climber9

I have a Sig Midstar with an OS 40. I'm looking to convert it to electric. I don't need mega speed as I prefer light aerobatics. I'd really appreciate any suggestions on a suitable motor/esc/battery layout.

From what I've read, brushless is the way to go, along with LiPo batteries. That's pricey! I'm probably going to invest in the brushless motor but with NiMH batteries for now.

I'm not sure what the extra weight of the NiMH batteries will do to the equation (in terms of motor size, prop size, speed, flight time, etc).

Anybody tried converting a Midstar or have an opinion on how to proceed?

Matt Kirsch

My Feedback: (21)

I love to do conversions! One of my possible future projects is the Great Planes Easy Sport .40, a similar plane to the Midstar. If I can ever find an unbuilt kit (discontinued) it's mine.

Anyway, you should start with the battery. This is a .40-size plane, so we're talking about Sub-C cells, like the ones used to make up car batteries. The best bang-and-duration-for-the-buck right now is GP3300 (brand and model) NiMH. Number of cells is what determines how much power you'll have. More cells is more power.

You need a cell count, and a target current. I like to use 40 Amps as my target current because IMHO, it gives a good mix of duration and power while keeping the battery weight reasonable. For sedate flying, 10 cells. To get performance equal to a good ball-bearing .46, 16 cells is the way to go. I would choose 12 or 14 for this plane.

For motor, the simplest way to go is with an outrunner. No gearbox takes a lot of complexity out of the equation. I like the looks of the AXi 2820/12 on 12 or 14 cells, with a 12x8 or 11x7 prop, respectively. http://www.modelmotors.cz lists a bunch of prop combinations that they've used. The Jeti 45/3 is also an option.

climber9

Matt,

Thanks for the info. I have much better feel for what I'm after now. Do you recommend Motocalc or Electricalc for modelling the power needs?

jonnyjetprop

My Feedback: (3)

Try motorcalc free for 30 days, then make up your mind. Just download it off the web.

John

climber9

What about http://brantuas.com/ezcalc/dma.asp

Are you familiar with this free, online, no-download-required app? Seems a lot easier than motocalc.

Matt Kirsch

My Feedback: (21)

P-Calc (the link in the above message) is okay, but it's not always accurate, and does not have many of the newer motors listed. It does best with simple brushed motors, especially cheap can motors. No AXi motors are listed, and they're hard to model anyway.

Motocalc is what I've used, but I haven't used it much.