Launch Control

The Rocketry Forum

Help Support The Rocketry Forum:

rklapp

NAR# 109557
TRF Supporter
Joined
May 8, 2020
Messages
382
Reaction score
209
Location
Oahu, Hawaii
Here’s my DIY launcher. I have the battery pack on order. I thought I might try a 9v battery but determined that it won’t ignite the starters. So why will 4x 1.5v batteries ignite but not one 9v battery? What is the comparison in amps?

C8369206-D732-4B27-A66C-86696CEAB9C7.jpeg
 

Reinhard

Well-Known Member
Joined
Jan 18, 2009
Messages
1,022
Reaction score
182
Location
Austria
Here’s my DIY launcher. I have the battery pack on order. I thought I might try a 9v battery but determined that it won’t ignite the starters. So why will 4x 1.5v batteries ignite but not one 9v battery? What is the comparison in amps?
The delivered current can be calculated by dividing the battery voltage by the total resistance. The resistance is mostly summed up by the igniter resistance, the contact resistance of the alligator clips, the wire resistance and the internal resistance of the battery. 9V batteries usually contain 6 tiny AAAA cells, with lots of internal resistance (especially off-brand batteries). The 1.5V batteries are bigger and have less internal resistance.
If you really want to use 9V batteries, you can connect multiple ones in parallel (same brand and discharge state), but I wouldn't do it. If you need more power, you can replace your 1.5V batteries with 14500 size Li-Ion batteries. This will increase the power output a lot (higher voltage AND lower internal resistance), but not every launcher can handle them safely, so you would need to check that first before attempting it.

Reinhard
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
6,307
Reaction score
2,864
Location
Butte, Montana
All batteries have an internal resistance. That internal resistance will limit the current that the battery can provide. Different battery chemistries have wildly different internal resistance. Lithium batteries have very little internal resistance so sometimes current limiting circuitry is built into lithium cells.
As Reinhard says the 9 volt battery you tried had a higher total internal resistance than the larger cells that you placed in series.
 

rklapp

NAR# 109557
TRF Supporter
Joined
May 8, 2020
Messages
382
Reaction score
209
Location
Oahu, Hawaii
Mahalo guys. I have the wires soldered up, just waiting on the battery pack to arrive.
 

John Kemker

Well-Known Member
TRF Supporter
Joined
Aug 25, 2019
Messages
1,382
Reaction score
571
In answer to why a 9v won't work, look at this page on what's inside a 9v battery. Basically, a 9v is 6 batteries, all smaller than a AAA (AAAA? AAAAA?) Not enough current to work properly.
 

rklapp

NAR# 109557
TRF Supporter
Joined
May 8, 2020
Messages
382
Reaction score
209
Location
Oahu, Hawaii
I previously compared current, which the 9v has 10x that of AA, but I didn't think to compare resistance.
 
Last edited:

jrap330

Retired Engineer, NAR # 76940
TRF Supporter
Joined
Jan 25, 2020
Messages
291
Reaction score
79
Location
NJ
I previously looked up resistance comparison and 9v has 10x more than AA but in my head, I was thinking that more is better. Doh. Good thing I’m not a rocket scientist.
I previously looked up resistance comparison and 9v has 10x more than AA but in my head, I was thinking that more is better. Doh. Good thing I’m not a rocket scientist.
ohms law Current (I ) equals Volt/Resistance
 

jrap330

Retired Engineer, NAR # 76940
TRF Supporter
Joined
Jan 25, 2020
Messages
291
Reaction score
79
Location
NJ
Someone did the 9 v battery analogy a few weeks ago. I never knew it was made up of smaller batteries. They do fire the older ignitors. Nice looking box that is one big switch and contin light.
 

OverTheTop

Well-Known Member
Joined
Jul 10, 2007
Messages
3,832
Reaction score
1,149
Location
Melbourne Australia
There is a sticky on the electronics subforum that discusses 9V batteries:

9V batteries can be quite random so if you are using them then consider cutting one of the same type apart so you know what you are flying with.
 

deangelo54

Well-Known Member
Joined
Aug 21, 2015
Messages
202
Reaction score
32
About a month ago, I built a mid power launch pad that is similar to one that Pratt Hobbies used to sell. Very inexpensive to build given the low cost of PVC.

