Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
April 22, 2019, 06:31:17 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
News: Help Support Hip Pocket Aeronautics Builders' Forum and Plan Gallery

You can help support our forum and gallery
by having plans printed by Ratz.

Details and Feedback here: Help Support the Forum & Gallery - Plan Printing
 
Home Help Search Login Register
Pages: 1 2 3 4 [5]   Go Down
Print
Author Topic: Peterborough timer  (Read 8708 times)
0 Members and 1 Guest are viewing this topic.
ferfecir
Bronze Member
***

Kudos: 0
Offline Offline

Turkey Turkey

Posts: 27



Ignore
« Reply #100 on: April 25, 2012, 03:49:27 AM »

Thank boffin99
Logged
ferfecir
Bronze Member
***

Kudos: 0
Offline Offline

Turkey Turkey

Posts: 27



Ignore
« Reply #101 on: April 25, 2012, 03:56:55 AM »

Thanks devid
 Claims the following materials are suitable for Pistacio olurmu scale?

http://www.hobbyking.com/hobbyking/store/__7565__ZIPPY_50mAh_20C_single_cell_.html
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10000
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18769

Logged
PeeTee
Titanium Member
*******

Kudos: 48
Offline Offline

United Kingdom United Kingdom

Posts: 2,227



Ignore
« Reply #102 on: April 25, 2012, 10:51:21 AM »

I've used the Zippy 1S 50mAH lipos before and they are good. I can't find mine at the moment to tell you the weight, but I've just weighed a Zippy 70mAH cell and it's 2.18 grams - the 50 mAH cells aren't much smaller or lighter. That still sounds a little heavy for a Pistachio model, as Paul (DaddyO here) writes that his pistachios weigh less than 3 grams. Perhaps if he reads this he would like to advise you.

Peter
Logged
Yak 52
Titanium Member
*******

Kudos: 60
Offline Offline

United Kingdom United Kingdom

Posts: 2,389


Free Flight Vagrant



Ignore
« Reply #103 on: March 22, 2018, 09:06:32 AM »

Some recent FET timer developments:

Going small:
http://peterboroughmfc.org/technical-articles2018/Miniaturising_FET_Timers.htm

A really clever idea for a more accurate zapper:
http://peterboroughmfc.org/technical-articles2018/Zapper-Chris.htm
Logged
raggedflyer
Bronze Member
***

Kudos: 1
Offline Offline

United Kingdom United Kingdom

Posts: 70



Ignore
« Reply #104 on: March 22, 2018, 03:05:48 PM »

I think the  power dissipation quoted is overly pessimistic.

When the FET is switched fully on and the motor current is 350mA the voltage drop from drain to source is of the order of millivolts (because Ron is probably milliohms) not the full battery supply voltage of 4v nominal.

As the FET starts to turn off at the end of the timed period the dissipation will rise but for seconds. Let’s imagine when the FET is ‘half off’ the voltage across the FET and motor will both be 2v but the motor current will now be 175mA. The FET power dissipation will then be 350mW. The key thing is that the 4v and 350mA can’t occur simultaneously across the FET but this is the maximum power drawn by the motor when the FET is fully on.

A few assumption made but I hope the point is explained.



Logged
Yak 52
Titanium Member
*******

Kudos: 60
Offline Offline

United Kingdom United Kingdom

Posts: 2,389


Free Flight Vagrant



Ignore
« Reply #105 on: March 22, 2018, 04:27:10 PM »

Ah ok - I was thinking that PD would be the voltage put through the drain-source rather that the voltage drop over the FET.

So you would be suggesting that twice the 350ma would actually be ok?

ie max PD = 1.4W so

in the 'half off' condition

2V x 700mA = 1.4W

I must admit to being a little sketchy on this stuff as yet. I suppose the PD when switching is very brief anyway so you might get away with more current still?
Logged
Pages: 1 2 3 4 [5]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!