Metal Hobi MH-245 kit as Hitachi ZX245 excavator

[Blender]

Here's a build thread of the Metal Hobi MH245 excavator kit. It's the 3 valve mono boom in 1:14.5. Had the 7 valve split boom with plow been available that would have been my choice. This is my first equipment kit although i have a mostly finished telehandler scratch build. Something easy to complete will renew my interest in the hobby. There is very little info about this kit online. Even tried searching the big German language boards with minimal results. I like the short tail appearance and it fits with my preference of smaller models. Unlike their larger Hidromek models, this excavator uses brushless electric drive on the tracks and slew. Much simpler.

Before committing to the kit a "test" order was placed for a modest value, but useable item to see how the transaction would go. The test purchase was a micro brushless pump. It's rated for high pressure ~25-30 bar. i measured flowrate to be 200 mL/minute although conditions were not ideal. Not sure what i'll use the micro pump for yet. The excavator order was a smooth transaction and allowed paypal which offered some monetary protection.

On to the pictures:





initially i acquired proper John Deere/Hitachi construction paint, but test sprays where not to my liking. Said paint would not lay smooth and still had the gall to run/drip. I've never had such an undesirable experience. To salvage my effort i used the sample spray as color reference to find appropriate colors in an easy to use paint:

Hitachi Construction Grey is very similar to Dulux charcoal grey. A pretty good match to my eye.
Hitachi Industrial Orange is approximately PMS166C. Match is not perfect. The pantone color is a bit lighter/brighter, but good enough.

Next couple of weekends should hopefully have good painting weather before it gets too hot.

[Blender]

Chassis is painted and assembled. No issues to report, but i did fish a little piece of grit out of the tower bearing. Now it's silky smooth. Decided to leave the tracks raw black so they don't gum up with paint. Superstructure is still getting sanded and recoated, so assembly is halted.






Pressure sensor for telemetry arrived. It's big, maybe too big but will let me test with it. It's available off the shelf so it was easy to get ahold of. Center hole was the perfect size to tap M4. No need a bunch of fittings. This one runs on higher voltage to output 10.0V at 1000 psi. Should output 4.50V at 450 psi. Didn't come with a calibration curve which is kind of lame.

Also been dabbling with a tool for this machine. A concrete barrier lift mechanism. It's a small excavator so it deserves a small job. The full-scale piece uses a bi-stable latching mechanism to hold the jaws open every other cycle. I'd like to duplicate how they do it, but it may not translate well to a small size. Time will tell. Plan is to braze together the parts without this feature to verify the design is able to lift plaster jersey barricades.

[frizzen]

Wow, that's a really awesome looking machine!
The orange and grey livery should look really good on it.

Sweet looking barrier tool, thats pretty wild

[Blender]

Still doing a ton of painting sanding polishing. Connected the drive and slew motors to try them out, but otherwise no real assembly progress. I did decide to add hydraulic quick disconnects off the valve block which have not yet arrived. Custom "dry transfer" decals are in progress.




The barrier lift was brazed together to see how it works. I'm pleasantly surprised how well it lifts. It's missing the bi-stable latching mechanism which now needs to be figured out.

[Blender]

Decals are looking pretty nice. They are dry transfer style so there is no carrier layer left behind. The ink is directly backed with an adhesive. As good as a pad print without the need to create any tooling. Had to learn Inkscape software to make vector images. It's free. A bit different than Photoshop or CAD, but I managed to bump my way through it. May have put the model number on crooked.


Included slew motor is a 37mm OD gearbox ~150:1 with an 1806 brushless motor. It worked just fine, but was too loud for my liking. Grease helped, but not all the way since it's an 8-10 stage unit. From my reference photos it's just about the right size to be scale though. Gear mesh for the slew is not adjustable and had a little bit of free play at the bucket <4mm at full reach. Not bad, but I can't leave things alone. I used this opportunity to make an adjustable motor mount for the stock 37mm OD gearbox shown below on the left. I also made a plate for a smaller 22mm OD planetary gearbox (right). Adjustment is done blindly before final installation, so it's fumbly and takes some trial and error.



I installed a 22mm 104:1 planetary gearbox on the new adjustable mount with an oversized outrunner. I was able to tighten up the gearmesh to allow only 2mm play in the slew at full reach. I think I can get it a little tighter when I swap out the used 22mm gearbox with an improved unit. The shaft of this one has some radial play from being old and beat. The new 231:1 22mm gearbox has a much tighter shaft. I still need to turn down the tip of an appropriate sized outrunner before final assembly.

[Blender]

I really struggled with the hose installation. Flat nose pliers would mangle the hose, and heat would melt the end 9 times out of 10. The German forums' talked about "hose pliers" which sent me on a search. I found nothing. Maybe it was a translation inconsistency? Instead I acquired some brass pliers and modified them to my needs. Drilled a 3.8mm hole for 4.0mm OD tube. Chamfered the ends and hand filed the remaining edges smooth. Works well. The 3mm OD lines were much easier to get on and required no specialty tool.





Took quite a while to figure out a new to me radio system and fine tune the hydraulic system. I'm really liking the Jeti radio so far. Time on the controls will help determine what needs more adjustment and what just needs practice. Using SAE controls. Lastly, here is my atrocious operation:

Starting to get familiar with bucket/stick synchronization, but having difficulty raising/dipping the boom at appropriate times. Mental overload.

Putting together a game plan to organize the electrical. Shortening cables is starting soon, along with some power distribution. Ease of maintenance is critical since this is such a densely packed machine.

