RC Locomotive 'Diesel-Electric'

[Roog]

I think you would be better off pulling air in somewhere else (like near your motor(s) and use the vent above the engine as an exit, since heat tries to go up. You'd be fighting that to push the heat to some other exit otherwise, while heating everything up along its path out of the body.

I would treat the loco body as a computer case. Posititive pressure works best. So a push pull config. A couple intake fans with a single exit fan, while sealing everything else up as best you can. You could do that with some dryer vent tubing. But make sure the nitro gets the air flowing directly by it on its way out of the body. Or you could consider water cooling the head by wrapping a water tube around it. But then you'd still need a fan or two and a radiator. Look at 240 size AIO coolers if you want to look into it. Not sure if that would fit though. But you could find a small heater core out of a car and build your own cooler.

If you go the fan route, look at HP Server fans. They move a ton of air, are really loud, and would make your loco sound even more realistic

Computer cooling did cross my mind, if I could find a marine engine of suitable capacity and small size a remote radiator would be a good call. Push and pull fans mounted in the top of the bodywork could be a neat solution. I have first hand experience of full sized bespoke generator cooling from above and what we found was the air short circuited, in that it didn’t properly pass over the engine block.

I remember the old modelling books, with the absence of purpose made marine engines people were forced into wrapping coils of copper tube around the cylinder head, never been sure how effective this is. Of course I would have to pump the water around the cooling circuit, are there suitable low voltage pumps? Yet more systems!

 

[Roog]

A small diversion, my IC tethered car is in the garage i.e. on a baking tray drip catcher both RX and on board glow plug battery are on charge ready for its spring outing this week.

Weather permitting

 

[CertifiedMike]

Cheers @Doom! The mechanics are a bit “doo hicky” but I am looking forward to introducing some RC gear to the project soon. Yet another Roog project with no means of steering! Seems to be a bit of a theme .

Steering is optional!

 

[Roog]

A small diversion, my IC tethered car is in the garage i.e. on a baking tray drip catcher both RX and on board glow plug battery are on charge ready for its spring outing this week.

Weather permitting

View attachment 270921

Looks like the poor thing is on life support!

 

[WickedFog]

Computer cooling did cross my mind, if I could find a marine engine of suitable capacity and small size a remote radiator would be a good call. Push and pull fans mounted in the top of the bodywork could be a neat solution. I have first hand experience of full sized bespoke generator cooling from above and what we found was the air short circuited, in that it didn’t properly pass over the engine block.

I remember the old modelling books, with the absence of purpose made marine engines people were forced into wrapping coils of copper tube around the cylinder head, never been sure how effective this is. Of course I would have to pump the water around the cooling circuit, are there suitable low voltage pumps? Yet more systems!

Yeah, I am sure there are. I would make one if not.

I would create a tube and a shroud around the engine and force the air to surround the engine head. I have actually seen this exact same thing in old nitro boats. Kinda like this water cooling setup, but bigger to flow air around the head. The external surface only gets to about 220° or so right? That shouldn't be too hard to keep cool.

Or direct air through a tube to blow across the head, and put a fan on the back end of the body. You should be able to get more than enough air across the head to keep it cool. Server fans sound like a scaled down tornado, and will easily blow more air than a nitro sees teaveling at speed. I tried one on my 3d printer for cooling the print. It was blowing so much air with so much velocity it blew the filament out from under the nozzle.

 

[CertifiedMike]

You don't want it to be too cool either. 220° should be a good operating temp.

 

[WickedFog]

You don't want it to be too cool either. 220° should be a good operating temp.

You can control the server fans with a pwm signal. @tudordewolf would likely know for sure the best way to set this up. So you should be able to control the fans with a trim switch if you can get the right pwm signal to them with a translater or something.

Sounds like a perfect job for the Radiomaster MT12

I looked into this years ago, and I believe the fan uses a much higher signal than our RC gear. I was looking into using an arduino to slow the fan down for my printer. But they were so much overkill I went with a regular fan.

Server fans are also 12v. So you would need to use a BEC to drop voltage down to 3s power if using anything bigger. But if it were me, this is exactly the direction I would go, and not only because they would definitely cool the engine, but they are so loud they would add to the realism.

