LEGO TECHNIC : 16686


Technic / 16686	16685 \| 16687

Subject:	Radial Compressor
Newsgroups:	lugnet.technic
Date:	Sat, 4 Jul 2009 13:21:03 GMT
Viewed:	21878 times

I wasn’t planning on posting this here, but after Eric Sophie’s call for participation I thought the least I could do is get things started.

One of the GBC modules I presented at HispaLUG last year was a fully automated pneumatic excavator. It requires a considerable amount of air and since I finished it only a couple of days before the event I quickly threw together a compressor consisting of an RC motor and two small pneumatic pumps connected to the innermost shaft. The solution was adequate but rather ugly, and I wanted to make something that looked nicer.

After trying out several closed geometries with angle connectors I decided that a square configuration would be my best option. I used the RC motor in the earlier compressor because of its speed, but it’s harder to integrate so I decided to use the PF ‘XL’ motor which has a much slower speed (about 220RPM). If two pumps on an RC motor with an approximate speed of 1300RPM gave me the right amount of air, a radial configuration with 4 pumps should turn at around half that speed, so using the XL motor I needed a 3x multiplication which I got by using a z36 gear connected to two z12 gears (in case that wasn’t clear enough 2 pumps x 1300RPM ~ 4 pumps x 220RPM x 3):

(Click on the images to make them larger)

That left me with two eccentric connection points and once I figured out the correct configuration for the pumps I also noticed it would be very easy to make the model include another 4 pumps:

The motor speeds are based on Philo’s excellent website but I was curious to know how much the motor would slow down due to 1) the weight/friction of the construction itself and 2) the pressure build-up, so I decided to attach a Speed Computer to measure the actual speed. One of the problems of the Speed Computer is that it’s terribly inaccurate. It only reports multiples of 20RPM, and so to get a reasonable accurate measurement I decided to gear it up 5x (36:12 and 20:12)

I used two motors, both to make sure I’d have enough torque once the pressure went up and to ensure a symetry of weight for reasons I’ll explain further down.

I measured two values: 1) with the compressor running free and 2) with the output completely blocked. The results were as follows:

                 Measured  Real Speed
free spinning      1060       212
output blocked      960       192

Another one of the problems I wanted to address was the noise a compressor generates due to the vibrations and the fact that when you place it on a table this noise is amplified. In the case of a radial compressor these vibrations are even more important due to the weight of the central piece and the fact that it rotates eccentrically. After several tests I came up with the following configuration which absorbs 99% of the vibrations: working at top speed the baseplate on which the model is placed doesn’t move a mm, whereas previously it would dance all over the table.

I also made a short video with my mobile phone. Unfortunately, the refresh rate of the camera is quite low so at higher speeds the core of the compressor appears to be static, and the vibration of the compressor vs the baseplate is hard to see, but I think it’s worth viewing:

http://www.youtube.com/watch?v=JotIkUGN0ks

Next up: 8 pumps...

Message has 3 Replies:

		Re: Radial Compressor
Excellent work. I like seeing all the technic bits and that speed computer! I was just looking at all the pnuematics I have that are unused too. I would have tried a racer motor too, I don't have any of the power functions motors, (you would (...) (15 years ago, 4-Jul-09, to lugnet.technic)

		Re: Radial Compressor
(...) I too regret the showdown of Lugnet. Even if the main discussion occurs elsewhere it doesn't cost a lot to at least put an announcement here... (...) Now that's a compressor! (URL)(with corrected link) Philo (15 years ago, 6-Jul-09, to lugnet.technic, FTX)

		Re: Radial Compressor
It looks like BS is back online so now is as good a time as any to show you the pictures of the 8-pump compressor I built amplifying the 4-pump version. I wanted to keep the compressor as small as possible so I started by changing the end parts to (...) (15 years ago, 13-Jul-09, to lugnet.technic, FTX)

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