Little bit of help needed, Spur on 30DN SDT?

[m4inbrain]

Hey,

 

after faffing around with me large scale stuff in front of my new home, a few neighbours got interested and basically immediately bought large(ish) scale rigs too - the entire road here now is into RC. My neighbour bought a 30DN SDT, he runs it on 8s and i'll be entirely honest, it's stupendously fast. After a brief check we figured out that it runs a 1200kv motor on a Max6 - and is geared 19/37. Which imho will not last. We had one run now, and i'm 100% convinced on the next one something will give. 

 

Now, spur gears. I suggested getting a 50t spur to run it 19/50, or should we look into 19/46? I've never fiddled with gearing - can we use any spur gear (i got a traxxas 46t off my X-Maxx for example, can we install that?)?

 

Thanks for suggestions/help in advance.

[Tug]

Basically no, not really. It depends on how the spur is mounted. You may get lucky, especially as it's a clone, they might have copied the internals from something entirely different. From what I've read, the main outer components are near identical to the Losi, but internally it's much different. 

[Tug]

Or just drop three teeth off the pinion, much easier and more effective at lowering the gear ratio. 

 

Dropping two teeth off the pinion would probably equate to having to drop ten teeth or more from the spur. 

 

Running that thing stock on 8 cells will lead to motor, ESC or both failing rapidly. 

[m4inbrain]

1 hour ago, Tug said:

Or just drop three teeth off the pinion, much easier and more effective at lowering the gear ratio. 

 

Dropping two teeth off the pinion would probably equate to having to drop ten teeth or more from the spur. 

 

Running that thing stock on 8 cells will lead to motor, ESC or both failing rapidly. 

 

Yeah i figured, the ESC/Motor were close to meltdown earlier today, at least that's what it felt like. 

 

I'll have a look at pinions, don't know what pitch it has - but should be relatively easy to find out. Even with a 16t pinion, still a ratio of 2.31 - that's better than the 1.91 that it's running right now, but still quite high for 8s imho. How does 15t/14t sound like? 14t would be 2.64, or 2.46 for the 15t. I just don't wanna have it blow up constantly, they're both new to the hobby and i know i'd be quite "miffed" if my truck blows up on the second run already, and every second one after that. 

[Tug]

I'd expect mod 1.5.

 

14 or 15 should provide a sufficient drop in load. No temp guns between them?

[m4inbrain]

24 minutes ago, Tug said:

I'd expect mod 1.5.

 

14 or 15 should provide a sufficient drop in load. No temp guns between them?

 

None, and you can't really reach anything in the 30DN while running. Neither ESC heatsink nor motor are reachable without partial disassembly. But it was hot hot today, running in sand/dunes. 

 

I had a look, if it's anything like the SBR that it's based on, he can't run a 14t or 15t pinion - the motor plate is "pre-meshed", there's mounting holes that correspond to pinion size - smallest being 16t. It also doesn't just have a spur gear by the looks, but an entire center transmission. Which looks cool and all, but is really inconvenient in this case. I'm not entirely certain why they'd gear it like that, and tell you you can run it 8s no problem. This will go out of the box easily over 75mph, and is basically uncontrollable on throttle. 

 

edit: @.AJ. was it you who had one of these? I can't for the life of me remember who had one.

Edited August 31, 2020 by m4inbrain

[Tug]

AJ had the Losi, modded very nicely. 

 

A 16 will make a significant difference, but no guarantees it'll be enough. 

 

Could he not just do what he's supposed to and run 6 cells?

[m4inbrain]

I'm not 100% on this, but looking at pictures (best i can do for now), the internal stuff from the SDT looks similar/identical to what the SDR looks like. I only checked the pinion on the SDT since that came lose (no locktite from factory -.-), so i only saw a glimpse. But looks very similar to how the Losi is set up. 

 

Yeah i'm with you, 16t will clearly be safer than 19t for now, but i told him that he's always gonna run a risk of basically releasing the magic blue smoke. I also tried to get him to buy 6s packs (or rather, 2x3s), he instead ordered another 8s pack because "he likes how it goes". Which is understandable, it flies, but i can't seem to stress enough that he'll blow it up that way. On the other hand, if he does, i mean.. There's probably space for a Max5 plus some big can that can handle that kinda gearing, it's just what has to be done in that case. We're all grown men, i warned him and tried to stress it, but as the saying goes in germany - wer nicht hoeren will, muss fuehlen (which paraphrases "he who doesn't wanna follow the rules shall feel the consequences"). 

 

In the end it's his RC, i'm not paying for the new internals potentially (well, imho definitely eventually) necessary. 

[Jumper]

The esc is rated for 8s, the motor however is rated for 6s. Yes gearing down might help a bit, but instead over overheating the esc the rotor will probably break instead due to the higher rpm. It might last a while though. Will be interested to see if and when it does blow up. 

