Humpty Dumpty (Hobao DC-1)

[Joonatin]

So, I ended up ordering one of these, it was cheapish and not many of them seem to be around yet. This will not be a full build report as Soze did an excellent work on that already (Soze's Hobao DC-1 kit build). This will mostly be about some minor modifications I've done to it, possible upgrade parts when they become available and such...

Some things to know about the car:

• Lexan body, with an insane amount of detail parts and front interior.
• Front motor, placement ok.
• Two-speed transmission, though the difference isn't really that big between the gears.
• Driveline feel is generally very robust, not likely to break anything soon, all gears are metal.
• Axle housings are really thick plastic, there's only room for the driveshaft inside, not likely to break. 15t:36t gears in the diff.
• Diff covers on both sides of the axle, will be interesting what people come up with for this. Hoping for smaller pinion options, Hobao does make 11t and 8t gears for their buggies which might fit with a new cover.
• Very good aluminium shocks right out of the box. Excellent design taken from the buggy world where the shocks can't leak all the time. Shocks are mounted front to back, so angle adjustments are easy to do.
• Chassis rails are thick aluminium, CNC. all the parts, skid plates and such, have slots for them.
• The bottom of the car is really smooth, there's big inner fenders and overall there's not much that would catch on rocks and sticks.
• Stock tires are a bit weird, foams are way too soft.

WRRROOOOOOMM!!!! Tires are Rock Beast XOR on Gmade SR02. I want some different ones but these'll do for now.

A small clip of driving around https://www.youtube.com/watch?v=IewBjTWuGvw

[Joonatin]

First thing to improve in my opinion (excluding the tires) is the weird way the link carriers are mounted on the axles. The bolts are supposed to come from the top and you should the screw the nuts under the axle. I suppose these would be sticking to every rock you drive over. I swapped to button heads, 22mm long should be good. You could of course use countersunk screws too. I just didn't have any of proper length around right now, so these'll suffice for now.

In the picture above you can also see that a cap headed screw is also used on the steering knuckle. This will limit the amount of turning you get. I swapped these to countersunks.



There, now she's pretty and turns like a champ.

[Joonatin]

As mentioned before the shock design is excellent. Straight from the buggy world. Aluminum body, two o-rings sandwiched with plastic washers. These aren't likely to leak any time soon. Be careful that you don't put too much oil in them. Just enough to get zero rebound when you close the cap.



The pistons are also a bit different from what we are used to. There are no holes. Just little cuts on the side. The pistons are also quite snug in the shock body. You want to be careful that you leave no flash on them when cutting them from the sprue. I sanded mine a little with 1200 grade paper. I also cut the sides a bit bigger to allow a wider range of oils to use. The irginal notches are so small that they are okay with the water like oil that comes with the kit. I cut maybe 0.5mm more off the sides and use 500cst oil. Seems quite good for now.

Stock springs seem a little too hard. I switched to some softer ones from a local hardware store but they are a bit too soft. I'm using almost full preload for now. Once I get a bit more steel on the chassis the stock ones might be good to go.



Savöx servo isn't a straight fit. There's some extra plastic on the top side of servo mounts which you'll have to cut away to fit your servo in the car properly. Also, you'll need an offset (couple of millimetres) servo arm. The one in the picture has trouble clearing the chassis properly.



Servo placement is a bit tight but those metal washers you see are really good. They support the servo really well and are maybe 2mm thick.

[Joonatin]

I painted the body with plastidip for now. Quite a hassle free job with no need for masking. Just cut and peel away. I will repaint it soonish. It'll probably be a lime green metallic in the end.



And as said before, there's a lot of details for the body. Everything is mounted with washers on the back so they wont come through the lexan too easily. And the body is precut and drilled, though mine was missing the holes for front wipers.

Here's a comparison video of my car versus a friends SCX10. SCX has way more weight on the front than mine. Of course, I added around 100g of wheel weights to the front bumper after the video.

[Joonatin]

Nudie pic:


Electronics are HW 1080WP ESC, Etronix 35t motor, Sanwa MT-44 radio, Savöx 1210MG waterproof, Hobbyking cheapo for transmission, random 1600-2500mAh 3S batteries.

To-do list:

• CI foams for the tires (or make my own), the stock Pitbull foams are quite hard.
• Metal sliders to the sides
• Metal bumpers, once I figure out a design
• Repaint the body
• Move the battery pack on the sliders to get more weight forward, some of my 1600 mAh pack would fit in front of the motor and servo too
• Experiment with link geometry and stainless steel links

[Joonatin]

Welp, I've run a couple of packs through the car now and am still liking it quite much. I've added 100g of extra weight to the front bumper and messed around a bit with the shock preloads. Seems to work well now, though the foams were a bit hard to my liking. Better foams are on the way to me, but I still decided to open the rims (ugh) and cut up the foams a bit with a criss cross pattern and plucked a bit of it away. Cutting with a hacksaw blade works extremely well, at least for the really hard Pitbull foams.





