply the amps the servo wants the voltage will drop even more significantly. The average servo will have an average amp draw of about .75 amps with spikes around 1amp. The average draw and amp spikes will go higher if the endpoints aren't set properly. Obviously the less voltage drop under load the higher the servo performance will be. Achieving this requires more mah, as much as possible.

As as far as how high of a voltage you can run, that depends on the servos and the reciever. I'm pretty sure Traxxas stuff is only rated to 6.0 volts. If you have a servo that's rated for more it can be powered separately from the reciever instead of through the reciever. The 1/5 guys do this as the reciever can also limit the amount of current the servos are able to receive because it acts as a bottle neck. You can buy a harness to do this or you can make one out of a y-harness. You simply connect the servo, battery and reciever into the y-harness and remove the red wire from the plug that goes into the reciever. The servo is now powered by the battery while the white signal wire and ground wire provide the signal from the reciever.

Last edited by Maj_Overdrive; 06-05-2014 at 12:44 AM.

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