Question on Electric Brakes
07-10-2014, 01:38 AM
#1
Thread Starter
Question on Electric Brakes
How do they work?
Specifically, will they hold a model static on tarmac against the idle thrust of a jet?
I realise that it is possible to use electro magnetic forces to slow down a model (electric motor in reverse) but I am doubtful about their static hold.
Specifically, will they hold a model static on tarmac against the idle thrust of a jet?
I realise that it is possible to use electro magnetic forces to slow down a model (electric motor in reverse) but I am doubtful about their static hold.
07-10-2014, 02:09 AM
#2
Hi Alasdair, I think you have the wrong impression regarding how they work.
I take it you think they work like the brake function on an electric powered model?
The type I have experience with is the Kavan electric brakes, most work the same.
A simple electric coil (an electromagnet, like the gismo that picks up the scrap iron at the metal recyclers)
is used to pull a metal plate towards the coil. The metal plate is attached to & rotates with the wheel.
As the coil is energised the plate contacts the metal body surrounding the coil slowing the wheel.
I guess they could also use a friction material between the plate & magnet but obviously the magnetic pull
would be reduced as the plate would not come in contact with the magnet.
Their static hold is actually greater than their dynamic hold. As an example I use them on the nosewheel
only & as I throttle up against the brake for take off from grass the wheel will skid from about half throttle,
the brake does not slip.
The Kavan brake is designed to a 9V 'transistor' battery for power, I just feed it from the 2 cell lipo ECU battery
via a micro switch on down elevator, either on or off.
Some of the more sophisticated systems use an electronic control unit to have proportional braking.
I recently bought a set of these, haven't tested them yet but cannot complain about the price.
http://hobbyking.com.au/hobbyking/st...heel_2pc_.html
John.
I take it you think they work like the brake function on an electric powered model?
The type I have experience with is the Kavan electric brakes, most work the same.
A simple electric coil (an electromagnet, like the gismo that picks up the scrap iron at the metal recyclers)
is used to pull a metal plate towards the coil. The metal plate is attached to & rotates with the wheel.
As the coil is energised the plate contacts the metal body surrounding the coil slowing the wheel.
I guess they could also use a friction material between the plate & magnet but obviously the magnetic pull
would be reduced as the plate would not come in contact with the magnet.
Their static hold is actually greater than their dynamic hold. As an example I use them on the nosewheel
only & as I throttle up against the brake for take off from grass the wheel will skid from about half throttle,
the brake does not slip.
The Kavan brake is designed to a 9V 'transistor' battery for power, I just feed it from the 2 cell lipo ECU battery
via a micro switch on down elevator, either on or off.
Some of the more sophisticated systems use an electronic control unit to have proportional braking.
I recently bought a set of these, haven't tested them yet but cannot complain about the price.
http://hobbyking.com.au/hobbyking/st...heel_2pc_.html
John.
07-10-2014, 02:22 AM
#3
Thread Starter
John,
Yes of course, I get it now. Many thanks.
I was indeed imagining some kind of electro-magnetic braking (non-contact) as in a motor.
So it is just like a disc brake pulled into contact by a magnet. Simple & obvious if I thought about it. I'll give them a try; they will work on jets.
Yes of course, I get it now. Many thanks.
I was indeed imagining some kind of electro-magnetic braking (non-contact) as in a motor.
So it is just like a disc brake pulled into contact by a magnet. Simple & obvious if I thought about it. I'll give them a try; they will work on jets.
07-10-2014, 03:08 AM
#4
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I have used a smilar set like the hobby king ones and they work but i wouldnt say they would hold a turbine static. The tyres are too soft for tubine operations more designed for electric or foamy models.
I have used Electron brakes and Intairco brakes and prefer the Intairco brakes due the their wiring is externale of the electromagnet.
I have used Electron brakes and Intairco brakes and prefer the Intairco brakes due the their wiring is externale of the electromagnet.
07-10-2014, 03:32 AM
#5
I have used a smilar set like the hobby king ones and they work but i wouldnt say they would hold a turbine static. The tyres are too soft for tubine operations more designed for electric or foamy models.
don't really need much braking to overcome that.
Yes, the tyres are soft. I mostly fly from grass so hopefully they will last but I can't see
them lasting very long on tarmac.
Electric retracts have become popular at the same time as electric brakes, a couple of guys
at my club have 'all electric' models, makes for a very clean install.
John.
07-10-2014, 03:36 AM
#6
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I have the GBRJet electric brakes on a 25kg, 3.5m ViperJet with a P200SX and they work just fine! They can brake a model from landing speed no problem so, obviously, resisting the few pounds of idle thrust is a doodle.
07-10-2014, 03:52 AM
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Having had some experience early on in this field as we produced one of the first of the 2nd gen brakes which most manufacturers now use/copy.
The system as detailed above is correct, an energised coil (electromagnet), a floating metal disc and a power source to power the coil (via electronics). There are some issues however which I am not sure are being addressed in all systems currently available.
If the metal disc is allowed to contact the coils metal casing then even when the power is removed to the coil the disc becomes partially magnetised and can remain 'stuck' to the coil casing causing binding.
Space inside the wheel hub limits the coil size and hence power it can deliver, this means not all models will be adequately braked as often the ideal size of electromagnet is restricted.
You can reduce the amount of magnetism transferred to the disc in two ways, first drive the coil with a continuosly reversing current (ours changed 100's of times a second), and second apply a thin abrasive brake pad material between the electromagnet and the disc so both cannot touch. The introduction of a brake material helps provide better surface contact for braking but as mentioned above does reduce the electromagnetic power available. Our brake material was .3mm thick.
Electric brakes have moved on considerably and will be reliable and standard fitment I am sure very soon - just a few little niggles to iron out yet.
Some custom brakes we made a while back for a Skygate Hawk and Viperjet. We don't manufacture 'electro-brakes' anymore, ours were custom made for each aircraft/wheel combination and as a result the time involved to make one set was un-economical to make the product cost effective.
marcs
The system as detailed above is correct, an energised coil (electromagnet), a floating metal disc and a power source to power the coil (via electronics). There are some issues however which I am not sure are being addressed in all systems currently available.
If the metal disc is allowed to contact the coils metal casing then even when the power is removed to the coil the disc becomes partially magnetised and can remain 'stuck' to the coil casing causing binding.
Space inside the wheel hub limits the coil size and hence power it can deliver, this means not all models will be adequately braked as often the ideal size of electromagnet is restricted.
You can reduce the amount of magnetism transferred to the disc in two ways, first drive the coil with a continuosly reversing current (ours changed 100's of times a second), and second apply a thin abrasive brake pad material between the electromagnet and the disc so both cannot touch. The introduction of a brake material helps provide better surface contact for braking but as mentioned above does reduce the electromagnetic power available. Our brake material was .3mm thick.
Electric brakes have moved on considerably and will be reliable and standard fitment I am sure very soon - just a few little niggles to iron out yet.
Some custom brakes we made a while back for a Skygate Hawk and Viperjet. We don't manufacture 'electro-brakes' anymore, ours were custom made for each aircraft/wheel combination and as a result the time involved to make one set was un-economical to make the product cost effective.
marcs
