Making a Custom RC Car (The Wrong Way)

I've loved RC Cars and have built them, drove them, and wrecked them with equal skill throughout the years. Through all of this, I accumulated a variety of parts (thank you, E-Bay) as well as partial cars. The cars I started with was a vintage, but broken Latrax LTX-40, and an equally vintage and broken Tamiya Blackfoot. I also had a ton of parts that I cannot say what cars they might have come from. The challenge was to combine as many parts into a single working RC Car. The end product was my very own, custom-made Hodgepodge Car.

As I had nothing more than basic hand tools, including a cordless drill, not much came out straight. I highly suggest having at least a drill press so you experience my difficulties. I didn't buy anything for this project, but used up what I had on hand.

Supplies:

Whatever you have on hand.:

Drills (preferably a drill press)

Files

Some way of accurately measuring (I used a metric/fractional ruler)

Basic hand tools (screwdrivers, etc.)

Some way of making accurate cuts (I used a mitre box and hand saw from Home Depot)

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Step 1: The Basics

The very beginning of the car is to create the powertrain. I started with the transmission of a Tamiya Blackfoot that I wanted to put onto the Latrax chassis. The problem with this was that the Blackfoot transmission was a swing-arm type of suspension (not very common) and the Latrax had no suspension. To combine the two required a fundamentally different approach that the Blackfoot powertrain wasn't designed for: I went with a wishbone suspension.

Along the way, I discovered a VERY important rule of suspension/transmission physics: the rotation point of the suspension has to be in line with the output of the transmission or the axle will fall out during operation. While it is obvious now, it wasn't then.

Another thing I did, which is in line with my current occupation, was to create an engineering model of the suspension as it attached and operated on the transmission. This enabled me to figure out all the problems I was having without practically ruining the parts in the process.

Step 2: The Axle Blocks

The beginning involves making the axle block for the rear axles. I had a block of plastic leftover from another project, so I used that. For simplicity's sake, I used a metric ruler as the Tamiya parts are in metric. The problem came with converting my fractional drill bit into metric. That's what the internet is for.

The axle block was simply drilled through as perpendicular as possible since I did it by hand and then the hole was enlarged to make the axle fit somewhat straight. Again, use a drill press, if you have one.

After I had repeatedly drilled to get the axles straight and working smoothly, I assembled the spare parts I had from a Blackfoot, although some were definitely after-market, as the original never had a dog bone axle, which is what I used. The reason I went that way was to provide a wider wheelbase than the standard Tamiya Blackfoot.

Step 3: Wishbone Suspension

For the wishbone suspension (sort of...) I used the remains of a picture frame I had made with a pallet I had scavenged from a local lumberyard. This wood I believe is Massaranduba, but no guarantees. It's amazing what you can get from pallets. Anyway, it's a very strong and dense South American wood, perfect for a prototype suspension. The cross brace I made from some small pieces of Mahogany that I found lying around from yet another project. Really, anything would have worked.

The measurements were strictly for the length of the axle, which will change depending on what you have, so I won't include any measurements other than to say to drill in the center and drill straight.

Now, the way I designed this suspension was that the axle block would rotate in the frame of the suspension. This is not a double wishbone, but closer to a single, which is more typical of the front suspension on the older Japanese cars. With that said, you need a tie rod attached both to the pivot point of the suspension as well as to the axle block in order to make the thing work. Lessons, yet again. Another thing to not is to give the axle sufficient clearance in order for the suspension to pivot, or it will jam the whole thing up. There isn't a magic number for this, although I'm sure there is a formula out there. Just give it some room, but not too much or it will pop out.

Step 4: Assembling the Prototype Suspension

The prototype suspension was a piece of door skin that I attached to the transmission. Not being formed specifically for the transmission, some adjustments were needed in order to make it work. This is where I adjusted the length of the suspension arms and worked out the locations of the pivot blocks for the real suspension.

Step 5: Duplicate and Assemble

I didn't take pics of the drilling process or assembly process as most of the issues were worked out in the prototype, but there are always new problems that pop up. Here, the wheels were attached in order to begin the alignment of the axle block by adjusting the tie rods.

Early in the process, I thought of lowering the profile of the Blackfoot transmission, which is rather tall. While this increased the relative difficulty, it did reduce the profile of the transmission as well as provide me with more of the sheet metal that made up the sides of the transmission case to bolt to.

Step 6: Front Suspension - the Basics

The front suspension is an internal spring. This design was original to the Tamiya The Frog car. I used that concept to reduce the profile, although I used the parts from the Blackfoot. The front suspension block was also from the plastic that I had. Using wood might have been better from a material standpoint, but I was worried about the drilling not being straight due to grain interference. It turns out that I can't drill straight to save my life. Oh well.

Since the Blackfoot directly inherited the chassis from The Frog, parts for an internal front suspension were available. Be careful about using pilot drill bits, as they can heat up the material and snap, causing the mess that is in picture two.

Due to the wide wheelbase, I used two springs that I found in the general mess and assembled the suspension with the original piston pieces for The Frog with the brackets for the Blackfoot.

