Custom RC Rock Crawler

Hello, Everyone! today I will be discussing and writing about a project that I have been working on for the past year or so, That has been by far my most challenging and at the same time rewarding project so far. In this Instructable, I will go over all of the steps, challenges and testing that went into making this custom crawler chassis, as well as the materials to make your own if you are interested. Let's begin! Please remember to vote for my instructable in the Tech contest, if you like it and think it worthy...:)

Since I will only be designing and constructing the chassis for the rock crawler, I needed a base to build off of. That is where the Axial AX-10 Deadbolt Or the Axial Wraith come in. The AX-10 deadbolt and the Wraith are commercially available RC rock crawlers that are very capable in terms of trailing and light rock crawling. you will not, however, be seeing these trucks competing in any higher level of rock crawling, because the chassis and design of the truck itself (whichever one you have) are not specifically designed with competition rock crawling in mind. My goal for this truck is to design and make a chassis that is much agiler and capable on the rocks, but that can still rip around a trail and have fun with friends when the time comes. We will be using all of the mechanical parts of the truck in our build, but we will be constructing a new chassis, as well as re-arranging the existing parts of the truck to reach our goal.

To begin our build, we will need some simple parts from local stores around your area, as well as the parts from your axial AX-10 Deadbolt or Wraith. since these two trucks use the same axles, shocks, and transmission, which truck you start out with doesn't really matter, because these are the parts we will be using. however, we will need to buy a few materials before we can get started. first of all, we will need to get two large plastic cutting boards that are a 1/2" thick. These will make our chassis plates. Secondly, we will need some screws to hold it all together, so get 8 1'' long steel screws and 8 2" long steel screws. These screws are available at you local hobby store, and you will need matching hex drivers to put them in. In case you want to build your own RC crawler, here is the parts list;

-Two Axial Wraith complete axles with links included, available from e-bay among other places

-An Axial Wraith centre transmission with the motor plate and gear cover with axles. you may have to buy the axles separately, but the axles used on the Traxxas slash work great, once you drill the bottom out.

- a set of electronics, ie a brushed or brushless speed control, a motor, a servo (the bigger the better), a transmitter and receiver set and a lipo OR nickel metal hydride battery

-A set of four shocks, with long travel (the axial ones are good). plastic or aluminium body, it doesn't really matter for our purposes

- Four bead lock wheels and four rock crawling tires

-All assembly screws, which should come with the set of axles, transmission and extra parts. If they do not come with hardware, then you will have to buy them yourself.

We will need very simple tools for this build. The cutting boards (or Delrin) are fairly soft materials, but with a lot of strengths when braced and assembled properly. due to this, we will need a coping saw, available from any home improvement store for pretty cheap, and a cordless drill as well as some 60 grit sand paper and some 150 grit sandpaper. A sanding block is optional but recommended. Drill bits that are slightly smaller diameter as the shaft of our screws, but leaves room for the threads of the screw to bite into the plastic of our chassis to hold it together will also be required. Finally, we will also need hex drivers (1.5mm, 2mm, 2.5mm) to disassemble the original truck and assemble our chassis. A drill is good since the plastic is pretty tough, and we can save time and our wrists by putting the screws in most of the way with the drill.

Now comes the design of the chassis itself. do design the chassis, we first need to look at what makes a successful rock crawler chassis. after many hours of looking on the internet, I have narrowed it down to two things; the overall GC (lower to the ground is better) and the amount of grip and flexibility the chassis has, in terms of keeping the wheels on the ground. This Includes having the most ground clearance possible. Now this is simple for a motor on axle crawler (for example, the Axial XR-10) where the motors are on the axles so there are no driveshafts in te way. however, we are working with a shaft driven design with only one motor. Almost all competition rock crawlers have a chassis that is centred on keeping the weight low to the ground, and that is hat we will base our chassis design off of. We will design a chassis that has enough ground clearance for our needs, as well as a low centre of gravity to keep the weight low.

