› Project: Mod Clod

A unique take on Tamiya’s sig­na­ture mon­ster

RC Car Action - - CONTENTS - By Kevin Het­man­ski

I had a blast when I com­peted in the first Mon­ster Jam World Fi­nals RC race in Las Ve­gas. I also learned a lot about the two trucks that I brought to the race. When Bari Mu­sawwir gave me a call and in­vited me back to the World Fi­nals, I de­cided I wanted to step up my game in the mod­i­fied Clod Buster depart­ment. Now, there are plenty of great of­fer­ings out there for chas­sis and sus­pen­sion kits, but I was look­ing for some­thing that didn’t yet ex­ist, so I took mat­ters into my own hands and de­cided to de­sign and build the ul­ti­mate chas­sis and sus­pen­sion kit for the Tamiya

Clod Buster. That way I could show up to the race with some­thing that would be fast and tun­able in just the way I wanted. Af­ter work­ing on it in­ter­mit­tently for months (in be­tween other projects), I fi­nally had a truck that I could plug a bat­tery into and pull the trig­ger. Here’s how I made it hap­pen.

Car­bon-fiber Chas­sis

When the time came to de­sign the chas­sis, I de­cided to go with some­thing that looked a lit­tle more real­is­tic. This meant that I had to use a

4-link sus­pen­sion that had the up­per and lower links closer to­gether. Af­ter fig­ur­ing out what

I was go­ing to do with the 4-links, I was able to move on to my chas­sis de­sign. I didn’t have time to draw the Clod Buster gear­boxes so that I could use them while de­sign­ing parts, so I took a bunch of mea­sure­ments and hoped for the best. I de­signed it to be wide enough for mo­tor clear­ance and long enough for gear­box clear­ance. I had the car­bon plates cut, but made the bot­tom plate and all the cross mem­bers my­self.

4-Link Sus­pen­sion

You can’t re­ally have a mod Clod with­out a 4-link sus­pen­sion, so that’s what I de­signed for my truck. A 4-link sus­pen­sion al­lows the gear­boxes to move up and down freely and ar­tic­u­late smoothly. I laid out the links on the com­puter and used that in­for­ma­tion to make up­per and lower links out of alu­minum rod with Traxxas rod ends. The mount­ing points are in line with each other, and the links are par­al­lel to keep the gear­boxes from twist­ing when mov­ing up and down. The gear­box side of the links are mounted in cus­tom­made C-chan­nel alu­minum mounts, which are se­cured to some square stock that runs from the gear­box out to the hub car­rier. This al­lowed me to move the links in more for im­proved tire clear­ance, and the square stock strength­ened the hub car­ri­ers a bit. On the chas­sis side of the links, there are three mounts for the up­per links, which al­low me to al­ter anti-squat, while the lower links are se­cured to the lower plate with hingepins that I made. A 4mm hex-head screw on each side se­cures the plate to the chas­sis and keeps the pins in place.

Heavy-duty Steer­ing

Since I didn’t have tra­di­tional axle tube stiff­en­ers in my truck, I had to fig­ure out a new way to mount my steer­ing servo since I couldn’t use the stock stiff­en­ers as a mount. I ended up run­ning out of time, so in­stead of de­sign­ing my own servo mount, I went with a gear­box-mounted one from Craw­ford Per­for­mance Engineering. It uses a plate, two spac­ers, screws, and Traxxas servo mounts to se­cure the servo to the gear­box. Be­fore mount­ing my Spek­trum S6280 servo, I drilled new mount­ing holes in the plate so that I could mount my servo far­ther back and out of harm’s way. I made steer­ing links out of alu­minum rod and Traxxas rod ends, and bent the up­per link so that I would clear the servo and its mount.

