Recty

I'm looking at building a hovercraft from scratch, using electric power.

I already have a LiPo and a receiver/speedcontroller that work together and a motor for thrust. My problem is that I want to also have a second motor for providing lift, it will inflate the skirt so that my hovercraft actually hovers.

Is there a way to use just one LiPo battery to power both motors? The lift motor doesnt need to have a speed controller, as I'd rather it just be a toggle. Turn the lift motor on, the hovercraft hovers. Turn it off, it doesnt hover. I'll use the speed controller in the back to increase/decrease the amount of thrust the hovercraft is getting.

Anyway, someone please tell me if this is possible using one battery. And if it isnt and I have to get two batteries, I'm not sure how I would hook that all up to one receiver, so if that is the case, please describe that to me as well

Or if you have a better idea on how to run 2 motors on one RC vehicle, I'm all ears.

ChopperMike

There won't be any problem using 1 battery as long as the battery can supply enough energy to both motors.

It makes no difference how many batteries you use as far as the RX is concerned. Only 1 or them is providing power to the RX through the BEC of the speed control.


Mike

Recty

So how would I wire that?

Obviously the one motor for thrust would be set up normally... battery to ESC to motor, with a wire also going from the ESC to the receiver. So would I have to get a splitter basically to run power to the second motor? Just have it split before it goes to the ESC, so that one side can go to the ESC and one can run off to my life motor? And just have that lift motor be plugged into Channel 4 on my receiver which is what I normally use to activate flaps, so its basically just an on/off switch?

ChopperMike

Unless you use another ESC or an electronic switch of some kind for control of the lift motor you won't be able to control it from the TX. You'll need to use another ESC, which can be powered by the same battery as one providing power to the thrust motor's ESC, or a relay of some kind. There was a question on another forum regarding an electronic switch to control some lights on a model. There are several sources for these types of electronic switches which allow you to control something from one of your RX's channels.

The easiest option would be to have a toggle switch mounted on the hovercraft, a simple series circuit from the battery to the switch to the lift motor and back to the battery.


Mike

Recty

So basically there is an electronic switch I can put between the battery and the lift motor that plugs into a spot on the RX? And when I flick the switch on my TX that corresponds to that spot on the RX, it will activate the switch, letting power through and turning the motor on?

ChopperMike

Yes. Something like this

http://www.dimensionengineering.com/BattleSwitch.htm

This one I found is good for 10A. There may be others available. I Googled "radio control switch" to find this one.


Mike

Recty

Cool, that helps a lot. I wish I was ordering the parts right now, but for the moment I'm trying to get things figured out and then I'm ordering everything.

Kind of sucks being up in Alaska... if I order a part that doesnt work with what I want, I have to wait another week at least to get a new part in.

John 38

Recty,

Your Lipo battery will not be protected against low voltage failure unless that is also incorporated into the seperate lift electronic on/off switch.

On the other hand, with a simple on/off switch for lift, when the low voltage on the thrust ESC cuts out your thrust, you can always stop your lift motor immediately to protect the Lipo battery

John

Recty

Ah true, I hadnt though of that, good to know.

I really havent done much with electronics in RC. I know the basics but nothing that detailed, I'm pretty sure my IFO that I fly around now doesnt even have a low voltage cutoff, because I used to fly it until it basically couldnt spin the prop anymore.

Oddly enough, it recharges just fine and I've never had any problems with it, but from everything I read my battery should be toast.

John 38

Recty,

the early electrics ready to fly had nicad or nihm batteries and cheap controllers and as you said fly around until out of puff. generally these types of batteries could take that treatment and still recover as the volyages never got too low ( but not always ).

Lipos on the other hand will fail if voltage taken too low. All modern ESC's have low voltage protectors that cut out power to drives and leave enough power for the radio control to get model SAFELY BACK TO THE GROUND. The ESC cut off is therefor dual purpose in protecting both model ( the prime purpose) and secondly the battery.

apologies if you already knew this, but for any beginner reading these posts.........

john

Recty

I did already know that, but I dont mind reading it again. I got into electronic flight about 6 years ago when I bought my IFO, so it has been a while since I've really done any research on it.

Weirdly enough though, my IFO is using LiPo batteries and I ran them to almost dead state before charging them. I had always heard you needed to cycle batteries (which I know now doesnt apply to LiPo) so I always tried to get them dead before I'd stop flying. If for some reason I damaged the IFO and couldnt finish my flight time, I'd have my brother hold it while I went full throttle until the thing died.

I dont think my ESC has a low voltage cutoff like modern ones do, because it would just slowly start losing power until it could barely spin the prop. I think the low voltage cutoff just WHACK stops the power going to the motor, right? It doesnt slowly limit the power the motor is receiving?

John 38

Recty,

it sounds like power reduces to a level not worth anything before voltages get low enough to do damage ??

I am not an expert and have limited experience re electrics, but my ESC's lo volts cut off just stop motor dead. batteries then recover slightly to give a bit more power if applied gently to assist landing.

Not sure if you can get ESC's which will reduce power first giving flier early warning to start landing approach - i think I 've seen reference to this but whether it was wishful thinking or an actual product mu failing grey cells cannot recall.

best of luck with your hovercraft project.

incidently I live a few miles from where Sir Christopher Cockerell developed the hovercraft. however there is not a lot left around here to show for it

John

ChopperMike

Castle Creations ESC's have the option of either a Soft Cutoff or Hard Cutoff. With Hard Cutoff the motor power is shut off competely and when the throttle is dropped to minimum it resets so you can restart. With Soft Cutoff the motor flutters basically, which is a better setting if you're flying a model that shouldn't have the power ubruptly cut off.


Mike

Recty

Thank you both for all the advice, this is helping a lot more than you can realize.

Let me see if I can upload these two pictures and make sure I have this laid out right... So basically one picture shows the hovercraft being run with 1 LiPo, the other picture shows the hovercraft being run with 2 batteries. Do both drawings I made look like they are set up correctly? I havent decided which way I want to go, 1 LiPo would be less weight, 2 LiPos would be increased flying time.

Recty

By the way, here is a sketch I did of the hovercraft. I plan on making sure the thing hovers and is sufficently balanced, then I'll be attaching some wings and flying about 6" to a foot above the surface of the local lake using ground effect.

John 38

Recty,
both diagrams are OK - my earlier comment on lo volts protection still applies

good luck on the combined hover/ground effect

john

Recty

Thanks. I dont really think the ground effect flying will be that hard. Normally the hardest part of getting something into ground effect is the drag from the water, most ground effect vehicles are boats. So you have to get enough lift to actually pull free of the water, which isnt an easy thing to do.

With a hovercraft, I'll already be free of the water, making it require a lot less speed to actually get into the air.