Compressor advice needed pls

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
poriet
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Compressor advice needed pls

Post by poriet »

Hello,
I'm a relative novice at this stuff and in the UK.

Previously on 'rockets are us' I have used a bicycle pump ( the more powerful 'styrup-pump' type ). The bottles are 2L bog-standard PET whose max recommended pressure, IIRC, is 100psi. Give or take. Give or take the odd explosion, I think.

I have decided to go for a compressor ( one I can power from the car ), and that opens a real can-of-worms. You can get 12V tyre inflator for as little as 5 quid, but I bet they're rubbish. Proper compressors are usually mains operated.

Rather than mess about, I was looking at the Ring Automotive RAC900. This is a proper beast ( 70 quid ) designed for those ghastly 4X4 drivers, but is reputed to go to 150psi and delivers 50L/min. My calculations ( if you can call them that ) lead me to belive you could get a 4L wrocket to launch readiness in about a minute or so, which isnt bad.

Opinions, experience, insults and abuse please, guys.

Bruce
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Re: Compressor advice needed pls

Post by U.S. Water Rockets »

poriet wrote:Hello,
I'm a relative novice at this stuff and in the UK.

Previously on 'rockets are us' I have used a bicycle pump ( the more powerful 'styrup-pump' type ). The bottles are 2L bog-standard PET whose max recommended pressure, IIRC, is 100psi. Give or take. Give or take the odd explosion, I think.

I have decided to go for a compressor ( one I can power from the car ), and that opens a real can-of-worms. You can get 12V tyre inflator for as little as 5 quid, but I bet they're rubbish. Proper compressors are usually mains operated.

Rather than mess about, I was looking at the Ring Automotive RAC900. This is a proper beast ( 70 quid ) designed for those ghastly 4X4 drivers, but is reputed to go to 150psi and delivers 50L/min. My calculations ( if you can call them that ) lead me to belive you could get a 4L wrocket to launch readiness in about a minute or so, which isnt bad.

Opinions, experience, insults and abuse please, guys.

Bruce

Hi Bruce,

In general, the small 12V compressors that are used in cars tend to be more efficient due to their DC motors. Because they generate less heat and higher torque over a broad range of RPM they are almost always used in higher pressure compressors. It is not uncommon to find a small compressor that goes to 250PSI or 300PSI. The typical AC (plug-in) compressors will range from 100 to 150PSI (for a good one) and they usually cost more.

Either of these compressors will serve well if you avoid pushing them near their pressure limit for a prolonged time. What usually happens is they get too hot and the components fail from heat and stress. Nylon gears are a common failure point.

So, the key to any of these compressors is to get the lowest cost compressor and don't max it out and give it plenty of extra time to cool. Someone on this forum once suggested getting 2 or 3 cheap compressors and running them in parallel to minimize the time they heat up and speed up the pressure process. You might be able to create a "Frankenstein" compressor from several cheapo ones and get much better performance than the one expensive one!
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Tim Chen
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Re: Compressor advice needed pls

Post by Tim Chen »

U.S. Water Rockets wrote:
poriet wrote:Hello,
I'm a relative novice at this stuff and in the UK.

Previously on 'rockets are us' I have used a bicycle pump ( the more powerful 'styrup-pump' type ). The bottles are 2L bog-standard PET whose max recommended pressure, IIRC, is 100psi. Give or take. Give or take the odd explosion, I think.

I have decided to go for a compressor ( one I can power from the car ), and that opens a real can-of-worms. You can get 12V tyre inflator for as little as 5 quid, but I bet they're rubbish. Proper compressors are usually mains operated.

Rather than mess about, I was looking at the Ring Automotive RAC900. This is a proper beast ( 70 quid ) designed for those ghastly 4X4 drivers, but is reputed to go to 150psi and delivers 50L/min. My calculations ( if you can call them that ) lead me to belive you could get a 4L wrocket to launch readiness in about a minute or so, which isnt bad.

Opinions, experience, insults and abuse please, guys.

Bruce

Hi Bruce,

In general, the small 12V compressors that are used in cars tend to be more efficient due to their DC motors. Because they generate less heat and higher torque over a broad range of RPM they are almost always used in higher pressure compressors. It is not uncommon to find a small compressor that goes to 250PSI or 300PSI. The typical AC (plug-in) compressors will range from 100 to 150PSI (for a good one) and they usually cost more.

