HBX Devastator = Sumo XL

[spoo76]

Great stuff. Hard to argue with HK prices. Don't think you'll be disappointed with the HBX either.

Well my battery is definitely shagged. It is reading 8.1v on the multimeter but doesn't want to share those volts with the truck - goes a bit then kind of browns out, goes a bit etc. Maybe I was just unlucky.

I'm not particularly bothered as I wasn't planning on keeping it. I have plenty of small lipos (super cheap from HK) and the good news is the esc seems to handle the extra 1v without any trouble.

I'm getting too excited about the whole Formula Offroad idea. Parts are winging their way to me from the four corners of the globe as I type...

are you positive its the battery and not the electronics? Ive read the HBX/HSP versions dont like 2S lipos and the voltage is above its spec.

I read somewhere, here I think, where someone put small outrunner on their Trekker. That may be a cheap option for more wheels speed for yours.

Most out runners will give you more torque and less speed. It really depends on the KV rating of the motor. Either way it wont work with stock brushed electronics as they are brush less motors. Depending on your needs and what you have a 130 can PN racing motor or even better A Predator DDT motor from Danally would be a better choice. he can custom wind the stock losi crawler size, the 130 big block, or the 180 stroker. https://www.facebook.com/Microcrawlermotors?fref=ts

 

[Sparks1337]

Thanks for the info Spoo. It is definitely the stock battery that is the issue. After its first charge the truck started playing up and it hadn't been near a lipo at that point. Once I put a lipo in it ran fine again. The esc/rx unit is different from both the Sumo and HSP and I've not found any info on it so far - good or bad.

It has had two full lipo packs through it so far with no sign of complaint, but the manufacturer's choice of 6.4v Li-ion must be for a reason. Even if it is okay with lipos the 5-wire servo leads aren't helpful for anyone on an upgrade path.

Thanks for the advice on outrunners too - I have zero experience of them so that is useful to know. I think I'll be sticking to brushed - I already have an 80T big block from Danally in my other McRc so might be going back to him very soon

I need to work out my chassis and suspension layout before I commit to a powerplant though. I really like how they've clocked the Sumo tranny and used a bigger motor. It pushes the CoG down really low,but limits options for link length and mounting so I' may not be able to keep it that way. I've ordered a set of ball bearings and once they arrive the truck will get stripped down for a closer look and I'll post some more pics.

 

[Brake Weight]

Is the stock Tx/Rx proportional for the rear or is it just a simple push button side to side? I've got a dx3e and may just get a couple of those orange Rx and have some for the next project.

Are the servos the same size as the Trekker?

 

[Sparks1337]

Servos are the same size as trekker/HS56/MG90 but use a 5-wire system with non-standard connectors to the rx.

stock tx is proportional for both servos with a push button to cycle between steering modes - front only, 4ws, crabbing and rear only.

Also for general info, the rx doesn't have a bind plug or button and the tx/rx seem to start in bind mode every time it is switched on until they find each other.

Well my micro gearmotor arrived from polulu and it is a much smaller size can. Serves me right for not taking time to measure up before hitting that buy button

I was hoping to avoid using the losi trans by using a higher geared motor. Back to the drawing board for my go-fast project!

 

[Brake Weight]

Thanks. I may try to score some cheap Chinese MG and use my dx3e. It'd be the same setup I'm using on my Trekker/Bug.

 

[Sparks1337]

Well I stripped down the axles and trans to install ball bearings and found a bit of a mixed bag.



I dropped the trans first, and found to my surprise it is already ballraced. Apart from the middle gear which seems to have an integral axle running directly in the trans case - no bushing of any kind that I could see :shock:

I've looked around and this seems to be the same in the sumo, unless I'm missing something.

Anyway, this got my hopes up for the axle, but that was a completely different story:



The central shaft is a single piece of metal, with the gear and bushes captive on the shaft. So the bushes can't be replaced or upgraded. Worse still, the outer set of bushes is completely missing! And replacements can't be threaded over the dogbone. That can't be good.

I found a parts diagram for the Sumo and the Redcat axle is made of three pieces - the central collar that the gear and main bearings sit on, and two dogbone shafts that push in, with the outer bushes clearly shown. The axle housing has the recess for an outer bearing too.

Weird cost-cutting choices by HBX. I checked on Banggood and they stock a replacement one-piece axle, with just the gear and two main bushes on it. I tried holding the centre in a vice and pulling the dogbone but it won't budge and appears to be a single piece of steel.

