C-Shack

I just purchased a used E-Maxx 3905 off of E-Bay and i'm hoping someone can help me get this thing running up to par. I'm fairly new to RC Cars but have been flying electric FP Helis for a few years, so I have decent knowledge of electronics. The truck has some upgraded aluminum parts and overall, I feel it was a fair purchase. However, upon receiving the truck I noticed the Steering servo was very week. It can only turn the wheels while the vehicle is moving. Is this normal? I ordered a high-torque servo to replace this. Secondly, I'm getting very short run times with the two 3800mah NiMH packs that I am using. I'm typically getting less than 5 minutes. I didn't feel any binding but I took the gear cover off to inspect the gears and pinions. I noticed that the motor pinions were very tight against the main gear. I backed them off a bit to allow a smoother run. I also noticed that the Shifter Servo has been replaced with a Futaba servo. According to the Tower Hobbies website, it states that this servo has a high current draw and should only be used with NiCad or certain Lipo or NiMH packs that can handle a 2a draw. Since I'm not sure if my packs can handle that, I plan on replacing the servo with a standard servo. For now, I'm going to leave the transmission in one gear and disconnect the servo to see if it makes a difference. I need to recharge the packs tonight and re-test. I'm wondering if there is anything else that I'm missing that can be causing the quick battery drain. Could the ESC or receiver cause high drains and be at fault? Any help, ideas or suggestions would be greatly appreciated.

t9dragon

My Feedback: (11)

Sounds like the steering servo needs to be replaced. What brand and how old are the NIMH packs you are using. As for the run times that sounds about right for the packs you have.

C-Shack

T9Dragon, thanks for the response. I've already ordered a new steering servo. As far as the packs, they are only a couple months old. I use them on my TT-01 brushless set-up with 15-20 min runtimes.

john01374

The E-maxx is hard on batteries and long run times are not in the cards.. On a set of 2S 5000 lipo's my Stock 3905 ran about 15 mins if I was hard on it. Never tried in on Nimh but I would imagine the run time would be somewhat shorter. I've heard of people only getting 10 to 12 minutes of run time using Nimh on the E-revo but I have not seen this first hand.

The E-maxx's are fun but they are hard on Nimh batteries.

xxSLiMxx

1st, Stock servos suck! I own 4 of these babys and what you wanna do (if you can afford it) it get ur self a Hitec 333oz servo or something close to it. It will turn even the biggest tires standing still. I swear by that servo! As for your batterys, it depend on how old they are and how many times they have been charged. If there used then yeah ur runtimes seem about right. Look into getting some 7cell 5000mAh or some 2S 5000mAh Lipos (dont for get your cut off if your still useing the stock ESC) You will see alot better runtimes. (30mins+ depening on ur driving) Good Luck with your E-Maxx, (best basher truck out there by far!)

Slim.

mazdaprotege4

My Feedback: (32)

You could save up and buy a single motor brushless system. It should be more efficent and have longer run times.

C-Shack

Thanks for the responses. I figured that I'd have to put some effort into this before I was satisfied but I'm trying to keep it at a minimum. I'm sure the brushless conversion is well worth it, just not financially feasible right now. Slim, you mentioned using 7 cell packs but that will up the volts to 16.8V. Will that be comaptible with the stock ESC? Also, the 2s Lipo's that I've researched are 7.4v. Same question, will 14.8v be too much for the stock ESC?

t9dragon

My Feedback: (11)

The E-Maxx that you have should have the EVX-2 which can easily handle 16.8v.

samguan

Get some 2s 5000mah hobby city lipos. They are both good and cheap in price. They are cheaper than nimhs.