[Blender]

Trying the drive with side sliders is rough. Instead there are three flight modes:

1.) "Default" allows fully control of the machine. SAE excavator controls on the sticks and the tracks are driven by the side potentiometers. Kind of awkward, but will be needed for advanced maneuvers.
2.) "Drive" leaves the left stick as boom/slew, but reassigns the right stick to the tracks. Much easier to maneuver like this.
3.) "Park" has the standard SAE controls on the sticks, but restricts the track channels to a flat zero travel curve. Effectively disables the side potentiometers. Prevents the machine from running off a table from accidental inputs. May have had a close call one evening

[pufferfish]

Very interesting report. Thank you for sharing.
I cut my 4mm od hoses simply with a sharp scissor.
I have not noticed negative impacts so far.

[BlackCat]

Originally Posted by Blender

Was it expensive the sendcutsend service?

[Blender]

Originally Posted by BlackCat

Was it expensive the sendcutsend service?

They're mid-priced. All the parts in the photo were $71 shipped. Enough to build 2 with some spares.

[Blender]

experimented with a gimbal motor for the slew. It's a 2208 outrunner 127kV so it's super slow. Paired it with a 62:1 gearbox. It's ultra quiet and smooth, but still cogs a little at startup so it loses the precision of small movements. Not as much torque as was I was expecting either. Disappointing.

[Blender]

Decided I'm going to rewind the GB2208 gimbal motor for use on the slew. I've done that a few times before on RC crawlers. Would like to increase the current quite a bit too. Lots of trial and error but eventually it should work. Waiting on another telemetry ESC to be in stock to allow direct RPM readings.


Been running with rats nest wiring. All kinds of adapters and splitters. Some stuff soldered and other had connectors. A real mess for maintenance and future troubleshooting. To solve this I layed out a simple PCB to act as a power distribution board. One input and 7 outputs, one of with is a big connector for the pump. Probably should have added a tiny fuse holder. Maybe next time. Housing is 3D printed and mounts where the kit's included 3x brushless ESC block is meant to hang. I'm using tiny BL Heli ESC, so this space is free.



paint job isn't real smooth



Rewired. Not perfect, but useable. Extra servo cable length was removed from everything. External BEC will be omitted once the Mezon Pro ESC with built in ESC in back in stock. This will free up more space for a permanent telemetry pressure sensor to be installed.


Also wired in Voltage/current sensor: Jeti 30A MUI. Started with a 50A since the excavator kit had a huge 40A esc and 20A BEC. It didn't fit in this spot and current draw is way less than 50A. I think i've seen 12A peaks. Usually the system runs under 2A during "easy" use.


It's still hot here, so mostly I've been digging buckets of gravel inside. Way more fun than it should be.

[jerry56]

That is such a sweet excavator....You really did it justice....
I like that power distribution board... doing something similar on mine ...well not as neat... or professional but same concept....

[Blender]

Thanks for the kind words.

I started by looking for something off the shelf. Best option I saw was for drone/multicopter. Those were not quite right, but workable.

[egronvold]

Great buildthread!

[Blender]

Thanks Egronvold.

Time to step away from the ZX and tackle the barrier lift mechanism. The full scale looks to operate with a bi-stable latch which allows the jaws to engage every second plunge. Well suited to RC play with no electronics needed. Completed the CAD work to carve a path inside the housing. A 1mm spring pin is what follows the groove and keeps the plunger from falling out.

Parts look great and assembled well, but the latch only advances to the next position on rare occasions. Everything is internal, so there is no real troubleshooting i can do. Full redesign is in order

[frizzen]

I'm not 100% sure on your design of that last piece, but think i've got a basic enough idea.

Instead of doing a full redesign for the bi-stable latch I might try to file some directional ramps on the lower side of the plungers 'paddle looking section' to help them ease into next position. Then cross-drill the plunger shaft for a pin near the coupling sleeve maybe like 45 degrees out of phase with the paddle, so that at weight-released full-down it can act against a couple bumps on the collar to start rotation to advance next position?

If it still doesn't want to advance, you might be able to mill a zigzag path in plunger shaft, then a pin in the collar rides in zigzag to keep it moving.

I dunno, worst case you could take apart some 'pop-up bathtub drains' for some other design ideas.

[Blender]

I drew out the path and also where it could be getting lost. The guide groove is inside the bore which is 4.5mm. Difficult to even see if the contours are well formed by lost wax casting.

Comparing the partial rotations to the CAD model I think it's switching which incorrect path to take randomly. Sometimes it start backwards, others it will start out ok, but get caught on that flat. Maybe it could be adjusted and rebuilt.

[Blender]

Been looking for an easy way to add some aux connections near the bucket. Technically there is room for 4 more valves, but I'd rather not be that tightly packed. I'm going to do electric. Will be good enough to run simple accessories. I'm done messing with the bistable mechanism for the barrier lift and am going to stick an electro magnet in it to hold it open.

Looked far and wide for a small 3 conductor connector and I think I found something suitable which is 6.4mm OD.


Each port has 3 conductors so it's able to power and control a servo or similar. Ideal for a bucket quick coupler


Hydraulic quick connects on the left and electric on the right. Male end is notable longer. Looks OK.


Done adjusting the cabin parts to fit an operator. Needs to be detailed out.

[Blender]

Electromagnet in the barrier lift works pretty well. Ended up using a brushed ESC instead of a switch so I can power it with fully battery voltage, then limit it to 5V via travel endpoints on the radio. Tested it with an umbilical to the excavator for now.