With our goal and theories in mind, we can start the design. My personal idea was to have the ability to use full stick packs, such as a 5000mah 2 cell lipo in my crawler for longer run times, while still being able to use a smaller battery out front to help with more challenging sections and competition courses. I found out that the only way to mount the battery lower in the chassis but still use a large battery was to mount the battery in front of the spur/pinion gear cover, but resting on the transmission case, as shown in the pictures. This posed a problem, however. It meant that when I ran the motor in the forward "normal" direction, the wheels were turning backwards. In my case, I simply took apart the axles and reassembled them upside down (flipped over). However, this could be avoided by simply wiring the motor backwards, with the positive to the negative and so on. This will not damage the motor, and will just reverse the rotation of the motor. Be aware, however, that this may require different driveshafts to make work. The Traxxas plastic driveshafts work well, but the bottom needs to be drilled out to for the axle and transmission yolks to fit. To mount a smaller 2200mah 2 cell lipo in the front, like those used in a 1/16 scale Traxxas car/truck, I found a 1" wide piece of a brass flat bar at my local hobby store and cut it to 6". I then mounted my servo to one side and left the other side for the battery. It was a quick fix but seems to work very well for what I need. I then made a 4" long link with some steel tubing and threaded rod, as well as some ball ends to complete the front battery tray.

Included here are a photo of the plans for the chassis of the crawler, as well as the other pieces used in construction. This has proved to be very strong and resistant, however, there are a few improvements that could be made to improve the overall fit and finish, as well as the simplicity and cleanliness of the design, including rounded edges on the corner to fit the top on tighter.

This is by far the most labor intensive part of this build, the cutting. As mentioned before, this is a very tough material and is relatively difficult to cut by hand. however this stuff also has a very low melting temperature, which means that any high-speed tool (Sawzall, etc.) will just melt the plastic. in this case, a very slow reciprocating saw or band saw can be used, but be careful not to begin melting the plastic. with all of the shapes cut out, you can now drill holes where indicated in the plans. once all of the labor intensive stuff is done, grab yourself a cold drink and sleep off the pain...:). Worth mentioning that the holes drilled in the middle of the two holes used to hold the chassis the motor mount plate are not all the way through, just enough so that the pegs can seat in nicely. I put in two aluminum tubes to give the truck a sort of grill. This is not necessary as the velcro strap will hold the battery in nice and tight regardless

The video shows the construction of the truck, from its separate chassis pieces into the final product. As discussed earlier, the transmission is mounted backwards in the truck to allow for better battery placement. This also means that the motor needs to be wired reverse; negative to positive, and so on. Otherwise doing what I did would be the best option, which is flipping the axles. There is only one extra step, and that is to flip the shocks upside down so that they can fit on the chassis properly. It is not a perfect solution, but it works. Fitting the transmission in is pretty easy if you simply separate the two halves and slide the motor assembly in.

Now that we have a very strong and versatile chassis, we need to find a way to cover it up to protect all of the electronics and the battery. To do This, I purchased some velcro strips from my local hardware store and cut them into strips 1/2" wide. I then ran them down the vertical plates of the chassis and tacked them down with extra screws. This could also be done with small nails if a small pilot hole was drilled. This velcro will hold on the top, with the opposite side of the velcro going on a 10" by 3 and 3/8" piece of Lexan. This can be painted to make any colour you want, and I added googly eyes to mine ;). This allows for very cheap and simple body cover replacements because one sheet of levan costs about 5$ and you can make over 20 from one sheet! I prefer 1/16" Lexan because it is tough and resists crashes well.

One of the biggest problems with using a cutting board, and one huge advantage to using Delrin, is that because they are made to cut food on, the plastic is infused with a nonremouvable oil. Long story short, nothing sticks to it. In my case, I found that using small screws to fasten in some lexan allows for a double sided tape friendly ESC and receiver sticking surface. I decided to mount my electronics underneath the back plate, and this has been solid since the day I built it.

During all of my tests, I discovered that my custom chassis out-preforms the stock chassis in almost every way. The higher ground clearance and much lower centre of gravity work wonder for this truck, and can complete my local competition rock crawling course with ease. My next step is to bring it to a real chafty comp and see what the professional rock crawlers think of it. As far as my criteria go, this has been a resounding success in terms of the trucks performance, and the ease of use of the truck itself. This truck quickly became my favourite build so far, and I am very pleased with the way it turned out. Thank you guys for spending your time reading my instructable, ad I hope you guys are having as much fun in this RC hobby as I have. Till next time

Cheers!

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