The single piece shaft is kind of a good idea, and I could even have lived with brass bushes, but to have those outer ones deleted is inexcusable in my book. I can't see it holding up long with high speed and brushless power. Mightily disappointing. Made worse by the fact that the only suppliers of Redcat parts I can find are stateside and none of them seem to offer international shipping.

 

[spoo76]

Hmm, that's interesting. You may be able to cut the axle with a dremel or something in between the bushing and output. Then replace with bearings and sleeve with brass and solder. It works for extending. it should work as well for removing bearings. maybe even make the cut at an angle so its stronger when you solder.

 

[Sparks1337]

Yeh good idea I was starting to think along those lines, I just wasn't sure how strong the joint would be.

Can't hurt to try though. I'll have to see what brass tube I've got lying around :mrgreen: The spare axles from Banggood are only £5 each so I've ordered a couple of sets 8)

For now it has gone back together with a ball bearing behind the pinion and a 0.5mm shim on the driveshaft side to remove slop. I added bearings in the hubs and another shim to keep the diff gear steady. Axles run with much less slop now.

I also took the opportunity to shorten the links down to their minimum length. This meant I had to move the shock tops back one hole to regain some movement. It is now 135mm wheelbase - 9mm less than out of the box which should give the drive shafts a bit of a break.

 

[Brake Weight]

Did you try any heat?

 

[Sparks1337]

You mean to try and separate the axle? Thought about it but it would risk melting the diff gear, especially with me in control of the gas torch

I'll have a proper go at one of the spares when they arrive

 

[Brake Weight]

Torch or a toaster. The bushings look to be brass or bronze or some other metal. It should expand at a lower temperature than the steel axle.

 

[spoo76]

But then the plastic gears would be melted. I don't see them being able to handle much heat

 

[Brake Weight]

I didn't realize they they were plastic.

 

[spoo76]

I wish they weren't. The micro T-rex RC4WD had were the only metal ring and pinion micro gears I've seen from a production axle

 

[microcrawlers]

this looks like a bada** rig just because of that chassis and the stance... are the tires solid rubber or hollow? the dont look like great quality but i like them because them look monster trukish, which is where id go. i may have to pick one up for my little bro.. great entry toy rather than expensive rig yes?

 

[Sparks1337]

Yeh it looks pretty well with the chassis and big tyres and I'd say it makes a great entry-level rig.

Provided the battery issue I had isn't common you don't need to spend any money on upgrades to have a very capable little crawler - just shorten the links a bit or you'll need new driveshafts pretty quickly.

It is hobby-grade though rather than a 'toy', so mods and upgrades will inevitably beckon ... mine has already started its assault on my finances

The tyres are hollow and surprisingly soft and grippy. No foams as far I can tell and either the tyre or wheel is vented.

 

[Brake Weight]

Are the wheels a true beadlock or is it just looks? I expect mine to arrive in 3 weeks or so.

 

[Sparks1337]

Good question. I just had one apart to find out and they are true beadlocks:



The wheel is vented. You can just see the hole in this pic.

Funny mix of cost-cutting and nice features on this truck.

 

[Brake Weight]

Nice. What size wheel? Hex?

I just ordered 3 more mg90s servos to do this rig and my Trekker for rear steer.


Edit: should be able to pile the BBs and lead weight into those big wide tires, too.

 

[Sparks1337]

Wheel is micro standard 25mm dia, 7mm hex. However they are 20mm wide and fully offset.

I'm feeling this whole FOFF thing. It's been done before with sumo axles but this body lends itself perfectly for it. I've been playing around while waiting for parts to arrive:



Obviously just a mock-up. The front wheels are about as far forward as I can put them without losing the grille - the rears will come in another 10-15mm and I'll trim the rear arch. It may have to sit a little higher than this but I want to keep it as low as possible.

I had some very thin aluminium scrap that a contractor left behind at work. It turned out to be perfect for a roof I just need to shave a bit off the figure's butt so he fits.

While the wheels were off I added a set of CrawlerX wideners I had lying around. There is just enough thread on the axle to keep the stock locknuts, but they needed the inner face shaving a tiny bit to stop them binding.

Overall width is now a FOFFtastic 130mm :shock: I may have gone too wide, as the wheelbase is going to end up at around 125mm! So not sure if I'll keep it.

Once I've settled on my motor/trans and chassis choices I'll start another thread and try and keep this one on topic