Constant drop-rate pulley/rack.... for science equipment

Discuss caving lights, packs, helmets, clothing, etc.
For rope and vertical equipment, go to the On Rope! forum.
Cave electronics enthusiasts can also visit the Communications and Electronics Section forum.

Moderator: Moderators

Constant drop-rate pulley/rack.... for science equipment

Postby ggpab » Mar 4, 2019 6:08 pm

Hello everyone,
I regularly need to lower science equipment at a constant drop rope, most often in water. Wondering if anyone could recommend a device that would help with this. Specifically I have a hydrolab (multiparameter probe) that only weights a few pounds, that needs to be lowered at ~2cm/s down into water, often over 10-50 m water depth. At 2cm/s it can take 30+ minutes to do a profile in a deep cenote/sinkhole, and manually doing this is not giving even quality profiles. Is there a mini-rack, belay device, pulley, or other system that could help with this? The idea is to tie this off somehow and have it just lower the instrument. I could add more weight if that helped.
All suggestions welcome!
Cheers,
Trish Beddows
ggpab
Occasional Poster
 
Posts: 47
Joined: Nov 19, 2006 5:30 pm
Location: Evanston, IL.
Name: Patricia A. Beddows
NSS #: NSS#47929
  

Re: Constant drop-rate pulley/rack.... for science equipment

Postby bobby49 » Mar 5, 2019 1:47 pm

This will sound strange. Have you considered dropping the equipment to the bottom first, and then raising it at a constant rate? I ask, because it is pretty simple to apply a small battery electric motor at the top and have it winch up the load at a constant rate. I designed my own rig to do this years ago, and it wasn't too hard.
bobby49
Frequent Poster
 
Posts: 74
Joined: Jun 20, 2018 12:57 am
  

Re: Constant drop-rate pulley/rack.... for science equipment

Postby ggpab » Mar 5, 2019 2:21 pm

Hi - There are reasons why the profiles are "better" on the descent - mostly since there is serious thermal hysteresis in the data due to the salinity and temperature profile of the water column, and down has become somewhat of a convention.... but not required per se. There is also an issue that the oxygen sensor craps out (technical term there....) when it goes through the hydrogen sulfide layers, and so we only get the DO on the way down..... and that would be lost with an up profile. That being said - one day I will have an optical DO sensor and this problem will be mute.

I can't imagine why the the motor couldn't be equally used for the descent though too. I was just pondering none battery options - but why not! Suggestions / links on small battery powered motors most welcome - what do you find works and survives! caving?

Trish
ggpab
Occasional Poster
 
Posts: 47
Joined: Nov 19, 2006 5:30 pm
Location: Evanston, IL.
Name: Patricia A. Beddows
NSS #: NSS#47929
  

Re: Constant drop-rate pulley/rack.... for science equipment

Postby Billy » Mar 8, 2019 3:28 pm

First off, you need to get an optical DO meter especially if you're in low do environments, and if you have H2S, then nuff said.
Second, I'd suggest that unless you're getting a depth-integrated water-quality sample at the same time, then a constant descent rate isn't imperative. And if you're still using a hydrolab that has a clark cell on it for a do, it's probably old enough that it's not that great at quick continuous monitoring. I'm assuming that you're using continuous monitoring data collection, if so, I'd recommend synching time pieces in the sonde and one above water and marking time and exact depth for data collection as you go.
Third, it's been ages, but Gene Perry near you (Northern Illinois University) has done geochemistry in cenotes years ago, you might want to check out <old> methods they may have used.
Billy
Frequent Poster
 
Posts: 87
Joined: Dec 17, 2005 8:10 pm
Location: Illinois
NSS #: 53221
Primary Grotto Affiliation: Near Normal
  

Re: Constant drop-rate pulley/rack.... for science equipment

Postby bobby49 » Mar 9, 2019 11:35 am

The size of the battery-electric motor will depend on lots of stuff, including how much weight you are trying to lower or raise. I built my own rig based on a DSLR camera "slider", and that was used horizontally on the surface, not in a cave. However, the battery and parts are cheap enough that it is not an impossible thing, and automatic controls are easy if you are good.
bobby49
Frequent Poster
 
Posts: 74
Joined: Jun 20, 2018 12:57 am
  

Re: Constant drop-rate pulley/rack.... for science equipment

Postby ggpab » Mar 9, 2019 1:19 pm

Hi Bobby49 - got any pictures of your rig in action? Would be great to see. I am not easily envisioning how this might work.... but I only just googled DSLR camera slider and so not sure if am looking at the right kind of rig.
Weight in only a couple of pounds negative underwater.
Thanks!
Trish
ggpab
Occasional Poster
 
Posts: 47
Joined: Nov 19, 2006 5:30 pm
Location: Evanston, IL.
Name: Patricia A. Beddows
NSS #: NSS#47929
  

Re: Constant drop-rate pulley/rack.... for science equipment

Postby bobby49 » Mar 9, 2019 9:24 pm

The camera had a sliding trolley on a horizontal rail. Then there was a cord on a pulley that could pull it one way or the other, depending on the power to the motor. You are doing something similar, except there is no rail, and you are just trying to run it up and down and into water. It might be necessary for you to put ballast on the bottom of yours in order to get it to descend reliably.
bobby49
Frequent Poster
 
Posts: 74
Joined: Jun 20, 2018 12:57 am
  


Return to Equipment Forum

Who is online

Users browsing this forum: No registered users

cron