Power consumption

I had two supprises today! Missed the midland Footy race (turned up omn the wrong day) and had a sail and ran out of power. I an using what I thiugh would be a forever system, a 7.2 v Li-Poly which runs my 540mm twin rotore helcopteri for 8 minutes. I expected forever out of the same system running just two servos. It only lasted 30min! What capacity batteries do folk use and how long a sailing time do you get? On the good side the Una rigged Papaya III with the 507 una rig set up to have the same CE position works well to my amature eyes.

I use 4.8 nimh packs of 400mah.
during a race day, I swap one pack every 3 races circa, and never went out of battery.

How long is a race?

a typical race:
throw the boats in the water
2 minutes of starting procedure
one or two turns of the course, depends on the wind
then I take the boat out of the water and switchit off
usually I make 3 races ad then swap batteries, to avoid any risk

UshCha - You would do well to spend some time researching the questions you have. This forum has had quite a few threads devoted to batteries, you just need to use the search feature and commit to do some reading.

A model yacht race heat is generally around 20 minutes long, depending on course length this can vary. Footies, if sailed on a course that larger classes take 20 minutes to complete, will take longer. A course set just for Footies would be ideal, one not much longer than the pit area or vantage points would allow, perhaps sailed more times around than usual with bigger boats.

A heat time of 20 minutes is a good target when setting a course for a Footy race. In setting course length you have to take in account the wind strength as well as obstacles (there are usually more of these closer to shore). Keep in mind that these boats are hard to see fairly close to shore much less at distance so keeping the wing or reaching mark pretty close in is a good idea.

The best way to learn about racing and gear choices is to go to a local race and ask questions. Model Yachtsmen are opinionated people, they love to give you theirs. But, as a new guy, the tendency is to shy away from the best sailors under the impression that they would not give you the time of day. Wrong! These are the guys you want to learn from! They can give you the best advice for sailing in your area’s conditions. If they feel that you are serious and that you listen and understand what they are telling you then you will have a source for answers.

I don’t sail footy’s, but power use is power use, no matter what the system is in. You should be able to look up what the power draw of each of your servos is, and your RX. I usually look at the servo page at servocity.com for max torque draws (current draw at stall). Add them up and compare to the Mah capacity of your battery pack. The higher voltage will actually result in a little more current being used, but you also get more torque from that extra voltage. If you are using say 350 mah, that will drain a 350 mah battery pack in one hour. Actually less than that since nothing is 100% efficient, and you don’t want to drain your Lipo’s completely either. Look for battery packs with higher Mah capacity or swap them out frequently.

I just looked at the current draw for a Hitech 225mg, 8.8mah at idle, but sucking 340 mah at 6v when under no load, just rotating back and forth! Add in a rudder servo and a little wind and they will eat up those little packs.

I use 2500 mah packs in my IOM and 1600 mah in my Victoria and usually swap them out mid day at regattas.

With a pack of 4 NiMh 900 mAh, depending on the condition I just swap the battery, just to be sure, about 3/4 of the sailing day (say, after 7 race out of ten). The race is like Mario decribed, but I keep the boat sailing also after I finish. Let’s say that I can have 3 hours of sailing.