 

Also the motor magnets get weaker when they get too hot which raises the kv even higher. 

 

[m4inbrain]

1 hour ago, Jumper said:

The esc is rated for 8s, the motor however is rated for 6s. Yes gearing down might help a bit, but instead over overheating the esc the rotor will probably break instead due to the higher rpm. It might last a while though. Will be interested to see if and when it does blow up. 

 

Also the motor magnets get weaker when they get too hot which raises the kv even higher. 

 

 

.. is it? It looks mighty big for a 6s motor only. I'm not entirely certain there. 

 

I've sent him a link to this thread, he'll read through it tomorrow i assume. We'll see where we go from there - in the end, if the motor delaminates, he just has to invest in a 800kv 1/5th can, if it'll fit. As i said, i can only voice my concerns (which i did) - he's gotta take it from there. This was just as a last ditch effort to maybe get the truck reliable enough that it isn't guaranteed to go poof soon, which would fall back on to me because i recommended it. 

 

He can read here now that it's not just me guessing that it's not "when" but "if" it blows up. 

Edited September 1, 2020 by m4inbrain

[Tug]

It will fail at some point, no doubt. Given the reliability of Hobbywing ESCs these days, I'd reckon the motor will cook first, but in reality it's anyone's guess. 

 

16 tooth pinion will prolong the inevitable. 

 

Are they aware of after-run care if they're running wet?

[Jumper]

6 hours ago, m4inbrain said:

 

.. is it? It looks mighty big for a 6s motor only. I'm not entirely certain there. 

 

I've sent him a link to this thread, he'll read through it tomorrow i assume. We'll see where we go from there - in the end, if the motor delaminates, he just has to invest in a 800kv 1/5th can, if it'll fit. As i said, i can only voice my concerns (which i did) - he's gotta take it from there. This was just as a last ditch effort to maybe get the truck reliable enough that it isn't guaranteed to go poof soon, which would fall back on to me because i recommended it. 

 

He can read here now that it's not just me guessing that it's not "when" but "if" it blows up. 

yes. on the rcmodelz site it lists the motor as rated from 6.5-25V

• Name: BWS 5688-3.5D-1200KV
• Rated Voltage: DC6.5-25V
• Rotation: CCW
• Temperature and Humidity: -10°C~+90°C. 5%~85%RH
• No Load Speed: 17200rpm ± 10%/15V
• No Load Current: 4.0-5.5A/15V
• Maximum Current: 120A max
• imensions: Ø57.8 * 87mm

[m4inbrain]

3 hours ago, Tug said:

Are they aware of after-run care if they're running wet?

 

Yep, we went through that.  👍

 

@Jumper

 

I stand corrected. Quite surprised with that kinda can, but can't argue the facts. 

 

 

 

Well, it is what it is. Cheers for the help guys, appreciated - we'll see where it ends.

 

 

[Tug]

In a fireball? 🤔

[m4inbrain]

Good news, just had a brief door to door talk with the neighbour, he ran it this morning on a borrowed 6s pack and he likes it, so crisis potentially averted. 

 

@.AJ. do you know by chance the shock oil weight of the SBR? According to RCModelz, the SDT comes with "whatever fluid they got in the factory at the time", which in this case appears to be water. I'm thinking 50wt-60wt - what did the Super Baja Rey come with?

[.AJ.]

Sorry is was a few years ago and tbh I didn’t really mess with it a lot, I only added light bar covers and a lighting controller 👍 

[m4inbrain]

1 hour ago, .AJ. said:

Sorry is was a few years ago and tbh I didn’t really mess with it a lot, I only added light bar covers and a lighting controller 👍 

 

No worries  pal, we be trying 50wt for now.

 

Runs fine on 6s, he enjoyed it - temps were fine,  but pinion slipped again (no loctite from factory and i'm out) so it got cut short a little.

[babylon]

Sorry to raze this from the proverbial dead,  But has your neighbour still got this, How's it holding up, Any good. 

[m4inbrain]

9 minutes ago, babylon said:

Sorry to raze this from the proverbial dead,  But has your neighbour still got this, How's it holding up, Any good. 

 

He does, but.. How to put it. 

 

It's what you'd expect from a clone 65% of the price of the original. Shell cracked first run, nothing goes together well, shocks/diffs were filled with nonsense (i actually messaged the guys where we bought the truck, they told me they fill diffs/shocks with whatever is available in the factory), suspension arm broke on a field, tyres unglued multiple times and two tore, etc. I.. don't feel comfortable suggesting it, it does need a lot of work quite some money to make it reasonably good, at which point you might as well just buy an SBR. 

 

Lesson learned, for us. He's now basically £850ish in, including new shell (SBR shell, funny enough), and it's okay now - but that's the price for the SBR 2.0, which requires way less work and is still better.

[babylon]

Cheers, May give that a miss then.