Build Article: Hobao DC-1 KIT

Building Hobao DC-1 KIT
Article By: Joona Kankare

The winter was quite uneventful for RC hobbyists in Tampere. This year it was cold and we had some snow as well, which limited the possibilities to drive outside and the chances to drive indoors were also limited. When the spring came, I couldn’t resist the urge to buy myself something new to play with. After a lot of thinking, I ended up getting the Hobao DC-1 assembly kit.

DC-1 is a scale crawler with 313 mm wheelbase. The Lexan body is not licensed, but it’s something between a G-Mercedes and Defender. There are a lot of body options for 313 mm wheelbase from several brands, ranging from Lexan to hard plastic. The car has a front motor, so the center of gravity is in the front (not surprisingly). The motor is placed as low as possible, so the center of gravity does not rise too much. The car has a few placement options for the battery mount. The car has two gears, so a radio with at least three channels is needed. Alternatively, you can lock the gear switch to either one of its extreme positions.

No electric components are included in the assembly kit. I had a spare 4-channel Sanwa MT-44 with a receiver. For speed controller, I chose the good old Hobbywing 1080 and for the servo, the waterproof Savöx SW-1210 with 20 kg torque. For the gearbox, I had an old Chinese servo lying around, which unfortunately is not waterproof. In addition to all of these, I will also need a battery and a charger. It’s best to plug all the wires in only after you’ve finished assembling the car. Otherwise the wires will get in the way when installing the body.

I didn’t get a lot of details about the car beforehand, but here’s where I made some modifications:

1. You can tell already from the pictures that the original bolts and nuts of the links and springs are going to get stuck in rocks and tree stumps.

2. The original springs are a little stiff, though they work alright especially with a larger battery pack. I myself prefer 2000 mAh batteries. The larger and heavier motor also makes the springs feel a bit stiffer.

3. The wheels were a little weird and the grip wasn’t that good in all terrain types. I got GMade steel beadlocks (the tires are not glued) which bring the center of gravity lower, and for the tires I got Pitbull Rock Beast XOR.

I’ll get back to these along the assembly. The changes are in no way necessary but are easy to carry out especially because of the screws of the axle.

Let the assembly begin

The assembly kit contains all the needed basic tools: 1.5 mm, 2 mm, 2.5 mm Allen keys and a couple of socket wrenches of different sizes. And in addition, you can find Vaseline, shock oil and thread-locker in the package. The thread-locker had leaked inside its bag, but I had some left from previous car projects as well as a bunch of other useful things. In addition to the provided tools, I would recommend getting a hobby knife, long, ball-headed socket wrenches for spots that aren’t easily accessible, regular pliers and side-cutting pliers. It’s good to have some spare Vaseline and there’s really no reason to go easy on it during the assembly.

The manual is pretty clear with the exception of a few mistranslations and instead of thread-locker the manual speaks of superglue, which is not such a good idea in case something needs to be disassembled. The bolts and nuts in the package are decent quality. The nuts are all nylocks and can be opened a couple of times without problems. The parts all come in bags and the manual tells you which bag to open at each stage. At some stages you’ll need to find the needed tools yourself.

NOTE: ALL THE SCREW SIZES AND LENGTHS MUST MATCH.
I had some issues fitting some of the parts in their place after using the wrong screws. There were several spares for most things, so no need to panic about that.

The drivetrain The assembly begins with the drivetrain and the gearbox. Use thread-locker when tightening the small screws so they won’t loosen during runs. Moderate force while tightening is enough. There are plenty of bearings in the assembly kit and they seem to be fine.

The quality of the gears and axles is good. So far nothing has broken down. The gearbox and the transfer case are assembled first. They will be connected to each other when the chassis is assembled.

