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/diy/ - Do It Yourself

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1382813 No.1382813 [Reply] [Original]

Hey /diy/,

I'm building an RC Tank out of 3d prints reinforced with metal (bike chains with 3d spacers for tracks, metal plate chassis, steel rods for shafts/axis/suspension, etc) and I bought a 4 stroke 0.7cc airplane glow engine to go with it.

As this is a plane engine I need to manufacture a flywheel and have a way to start it. I can cast lead, zamak and aluminium and have a few simple machine tools (As in I can make straight holes...) . I'm not sure about starting it (electromechanically) tho, I'm having problem with the idea of interrupting transmission (diy transmission disks) in such small scale. Motor in picture

>> No.1382831

Electric motors would really be better choice for tank as it must reverse tread direction frequently on both sides (to execute turns and such). If you have your heart set on gas engine though, look into the reversing setups for RC gas models-they figured out a cheap and easy way to do it years ago which you could duplicate. You'll need centrifugal clutches for sure.

>> No.1382832
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1382832

>>1382813
You are going to have trouble keeping that engine cool, even if you design the flywheel to also be a giant fan. They run hot even being totally exposed cruising around at 40-60 mph in small rc airplanes.

t. someone who has a bunch of saito 4 strokes

>> No.1382837

>>1382813
will this be the loudest most annoying tank ever?

>> No.1382839

>>1382832
Random question: are little 4cycle engines like that harder to cool than a similar 2cycle?

>> No.1382841

>>1382832
>>1382839
Oh and what about lubrication on those little things? Pre-mix or you manually do it between uses or they have tiny oil pumps?

>> No.1382842
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1382842

>>1382831

I know, but the start of the project was to make a Tank's double differential (pic of one side) but it was powered by a single double planetary reduction from an old electric screwdriver :)

>>1382832

I'll have a 6v 4500 mAh lead acid battery in it for the electric systems, I can run a big cooler on it. Plus airplane runs at full throttle all the time, I'll be much lower rotation.

>> No.1382845
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1382845

>>1382831

Also, I would really like not to use "freewheels" (the default transmission in RC) but make my own servo-controlled clutch system. I need three of those to engage the starter/alternator (maybe not), to engage the power to the tracks and to engage/disengage the motor on startup (that could be a free wheel)

Pic shows what I have so far (Had the full back transmission but I'm in the middle of printing a new version)

>> No.1382850
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1382850

>>1382839
>>1382841
It's not that they are harder to cool, it's that high temperatures are detrimental to them. 2 strokes use a press fit ringless piston with ABC construction (the ovewhelming majority anyway). If they get hot they'll just get tight and lock up, but once they cool they run nearly as good as before. The 4 strokes are typically nickel alloy, with the weak spot being the exhaust valve and seat in my experience.

>> No.1382851

>>1382842
>Plus airplane runs at full throttle all the time, I'll be much lower rotation.
No they don't friendo. For takeoff and vertical maneuvers, sure. But most flight is 40-60% throttle.

>> No.1382855
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1382855

>>1382851

Can't rely on forum info, 40%- 60% is more of my case.

Anyway, I have a thermal camera and alot of fans...

Any ideas how hot do they get under say, 25%, 50% and 100% load?

>> No.1382861

Meant to say in the last post these engines are run on premixed fuel just as the little 2 strokes are.

>>1382855
Temp is directly related to how you have the engine tuned. A sloppy rich engine will be much cooler than a lean engine. I have never taken a temperature reading on one, sorry.

>> No.1382869

>>1382861

How far have you gone in adding oil as coolant? I have access to chemicals so bought the Methanol/Nitromethane and "Mamona" (Ricinus/Castor) oil is REALLY cheap and easy to find here.

The reasoning is to add say, 30% oil to improve cooling and make it up the power with Nitromethane, could something like that be done?

>> No.1382888

>>1382850
Ok I see what you mean, a lot more parts to fuck up when when you do overheat them.

Is that pic how you oil them? Before/after use you hit the rockers and all that stuff and they’re good for another run? Is that the same for the crankshaft and pistons and all that or is there an oil reservoir somewhere?

>>1382861
Oh, wait, so piston and cylinder is oiled via premix?

>> No.1382895

>>1382888
Yes, piston, cylinder, and crankshaft bearings are all lubricated via fuel premix. You typically oil the rockers separately since they are not exposed to the fuel/air mixture once per run. A run is 15 minutes or so.

>>1382869
My current 4 stroke fuel is nearly 20% oil, but I'm sure you could add a bit more for increased cooling.

>> No.1382896

>>1382813
We used to make RC boats at school. Brass flywheel started with a sewing machine belt in the v slot me machined in them.

The teacher ran a 2 stroke enya plane engine with a DIY water cooling heat sink attached to the engine simply clamped ever the existing air cooling fins.

If I was building this tank I'd go electric or look at get one of those electric start 50cc mini bike engines. They have an inbuilt starter/ generator which could drive electric motors.

>> No.1382898

>>1382896
50cc is far too big for my setup

>> No.1382899

>>1382869
>>1382895
What about running extra rich to improve cooling? Is it possible to adjust that quickly on the carb if you know there’t a hot run coming up? That’s a tactic with gasoline engines but I don’t know shit about nitro, hence the questions.