Either of these compressors will serve well if you avoid pushing them near their pressure limit for a prolonged time. What usually happens is they get too hot and the components fail from heat and stress. Nylon gears are a common failure point.

So, the key to any of these compressors is to get the lowest cost compressor and don't max it out and give it plenty of extra time to cool. Someone on this forum once suggested getting 2 or 3 cheap compressors and running them in parallel to minimize the time they heat up and speed up the pressure process. You might be able to create a "Frankenstein" compressor from several cheapo ones and get much better performance than the one expensive one!
Yeah Bruce,

We had a discussion some time ago about making sure you follow the cool-down recommendations in the manual that comes with your compressor. They usually say in the manual someplace that you should never run it longer than X minutes and allow Y minutes of cool-off every time you run it. If you follow those rules then the compressor (even a cheapie) will last a good long time.

That's how we got on the subject of a bank of compresors to increase the CFM of the fill and reduce the run-time. This should all work well in practice.

USWR.
Thanks for explaining about the DC motors. Now I get the idea why a big 110V power line compressor never seems to have as much pressure as a little battery operated one!
Tim Chen
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poriet
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Re: Compressor advice needed pls

Post by poriet »

OK guys, thanks for that.
I do have a 12V compressor ( tyre inflartor ) which I got for Xmas donkey years ago and never used. I tried it on the car once and it was so slow I never bothered again. I would never have considered it for rockets before this thread. So, I pulled it out today and tried it on an empty 2L bottle. It is still slow, but did get to 80psi before my nerve failed. It was a Heath-Robinson ( Rube Goldberg? ) set-up with no saftey features and I was inches from the bottle.
The interesting thing is that, AFAIK, this is not a quality pump: it's an el cheapo pump, meant for occasional use on standard small cars, and certainly not 4X4s or lorries. It comes in a presentation box with a light and several ohter features and is essentially a cheap electric pump, done up as a handy Xmas present. Nevertheless, the gauge reads to 300psi, which I find astonishing. You'd never get a standard bottle anywhere near there I dont imagine, but I'd be interested to see just how much balls it really has.
Bruce
poriet
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Re: Compressor advice needed pls

Post by poriet »

Hello again,
It seems everybody's gone to sleep. There havnt been any new posts for days.
I thought I'd mention one other problem with my el cheapo tyre inflator: there is a 12V cable for the battery which is very long, but the tube from the compressor to the tyre is very short. This means that, in order to see the gauge, which is next to the pump in the presentation case, you have to stand very close to the pump, and, therefore, the bottle you are filling, which isnt quite the idea when you're testing the bottle/pump for maximum prerssure. The last thing I want to do to this pump set-up is to start hacking the pressure tube. It's all problems, problems, problems, but then, solving problems is part of the fun, I guess.

I've never had a bottle go 'bang' on me, but then, I've never gone over 100psi. However, one bottle I'd used several times started to bulge alarmingly in the middle, at 50 psi. I guess the PET fatigues with use.

Bruce
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Re: Compressor advice needed pls

Post by WRA2 »

poriet wrote:Hello again,
It seems everybody's gone to sleep. There havnt been any new posts for days.
I thought I'd mention one other problem with my el cheapo tyre inflator: there is a 12V cable for the battery which is very long, but the tube from the compressor to the tyre is very short. This means that, in order to see the gauge, which is next to the pump in the presentation case, you have to stand very close to the pump, and, therefore, the bottle you are filling, which isnt quite the idea when you're testing the bottle/pump for maximum prerssure. The last thing I want to do to this pump set-up is to start hacking the pressure tube. It's all problems, problems, problems, but then, solving problems is part of the fun, I guess.

I've never had a bottle go 'bang' on me, but then, I've never gone over 100psi. However, one bottle I'd used several times started to bulge alarmingly in the middle, at 50 psi. I guess the PET fatigues with use.

Bruce
Hi Bruce,

You have a few options on seeing the pressure gauge:

1. buy a long hose:
advantage - cheap
disadvantage - will take longer to fill the rocket as you would also fill the hose as well.

2. use a wireless webcam to view the pressure gauge and control the pump at the power source:
advantage - less volume of air needed to fill the rocket
disadvantage - will cost more than a hose - extra equipment to bring with you to a launch.