If you decide to do something similar, make more cuts and pluck away a bit more. The contact patch is noticeably larger but could have been even bigger. I didn't really plan these before too much. Just tried it.

[Joonatin]

Also, did some magic on the rear geometry, as the car seemed to like to raise the front a bit too much on steeper inclines. I spent a good amount of time measuring stuff, putting measurements in excel, taking the car apart a bit, drilling and putting it together again.

WARNING, BORING MILD THEORY STUFF AHEAD! Excellent Excel file for us boring people here

So, the car geometry. Anti-squat is about 97% with the heavy wheels which considerably lower the center of gravity, and the lower ride height I'm getting with the softer springs... The measurements should be fairly accurate, except for the CG which was approximated by hanging the car from threads attached to axles, bumpers and such and finding the intersection point. If I don't completely suck, it's about 106mm high for the car. Even if I am, at least the changes I do will move the AS to the right direction anyway.

So, stock with the heavier wheels and lowish ride height. 56k warning... Sorry for the big picture. 97% of anti-squat, Instant center almost on the front tires center patch... Someone has probably been doing some real planning for this. I didn't give the Excel file any link lengths but it counts them anyway and they were within 0,5mm of the real ones so the measurements should be quite accurate.






I'm also thinking of having someone do a part that allows me to actually adjust the AS without drilling more holes. If I really wanted to do it at least. Might just stick with the change I did already if it's any good. It could be fun to do it though, even if there's no other purpose. Of course I could make it active too with an Arduino, a strongish servo and and a gyro or something... Would be interesting to have it adjust front and rear suspension to suit the inclines, declines and such. Though most likely it would end up being useless

I also have some Revo rod ends on order and thicker heavier steel for the lower links. They are sturdy enough but could be a tad heavier. The same 6mm steel tube will probably make up the new sliders too.

[Joonatin]

Color update! Looking a lot better in my opinion... Now if those new wheels just decided to show up at my door someday.

[soze]

Great job man! I still need to get out and run mine more thoroughly. Hard with my job getting in the way and all....

[JatoTheRipper]

Originally Posted by Joonatin

Also, did some magic on the rear geometry, as the car seemed to like to raise the front a bit too much on steeper inclines. I spent a good amount of time measuring stuff, putting measurements in excel, taking the car apart a bit, drilling and putting it together again.

WARNING, BORING MILD THEORY STUFF AHEAD! Excellent Excel file for us boring people here

So, the car geometry. Anti-squat is about 97% with the heavy wheels which considerably lower the center of gravity, and the lower ride height I'm getting with the softer springs... The measurements should be fairly accurate, except for the CG which was approximated by hanging the car from threads attached to axles, bumpers and such and finding the intersection point. If I don't completely suck, it's about 106mm high for the car. Even if I am, at least the changes I do will move the AS to the right direction anyway.

So, stock with the heavier wheels and lowish ride height. 56k warning... Sorry for the big picture. 97% of anti-squat, Instant center almost on the front tires center patch... Someone has probably been doing some real planning for this. I didn't give the Excel file any link lengths but it counts them anyway and they were within 0,5mm of the real ones so the measurements should be quite accurate.

I'm also thinking of having someone do a part that allows me to actually adjust the AS without drilling more holes. If I really wanted to do it at least. Might just stick with the change I did already if it's any good. It could be fun to do it though, even if there's no other purpose. Of course I could make it active too with an Arduino, a strongish servo and and a gyro or something... Would be interesting to have it adjust front and rear suspension to suit the inclines, declines and such. Though most likely it would end up being useless

I also have some Revo rod ends on order and thicker heavier steel for the lower links. They are sturdy enough but could be a tad heavier. The same 6mm steel tube will probably make up the new sliders too.

That link is awesome! Thanks for sharing!

If you wouldn't mind measuring, please share the length of those shocks either eye to eye or overall.

[Joonatin]

Originally Posted by JatoTheRipper

That link is awesome! Thanks for sharing!

If you wouldn't mind measuring, please share the length of those shocks either eye to eye or overall.

About 95mm eye to eye, plus it’s limited a couple of millimetres internally with plastic washers. Without the washers I’d guess 100mm eye to eye.

And yay! New wheels and I also finally put my CI foams in...

[JatoTheRipper]

Originally Posted by Joonatin

About 95mm eye to eye, plus it’s limited a couple of millimetres internally with plastic washers. Without the washers I’d guess 100mm eye to eye.

