Got bit by a Tarantula

[Gramps]

I have a Injora Rock Buggy and the UtB18, I like that tube chassis look and both the Rock Buggy and UtB18 are good crawlers. Do I decided to turn the TRX4m Defender into a Tarantula. Finally got around to putting the chassis together today. The instructions are just pictures but pretty easy to follow if you've done any building. The plastic seems a little on the soft side so one needs to be careful when tightening the screws. Started with the right side frame and installed all the cross members. I then joined the left side frame to the right, leaving the screws a little loose to make it easier to get the skid plate installed.



Both sides of the frame all put together.



The running gear all ready to have the frame dropped on it.



The completed roller. Started with the shocks in the middle hole but I think the springs are to stiff for the weight of the Tarantula so I ordered some softer ones to see how much difference it makes.



I used the TRX4m battery tray as it keeps the battery low to help with the CG. I'm going to use the Injora MB100 esc. I weighted both the battery and the MB100 with the wiring. The battery came in at 36g the esc at 22g so I think I'm going to try installing the esc on the rear tray. I guessing I'll need to add some brass to the front to get some decent weight bias.

 

[King Dork]

So, a Traxxas UTB18? Love it man! Curious to see how it compares to your UTB18 Capra. I have a UTB18 also and love it. I did put quite about of money into it, but aside from the jumpy esc and high cog it’s pretty capable stock. The shocks are also a bit of a pain to dial in.
Also enjoying your thread on your Hobby Plus Evo Pro. I’m mildly interested in that rig, but becoming more and more interested.

 

[King Dork]

Just spotted your AX24 in the back. I have one of those too, moderately modified, and it’s a capable little beast.

 

[BerticusPryme]

I have one of the Tarantula chassis and I love it. Best money I spent on it was the Rampcrab +5 kit. Steering is better than 45 degrees and it adds some brass weight down low where it needs it.

 

[Gramps]

Figured it would be a good idea to get a base line before I started modifying the Tarantulas so I put it on the balance scale and got the base readings. There were no electronics except the stock servo and the stock battery.
Weight bias F/R 55% - 45% which isn't a bad start
Weight: 353.7 grams. The Defender weighted 519.2 grams


I wanted to keep the CG low so I wanted to mount everything as low as possible. The battery weighs more than the the esc & rx so I mounted the battery in the original tray. Had to have access to the power button so I decided to mount the esc on its side except the plug to the rx would not clear the transmission. I thought about taking the top off and soldering the wires to the pins, but kept thinking that if I wanted to use it in something else the wire might me to short. So instead I removed the wires from the plug. I then put some strink wrap over the pins so noting could short out. The bent them to a 90 degree angle after installing them. The esc now sits how I think I want it.



Stood the esc on its side with the power button up and towards the windshield. This allows turning on/off the esc. The switch is some sort of electronic switch that reverts to off when you unplug the battery otherwise I'd just leave it on all the time and use the battery plug to turn it off.



I ordered some Injora Swamp Kings mounted on 1.3" rims and also some Injora silicone foams for them. Also brass steering link and a bearing set. The goal is to get it to a 60/40 bias without adding a ton of weight and making it a pig. I think the 1.3" wheels weigh 28g each so that is going to put me close to stock weight but with a lower CG.

 

[King Dork]

Hey Gramps, is that esc programmable? Haven’t seen any feedback on it, but interested. Loving this build so far!

 

[Gramps]

Hey Gramps, is that esc programmable? Haven’t seen any feedback on it, but interested. Loving this build so far!

No it is not, I first but it in the TRX4m Bronco and the low end resolution was very good. Reverse is set to 50% at the factory and can't be changed. Comes with all the cables needed to use it in a TRX4m or SCX24 including an adapter for the funky Traxxas plugs on the TRX4m battery. My 1st impression is that I like it despite that it really can't be uncased easily & the power button is electronic and revets to off when the battery is unplugged. Not really game changers for me. Much better than the IDT70 or what ever it's called I sent that sucker back and it was programable sort of.