I would like to build a 12 volt launch controller. I'm not sure exactly what specific components to buy and where to buy them. Years ago I used to do a lot of soldering so I am comfortable around a soldering iron.

Any input is appreciated.
 

OverTheTop

Well-Known Member
Joined
Jul 10, 2007
Messages
3,832
Reaction score
1,149
Location
Melbourne Australia
Here is one I built a few years ago. Still works ;).
 

deangelo54

Well-Known Member
Joined
Aug 21, 2015
Messages
202
Reaction score
32
Thanks for the information. You did a great job.
I would like to have a continuity light, a launch button and another switch that must be on in order to launch. I would like that switch to spring back to the off position after you release it. I like those launch buttons that have the cover that has to be lifted up.

Just wondering where people buy electronic parts these days? RIP Radio Shack.
 

OverTheTop

Well-Known Member
Joined
Jul 10, 2007
Messages
3,832
Reaction score
1,149
Location
Melbourne Australia
Ebay typically for me, and my local shops would be way non-local for you :).

Do Fry's over there do components and such things still?
 

ep29030

Mark N.
TRF Supporter
Joined
Dec 20, 2011
Messages
111
Reaction score
10
Location
Lebanon,IN
Thanks for the information. You did a great job.
I would like to have a continuity light, a launch button and another switch that must be on in order to launch. I would like that switch to spring back to the off position after you release it. I like those launch buttons that have the cover that has to be lifted up.

Just wondering where people buy electronic parts these days? RIP Radio Shack.
All Electronics (www.allelectronics.com) is one place to get parts. eBay also has lots of options as well.
 

ep29030

Mark N.
TRF Supporter
Joined
Dec 20, 2011
Messages
111
Reaction score
10
Location
Lebanon,IN
Over the years, I have settled in on 12V launcher systems. I make my battery connection to fit a lawn mower or car battery. I normally keep a battery in a home-built box with a handle-just for launches. Use a cheap mower battery from Menards. Replace it every 5 years. The alternative: just drive the mower or the car to the launch site. This works when I'm launching with the kids at home.
 

Greg Furtman

Well-Known Member
TRF Supporter
Joined
Nov 10, 2018
Messages
1,216
Reaction score
570
Location
Webster, Wisconsin
I built a 12v launch controller based on James Fletcher's design from this thread.

https://www.rocketryforum.com/threads/next-launch-controller.34774/post-329902

Just make sure that you use relays that are designed to work with LEDs and other lower current devices. These types of relays have an internal diode.

I also used a 12v 7AH lead acid gel battery like those used in computer UPS's. Around $20 new.
 

deangelo54

Well-Known Member
Joined
Aug 21, 2015
Messages
202
Reaction score
32
Thank you all for your replies. Very helpful.
OverTheTop asked about Fry's. We used to have one around the Boston area but I think they are long gone.

Someone in my club mentioned You Do It Electronics in Needham, MA.
If I went over with a diagram, I wonder if they would be able to grab the parts for me?

Check out the diagram at 1:53. That looks like what I would want to do. Seems simple enough.
 

neil_w

Hunkered down and slowly going crazy
TRF Supporter
Joined
Jul 14, 2015
Messages
9,085
Reaction score
2,410
Location
Northern NJ
Someone in my club mentioned You Do It Electronics in Needham, MA.
If I went over with a diagram, I wonder if they would be able to grab the parts for me?
Not if it's the diagram at 1:53 in the video, which just shows generic symbols for all the components. For each of them, there are about a 6.4 million (I counted) variations available. You'll need to get a whole lot more specific than that, if not actual part numbers than at the very least some reasonably detailed specs for each part.
 

