Outer planets: Jr drill - Convert-o-tron 125 - fuel cell ratio?

[Magzimum]

I want to build a planet-hopper for Dres. A little 5-Kerbal ship that can go from the surface to an orbital station and back. (Dres needs love, so it will get more infrastructure than it strictly needs).

The ship is quite small, built mostly out of Mk1 parts. I want it to be able to reach all corners of the planet with fuel to spare, so I want to equip it with the small ISRU (Convert-O-Tron 125), and some Junior drills. Putting 2 large drills onto this small ship makes it look like a mining-ship, which is not the look that I want. 

However, I am running into an issue. The ships needs 30 electric charge for the Convert-o-tron, and some for drills, radiators and optionally lights. The ship is shown below, stripped of all electricity-generating parts... equipped with just 2 drills, but more can be put on.

The formula that I am on right now is 4 or 6 drills, with 2 large fuel cell packs for electric charge (and two nuke-generators for when I am in orbit). But I am not sure whether this is the best combo. 

Other people surely used the small Convert-o-tron 125 on e.g. Eeloo, Laythe or Tylo, and therefore ran into the same problems... so any tips are welcome. What I would you do so that this thing can generate fuel on most spots of Dres (also those with low ore concentrations)?

Note: I also considered solar power (but 15-18 gigantors seemed a bit much for this small ship), and nuke-generators (but spending >1 million funds seemed a bit much for this small ship). 

[Starman4308]

The biggest suggestion is to have the 2.5m converter with a high-ranking engineer. The 1.25m converter throws away 80% of the ore used, and it's quite possible you'll get into a situation where you're running a net deficit of LF+O trying to keep your drills and converter running on fuel cells. Combine that with the (frankly insane) bonus that high-level engineers give, and it becomes clear that the best approach is a 2.5m converter with at least a three-star engineer running it. Between the 17x engineer bonus and the 5x efficiency improvement of using the 2.5m part, you're getting 85x more LF+O for your time and electricity.

The only use case I see for the 1.25m converter in stock is for missions where you have an external power supply (solar or RTGs) and a great deal of time to refuel a relatively small probe. Squad doesn't make lightweight ISRU easy, which probably makes sense for stock (with its tiny planets and minimal dV requirements), but, well, for 6.4x, I long since decided to write some configs to mod them into being much more mass-efficient.

Edited November 28, 2016 by Starman4308

[Ripper2900]

The small ISRU is super for your needs of small hopper - if you have enough time!  But the in ksp is pretty much the only thing that comes for free... 

I've made several Jool-5 capable landers with the 1.25 isru and 2 small drills. Power provided by 2-6 rtgs and you can mine away - slowly. But the game mechanics are made so that if you use time acceleration at 1000x or more, you're probably just burning time, and thus the electricity comes for free! It gets generated by the two rtgs at a higher rate than the mining/refining can consume. 

http://m.imgur.com/a/YvGhw

Here's the lander/tanker of my latest mission. It's fully capable of landing 4 kerbals on Tylo, and with a separate aerodynamic nose, also on Laythe, so Dres should be no problem. 

Happy mining

Edited November 28, 2016 by Ripper2900

[Magzimum]

Thanks for the responses, @Ripper2900, @Starman4308.

I noticed that with RTGs, I can fill the ore tanks with the ISRU turned off, then shut down the drills and start up the ISRU to get some fuel. Repeat until fully fueled.

I managed to further optimize the hopper by giving it 6 drills and 4 fuel-cell packs (the six-packs), so that at ore concentrations of 6% and higher it will just run continuously and fill the tanks. But it's a thin line: at lower concentrations the rig will first drain (while the ISRU is warming up and not running efficiently) and then fill the tanks. I managed to run into trouble when I tried this with empty tanks - the rig shut down before the ISRU was warmed up.

Finally, I went with the suggestion to use a 2.5m ISRU and 2 of the big drills. Because this Dres mission is more about having fun (and giving Dres some love), so I replaced that stupid Mk1 stuff with Mk3 tanks and 4 Rhinos. The hopper went from 17 tons to 180 tons (still only 5 Kerbals, lol). At least it has a TWR (on Kerbin) of 5.5 when fully fueled, and it can go to orbit and then land twice without refueling on Dres. I realized far too late that efficiency has no place in this Dres mission . Still, lessons learned here will probably prove valuable another time.

[Sharpy]

3-star engineer makes fuel production and consumption to break even between fuel cells and large ISRU+drills. If you want actual fuel surplus, you need either 4-star engineer to increase production, or at least one RTG to remove some burden from the fuel cells.

[Terwin]

On 11/28/2016 at 2:36 AM, Sharpy said:

3-star engineer makes fuel production and consumption to break even between fuel cells and large ISRU+drills. If you want actual fuel surplus, you need either 4-star engineer to increase production, or at least one RTG to remove some burden from the fuel cells.

That depends on your ore concentration.

Engineers only help the drills, so a 3-star engineer at 1% ore concentration produces the same amount of fuel for the same amount of electricity as an unmanned probe drilling at 17% concentration.

the 1.25 ISRU and small drill are *not* what you want to use when relying on fuel cells however!

[Sharpy]

25 minutes ago, Terwin said:

Engineers only help the drills, so a 3-star engineer at 1% ore concentration produces the same amount of fuel for the same amount of electricity as an unmanned probe drilling at 17% concentration.

Are you sure drill power usage doesn't scale with ore concentration?

I'm pretty much positive it scales with drill's "thermal efficiency", had rigs that would begin running out of electricity when the drills heated up. And ore supply is directly proportional to that. I'm not sure how that works with ore concentration, but I think I recall mining asteroids (70+%) being more energy-hungry than mining planets.

[Terwin]

1 hour ago, Sharpy said:

Are you sure drill power usage doesn't scale with ore concentration?

I'm pretty much positive it scales with drill's "thermal efficiency", had rigs that would begin running out of electricity when the drills heated up. And ore supply is directly proportional to that. I'm not sure how that works with ore concentration, but I think I recall mining asteroids (70+%) being more energy-hungry than mining planets.

Thermal efficiency is all about how close the drill is to it's optimal operating temperature.

It starts cold and warms up.  If you have radiators, it stops at 100% efficiency.  If you do not have radiators, it goes above the ideal temp and starts losing efficiency.

This is true for both drills and converters in the stock game and has nothing to do with how much ore is in the ground.

As far as I am aware, power required for drills is independent of ore concentration. 

If you run your ISRU while drilling and it catches up to the drills, then it will only refine as much ore as it gets from the drills, reducing the amount of electricity is uses because it is not running at full capacity.

Drills always take 15 energy/sec to run at full capacity(3/s for the small ones), and both ISRUs use 30 energy/sec at full capacity.  Either one will run at partial capacity if it does not get enough energy to run at full capacity(with ISRU having priority over drills so long as it has ore to process)

In your case, it sounds like you did not have enough power to run both your drills and your ISRU at full power and when the ore concentration was high enough, the ISRU would draw enough power that it would start to deplete your energy reserves.   It would have happened the same way if you filled up your ore tank and then moved to an area with low ore concentration and started both ISRU and drilling.

Asteroids are more energy hungry than planets because you get more ore to feed to your ISRU.  If you turn off your ISRU then your drills will take the same power regardless of the ore concentration.(and if you run your ISRU with a full ore tank, it will always take 30 energy/sec if it can get it, once it has warmed up to 100%)