 

[Gramps]

Had the idea of trying the Injora Silicone foams in some 1.3" tires/wheels on the Tarantula. Ordered them and they arrived yesterday, already had the tires and wheels.



When I put the ring in the foam it squished it, I put it in a tire and it was stiffer than the stock foams which are on the firm side.



This shows the comparison between the foam with a 1" ring and a 1.3" ring. For now I have the stock foams in the tires. I think I might try to 3D print my own foams for it.

 

[JBurke187]

I’m curious to see what you think of those inserts.

 

[Gramps]

The springs were too stiff for the light Tarantula body so I ordered the softest springs Traxas had for the TRX4m. I think the front were already the soft ones but to be sure I swapped them out anyway. While I had the shocks off I drained out what little 20w oil they had in them and replaced it with 30w.



Also replaced the front diff cover with a brass one. While I was in there I replaced the bushings in the front diff with bearings. This brought the weight bias up to 59%/41% which is real close to my goal of 60/40. Now thinking brass C-hubs might do the trick.



Still working on the 3D prints foams, when that it complete it will be ready for a test run.

 

[JimK]

Looking good Gramps!! Coming along nicely for sure.

 

[Gramps]

For reference here are the different spring rates available for the stock TRX4m shocks.

 

[Gramps]

Added some Injora brass c-hubs they fir well but you need to press the bushings in from the inside. I used a pair of pliers to help seat them. Don't loose any there are no extras. Was hoping that these would push me to the desired 60/40 bias but it didn't still 59/41. At this point I'm going to take it on the rocks and see how it handles.





Put the panels on and discovered that the stock servo hits the hood. Maybe because the shocks are tilted back. They include 2 hoods but the other one has half a blower sticking out with the blower hat. I think it looks dorky on a crawler buggy.





Still needs tires and wheels as these were the ones from the Defender and they were put on for scale looks don't think they will crawl well.

 

[JimK]

What are you going to do for tires Gramps? Injora's new 1.3" x 72mm XHX pin tires would look/work great on that rig!!

 

[Gramps]

What are you going to do for tires Gramps? Injora's new 1.3" x 72mm XHX pin tires would look/work great on that rig!!

I have a set of the Injora 64mm pins and they didn't work very well in th places I crawl. However I do have a set of 1.3 Swamp Kings that I will be putting on it. These are the tires and wheels I'll be using minis the Injora foams which didn't work in the 1.3 wheels.

 

[JimK]

Nice! That's a good looking set....can't wait to see them on the Tarantula.

 

[JimrC]

Such a cool build to follow along Gramps "thumbsup" Liking those wheels "thumbsup"

 

[Gramps]

As I said the 2nd hood that came with the Tarantula was dokey looking in my opinion so I created one in Freecad and 3D printed one. I cut the original scoop out and enlarged the whole just a bit so I could slide the new scoop in the opening. This now lets the suspension do full compression.

 

[Gramps]

Put the 1.3 Swamp Crawlers and wheels on the Tarantula tonight. The front tires hit the frame when at full lock so I installed 7mm brass hexes on the front this helped but I still had to limit the travel in the MT12. They are the Injora ones and came with some little cone shaped washers to help keep the nut from coming loose.







The esc is standing on it side on the left side so I can reach in and turn it on /off on the right floor board (slider) I mounted the mini RadioLink rc, the battery sits in the stock mount with the strap removed and replaced with 2 rubber bands to hold the batter n place.


I tested it on the indoor course and discovered real fast that I had not put the crawler gears in the Defender (doner) I was going to leave it that way but it didn't take long for me to decide that it needed the crawler gears. So this project is on hold until I get some gears and get them installed.

 

[Gramps]

The Traxxas crawler gears arrived and I installed them and the bearings for the transmission. While I had it apart I also installed the bearing in the rear diff. Neither diff or the transmission had any grease in them. While I was in there I lubed them np with Lucas Red-n-Sticky which I have used for years and it works well and doesn't have any effect of the plastic.



Took it for a test run on my indoor course and it did fine, the course was built for 1/24 so for the most part it isn't that much of a challenge for the 1/18 scales. I hoping to be able to get it outside on the rocks today and give it a real shake down.