The gearbox is mounted on a metal plate, and the motor is mounted on the plate with a middle piece with a heatsink enclosure. The spur remains in the middle with its slippers and the pinion. The gears are 32p-sized in case you desire alternatives for the pinions. The original 15-tooth pinion is decent, but you can try a larger or smaller one. You need to leave a bit of play between the spur and the pinion, so that when you spin the spur gear with a finger you can feel just a tiny bit of play. Spin the gear all around to see it doesn’t drag at any point or feel like there’s too much play. Otherwise you’ll need spare parts soon when you’re missing teeth from the gears.

The transfer box delivers power to the front and rear axles. The transfer box is where you’ll attach the center universal axles, which in this kit are plastic. The plastic is thick and, in my experience, durable. The bores are big enough

The chassis, links and the others

The chassis differs from the typical crawler design with the u-blocks. The chassis is made from solid material and has places for all the components. The fixed places for the components make the car more durable but remove the possibility to move around the components. For example, you can forget about increasing to the wheelbase. However, you can reduce it by a couple of centimeters without causing permanent damages.

The bumper mount, gearbox, center rear, front skid plate and the other parts are on the chassis. Looks pretty and the bottom is smooth. It shouldn’t get stuck on every corner and stick on the ground. There are small brass wheels under the skid plate which are meant to help sliding over obstacles. It remains to be seen how those will work.

The car has a traditional 4-link in the rear, 3-link in the front and a Panhard, because the servo is mounted on the chassis. The links are assembled with aluminum pieces that have a smart design. The ends of the links are attached with M3x12 screws, which, in my opinion, could be a couple of millimeters longer.

Some of the balls are a little too big for their cups, so you can use a drilling machine to make them work smoothly by spinning the balls inside the cups few times. The easiest way is to get the balls in the cups are by placing a small shell under the cup and pressing them carefully with pliers.

Now, the links are installed. The outer links are installed directly to the chassis. If you want to mess around with geometry, you’ll have to find an extra piece to get additional places for the links.

The Savöx servo needs a bit of modification. There’s an extra supporting piece on the servo mount that you’ll have to cut off, otherwise the servo will not fit. Also, there won’t be enough space for the servo arm to move around the chassis (as you can see in the image). I didn’t want to use the original plastic servo arm because in those, the bores in them will wear out fast. So I cut holes for sunk screws in the arm and now the servo arm can move freely (not visible in the image because I did this afterwards) I recommend using the original as a reference and trying to find an equivalent metal arm, for example Hudy’s Offset arm. This will depend on the servo too, in some brands the arm might be higher.

The space for the servo is a little tight. There aren’t a whole lot of space in any direction. You might need to replace one of the screws in the chassis with a shorter one, so it won’t hit the servo. Though I may have used a longer screw by mistake.

The battery mount is pretty nice and you got two options for placement, either in the back of the car or a bit more toward the front. The battery is mounted with a rubber strap, which seems to do the job well with a suitable sized battery. Smaller batteries might require a bit of stuffing around them, for example foamed plastic. Sliders are also mounted on the chassis (make sure to pick the very thin screws, I tried with the wrong ones at first), as well as the bumpers and body posts.

Axles

The axles in the DC-1 are a little different from the usual. I modified them a little to improve the angle of turning and so they’d slide better on rocky terrain. The material is very thick and strong plastic. There’s some space in the middle for the driving axles.

There are two similar axle housings – one for the front and the other for the rear. The angle of the pinion gear is a bit upwards, perhaps to reduce straining on the universal shaft joints. There are separate diff caps for the axle, so there’s hope that in the future the axles can be assembled for possible multi-axle configurations. The other lid also serves as a mount for the inner links. Be careful not to mount the box upside down.

The gears seem to be machined. They look very similar to those in Hobao’s buggies, so they must be durable. The axle spacing is 36/15, the pinion could be a couple of teeth smaller but it’s fine as it is. The gears are set with a guiding system that I’d never come across before, but they settled right away without any need for shimming.