And yay! New wheels and I also finally put my CI foams in...

Thanks! I really Hobao releases the shocks separately.

[soze]

Originally Posted by JatoTheRipper

Thanks! I really Hobao releases the shocks separately.

They do from their site, but I might be able to get them through my friend. Need to find out more info from my friend.

[Joonatin]

The Finnish shop I ordered the kit from has them available and in stock (45€ A pair, expensive). Don’t know about US vendors though, might have luck with ebay. I’d probably go with some big bores if I wanted shocks, but these are definitely good. And if you’re thinking about the closed pistons with cut sides, at least Xray should have those available. At least I think I got some with my XB4 some years ago. Xray shocks are quite amazing too if you can find a good size, XB8 might be long enough for crawlers.

[hillbillyrc]

Originally Posted by JatoTheRipper

Thanks! I really Hobao releases the shocks separately.

They have.
230060 Complete Shock Set*| HoBao Enterprising

[JatoTheRipper]

Originally Posted by hillbillyrc

They have.
230060 Complete Shock Set*| HoBao Enterprising

Sweet! Thanks! Now let's hope they hit the streets with a more realistic price. I'd pay $50 or $60 for a set, but not $100.

[hillbillyrc]

Thats the only place I've found parts. I picked up the panhard mount for my project.

[Joonatin]

Well, this is a bit of a bummer. The car crawls absolutely great. I still haven’t even updated the sliders or bumpers but it can drive some quite hard looking lines and it handles many places pretty much as well as some of my friends more tuned cars. Also I think it runs better than my Ascender. The problem is I’ve now broken both my front CVDs from the same place. First one replaced by EuroRC where I bought this from but they are now out of stock, waiting for a resupply from Hobao, so no driving with this one for a little while (luckily I got a dirt cheap AX10 with a DNA Slingshot chassis, dig unit, good servos etc. etc. so I have other stuff to do).



The way it breaks is very similar to the early Ascender axles. Both shafts have pretty much broken in the exact same way... I tuned down my steering a bit after the first CVD breaking, but that apparently didn’t help. I’m atill wondering if they break because of some minor misalignment, material strength or design errors. I’ll have to admit though that I’ve really been pushing the vehicle on some serious terrain as it is still new and exciting, but I’m somewhat careful on the throttle usually if there’s a risk of binding the wheel.

On better news, while waiting for the local supplier to restock, I contacted Hobao directly and they seem to be taking the problem seriously and are looking into it. One other Finnish guy has also broken a CVD, but it’s been fine after the change so it might have somethhing to do with tolerances or a bad batch. Anyways, they seemed to appreciate the suggestions I had on the vehicle and promised to send some CVDs my way directly. Otherwise the rig seems bombproof so far.

On other news, I’ve cut down and moved the battery holder forward and down as much as I could. When I make new sliders, it might drop down a few millimetres more and I’ll probably think about buying more of the relatively thin and light 1600mAh Nanotechs.



Here’s a shot from the latest trail ride. Oh it’s shiny and pretty and nice for a while still.

[Joonatin]

I’ve done some stuff again! Go Me!

Firstly, I got the shafts from Hobao. They sent me FOUR CVDs so I should be good for a while. I haven’t broken any after swapping them to new ones though, might have been a bad batch or something.

Second, a new bumper! Take some 30x20mm steel profile, mig welder and a grinder and add the tiniest bit of old Jtin magic and stuff happens! Perfect work to do with the current temperatures of around 30+ degrees C. The summer here has been the warmest in a hundred years or so. Fookin’ hot!



Slave to the grind



Welding, welding



It’s similar to the original, but the lowest part is a bit higher. Plus it’s extremely heavy at 320g (about three goat toes and a quarter of a pebble in Imperial measurements). A bit too heavy but the back part is made of 10mm steel plate I’ll have to cut some away. I’d hazard a guess that 240g would be good. On to make the sliders and rear bumper next.

[Joonatin]

Also, I attended a competition last weekend. As I didn’t have prior experience and haven’t gotten around to getting a winch yet I decided to stick Mini Pitbulls under the car and go to C1. Not a bad choice. With my amazing about 28 scale points I was 6th out of 8. With more scale points I’d been 5th and without a couple of the derps I did on the first two courses I could have placed 4th.

I got the best points on one of the tracks with only three reverses.

So over all, not bad when I didn’t drive the car for three weeks and had the way too heavy bumper on front and used tires I hadn’t tried before

I also tried the C2 tracks with my XORs. Results were actually quite good, though none of the bonus gates were doable without a winch. Mainly the fenders and sliders/step plates/whatever were sticking to everything on tighter places.