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        Question Advice on Circular Hovercraft design.

#1 dualplover May 04, 2012 07:35 PM

Advice on Circular Hovercraft design.
 
Hi first of all i'm new to RC so please treat me like an idiot with any reply, ie please do not assume i know what your talking about.

i have been looking around but with so much choice in products i'm hoping someone here can help me narrow my final possible choices.

simply i'm trying to design and build a prototype of a RC hovercraft designed to navigate a maze using an online camera.

so basically speed is not a requirement what i desire is precision control and movement.

for this i envisage a circular design with a diameter of about 30cm (12 inches)

with a lift motor dead center and two EDF brushless motors on either side.

instead of a rudder i plan to steer using the two motors so i can turn on axis i would also like these motors to have reverse capabilities.

the construction may be skirtless with a skidpad type design

what i would like advice on is

LIFT motor
from what i've read an outrunner with a largish prop may be the best. but feel free to advise on what you have found works best.
besides the motors/ esc/ batteries and normal RC stuff the craft will also have camera+ transmitter onboard as well as some other rudimentary electronics. so far i don't have total weight as i havn't brought all the parts yet but some basic advice on what would normally lift something this size would be great.

LIFT esc
want something that simply engages whenever the trust is applied so is only drifting when moving and anchors at other times to save batteries and run time, maybe something that can be adjusted so if more weight is applied it can be bumped up to suit?

Trust motors
as i said this baby is not built for speed just accuracy and will need to have reverse capability, im thinking EDF 55mm units but am having trouble understanding KV especially when most talk online is all about going fast.

trust ESC
the two motors will need to work in tandem for steering so hopefully when one is 100% fwd and the other 100% reverse it will spin on axis. again dose not need to be fast as the craft are basically roaming a maze.

i'm hoping to run this on 2 cell lip batteries at 7.4v as thats what i have already from my previous project see.
http://dualplover.com/vinylrally/

any other advice on hovercraft building much appreciated especially anything i may not have considered.

#2 jpcwebb May 10, 2012 12:51 PM

This is eminently possible and has in fact been done by a member of our club. But first, you say "what i desire is precision control and movement" - why then choose a hovercraft? They are probably the least precise in terms of control that you could get! What is preventing you using wheels? The big benefit of HCs is that they have multi-surface capability. Here however, you have a carefully controlled and restricted environment in the form of a maze, so multi-surface capability is not really needed.

#3 dualplover May 10, 2012 11:01 PM

point taken but i'm wanting a vehicle that can turn on its own axis which i don't believe i can do with wheels as effectively as hovering, well unless its built from scratch but then i think it will be a bigger engineering feat than i can handle as opposed to a hovercraft.

maybe im wrong but in my imagination since this project started its been a hover vehicle

if someone else has built something similar would love to see links etc

#4 jpcwebb May 11, 2012 10:55 AM

I think you'll find that there is as much engineering involved in a hovercraft. For instance, the EDFs will not work well in reverse as they are not designed that way (plus reversing ESCs are expensive and you'll need two) . So your options are to either use only one fan to turn using channel mixing (i.e. so that to turn left, you'd have the right fan on full and the left fan off) or to somehow vectorise the EDFs with servos so that they can rotate 180 degrees. If you do the latter, it makes control setup more difficult. In contrast a circular vehicle with two independently driven motorised wheels either side and two caster wheels forward and aft should be easy to control using simple mixing.
Anyway, here's the one from our club: http://www.modelhover.org/node/452
Probably larger than you want, but same principle. Note you can't see it but the skirt is made from very thick/ deep pile fleece which works really well on smooth dry surfaces.
The lift fan doesn't need to be that big - for a 12 inch craft I reckon you could easily get good lift with a 4 or 5 inch prop. You should be able to use radio mixing to get the fan to come on when forward thrust is applied, though you may need to use a Y lead somewhere along the way, but it shouldn't make any difference to the choice of ESC.


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