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An off-season project of mine. For a pre-engineering class, we were required to build a 10 pound robot that could out-pull the other robots in the class on an 8 foot long tug of war field.
Since I could have easily snapped together a vex robot and called it good, I decided to challenge myself a little and build the vehicle from scratch...and on top of that, I discarded the globe motors supplied to me and substituted a pair of pneumatic motors.
The frame is out of angle aluminum, held with a some 1/4-20 bolts and some pop rivets. The motor mounts and axle mounts are 3/8 aluminum stock that I milled down and tapped for 1/4-20s. Wheels are made from pine boards, which I laminated together and turned on the lathe, sliced into segments on the band saw, and then hacked away at with the drill press. Power transmission is simply bicycle chain on some sprockets I salvaged from past year's robots.
For two weeks work, this thing really works quite nicely. With the right controls, it can operate with tank drive steering (although it can be run simply forward with just an air source) It has speed to spare running off of 80 PSI, but the air motors really don't put out much torque. Overall, its sure fun to drive around though.
Discussion
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02-06-2007 01:12
Smaug
Re: pic: Pneumatic
what kind of air motors are those and are the cheep?
my friend and i want to experiment with those before build season
02-06-2007 01:24
Nuttyman54
Re: pic: Pneumatic
I cant' help but notice how little chain wrap you have on the drive sprockets. did you experience much chain slippage?
02-06-2007 10:49
K.Porter
Re: pic: Pneumatic
Actually, chain slippage was one problem that I didn't have with the chains.
If you notice the front axle's connection to the frame in that picture, I've milled some simple slots for the bolts as a basic chain tensioning system. I just pulled the chain taught with the whole axle assembly before tightening the bolts. That tension kept everything pretty well in place.
One problem I did have with the chain, though, was that the added tension would attempt to pull the wheels slightly out of line with each other (there's a little bit of slop between the wheels and axle, allowing that movement) Occasionally this will get to the point where the chain will jam slightly on the wheel sprockets, but it's a minor problem.
As for the air motors, I found them in the back room of my school's technology classroom. The only information printed on them is "Gast Mfg. Corp." but looking at their website, the exact model seems to be out of production. As for cost, I really have no idea. Gast doesn't even list anything on their website for current models...
02-06-2007 15:20
Qbranch
Re: pic: Pneumatic
Checked on McMaster... the prices range from $135 (team numbers in everyday places 
) to $972 
.
One major major advantage to these motors is that in a low torque application requiring super high rpm such as engraving or micro-machining, these things rock... the cheapest air motor has a top speed of 10,000 rpm at 90psi, 18cfm... we used these at the place I work to do some engraving 1/32" ceramic end mills.
Well... I have a question about your robot too... how fast did it go? did you have variable speed? was it reversable? if you had variable speed, how'd you do it?
-q
02-06-2007 22:43
K.Porter
Re: pic: Pneumatic
How fast did it go: Well, I don't have a number for you (sorry) but: pretty darn fast, at least relative to the other vehicles it competed against. It could cover the 3 feet to the end of the table in under a second.
As for variable speed...yes and no. We basically used the main air valve for control (turn one way, go faster, turn the other slow down. Primitive yes, but it works.)
And, in theory it was reversible. Since I ran out of time to work on it, I couldn't finish my solenoid control box. I was planning on running a tether line to each of the four motor inputs (you can see the two un-used tubes in the picture) and then using the solenoids to reverse the flow to either motor, in order to turn or reverse. I prototyped the concept, but simply didn't build the control unit...
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