>> No.1382900

>>1382898
Oh shit you could have some fun with a 50cc mini tank. But I think at that size you should probably add a working gun barrel to it. Drop a 12ga in there.

>> No.1382903

>>1382899
Yes you can absolutely run it rich to keep it cooler. The carb is nearly infinitely adjustable with both a low and highspeed screw. Running rich comes with it's own problems though. Throttle bog and stalls for the most part.

OP I meant to ask you before (I'm at work and going 1000 different directions atm), what are you planning on using for a transmission? You will need to step down from 12,000 rpms or so.

>> No.1382907

>>1382903
Looks like he’s using these >>1382842

But the transmission itself is going to be the challenge.

>> No.1382909

>>1382813
>I'm having problem with the idea of interrupting transmission (diy transmission disks) in such small scale.

chainsaw clutch?

>> No.1382910

>>1382903
>>1382907

I don't wanna use the common free wheel RC clutch, I wanted something controllable, for motor reduction I'll use an rc steel gear and pinion

>> No.1383014
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1383014

>>1382845
those chains look like too much trouble you went through
you could just get two timing chains from Lada (pic related)

>> No.1383088
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1383088

why don't you print your chains and sprockets as well? seems like a lot of unnecessary extra work and cost making them from bike chains.

>> No.1383093

>>1383088
those break easily

>> No.1383176

>>1383093
No they dont. My design held 50kg before breaking.

>> No.1383182

Real tanks have combustion engines

>> No.1383256

>>1382813

Those nitro engines spin righteous fast, much faster than you'd expect.

I have a lathe and can turn you a flywheel if you'd like. Are you in the US? How big do you want it? What size bore?

Bookmarked.

>> No.1383345
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1383345

I saw this thing going. From memory it had a /diy/ mini V8.

>> No.1383435

>>1383256
Brazil, but I have a lathe to do it, I need some proper sized steel gears for initial reduction (say 15k to 3k) and then I'll go with planetary 3d printed.

>> No.1383487

>>1383435
>Brazil, but I have a lathe to do it, I need some proper sized steel gears for initial reduction (say 15k to 3k) and then I'll go with planetary 3d printed.

Do you have a hobby shop near you that stocks Traxxas RC parts? These are a cheap source for metal gears. IIRC the clutch gear for my son's Nitro 4-tec was $6 USD. :)

>> No.1383492

I've been in RC for over 40 years
I could think of nothing more boring than an RC tank. Cars and boats are for people that don't have the talent or skills to fly but a tank?
What next a remote control slug?

>> No.1383493

>>1383487
We have an "ebay" here that has those

>>1383492
I wanna fly too, need to learn a bit first tho

>> No.1383495

>>1383492
>I could think of nothing more boring than an RC tank.

... But how much C4 could it hold?

>> No.1383774

>>1383492
RC tanks are fun when you devote a few channels to electric matches and strap fireworks to them.

>> No.1383829
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1383829

>>1382832
>t. someone who has a bunch of saito 4 strokes

>> No.1384034

>>1382832
>You are going to have trouble keeping that engine cool, even if you design the flywheel to also be a giant fan

If Op makes a shaft adapter they could use the fan off of an alternator as a flywheel and fan.

>> No.1384035

>>1382842
>>>1382831
> I know, but the start of the project was to make a Tank's double differential (pic of one side) but it was powered by a single double planetary reduction from an old electric screwdriver :)

If this is still something OP is considering it's far more trivial to connect the Nitro to a brushless motor and use it as a tiny generator. Clever electronics could make it bimodal, generator in one mode and electric starter in another mode.

>> No.1384039

Yet another thread that's all blow and no go

>> No.1384043

>>1383774
>being 10 yrs old again

>> No.1384161

>>1383829
I have a .60 Saito 4 stroke Black Knight. Came with a cheap 1400mm Black Horse Yak 54 I got for $200, fully decked and with the accessories to maintain, fill and start.
I also have a .60 ASP 4 stroke that is just a slow 2 stroke, runs uneven and unreliable.

>> No.1385686

>>1384034

Yes, I've tought of that today too, using 6 neodimium mangnets on a plannar generator configuration (matching 6 static coils). I'm thinking of making that after the reduction gear tho, I'm not sure I can make something balanced to spin those magnets at 22k rpm.

>> No.1385689

>>1385686

Sorry, 12k, close to my angle grinder...

>> No.1385691

>>1384035
>If this is still something OP is considering it's far more trivial to connect the Nitro to a brushless motor and use it as a tiny generator. Clever electronics could make it bimodal, generator in one mode and electric starter in another mode.

Any idea of how much the outter part of those outrunners weight? I think I need more weight than that for a flywheel. Having said that it's much easier to add more weight to the shaft than designing a generator from scratch, I think I'll go with it.

>> No.1386071

>>1385691
>Any idea of how much the outer part of those outrunners weigh?

It depends on the motor. I've got one smaller than my thumb and another bigger than my wrist. :/

If you are using it as a generator (technically an alternator) it doesn't matter, really. go heavier than you think you need and it will help damp vibrations. For comparison, the prop on our old nitro plane weighed /maybe/ 15-20 grams. It was incredibly light. There was another 15-20 grams of mass in the spinner and hub adapter.