The axle housing has mounts for the links and the caster block can be adjusted with bores for different angles. The recommendation is 20 degrees backwards. I turned the shock mount forward so the shocks line up better. The link mounts are supposed to be installed with the nuts pointing downwards, but that doesn’t make any sense to me because that way they’ll only get stuck in sticks and stones. I recommend replacing them with M3x22 round-headed screws or M3x22 sunk screws (20 mm might be enough). You’ll need to cut slots for the sunk screws.

The ends of the axle are locked onto the axle housing with a couple bolts and nuts that seem sturdy. I recommend against following the manual when doing this and use sunk screws instead (M3x20, 18 mm might work too). The turning radius of the car is reduced a little bit and so far the drive shafts have been fine with that. The C-hubs are mounted with a couple of bigger bolts and a small metal bushing is installed between them to keep the plastic from wearing out. Be careful so you’ll get them the right way. A metal Ackerman plate is attached to the plastic hub with a couple of screws. The servo link is mounted on this plate and the turning link between the hubs. The turning link is installed to the bottom of the Ackerman plate, the servo link on top of it. Do this carefully to get them right, because otherwise you’ll have problems. Again, trust me – I know what I’m talking about.

When the axles are done, you can mount them with the links. At this point, make sure the axles move freely to every direction and that no parts are hitting each other. Fixing things is easier at this point when there aren’t that many parts to disassemble.

Suspension

The shock absorbers are exemplary in the crawler category. You can tell Hobao has experience with buggies. The shock bodies are aluminum, the O-rings are silicone and there are double O-ring seals on the shocks. The shocks are a bit shorter than 100mm, by removing the bottom caps you can increase the length by a couple of millimeters.

The structure of the shocks is similar to those in Xray. There are guiding plastic pieces on both sides of the O-rings and a small washer is placed in between. Before installing the O-rings, dip them in oil so they won’t leak. Tighten the cap only when the shock shaft is on its place.

The pistons differ from the norm, which I assume to be a good thing eventually. Usually there are holes in the pistons that get blocked by the e-clips when using thinner shocks, and their functioning depends on the piston’s position. In these pistons, there are no holes but small grooves to allow the oil to flow.

The pistons are pretty tight. Be careful when cutting them off the parts tree and make sure to remove all the molding debris. The piston is installed with two e-clips. The shaft should move freely up and down inside the body. If not, take the piston out and sand down the edges with fine-grit sand paper. I used 1000-grit wet-and-dry sandpaper to make it smooth enough. Once you’re happy with the result, add the oils. First about half full, then move the piston up and down a few times so the air gets out. Now fill all the way up and press the shaft in until the threading is almost level with the bottom cap. There’s enough oil when you push the piston up and the oil is 3 mm to the brim. Hold the piston still and insert the cap carefully. If the piston is moving outwards, remove a couple of drops of oil and try again. If there’s too much oil in the shocks, it’ll limit the shock’s movement.

I cut about 0,5 mm pieces off my pistons from where the groove is, but if you are using the oil that comes with the kit, don’t do this. I wanted better tuning possibilities with the oils, and I got a pretty good selection oils at home. After some testing, I chose 500cst oil for the shocks which, I’d say, turned out pretty well.

When you’re inserting the ball ends , you can hold the shock shaft still by squeezing it by the end of the threading with pliers. That’s the only place where you can get a good grip. You don’t want to scratch the shaft, because scratches will wear out the O-rings. When the ball ends are inserted, you only need to add the springs and mount the shocks. The Panhard link will be mounted together with the right shock in the front. Mounting the shocks goes the same as with buggies. The jointing is from behind toward the front, whereas with crawlers it’s sideways. This does not have any impact on how the car runs, but the positioning of the shock is easy to change by changing the order of the washers. By adjusting the position of the shock you can change how the suspension works in extreme positions, or it might be necessary if you want to change the axle spacing to fit another body.