Easy-tune Sway­bar

When you run in dif­fer­ent con­di­tions, you may want to al­ter the feel of the sway­bar, and on my truck, I wanted some­thing that was easy to change and tune. I came up with this ba­sic de­sign a few years ago and tried it out on two other trucks be­fore re­fin­ing it to what you see here. The main part of the sway­bar is an alu­minum rod that piv­ots on ball bear­ings, and those bear­ings are housed in mounts that I made on my Zeus 3D printer. In each end of the rod is a hole that is used to hold a steel rod by way of a setscrew. On the other end of the steel rod is a mount for the link that con­nects it to the gear­box, and a sin­gle setscrew se­cures it. When the time comes to change the rod, you sim­ply loosen the setscrew in the alu­minum rod and the one in the link mount. You can then re­move the rod and re­place it with the size of your choice, and it only takes about 10 sec­onds to change each steel rod. If you only need a slight change in sway­bar ten­sion, you loosen the setscrew in the alu­minum rod and move the steel rod to­ward the cen­ter of the chas­sis to tighten the feel or move it out to­ward the out­side of the chas­sis to loosen it.

Mul­ti­ple Shock Po­si­tions

Even when it came to the shocks, I wanted a lot of tun­ing op­tions. A truck like this can see a high-trac­tion and smooth car­pet track or a low-trac­tion and rough dirt track, so the sus­pen­sion can be eas­ily tuned for any con­di­tion that the truck might see. I can mount the shocks from the gear­boxes to the chas­sis for a stiff setup, or I can mount the shocks on the chas­sis and use a can­tilever to soften up the setup. When mounted di­rectly, the bot­tom of the shocks is se­cured to the link mount and the top uses one of three mount­ing holes in the chas­sis. The three holes al­low the shock an­gle to be changed to fine-tune how they feel. When us­ing the can­tilever setup, I con­nect the gear­box to the cant through a short link, then the bot­tom of the shock is mounted to the other side, while the top of the shock is se­cured to the chas­sis. The can­tilever has four mount­ing holes for the links; the far­ther you move them out, the softer the sus­pen­sion feels and the more travel you have. With this setup, you can have a stiff or loose setup with­out hav­ing to change any­thing on the shocks. My shock of choice for this truck is the Pro-line Pro-spec and the soft­est spring avail­able from Pro-line; in­side the shocks is 10wt oil.

Replica Body

Af­ter be­ing in­vited to the RC Mon­ster Jam World Fi­nals, I was as­signed a body for this truck to repli­cate one of the full-size trucks that were in­vited to the World Fi­nals. I was given Bounty Hunter, and my plan was to use the beat-up body from be­fore, but a sur­prise pack­age ar­rived from Bari Mu­sawwir. In­side was a new Bounty Hunter body, with the up­dated trim scheme. Bari used an old HPI Bounty Hunter body, made a wrap for it, and ap­plied it for me. Be­fore mount­ing it on my Pro­line ad­justable body mounts, I took the time to de­tail the front wind­shield with black around the edges and sil­ver dots to rep­re­sent the bolts that the full-size truck­ers use to hold them in.


Here I am, stand­ing next to the Bounty Hunter mon­ster truck at the Mon­ster Jam World Fi­nals in Las Ve­gas, Ne­vada. It al­most looks as good as my Clod!

I de­signed my chas­sis plates to have a scale look, and once the de­sign was done, I had them cut out of 2.5mm car­bon-fiber plate.

A Craw­ford Per­for­mance ver­ti­cal servo mount se­cures my Spek­trum servo to the gear­box. Be­fore at­tach­ing the servo and mount, I took the time to drill new holes and move the servo back a bit for more clear­ance.

Square stock be­tween the gear­box and hub car­rier al­lowed me to at­tach a C-chan­nel alu­minum sus­pen­sion mount closer to the gear­box, which pro­vides more clear­ance for the front tires when steer­ing.

An old HPI Rac­ing Bounty Hunter body was wrapped by Bari Mu­sawwir, and it fea­tures the newer ver­sion of the Bounty Hunter trim scheme.

My sway­bar de­sign may look a lit­tle un­usual, but it’s func­tional, easy to use, and very tun­able.

The Pro-line Pro-spec shocks can be mounted di­rectly to the chas­sis or on 3D-printed can­tilevers. The can­tilevers have mul­ti­ple mount­ing holes avail­able to ad­just the soft­ness of the shocks.

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