Can I use end point to limit max power

[i12fly]

Can I limit the top end power by using end point reduction on my Futaba C7?

Will this be OK or could it damage the esc?

At the moment I'm getting 720W and really want about 600W which would be ample for my 4.5lb Ballerina

Yes the motor I've got is 'a bit too powerful' and although suitable for 4s is really too high on the kv at 1100.

I've reduced prop size down to 9x5 etc

I'd like to stick with this motor as the cowl and mount are all suited to this and I don't want to buy yet another set of batteries (and I need the nose weight anyway)

[Gary Manuel]

Here's my opinion:

Don't change anything - just don't push the stick all the way to the top.

A little extra power is always handy to have in reserve.

[Martin Harris - Moderator]

The ESC will work a little harder at part throttle but as long as it's rated with a little to spare, it shouldn't matter. Rather than messing about with end points, can't you just avoid using full throttle?

[Biggles' Elder Brother - Moderator]

Yes there is no reason why what you propose won't work. It's probably better to calibrate your throttle initially at full setting then effectively reduce the throw to the desired amount.

Personally though I would be inclined to agree with Gary - extra power is sometimes welcome! Simply use less throttle.

Not a "dig" (honest) but just out of interest, if you were using OpenTx you could very easily either:

1. Make the setting switchable - so you could switch in/out on reduced throttle throw.

2. Or even "smarter" program a knob so you could vary full throttle setting from, say, 60% to 100%throttle of the actual - in the air! Now that would be handy!

BEB

[Gordon Whitehead 1]

600W on 4.5lb = 133W/lb which is pretty high-powered and 160W/lb with 720W is a hefty increase. Trying to stay away from this higher power/weight ratio by not using full stick movement has to be a pain.

On my electric models I use throttle management, ie spend a lot of every flight at low throttle, to enhance duration, just opening up at the appropriate time as required for aerobatics. That approach is frequently advised in the media anyway. So I can't see why using end point to permanently reduce max power should be a problem. Just ensure the esc is properly cooled with a blast of air over it. Regarding Martin's comment about the current rating of your esc, 720W on 4S will be about 50A, so if your esc is rated higher than that you should be OK to limit the top end via the throttle end point.

Gordon

[i12fly]

Thank you for your comments everyone. I've got a 60A esc fitted so should be OK. With a freshly charge battery it measured 48A max. There is quite a good opening in the slipstream just in front of the esc but I may need to open the outlet a bit more.

Like you Gordon I use quite a bit of 'throttle management', tearing about the sky doesn't appeal but aeros do.

I didn't manage to get the rpm due to the electric light but a previous test with a 9x6 prop gave 13200rpm so I guess it runs about 14k which would give about 380mph tip speed on the master airscrew prop. It is a bit noisy!

My next Tx will almost certainly be 'open source', I would have gone that way already but it would mean replacing 9 FASST Rx too so would be a bit pricey.

[Dave Hopkin]

You could also try a 9x4 prop on it, then the motor will be doing less work

[MattyB]

You are unlikely have any short term problems limiting max throttle via an endpoint, but depending on the type of ESC you could cause an early death to the FETS which are working harder at part throttle than full. Adding an extra heat sink to improve cooling might help with that though.

Ultimately you'd improve the whole setup with a lower Kv motor of the same size and weight - you could then turn bigger props that give more thrust at lower rpm, reducing noise and probably increasing duration too. Your only other option is to try 3S and bigger props, but you may need a larger esc and will be stressing your batteries more to generate a lower wattage.

[Frank Skilbeck]

I recently ran into a similar "problem" started off with a 4s battery and plane was way overpowered and actually felt touchy on the throttle, in that a small throttle stick movement gave a big response. I changed to a 3s battery and the plane now feels like it flies a lot smoother.

BTW I note the comments on FETs failing if you run at part throttle, I must admit that I don't fly my models round at full throttle all the time.

[Trevor Crook]

Have you any 3s batteries you could use? Mine flies very well on 3s 4000s, which with an 11x6 prop gives just under 450W with my setup. A bigger, slower turning prop is also more efficient than a small one whizzing around.

[GONZO]

i12FLY, if you do get a Taranis with the JR style external Tx module slot in the back and you wish to continue to use your FASST Rx then you require a Ripmax RM12-MX Tx module **LINK** or the Hobbico equivalent **LINK** . I have the Ripmax version for my Taranis and it works OK.

[Simon Chaddock]

MattyB

I really don't follow the logic on how generating a lower wattage by using a lower kV motor can increase the stress on a battery.

Surely less watts means less amps and its amps that stresses a battery.

[MattyB]

Posted by Simon Chaddock on 06/05/2017 11:29:15:

I really don't follow the logic on how generating a lower wattage by using a lower kV motor can increase the stress on a battery.

Surely less watts means less amps and its amps that stresses a battery.

Sorry, my original post was not that clear I admit. What I was trying to say was that the only other option if he doesn't change the motor is to go 3S and prop up to get the desired wattage. That should work, but pulling 600W out of a 3S setup is going to mean drawing 55-60A from his packs, a substantial increase in current draw over his existing 4S setup even though the maximum wattage on 3S will be lower.

Edited By MattyB on 06/05/2017 14:11:21