xxSLiMxx

Yes 7cell batts will work no prolem, infact if you buy a new 3905 emaxx now it comes with x2 7cell traxxas batterys. It will also handle 2S lipos but you will need a 2S LVC to make sure you dont end up droping the voltage to low on the lipos. I myself just got a new (used) emaxx for the winter. Its bone stock, only things iv dont to it was add my hitec 333oz servo, and rebuilt the shocks. I have the same ESC and i planning on picking up some 2S lipos/LVC for snow bashing (yes i know lipos are not water proof, they will be dipped in plastic dip, or i will be doing the "shower cap mod")

cat samich

can we get some pics? because the 3905 should have 2 steering servos, also it shouldnt have a servo for second gear unless its been converted to two speed with the trx 2 speed kit. even then the servo would be a trx micro servo included with the 2 speed kit. you might have a 3906. my 3905 had no problem turning a set of big joe 40 series tires while standing still. the servos are atleast a year old and im hard on the truck. now if your do have a 3906(black chassis, factory 2 speed) a novak 4.5hv or 6.5hv makes that truck fun with no more than a nice set of 6 cell 3800 packs. if it is a 3905(grey chassis, factory 16.8 evx) get a mamba monster 2200 and a set of 5000 2s lipos and it will be a riot. plan on running closer to 23 maybe 25 tooth pinions with the stock 68 spur. my 3905 with a set of 5000 2s venom packs gets close to 45 minute run times on pavement with hpi phaltline wheels and tires. 35 minutes with stock chevrons in the dirt. take your diffs apart and make sure the seals are in tact and that there are no broken teeth or screws, ive totally ripped diffs apart with my mamba so its possible you may have broken stuff in there. the previous owner may have already had a mamba in it and pulled it to sell it to you. any way you slice it though either emaxx is a blast and a great truck. i cant stress enough how important battery selection is. batteries are everything to this truck. afterall with two 2s lipos my truck comes in just under 15 pounds rtr. as far as servos, if you have a 3905 stock servos should be fine if your speed control is sending proper voltage to your rx and if you do have the 3906 definitely look into the 333oz hitec or look at the bigger jr servos they have some hi torque servos that are just monsters.

xxSLiMxx

x2 on pictures.

rebuilder

You can get an inexpensive setup that will give you some long run times (25-30 min) AND alot of power using the stock componenets. If your ESC is an EVX and its blue, then it can handle 16.8 nimhs or 14.8 worth of lipo power.

These batteries are WELL worth the very reasonable price, only $19.99 each for 5000 mah, you will need two:

http://www.hobbycity.com/hobbycity/s..._20C_Lipo_Pack

And you will need this LVC to protect the batts from overdischarge. I use this LVC in 3 EVX's.......they work great, easy setup too, if you go this route and need help installing the LVC let me know:

http://www3.towerhobbies.com/cgi-bin...?&I=LXPGN1&P=7

Dont think however, that the lipos will make the 550 titans run like brushless.....not gonna happen. What will happen is that they will run at their absolute peak performance with these lipos supplying the juice, it will run better than a nimh e-maxx on 14 cells.

Redvanmafia

less then 5 minutes?, thats a joke charge for 1 hour+ then its dead in 5 minutes

C-Shack

OK, so my bad. This is not the 3905, it's the older version with the EVX and 2 speed transmission. I stopped by the LHS on my way home from work and picked up an inexpensive throttle servo and some damper oil. I really think that the one that was in there was drawing too much current for some reason. Besides spacing the pinions and spur properly, I also re-soldered all the wiring and replaced all connectors with Deans Ultra and filled all the shocks. (There was less than a drop or two in each shock). I also noticed that the steering linkages were set up in a crazy way. I set it up the way that I believe it should be and it now steers quite well. I still have a high-torque servo on order, so it should be even better by the weekend. So with all that, I placed two fully charged 3800mah packs int he truck and took it outside for a while. Kinda hard to see in the dark, so it was mostly run on my driveway. Either way, I got about 10-15 minutes of run time out of it. Definitely a huge improvement over just 24 hours ago. Now I feel confident that I got a good deal. I'm still thinking that I want to run Lipos, so that will most likely be the next purchase. Thanks to everyone that responded. Definitely a lot of great info!!!

rebuilder

Do you have the Traxxas EVX by "Novak" ESC? If its the orange one, i have one of those too..............i run it on 4s lipo with the LVC i posted above and not one problem...............Its rated at "14.4v" but the 14.8v nominal i run thru it with the lipos is just fine. You could still go the lipo route if you wanted.

C-Shack

Rebuilder, yes it is the orange Novak ESC. Once I'm sure there are no other major problems, I'll probably go the Lipo route. Thanks again for all your help.