[BProckets] Testing motors - w/$10 amplifier question

[Dan Durachko]

Dang but that's sweet!  Now I've got another project and don't have time
for the ones already started!  I tend to favor the nail & screw type
projects for starters because of their low-tech ingenuity.  Plus,
lugging around a laptop seems to be a minor pain.  That said - I'll
still almost definitely be setting up a digital acquisition system
before next summer.  One of my sticking points in going digital right
from the get-go was the price sticker.  Well, now that hurdle has been
removed courtesy of Terry.

Can someone please direct me to plans for the $10 amp though and save me
some surfing time?

TIA,

Dan (soon "Digital Dan")

-----Original Message-----
From: bprockets-bounces at amateurrocketry.com
[mailto:bprockets-bounces at amateurrocketry.com] On Behalf Of Terry
McCreary
Sent: Thursday, September 23, 2004 9:42 AM
To: Black Powder rockets discussion list
Subject: RE: [BProckets] Testing motors

Hello all:

Jimmy Yawn has some lovely photos of his simple electronic test 
stand.  Looks a lot better 'n mine, that's for sure.

http://www.jamesyawn.com/electronicstand/

Such a stand could be constructed for about:
$10 hardware
$25 load cell
$10 parts for amplifier
$25 DATAQ 10 bit.
Laptop computer (beg, borrow, steal; or buy one from Ebay, heck, they
ain't 
expensive)

With such a system you should be able to get accurate thrust curves (+-
an 
ounce or so) and burn times good to 0.01 second or better.

The thrust stands that Sleeter describes are indeed ingenious---a good 
friend of mine used the homemade chart recorder system for some years.
But 
when you consider the amount of work put into constructing the device
and 
making hand-measurements, an electronic system that gives 240 points per

second and stores your data is a really nice and not very expensive 
alternative.

I'm headed to the friend's place on Saturday.  We're testing a dozen 
motors.  They should be finished in about two hours, most of which time
is 
usually spent waiting for the (reuseable aluminum) casings to cool down 
enough to handle and reload.

Best regards -- terry

At 08:26 AM 9/23/2004 -0400, you wrote:
>Check out Sleeter's new book.  He describes in detail a simple, elegant
>test stand made using common hardware store items.  Assorted springs
>provide adjustable "thrust capacity" for the setup.  [Springs extend in
>a linear fashion in relation to the amount of tension (read as force or
>thrust) they are subjected to.]  (Overstressing results in permanent
>deformation of course!)  You can make a safe and accurate stand to test
>motors putting out 60 pounds or more of thrust cheaply - I'd say easily
>less than $30 and perhaps much less if you have enough stuff lying
>around your shop.  I am making one right now but haven't gotten far
into
>assembly.  If you only want max thrust it's really cheap but Sleeter
>even describes how to make a cool homemade chart recorder to generate
>thrust/time curves from which you can then calculate specific impulse.
>
>-----Original Message-----
>From: bprockets-bounces at amateurrocketry.com
>[mailto:bprockets-bounces at amateurrocketry.com] On Behalf Of Tom Mueller
>Sent: Thursday, September 23, 2004 12:51 AM
>To: bprockets at amateurrocketry.com
>Subject: [BProckets] Testing motors
>
>Has anyone built or created a testing platform of some
>type to test out the thrust of a motor?  I am looking
>to create something to measure the maxium amount of
>thrust of my motors over a given time interval.  Any
>ideas out there not involving spending an arm and a
>leg?  Thanks.
>
>Tom Mueller