For me the suspension was a bit too stiff. I like driving with lowered suspension. I found spare suspension for my car in a department store, and they were a bit too soft. But suitable for my driving style anyway. The optimal choice would probably be progressive springs or a shorter stiff spring as an extension to a softer one. Testing continues... I know someone is going to ask about the spring size - it’s 75 mm long and the inner diameter is 12.5 mm. The diameter of the Axial springs was identical, if I remember correctly.

Wheels

I personally don’t like the type of tires that are glued on the rims, so I didn’t use the ones that came with the kit. The rubber is soft and might have a good grip on rocky terrain, but the pattern on the tire is so dense that it might not be good in mud or other soft terrain like that. The standard foams are also very soft and the car itself is pretty heavy. They probably run flat a lot. The nice-looking rims and the spare tire are a plus. There seems to be a spare tire hanging on the back of every crawler.

Body

The body of the DC-1 has a very smart design and it comes with a bunch of nice things. Very few kits come with a hard body and nearly everyone want to have a body of their favorite brand. In any case, the body seems like a mix of G-Mercedes, Land Rover and Japanese off-road vehicles. Mostly Mercedes. The body comes with inner fenders, roof stands, wing mirrors, door handles, door panels, rearview mirror, windscreen wipers for the front and back, snorkel, dashboard, front seats (Lexan), gear and hand brake handles, lenses for the lights (+led mounts), shiny stickers for the light cups and mirrors. There’s also a good amount of additional stickers for the interior. And masking for painting the windows.

The body is pre-cut and drilled. Mine didn’t have holes for the windscreen wipes so I measured the correct distance and made them myself (no one else has complained about this so it might be a factory defect). All the parts have sizable washers inside the body and plastic pieces to place under the screws so they won’t tear holes in the body on the first crash. The plastic is the same flexible and strong material as elsewhere in the car. I did a few test runs and the mirrors are still there. The inner fenders block the view into the interior of the car and there’s enough space for bigger tires (XOR, ca. 120 mm).

I wanted to test Rubbercomp (maston) to paint the body. It turned out to be a suitable choice for a Lexan body that protects paint from abrasions. There’s no need for masking, you’ll only need to remove the paint from the windows with a hobby knife. Watch out for dripping when using Rubbercomp. You’ll want to have multiple coats however, and the thicker the coat is the easier it is to remove later and it also covers better. I’ll probably end up with a different color, but I just wanted to test this out.

The interior is really cool. I’ll add some more color in there too and the stickers. The interior is placed in the body and it can easily be removed together with it. The dashboard has the indicators, navigation/radio, switches for AC and a bunch of other things.

In the image the car still has the protective plastic on, I won’t remove them before the final paint. That’s why the windows look dim and there are no stickers. In my opinion, the body is really nice and I recommend it for others who’d like a Lexan body.

Concluding words

The car works decent straight from the box. The center of gravity could be a little lower and more in the front, but it’s basically ready for racing as is. At the time of writing this article, I’ve driven for about 3 hours and there are no signs of parts breaking down. The car’s been put through a lot during the test runs.

The total weight with a 3S 2100 mAh battery is 3400 g and the weight distribution in favor of the front is 1800g/1600g. I’ll add metal sliders to my car when I’m in the mood for crafting. And while I’m at it, I’ll move the battery to the left side of the car. This will move the center of gravity a bit lower and toward the front. I also tried fitting a 3S 1600 mAh battery in front of the motor and the servo, and it would fit there without the need for any modifications. I might actually try that set up later on. I’ll probably replace the bumpers with metal ones with a nice design. Or if some other nice options appear in the markets.

I’ve nothing negative to say about this kit with the small modifications. The angles of the axles could be a bit rounder, but they don’t get stuck on things if you drive carefully. The bottom is already very smooth so that’s not causing any issues. The sliders aren’t optimal and in tight spots might get stuck on corners.

Someone at Hobao has had to observe what’s happening in the markets when they started designing this car. There are a few defects, but nothing that can’t be fixed. The price-quality ratio is good. The RTR-electronics are decent as well and their share of the total price is not that big.