deangelo54

Well-Known Member
Joined
Aug 21, 2015
Messages
202
Reaction score
32
Not if it's the diagram at 1:53 in the video, which just shows generic symbols for all the components. For each of them, there are about a 6.4 million (I counted) variations available. You'll need to get a whole lot more specific than that, if not actual part numbers than at the very least some reasonably detailed specs for each part.
I was hoping I could go to an electronics store, tell them I want to build a 12 volt system and give them a description of each part in addition to the diagram.
Work Box
Push button switch
Toggle switch that springs back
Resistor (I think he uses 2 Ohms)
LED
Wire
Aligator clips
Male and female banana connectors (Am I describing that correctly)
Some kind of connector for the battery.
I need a soldering iron. My soldering gun from 1964 doesn't heat up anymore.
Solder.
 

neil_w

Hunkered down and slowly going crazy
TRF Supporter
Joined
Jul 14, 2015
Messages
9,085
Reaction score
2,410
Location
Northern NJ
I was hoping I could go to an electronics store, tell them I want to build a 12 volt system and give them a description of each part in addition to the diagram.
You can try, but in my opinion that is somewhat above and beyond what I would ever ask for in a store. Those folks are unlikely to have any idea about the behaviors and requirements of a launch controller. A few of the items they could guide you to (work box, soldering iron, solder) but not everything else. IMHO.

If you're not familiar enough with electronics to at least be able to spec out those parts, I would suggest working from a more detailed plan that gives a detailed parts list.
 

heada

Well-Known Member
Joined
Jan 18, 2009
Messages
3,188
Reaction score
552
Location
Indianapolis, Indiana
Does Aerotech still sell their launch controller? (controller, not the Mantis launch pad) It is ideally set up to run from any number of power sources and is a good option for personal launches. I have one and just thought about switching the power connections from the alligator clips for a car battery to a set of Deans plugs so I can use a 3S 50C 6000mAh battery pack I have.
 

deangelo54

Well-Known Member
Joined
Aug 21, 2015
Messages
202
Reaction score
32
You can try, but in my opinion that is somewhat above and beyond what I would ever ask for in a store. Those folks are unlikely to have any idea about the behaviors and requirements of a launch controller. A few of the items they could guide you to (work box, soldering iron, solder) but not everything else. IMHO.

If you're not familiar enough with electronics to at least be able to spec out those parts, I would suggest working from a more detailed plan that gives a detailed parts list.
I was thinking about when I go to the Micro Center computer store. I give them a list, we discuss the brands and what the computer will be used for. Then we walk around the store with a basket, the sales consultabt helps me pick out what I need, and I'm off to build the computer.
 

deangelo54

Well-Known Member
Joined
Aug 21, 2015
Messages
202
Reaction score
32
Does Aerotech still sell their launch controller? (controller, not the Mantis launch pad) It is ideally set up to run from any number of power sources and is a good option for personal launches. I have one and just thought about switching the power connections from the alligator clips for a car battery to a set of Deans plugs so I can use a 3S 50C 6000mAh battery pack I have.
I think I know the one you are referring to.

It is impressive looking. Thanks for the advice.
 

neil_w

Hunkered down and slowly going crazy
TRF Supporter
Joined
Jul 14, 2015
Messages
9,085
Reaction score
2,410
Location
Northern NJ
I was thinking about when I go to the Micro Center computer store. I give them a list, we discuss the brands and what the computer will be used for. Then we walk around the store with a basket, the sales consultabt helps me pick out what I need, and I'm off to build the computer.
Not the same thing, unfortunately. IMHO.
 

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
3,647
Reaction score
886
Unless you're lucky enough to live close a place like Orvac Electronics in SoCal, storefront electronics stores are few and far between. Fry's is getting out of the parts business, so you can scratch them off the list. Apparently they'd rather lose money on major-brand appliances and consumer electronics than make money on high-margin parts... that's what killed off Radio Shack.
 

jrap330

Retired Engineer, NAR # 76940
TRF Supporter
Joined
Jan 25, 2020
Messages
291
Reaction score
79
Location
NJ
Thanks for the information. You did a great job.
I would like to have a continuity light, a launch button and another switch that must be on in order to launch. I would like that switch to spring back to the off position after you release it. I like those launch buttons that have the cover that has to be lifted up.

Just wondering where people buy electronic parts these days? RIP Radio Shack.
There were a few discussions this week on launch controllers this week..do a search on the forum....the initial topic was on clustering and Estes PSII controller. It has been brought up numerous times this year...
 
Top