how to slow it down

[goodychri5]

Hi there, new to the site so if I've posted this in the wrong place I apologise in advance.
I have a Trex 700e dfc fitted with a castle ice HV120 and a Gartt H700 530kv motor. The set up is as stock with the standard gearing and I have a 12s Lipo in it. I fly scale, gassers up till now and intend to fit this into a scale fuselage. I have a 4 blade head and a set of spinblade 700 4b to fit.
My problem is one of headspeed. I want to run around 1200rpm but the castle speed controller won't allow this in governor mode.
So, do I look for a different speed controller, motor or drive pinion?
If I go for pinion I will need an adjustable motor mount as the stock setup has no adjustment.
Any advice or assistance will be greatly appreciated.
Regards to all, Chris

[simplechamp]

If you've been playing with the CastleLink and gov settings you will know that it wants to be in the 80-90% output range for the Set RPM values. You get the warnings because trying to run low headspeed at partial output (say 40-50%) is stressful on the ESC.

Different motor is probably out unless you get someone to wind you a custom 240-270kv 700-size motor. Changing gearing might get you down a little bit but don't think you will get down to 1200RPM at 80-90% output like the ESC wants.

There are some ESCs like YGE and Kontronik that have a feature called active freewheeling. Without digging into the technical stuff what this feature means is the ESC has no problem running at 25% output or 90% output. Running at partial load doesn't cause additional stress and heat like on the Castle.

Another thing to look into would be low headspeed flying on a single 6S pack. Guys run a single 6S pack with a 12S motor at 100% output at around 1000-1200RPM headspeed and get low current draw and long flight times. But I'm not sure if this will work with a 4-blade head, since that will obviously be a much bigger load than a 2-blade head at the same 1200RPM. Might be worth asking about low headspeed with a 4-blade head in that section of the forum:

https://www.helifreak.com/forumdisplay.php?f=362

[goodychri5]

Many thanks for your response Simplechamp, new to electonics as well as you probably guessed. I will take your advice and check up on 6s running.
Kind regards,
Chris

[Andy01]

Please post details of your gearing - I do not know what pinion and main gear you have.

RPM = kV x 44.4V (for 12s) x 0.9 (efficiency) x pinion teeth / main gear teeth = RPM at 100% throttle towards the end of the flight.

With a CC ESC, the closer you get to 95%, the cooler it will run, so aim for between 90-95% of the number you get with the above calculation.

A slower motor is the only way to go as it is VERY unlikely you will find a pinion small enough.

Depending on what scale model, I think 1200rpm may be a touch slow. My Vario Long Ranger runs 2x 710mm blades at 1350rpm and it flies well. I have tried 1250rpm, but it can be a handful in windy conditions.

If, however, you plan to run a 4 , 5 or 6 blade setup, then 1200-1250rpm is probably OK, or if you plan to run longer blades (closer to 800mm). I think a 700mm narrow chord 4 blade would probably be OK on around 1250rpm to start with and work down to 1200rpm if it flies OK. So aim for 1250rpm at 95%, which allows you to drop a bit if it goes well.

Slower motors are fairly readily available - I have a 300kV XNova 4035 for my EC-145. KDE also makes a 295kV, but it is a very powerful (and costly) motor that is complete overkill for scale.

The scale forum is probably the best place to look, or scalerchelis.com

Colin

[00028cl]

Hi, I have a similar question regarding gearing. If my engine WREN 44 has a max torque of 2.9 ft-lbs @ 13500 rpm and I am using a gearing ratio of 10, then my output RPM = 1350? what will my torque output be?

[simplechamp]

Originally Posted by 00028cl

Hi, I have a similar question regarding gearing. If my engine WREN 44 has a max torque of 2.9 ft-lbs @ 13500 rpm and I am using a gearing ratio of 10, then my output RPM = 1350? what will my torque output be?

Your RPM is divided by 10 and the torque is multiplied by 10. So the input gear (pinion) is spinning 13500RPM and 2.9ft-lbs torque, and the output gear (maingear or idler) is spinning 1350RPM and 29ft-lbs torque. This is of course assuming a perfect coupling between gears. In reality you will lose some energy to friction and drag but I cannot say how much.