v8kid
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| posted on 2/12/12 at 08:56 PM |
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Pneumatic experts anywhere?
You may guess from this post I know hehaw about pneumatics but here goes.
For various reasons I want to automate my gearchange and after dallying with servo's wonder if pneumatics is the answer?
What would I specify for a cylinder that would have two positions and act in two directions?
i.e. position 1 is an 45mm extension and position 2 is a 90mm extension and be capable of reversing.
Any good practical websites out there like "pneumatics for dummies"? 
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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TPG
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| posted on 2/12/12 at 09:25 PM |
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Now then. You are after a double acting cylinder. It is driven both ways.....
Sadly that isn't all. It'll want a magnetic piston that will operate a mag' switch that will stop the stoke at the required
position. All this can be operated by a 5/2 valve...that is 5 ports. 2 ways of operating (One in and one out if you like) 2 of the ports are exhaust
ports, 2 are output.(One to extend the ram, one to retract) and the remaining one is the mains air in.
Simples heh?
Even though I do heart air,I'd be looking at a electrical actuator myself.
I will now attempt to draw something and upload it..whilst drinking beer.Drum roll please.
[Edited on 2/12/12 by TPG]
..Which was nice..
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v8kid
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| posted on 2/12/12 at 09:37 PM |
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quote:
Originally posted by TPG
Now then. You are after a double acting cylinder. It is driven both ways.....
Sadly that isn't all. It'll want a magnetic piston that will operate a mag' switch that will stop the stoke at the required
position. All this can be operated by a 5/2 valve...that is 5 ports. 2 ways of operating (One in and one out if you like) 2 of the ports are exhaust
ports, 2 are output.(One to extend the ram, one to retract) and the remaining one is the mains air in.
Simples heh?
Even though I do heart air,I'd be looking at a electrical actuator myself.
I will now attempt to draw something and upload it..whilst drinking beer.Drum roll please.
[Edited on 2/12/12 by TPG]
Plus standing on your head please
Is there a mechanical way of doing it with two pistons in series?
[Edited on 2-12-12 by v8kid]
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
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TPG
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| posted on 2/12/12 at 09:50 PM |
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Slow down Rumberlow, I thought of that while drawing this. Please bear in mind...These are the basics
You can see the "5" part of the "5/2"valve. 5 ports i have labelled them 1-5. The "2" part is the 2 squares you
can see. One square shows the valve in one state, The other square the other state or operation.
You may see that air flows in "one" through the valve and out of "2" to the ram. The ram moves and displaces air in its other
half out to the valve (port 3) through the valve an out via the triangle(?) shaped symbol on the 5/2 valve.
So if you want to stop the piston "mid" stroke you need to break the signal to the 5/2 valve. I.e the mag' switch or an external
micro switch.
Re using two pistons i'd say yes but you are moving, mechanically spools in the valves which all take time and you're back to an
electrical actuator that'll be faster and doesn't need a compressor and the extra gubbins there in.
I'd be interested in making the air work if you set on it though.
..Which was nice..
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v8kid
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| posted on 2/12/12 at 10:03 PM |
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Ok I see what you mean now - did not quite twig the "squares at first.
How accurate would the magnetic sensor be, I was thinking there might be some overshoot?
I think its about 40mm stroke 2nd to neutral and then another 40mm neutral to 3rd around the neutral position there is 2 or 3 mm slack. I could make
the actuating quadrant longer to increase the slack area but that would make the total travel longer and hence the change time slower.
How slow is slow? can the pistons move in 100ms?
Cheers!
PS I was going to use bottled air it lasts more than long enough with the bike engined crowd
[Edited on 2-12-12 by v8kid]
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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rf900rush
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| posted on 2/12/12 at 10:04 PM |
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If you do go for air cylinders, I have some various types in my loft.
Although the valves I have are X arcade (Moving game types) and operate on 110v so not much use.
But may be useful for experimenting.
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v8kid
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| posted on 2/12/12 at 10:07 PM |
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Thanks rf do you have any with around 100mm stroke and 25mm bore, double acting. (see I done learned the lingo!)
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
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TPG
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| posted on 2/12/12 at 10:14 PM |
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I am assuming this is on a back and forth 'bike style of change?
Air can be engineered to be very fast and very accurate. I give you most high speed packing machinery as an example. Overshot is stopped via the
loading on the 'ram. If you're operating pressure has been selected/set correctly the 'ram will stop dead because of physics..it has
come up against a force greater than it and all energy is dispelled forthwith..... Man it sounds like I've been on a Hobbit lecture
course?....so it will stop dead. There is no harm in putting hard stops in anyway. Throttle pedals have stops.
Movement of piston speed. For me a bit of a dark science. Again all into pressures and loadings upon the job. I have fitted exhaust damper and
throttles to pneumatic cylinders and messed with fitting sizes to alter speeds.
Have a Google for someone like Parkers or Norgeen to get spec sheets for speeds at given pressures.
..Which was nice..
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SteveWalker
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| posted on 2/12/12 at 11:42 PM |
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How about 80mm travel, spring biased to the mid-position? Use air to drive it one way for 0mm, vent the air for 40mm and use air to drive it the other
way for 80mm.