 

[Roog]

Cheers guys, air cooling would look to be lighter on hardware, I was thinking of a ducted solution aimed at the head and possibly a scoop to deflect the exiting air out through a side or roof vent.

Its a way off yet, and i will get to bench test the ‘generator package’ on the bench so i can test a few cooling systems on the bench. My issue will be running long enough due the neighbours

Can’t be much worse than a chipper or chainsaw surely

 

[Roog]

Thinking about the cooling I did wonder whether an RC helicopter engine might hit the spot? Never seen one bigger than 0.6/10cc mind. Designed for relatively enclosed operation at high power outputs.

 

[CertifiedMike]

Thinking about the cooling I did wonder whether an RC helicopter engine might hit the spot? Never seen one bigger than 0.6/10cc mind. Designed for relatively enclosed operation at high power outputs.

The blades of the heli are moving a lot of air for cooling the engine.
I would think the heli's cowling ducts air across the motor like you are planning for your train. Seems like a heli engine could work well.

 

[tudordewolf]

Thinking about the cooling I did wonder whether an RC helicopter engine might hit the spot? Never seen one bigger than 0.6/10cc mind. Designed for relatively enclosed operation at high power outputs.

If I had that kind of in-house fabrication capability I'd never leave the workshop, very impressive!

I agree that cooling is going to be your biggest challenge. Heli engines aren't cooled by the main rotor airflow, they typically have a centrifugal fan pushing air through a cowling that directs the air over the engine.

For enclosed-running nitro engines, look at RC cars and trucks - they need heatsinks practically as large as the rest of the engine to avoid overheating. An aero engine in locomotive duty is going to be struggling...

The smallest water-cooled engine I could find is a 23cc Zenoah, that's about the same power as a 120AX (20cc's). You could also get an SK-130 for 1/3rd the price of a 120AX, it's not like you need the premium of an OS engine for a locomotive application. I would try to go gas instead of nitro entirely though, if not the 23cc marine engine, a 20cc gasser would have the same footprint at the 120AX.

With your fabrications capabilities, I'm sure a liquid cooled head for any engine you choose isn't out of the question.

 

[Roog]

If I had that kind of in-house fabrication capability I'd never leave the workshop, very impressive!

I agree that cooling is going to be your biggest challenge. Heli engines aren't cooled by the main rotor airflow, they typically have a centrifugal fan pushing air through a cowling that directs the air over the engine.

For enclosed-running nitro engines, look at RC cars and trucks - they need heatsinks practically as large as the rest of the engine to avoid overheating. An aero engine in locomotive duty is going to be struggling...

The smallest water-cooled engine I could find is a 23cc Zenoah, that's about the same power as a 120AX (20cc's). You could also get an SK-130 for 1/3rd the price of a 120AX, it's not like you need the premium of an OS engine for a locomotive application. I would try to go gas instead of nitro entirely though, if not the 23cc marine engine, a 20cc gasser would have the same footprint at the 120AX.

With your fabrications capabilities, I'm sure a liquid cooled head for any engine you choose isn't out of the question.

Thanks @tudordewolf engine cooling is the big concern from other club members, they generally use larger Honda engines. Their models are also of much greater scale. Key reported issues with petrol engines have been petrol evaporation in the carburettor.

As you say petrol is good because of it’s relatively low cost and easy availability, on the down side the engines are physically bigger and especially taller, if I could make one fit I would prefer petrol power. I have made drawings of a number of different petrol engines and I struggled to fit them in.

Despite the additional mess from a two stroke, work I have seen relating to hybrid generators for long range heavy lift drones does seem to favour 2 strokes.

I would be very nervous machining the fins off a new engine, but I agree an attempt at creating a water cooling coil might be the best way to get cooling where it’s required.

Right now I haven’t bought the engine, so I have options, a used 0.6/10cc marine might be a good option, it will certainly fit but to get the power it will need to rev which means gearing down to drive the alternator.

This has been the hardest issue to resolve on this project, I would appreciate any advice you can.

 

[tudordewolf]

Thanks @tudordewolf engine cooling is the big concern from other club members, they generally use larger Honda engines. Their models are also of much greater scale. Key reported issues with petrol engines have been petrol evaporation in the carburettor.