As for the slowdown in posting, it is probably due mostly to the time of year with everyone thinking about the holidays and winter sports rather than launching rockets.
Lisa Walker,
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poriet
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Re: Compressor advice needed pls

Post by poriet »

Hello WRA2,
You forgot to mention that there is a 3rd option and that is to get a friend to stand over it. That way, whatever happens, you dont risk getting hurt, although you do risk losing a lot of friends.

I didnt want to hack the hose. And the wireless videocam sounds very neat, but they're probably a lot more expensive and less obtainable in the UK.

I did have another idea which I havnt pursued. I did blag one of those clever little solid-state pressure sensors (from 'Freescale'). Most of them are for low pressures, but this one will read up to 150psi, as I recall. I thought of burying this inside the launcher somewhere and using the readout ( just an analogue voltage; 0-5V ; IIRC )
I have some large 7-seg LED displays somewhere, and an A/D chip which does it all for you. Sounds simple, doesnt it, ho, ho.
I also have a 2 inch gauge I yanked from one of those regulators you get on big gas cylinders. That would be an easier option, but less elegant, and I did want to use that sensor. This is on its way to becoming one of those grand ideas we all have which never leave the drawing-board.

My parachute wrocket, on which I had pinned such great hopes, nose-dived into the deck. I couldnt believe the damage: almost nothing remained salvageable.
While I work on Mk2 I decided to use a simple 4L gadget with a disposable nose-cone: one that would act as a 'crumple-zone'. The first attempts failed because the zone wasnt 'crumply' enough.
I've redesigned the nose-cone, but each nose-cone takes rather too long a time to build and I need one for every launch.
We may well get another bash over Xmas, and I'll post some videos if we do.

Happy Yuletide, guys,

Bruce
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Re: Compressor advice needed pls

Post by Team Seneca »

poriet wrote: I didnt want to hack the hose. And the wireless videocam sounds very neat, but they're probably a lot more expensive and less obtainable in the UK.
Look on ebay for a video baby monitor, those sell cheap used and work well. They also have security cameras that work with older TVs and are low-def and so nobody wants them. They are cheap too. If that fails, you can always use a USB webcam or something with a long cable.
Bill W.
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Re: Compressor advice needed pls

Post by U.S. Water Rockets1 »

poriet wrote:Hello WRA2,
You forgot to mention that there is a 3rd option and that is to get a friend to stand over it. That way, whatever happens, you dont risk getting hurt, although you do risk losing a lot of friends.

I didnt want to hack the hose. And the wireless videocam sounds very neat, but they're probably a lot more expensive and less obtainable in the UK.

I did have another idea which I havnt pursued. I did blag one of those clever little solid-state pressure sensors (from 'Freescale'). Most of them are for low pressures, but this one will read up to 150psi, as I recall. I thought of burying this inside the launcher somewhere and using the readout ( just an analogue voltage; 0-5V ; IIRC )
I have some large 7-seg LED displays somewhere, and an A/D chip which does it all for you. Sounds simple, doesnt it, ho, ho.
I also have a 2 inch gauge I yanked from one of those regulators you get on big gas cylinders. That would be an easier option, but less elegant, and I did want to use that sensor. This is on its way to becoming one of those grand ideas we all have which never leave the drawing-board.

My parachute wrocket, on which I had pinned such great hopes, nose-dived into the deck. I couldnt believe the damage: almost nothing remained salvageable.
While I work on Mk2 I decided to use a simple 4L gadget with a disposable nose-cone: one that would act as a 'crumple-zone'. The first attempts failed because the zone wasnt 'crumply' enough.
I've redesigned the nose-cone, but each nose-cone takes rather too long a time to build and I need one for every launch.
We may well get another bash over Xmas, and I'll post some videos if we do.

Happy Yuletide, guys,

Bruce
Our very first camera rocket used a small video camera. The camera itself was a cube shape about 1 inch on each side. It ran off a 9V battery and transmitted to a receiver that was about the size of a deck of cards. It had such limited range that we quit using it for launches but we did use it for monitoring the pressure tests we did on our very first reinforced tubes. We had a VCR to record the video output from the receiver.

The whole camera setup was about $40 New at the time. They are probably a bit cheaper now.
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