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Thread: Axial RTC to comp crawler build

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Old 12-31-2010, 01:20 PM   #1
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Join Date: Dec 2010
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Default Axial RTC to comp crawler build

OK, the build is 99% done (I think I need a BEC ) and just got back from crawling - OMG!

What was impossible stock is now a walk in the park - or less even.

Start with an AX10 RTC
The Mods: (and why)
Wheels and Tires
Added 6 oz of lead to each front tire, 3 oz to each rear.
Vented the rims.
replaced the tires with Panther Cougar (better tires, these were free. kept stock memory foam).

Chassis
replaced rear lower links with hi rise alum ones (under stock power if a front wheel got jammed up the rear wheels would push, bending the rear lower links). Replaced fronts as well.
Moved rear upper shock mounts to outside the frame making them more vertical (to reduce aticulation). Added some preload. Stock oil seems OK so far.
Alum skid plate that moves the end links inside the frame.
Axial BTA steering - the stock plastic steering is a joke and it would hang on approach to some obstacles. This also included a plate to mount the lipo on the front axle.
I started with a 7 cell Nimh on the backbone and it was obvious that this was not a good choice, weight wise. I am now running a 3S lipo (1350mah) on the front axle. I also moved the ESC to the top of the front upper links and put the receiver on the top of the rear upper links.

Drivetrain
While I have not broken the stock driveshafts they are a weak link so I replaced the with integy CVD units...we'll see if they hold. If not I'll install MIPS.

Electronics
Tekin FX-R ESC (wanted drag brake and lipo power)
I got a good deal on a used Spektrum 3.0. The stock radio isn't bad but it lacks in adjustability - you need to change the throttle curve to get more low speed control, adjust the end points on the steering, etc.
Servo - the stock servo isn't strong enough. I went cheap and got a turnigy from hk for $30. We'll see how it hold up. It is a bit deeper and much heavier than the stock servo.
3S lipo from HK ($10) 1350 mah mounted on the front axle. Since I have several traxxas vehicles I put traxxas batt plugs on everything - yes, you can change the plug on a lipo and not grenade it.
I still have issues with the servo pulling power and leaving me 'stuck' when I jam a front wheel so I think a castle bec is next on the to-do list.

Summary
The changes have changed the vehicle's behavior immensely - it's unbievable how much better it crawls over any obstacle and how hard it is to roll over now. On a side hill I can't roll it- the tires lose traction first and I slide down the hill. Power bursts are incredible now -punch the throttle and watch it just come to attention and fly! (stock 55 turn motor and gearing).

Total cost? If you have to ask... I was told when I started looking at crawlers that to have a competitive machine I'd spend $500. Well, I have about $640 in it at the moment (including 2 lipos).

I still need a BEC and a good balancing charger and could probably do a bit better with rovers - so figure $700, more if the integy's fail or something breaks. I do have a complete radio/esc/servo now for use in something else (i'm resurrectong a 1990 RC10 for now) so perhaps deducting $150 would be allowable?

I don't know if starting with a scorpion kit would have been any more economical...I'd still have need most of these parts and the stock kit costs more than the RTC.

Now to go find a competition and see if all this effort paid off!
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Old 12-31-2010, 02:36 PM   #2
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Any Pics of your comp rig finished? Sounds like quite a lot of changes. No change to spring rates or shock limiting?
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Old 12-31-2010, 06:41 PM   #3
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Join Date: Apr 2010
Location: Central FL
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Yeah you really should use a BEC if you're running 3s. Thats a pretty nice mod list. Budget builds really are possible if you buy the right parts the first time around. I've invested way more than $700 in mine, but I also started with an RTR 'cuz I didn't know any better.





btw, let's see some pics!
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Old 01-01-2011, 09:05 AM   #4
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I"ll get some pics up.

What gave me a big leg I think was attending the local club's practice session. Talking with folks, seeing their rigs and more importantly seeing their course and trying to run on it, and seeing them run on it.

My first try on their course was a total and complete bust. A few mods there (got the tires, links) and with some practice made a big difference. I might have been able to tweak the thottle curve in the FXR rather than a but a radio but almost everyone there runs a dig so a third channel will be needed.

From all I've read the most articulation should be about 1 tire height - more than that and the other side should lift too to float over obstacles. Now the RTC comes with different shocks than the other AX10 models so I don't know how much difference that makes. I increased preload (stock was so loose the spring would rattle on the shocks at full extension). I gave more preload in the rear to counteract torque twist. When I was putting the links on the rear and replacing the skid plate I moved the top of the rear shocks out as far as possble on the chassis - this seemed to be the trick to limiting articulation (and some preload too). I couldn't do this on the front as the tires would hit the shocks even more than the do now (bta gives you more steering). I didn't have to put a limiter on/in the shocks -these shocks don't have that spacer thing on the one end that everyone moves inside so I'm not sure what all the differences are as I don't have a 'normal' ax10 to compare to.

With the power I now have I may have to find a better rear link - i ripped the all thread out of the aluminum link hoppin over logs. (at the course they have rocks bigger/taller than the crawlers - their technique is to get the front wheels on it and then full power getting one to 'hop' over/onto the obstacle. I'm not seeing much if any bounce upon landing so I'm holding steady on my shock oil (stock weight) for now.
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Old 01-01-2011, 05:53 PM   #5
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Join Date: Oct 2010
Location: McKinney
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Do your research, and take your time with your upgrades. Do it intelligently, and not twice. That's how this can get so expensive!

Admittedly, the stock AX does need a fair amount of work to be competitive. But keep working with your local group, and pick their brains. And read lots of build threads here, going back a dozen pages or more. The time invested will be worth it.

And don't be afraid to post your questions here.

Good luck, and enjoy!
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