As you say petrol is good because of it’s relatively low cost and easy availability, on the down side the engines are physically bigger and especially taller, if I could make one fit I would prefer petrol power. I have made drawings of a number of different petrol engines and I struggled to fit them in.

Despite the additional mess from a two stroke, work I have seen relating to hybrid generators for long range heavy lift drones does seem to favour 2 strokes.

I would be very nervous machining the fins off a new engine, but I agree an attempt at creating a water cooling coil might be the best way to get cooling where it’s required.

Right now I haven’t bought the engine, so I have options, a used 0.6/10cc marine might be a good option, it will certainly fit but to get the power it will need to rev which means gearing down to drive the alternator.

This has been the hardest issue to resolve on this project, I would appreciate any advice you can.

That's a very open-ended problem, so my suggestions are just things I would consider -certainly not criticisms of what you've done so far. This is the kind of problem I myself love breaking down bit by bit, the end result will be awesome however you solve each issue.

It looks like you could buy yourself some height by letting the bottom of the crankcase sit below the frame rails, placing the engine lugs more or less directly at the level of the rails. A rear-exhaust 15cc or 20cc gasser could fit more neatly than a side exhaust engine. You might be able to buy some room by tilting the engine ~45 degrees.

What alternator do you have in mind?

I would try to direct-drive a brushless motor of the right kv at the engine's desired RPM range. I figure something like a 360kv motor at ~8000RPM should do it. That'll give you around 20 volts from a 3-phase rectifier, perfect for regulation - you might be able to build in a throttle setting that produces a range of acceptable voltage outputs.

Instead of jacketing the crankcase, you might be able to get away with just replacing the head with a "plumbed" version, and for a 2-stroke, that's a pretty simple part - basically just a "cap" for the cylinder with a threaded hole for the spark or glow plug. Most marine nitro engines seems to do just that, and they can even run into over-cooling issues.

Despite the additional mess from a two stroke, work I have seen relating to hybrid generators for long range heavy lift drones does seem to favour 2 strokes.

That's a power-to-weight-ratio driven decision, not as important in this application. The mess isn't from 2 stroke versus 4, it's from glow versus gas, and those hybrid generators are all gas.

If money were no issue, you could fit a water-cooled, inline-4 mini gasser and solve all your layout problems

This video comes to mind - the #1 goal to every solution is going to be completion, not perfection.

 

[Roog]

I really appreciate any help I can get @tudordewolf, I have limited experience with these engines or indeed how they behave when they get too hot!

I agree, I can drop the engine to gain some height, although this frustratingly cuts into my designated battery space. Like you my preference is for a direct drive BLDC motor acting as the alternator, I have seen people use a VESC with this configuration with regen allowing the alternator to charge the battery. As a bonus the VESC can also drive the BLDC motor as an engine starter motor, provided that the combination can deliver sufficient torque.

So your critique of my engine choice has been helpful, I still have the opportunity to redesign the ‘generator pack’ I need to check out water cooled petrol engine options to see if one will fit, but also I have had an offer of an RC helicopter engine which might integrate nicely, again they are designed to drive the load via belt reduction or gearing which could work. My main concern with smaller engines is the need for higher revs thus greater gearing.

The model engineering club have tinkered with a couple of the new wave of multi cylinder engines from the East, results were not especially promising with long term durability a concern. They do look great though, a straight four would sound better than a single pot for sure.

And another point well raised in this thread is value for money, OS make a nice model engine but given that I’m not worried about finesse or light weight I could be well served by a lower cost option. I’ll take a look at the market.

 

[Roog]

I found this oddity, 26cc and 1.6kW at 15,000rpm not sure if it will fit dims on web site say: 163x153x170mm which is too big, but perhaps there is scope to strip it back? All a bit of a risk and not especially cheap, but it does include a water cooled head.

 

[WRM]

View attachment 271064I found this oddity, 26cc and 1.6kW at 15,000rpm not sure if it will fit dims on web site say: 163x153x170mm which is too big, but perhaps there is scope to strip it back? All a bit of a risk and not especially cheap, but it does include a water cooled head.

View attachment 271063

If it's too large for the frame, move on - there's no way to make that package significantly smaller. I do like the idea of using petrol vs. Nitro, but Nitro has such a fuel energy density advantage that it is worth exploring.