Step 7: Front Suspension - Finishing

The front suspension block was match-drilled to the Latrax chassis, which amounts to three screws. I tried to minimize the amount of extra drilling on the Latrax chassis in case I decided to ever rebuild the car. Chances are, I won't.

The rest of the suspension are directly from an original Blackfoot, minus the shock tower. The main difference in the front suspension between The Frog and the Blackfoot is the shock tower, so assembly wasn't too difficult.

Step 8: Rear Suspension Mounting

Here, you can see how I bent out the metal skin of the transmission and modified it to fit the Latrax chassis. You can see in the pics how I had to modify the rear suspension block to allow the motor to fit. The original design of the Blackfoot transmission didn't allow for what I was doing, so I had to make some design compromises, including drilling new mounting holes for the motor and reinforcing them. So far so good, and the motor hasn't torn itself out of position yet. That may come later.

You can also see the completed front and rear suspensions on the existing chassis with its original battery case. I wanted to keep the original design of the Latrax battery case as I originally anticipated needing a 14 volt battery pack just to make this car move. Fortunately, I only needed an 9 volt battery pack for initial tests.

Step 9: Rear Shock Tower

As most of you will notice, the rear suspension had no springs yet. I delayed the construction of the rear shock tower based on how I assembled the front and rear suspensions. The tower blocks were cut with the mitre box and formed with a large hand file to achieve the shape. A second one that was a mirror image of the first had to be made as well. These were drilled and mounted to the existing holes in the transmission, allowing fewer holes to be drilled to secure them.

Mounting blocks were made and attached to the axle blocks to attach the struts to the center of the axle. The struts were equipped with a pillow block type of base, which is essentially a rotating bushing that allows for imperfection in alignment. Needless to say, I needed that.

Step 10: Steering

The steering was possibly the most difficult outside of modifying the transmission to accept a fundamentally different suspension design. The major reasons for this were space constraints, lack of desire to modify the chassis, and not buying any new parts.

As seen, the turnbuckles were joined by a threaded standoff, as commonly used in the electronics industry and for the RC Car industry as well, although not for this purpose. The intent was strictly to increase the length of the tie rods to steer the car, as the front wheelbase was wider than any other car I had.

The initial mounting of the servo was a failed attempt at an initial rear suspension design. It was later cut down to make space and match drilled into its location using the existing holes in the chassis.

Step 11: Front Suspension Stabilizing

The bumper was the next, but that was ignored as stabilizing the front suspension was more important. The piece that I made to fit and stabilize the front suspension made for an effective initial bumper anyway. The piece of plastic was yet another leftover from another project that had been lying around for years. I used a chisel in order to set it in the chassis. The suspension tie rods are original Blackfoot, so I opted to continue with the existing design and make a piece to work around it.

Step 12: Test Run

The car was equipped with a vintage radio controller and receiver that I cannot say where they came from, except E-Bay some years earlier, when I was putting together a couple of Latrax LTX-40 cars and some Tamiya Rough Riders. Finding matching radio crystals close to the original frequency of the radio and receiver took some time, as well as rebuilding the radio itself.

As you can see, the mounting block for the steering servo was cut down to provide room for the radio receiver battery pack which was attached with old servo tape. A lot of servo tape was used. The speed control is from a Tamiya Rough Rider, although the linkage isn't. The speed control was attached to the motor with alligator clips in order to determine the correct polarity of the motor.

Additional adjustments to the steering servo and the speed control were necessary in order to bring them within the mid-range of the servo travel once the radio was powered on.

The radio receiver was mounted on the outside to the front suspension block due to space constraints as well as the future desire to upgrade the battery pack to a 14 volt or higher system. The distance from the motor and the battery reduces the EMF interference, especially on an older radio.

Blackfoot rims and tires were used to provide additional ground clearance, although wheels and rims from The Frog would have worked as well, the design being similar.

Step 13: Soldering and Body Mounting

The wiring had to be replaced, routed, and soldered. The wire came from an old fluorescent shop light that failed. It is 14 gage solid wire, typical of an indoor light. A standard 180 hook was used to attach the wire to the motor terminal. Wire routing was completed with electrical tape.

As a note, for the basics of soldering, just make sure that you clean up whatever residual mess yo've inherited with flux and solder wick to make a clean joint. Tin the wire you're about to solder before you form it into the hook and attempt to solder it on. Life becomes easier when you do that. Make sure you use some sort of relatively pure alcohol (Isopropyl Alcohol 90%, denatured alcohol, or something similar) and a cheap small paint brush to clean up the flux, or it will eventually corrode your solder joint and make any later fixes that much more difficult.

The body mounts were found in the general mess and screwed into the front springs block and the rear shock tower blocks. As a happy accident, I ended up snapping the head off of an aluminum screw for the front body mount, allowing me to thread the body mount onto the threaded stud and secure it.

Finally, the body itself was a left-over from a previous RC Car that no longer needed it and was repainted with additional holes made to mount it. Eventually, a bumper will find its way onto the car. But, for now, the car runs well and steers straight. The Hodgepodge runs!

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