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v8kid
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| posted on 3/12/12 at 09:55 AM |
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Thanks for the input chaps. No its not a bike change its a car H pattern box a renault UN1.
Steve - Would a spring bias work without any overshoot? Intuitively I imagine it occilating around a median position.
TPG - how do I load the ram? Do you mean air loading or mechanical stops? How do I get the second part of the travel then if its a mechanical stop
i.e. having done the 2-N travel how do I disengage the mech stop to do the N-3 travel (ignoring shifting across the gate for the moment).
If air loading I presume you mean switch the exhaust port to pressure and that stops the piston?
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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Theshed
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| posted on 3/12/12 at 10:11 AM |
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Me too! I have a sequential transmission that was originally pneumatically operated. Given that a ram costs about £20 and solonoids about the same I
cannot understand how commercial systems cost £3,000 - the clever bit - the ECU seems to be only a few hundred pounds.
I want to make a lo-cost version of this ...
http://www.geartronics.co.uk/paddleshift.htm
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v8kid
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| posted on 3/12/12 at 01:05 PM |
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Thanks Theshed that confirms that the numbers I was thinking of are in the same ballpark.
Geartronics are using 125psi and getting 700n (160lbf) giving a piston area of 1.28"sq or 32mm dia piston.
They say the od is 42mm and from the picture the stroke appears to be around half the overall length of 72mm so I guess that all ties in not too
badly.
The force seems high but if they are shifting cogs in 62ms it is reasonable to suppose that the force is much higher than for a static shift.
The closed loop control is interesting and confirms my musings but this is for a sequential box and does not to pause in the neutral position for 2-3
and 4-5 changes but with arduino's and the like it should be doable.
The sticking point for me is this pause at neutral and how I can tie it in to positional feedback to adjust the solenoid actuation points.
I'm sure there must be stock pneumatics stuff available that will do this
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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hughpinder
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| posted on 3/12/12 at 01:15 PM |
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Do you want to automate it, e.g flappy paddle style up and down, or just transmit the motion to some awkward location?
If its the latter, two hydraulic pistons (think single brake master cylinders) at each end are the simple way - forward/back on the gear lever moves
one cylinder and the appropriate one on the gear box end, and the second pait do the side to side. Obviously no limit switches are required. Hydraulic
cylinders could be quite small and the action instantaneous. Vary the areas of the actuating and actuated cylinders to make the action faster or
slower or longer/shorter stroke stroke etc.
Regards
Hugh
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v8kid
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| posted on 3/12/12 at 02:19 PM |
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Thanks Hugh But I think I need it to be externally powered to make it fast enough i.e. flappy paddle thingys.
This link duplex cylinder shows exactly what I need where can I get some!
Also I still think I need to make it a closed loop so i know when the gear is selected (or neutral selected) to release the ignition cut at the right
time.
The consequences of releasing early/late are shown at http://www.geartronics.co.uk/paddleshift.htm
TPG's suggestion of using magnetic pistons to operate limit switches seems to fill the bill.
However I'm still unsure how I cushion the cylinder when it comes to the end of its travel - surely if its just a metal/metal contact it will
soon deform?
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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v8kid
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| posted on 3/12/12 at 04:03 PM |
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See these Pneumatic 40mm Bore 50mm Stroke Compact Air Cylinder Sdasf | eBay
ebay if bolted back to back will provide a 3 position pneumatic solenoid.
Can I control them with this DC 12V 3W 250mA 2 Position 5 Way Pneumatic Solenoid Valve G1/4"' Exhaust ?
This would seem to provide an off the shelf solution to the pneumatics all i need now is to work out the truth tables and apply them to a controller.
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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phelpsa
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| posted on 3/12/12 at 04:39 PM |
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Are you planning to do this with a syncro gearbox?
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v8kid
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| posted on 3/12/12 at 05:03 PM |
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quote:
Originally posted by phelpsa
Are you planning to do this with a syncro gearbox?
Yes. The engine limiter is linked to the clutch so the engine cuts to the launch revs when the clutch is in.
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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TPG
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| posted on 3/12/12 at 05:06 PM |
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By jove I think you're getting it . It is quiet straight forward once you are in the mind set isn't?
By loading I mean the load the cylinder is moving "The loading on the ram" In this case the gear linkage. If you put a 50mm dia cylinder
on things will break. But if you match the cylinder to the (light in this case?) load things should stay in shape and one piece.
Most "ISO" (ISO is the industry name for standard sizing for mounts etc etc similar to motor frames and so on)spec cylinders have dampers
built into them. It is a "buffer" that is altered by adjustment of an 'screw at each end of the cylinder but this only comes into
play at the end of retract or extend also referred to as adjustable cushions.
Here is a link to Parkers
cylinder blah blah.
..Which was nice..
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TPG
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| posted on 3/12/12 at 05:18 PM |
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quote:
Originally posted by v8kid
See these Pneumatic 40mm Bore 50mm Stroke Compact Air Cylinder Sdasf | eBay
ebay if bolted back to back will provide a 3 position pneumatic solenoid.