Nitro Helicopters indeed use impellers & ducts for air cooling/circulation (I built/owned a Concept 30 w/OS .32 a few decades ago), and also owned an "off-shore Cat" powered by the water-cooled OS .81 (no longer in production). Like you said, "Nitro makes power at high RPMs", so unless you can find a suitable generator/motor, you'll need a gearbox to use Nitro, IMO. Between water cooled/marine and ducted air cooled/Heli, I think I'd rather work with the latter.

Can't wait to see this under power on the tracks!

 

[tudordewolf]

I have had an offer of an RC helicopter engine which might integrate nicely, again they are designed to drive the load via belt reduction or gearing which could work.

Between water cooled/marine and ducted air cooled/Heli, I think I'd rather work with the latter.

I'm starting to agree with the heli engine concept. I think direct-driving the genset is still viable, just have to spec the motor right.

Nitro has such a fuel energy density advantage that it is worth exploring.

Nitro offers better power density, but less energy density than gas. That's why gassers can fly longer on proportionally smaller tanks.

That brings me back to OS... their GT15HZII is a 15cc, (.90-size) gasser, claiming ~2.5hp @ 14k RPM, which is easily within the RPM range of a brushless motor-turned-generator. Might be a very viable choice & there's dimensional drawings on that page. Cooling will be crucial but if you under-load it you'll probably be fine. Pricey, though...

There's also the OS Max 105HZ, a 1.05-size engine with a whooping 3.5hp @ 15k, but that's probably overkill, and from what I read it can drink a gallon of fuel in less than an hour.

 

[Roog]

Thanks guys,

My main problem with these small petrol engines are that the suppliers don’t give proper dimensions so it’s a bit of a gamble.

Despite the fuel costs and availability I find low tune nitro engines quite manageable, I used to prefer starting my nitro powered models to my petrol lawn mower! That said I've witnessed others struggle with their nitro power.

I must touch base with my friend to see what helicopter engine he has, plus he said it was cheap!

Must check out eBay see what’s about?

 

[tudordewolf]

I think one of the reasons we don't see generators any smaller than what's commercially available today is that a power bank of the same size/weight becomes a more practical solution, and more cost-effective.

Don't get me wrong, I love the idea of a mini series-hybrid nitro-electric locomotive. I entertained the idea of a parallel hybrid nitro RC that could use the motor for regenerative braking and then accelerate harder with it, a mini ERS.... but you may want to consider what an "all-in" battery loco would look like, if you spent the difference on extra batteries, could easily get a couple kWh.

 

[Roog]

I think one of the reasons we don't see generators any smaller than what's commercially available today is that a power bank of the same size/weight becomes a more practical solution, and more cost-effective.

Don't get me wrong, I love the idea of a mini series-hybrid nitro-electric locomotive. I entertained the idea of a parallel hybrid nitro RC that could use the motor for regenerative braking and then accelerate harder with it, a mini ERS.... but you may want to consider what an "all-in" battery loco would look like, if you spent the difference on extra batteries, could easily get a couple kWh.

A battery loco is very much my fall back position, but the reason why I am pursuing this is because I know it’s possible and at a smaller scale than I am building it. 1 7/8” gauge, the model was a British diesel electric loco built by a fellow called Bob Symes, he featured in a number of UK TV programmes on model making in the 70’s and 80’s many of which are viewable on YouTube. His model used a genuine diesel engine, a now vintage Taplin twin running on castor oil and ether, of around 8cc I think. He later converted it to a glow plug engine and made it Radio controlled.

Watch from 3:26

Another one I've found is another UK locomotive a ‘Hymek’ at 3 1/2” gauge, this one uses a home made multi cylinder engine and I believe its hydraulic drive, which would be correct for the real loco type, very unusual as I have not seen another use this drive system.

So you can see, it must be done! :0)

And if I fail, then I can always fill it with batteries. :0(j

Incidentally, my calculations suggest the 600 Watts ‘all up’ would be fine even for hauling a handful of passengers, a principle supported by commercially available locos which have as little as 300W motor power per truck. My selection of more powerful IC prime movers is simply my need for overkill, fear of failure and being able to run the engine at lower revs and less stress.

I am prepared to fail, but not to try is not part of my plan. :0)