Espritmodel.com Telemetry Radio
Reply
Thread Tools
Old Aug 27, 2013, 12:40 PM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Discussion
Help with Griffon - handling problems

Hi

Recently finished building a griffon using mark porters plans.
I am strugling with the handling of the hovercraft. I cant seem to make it turn (180ļ), it just keeps widening the curve and sliding..
The skirt looks ok to me, is it weight diistribution? Maybe relocate the batteries a few inches to the back?

Thanks for your time
JS - Portugal
oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 27, 2013, 12:56 PM
Registered User
Joined Aug 2007
6 Posts
improving the turning movement of model hovercraft

Hi, you will need to move the weight a bit more to the front to get better turning ... but not a few inches, moving the CG about half an inch might already be sufficient.
Check which part of your model lifts first: the rear end should lift a little earlier than the bow.
If your craft has difficulties turning at high speeds, that is quite normal. The bow wave (hump) moves to the stern and the back piece of the skirt sticks more to the water's surface than the bow does.

Send some photos!
mluthard is offline Find More Posts by mluthard
Reply With Quote
Old Aug 27, 2013, 01:02 PM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Move the weight to the front? I was thinking all wrong...
I will try that but i dont have much room to do that...
I believe the front lifts first but i will confirm that tomorrow and then post some pictures or a video.

Thanks for your help
oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Old Aug 28, 2013, 01:56 AM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
203 Posts
Experience with Griffons is that they will nearly always lift front first because of the weight of the duct assembly and relative position of the lift fan. You may find that your lift fan is generating too much torque which is counteracting the turn of the craft. This can be reduced by using a low pitch prop and a lower power motor - if your skirt is correctly set up you won't need much power to lift the craft. Another thing to look at is the thrust and rudder arrangement. Do you have 2 or 3 rudders? What prop and motor combination are you using? What size is it?
jpcwebb is offline Find More Posts by jpcwebb
Reply With Quote
Old Aug 28, 2013, 05:37 AM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Hi,

The motors are:
Lift: KV 1400 with 6x4 propeller - 3 blade
Thrust: KV1900 with 7x4 propeller - 3 blade - 3 rudders

I will try moving the weight a little forward and reduce the lift power and see if it works.

Any other suggestion?

I will add pictures in the afternoon
oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Old Aug 28, 2013, 06:32 AM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
203 Posts
Hmm, I would say that your thrust is a little underpowered - most of the Griffons I have seen running successfully (mine included) have 8 or 9 inch props with higher kVs on 11.2v or higher. Also, the rudders need to be quite long and placed widely enough to generate good turning moment. Your lift setup sounds fine. How heavy is the model?
jpcwebb is offline Find More Posts by jpcwebb
Reply With Quote
Old Aug 28, 2013, 01:18 PM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Its about 3800 grams
Today i noticed that i had only 50% of the travel in the rudders because i had the dual rate switch on (dumb). After turning it to 100% travel it improved but the batteries died before i could test it more in detail.
The rudders are about 5 cm wide and they go all the height of the propeller...
oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Old Aug 28, 2013, 02:19 PM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
203 Posts
That would certainly account for some of your problem. 3.8Kg is a pretty good weight for a Griffon, but if you can reduce it in any way, that will also help. I replaced the side decks and cabin with Depron for instance and a few other mods which got it down to 2.5kg and that made a big difference in performance.
jpcwebb is offline Find More Posts by jpcwebb
Reply With Quote
Old Aug 29, 2013, 01:17 PM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Actually its "only" 2974 grams.
Here are some pictures. (click to enlarge) What do you think about it?







oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Old Aug 29, 2013, 04:27 PM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
203 Posts
Nicely built model and that is a good weight! It does look as though your rudders may be a little on the slim side though - I'd have probably made them at least 50% wider I think (based purely on the photos so I can't really judge properly) and this may account for some of your steering issues.
jpcwebb is offline Find More Posts by jpcwebb
Reply With Quote
Old Aug 31, 2013, 04:56 AM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Gluing the hinges to the thurst structure was a nightmare...
If it comes to make changes, the rudders will be the last place i am going to make changes.

I havent tryed yet with the weight more balanced to the front and with the servo movement to 100%. I am confident that this will make a big difference but if it is still not enough i will first change the motor
oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Old Sep 07, 2013, 03:05 PM
TheyreComingToTakeMeAway!
derk's Avatar
USA, ID, Coeur D'Alene
Joined Dec 2003
5,442 Posts
tape some depron to the rudders as a test to see if they do need to be enlarged. that way you dont need to do any major reworking to see if it is needed.
derk is online now Find More Posts by derk
Reply With Quote
Old Sep 08, 2013, 01:54 AM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
203 Posts
Agree this is a good approach for testing. Some folks use clear plastic to extend rudders to minimise spoiling the look (especially for scale craft). Can you not remove the rudder hinge pins? Or detach the rudders from the hinges themselves? Always a good idea to make rudders detachable as a rule in case of damage.
jpcwebb is offline Find More Posts by jpcwebb
Reply With Quote
Old Sep 15, 2013, 02:02 PM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
Hi again

Today i went to try it with the longer rudders as suggested but i blew the lift esc.
I usually use 11.1v 800mah lipos (from an Esky big Lama). Today i pluged a zippo Lipo with 11.1v 2200mah and 25c. Do you think it blew because of the battery or it was just a coincidence?
Can anyone suggest an esc good for the motor i mentioned and the zippo batery? A link from hobbyking or other online store would be nice... (dont want to spend more than 15 to 20 $ on the esc)
oacilamaf is offline Find More Posts by oacilamaf
Reply With Quote
Old Sep 15, 2013, 02:15 PM
Registered User
Portugal, Braga, Vila Nova de Famalic„o
Joined Oct 2009
132 Posts
What do you think about this one? http://www.hobbyking.com/hobbyking/s...k_50a_esc.html
oacilamaf is offline Find More Posts by oacilamaf
Last edited by oacilamaf; Sep 16, 2013 at 02:10 PM.
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! X Quad with Motor4 problems. HELP! rubinstudios Multirotor Talk 2 Aug 11, 2013 05:35 AM
Help! problem with my hubsan X4 - Any help at all would be appreciated rctech96 Mini Multirotors 6 Feb 21, 2013 06:32 PM
Discussion I Need Help with a Mental Problem Chophop Life, The Universe, and Politics 51 Feb 20, 2013 05:07 PM
Need help with Brake on Castle Creations griffon 55 ESC!!! bwaltz Castle Creations 5 Apr 05, 2004 02:30 PM
Need help with Brake on Castle Creations griffon 55 ESC!!! bwaltz Power Systems 0 Apr 01, 2004 02:44 PM