Can I control them with this DC 12V 3W 250mA 2 Position 5 Way Pneumatic Solenoid Valve G1/4"' Exhaust ?
This would seem to provide an off the shelf solution to the pneumatics all i need now is to work out the truth tables and apply them to a controller.
Yep. You will get position one: A ram extended.
Position two: B ram extended.
Position three: Both A and B rams retracted.
You will need two of your 5/2 valves. One for each ram. Or you'll have them both doing something with a shared air signal/input
[Edited on 3/12/12 by TPG]
..Which was nice..
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phelpsa
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| posted on 3/12/12 at 05:33 PM |
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quote:
Originally posted by v8kid
quote:
Originally posted by phelpsa
Are you planning to do this with a syncro gearbox?
Yes. The engine limiter is linked to the clutch so the engine cuts to the launch revs when the clutch is in.
If you use full force from the actuator immediately with a syncro box I can see you wearing them out very quickly. I would have thought that you need
to either dial in a progressive force with the actuator to feed the syncro (very difficult with basic valves), or make the change slow enough that the
syncros aren't really used (shich could become a pain).
Syncro boxes aren't really very well suited to automation as far as I can tell, hence the move to double clutch 'preselect'
arrangements.
I'm not meaning to be negative, but it's one of those fundamental reasons why is isnt generally done (apart from a few french hatches with
painfully slow changes).
[Edited on 3-12-12 by phelpsa]
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phelpsa
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| posted on 3/12/12 at 05:36 PM |
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quote:
Originally posted by Theshed
Me too! I have a sequential transmission that was originally pneumatically operated. Given that a ram costs about £20 and solonoids about the same I
cannot understand how commercial systems cost £3,000 - the clever bit - the ECU seems to be only a few hundred pounds.
I want to make a lo-cost version of this ...
http://www.geartronics.co.uk/paddleshift.htm
The reason the geartronics kit is 3k is that huge amounts of time and money goes into calibration, reliability and performance optimisation with
ongoing testing. I'm sure you can build a kit for less than 100 in that same way you can build a car for a few grand, but it wont be no ferrari
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Theshed
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| posted on 3/12/12 at 05:56 PM |
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I have every intention of buying the ECU........as for the rest I will give it a go and report back in say 25 years time when I finish the dammed
car.......
I agree that its not always the best to do everything yourself but you do learn a lot trying
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v8kid
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| posted on 3/12/12 at 06:02 PM |
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quote:
Originally posted by phelpsa
quote:
Originally posted by v8kid
quote:
Originally posted by phelpsa
Are you planning to do this with a syncro gearbox?
Yes. The engine limiter is linked to the clutch so the engine cuts to the launch revs when the clutch is in.
If you use full force from the actuator immediately with a syncro box I can see you wearing them out very quickly. I would have thought that you need
to either dial in a progressive force with the actuator to feed the syncro (very difficult with basic valves), or make the change slow enough that the
syncros aren't really used (shich could become a pain).
Syncro boxes aren't really very well suited to automation as far as I can tell, hence the move to double clutch 'preselect'
arrangements.
I'm not meaning to be negative, but it's one of those fundamental reasons why is isnt generally done (apart from a few french hatches with
painfully slow changes).
[Edited on 3-12-12 by phelpsa]
Ta for the input and I accept what you are saying sometimes the truth is a bit negative- however... The change is slow manually so it would not be
surprising if the pneumatic change was around the same speed.
Disengagement does not have the same limitations I can speed that up as is the cross box movement its the re-engagement that would be tricky.
So you reckon I have to build the force up progressively on the second cylinder engagement. Perhaps I could do that by blending two regulators one
high pressure and one low pressure brinf the low one in straight away to take up slack and put say 25% force on and then connect high pressure through
a metering orifice. Not ideal but it could work and is better than being slow
Worth a try?
Cheers!
[Edited on 3-12-12 by v8kid]
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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phelpsa
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| posted on 3/12/12 at 06:40 PM |
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quote:
Originally posted by v8kid
Ta for the input and I accept what you are saying sometimes the truth is a bit negative- however... The change is slow manually so it would not be
surprising if the pneumatic change was around the same speed.
Disengagement does not have the same limitations I can speed that up as is the cross box movement its the re-engagement that would be tricky.
So you reckon I have to build the force up progressively on the second cylinder engagement. Perhaps I could do that by blending two regulators one
high pressure and one low pressure brinf the low one in straight away to take up slack and put say 25% force on and then connect high pressure through
a metering orifice. Not ideal but it could work and is better than being slow
Worth a try?
Cheers!
[Edited on 3-12-12 by v8kid]
Anything that could get you closer to how a manual syncro gearbox is normally operated would be best IMO, ie building up pressure on the syncro until
the gear speeds match and the dog 'falls' in.
Using staged actuation might be a solution, but its one of these things that isn't repeatable so a bit difficult to set up. Its a topic that
interests me so i'm gonna keep thinking, if I think of anything i'll put it on here.
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TPG
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| posted on 3/12/12 at 07:10 PM |
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Just a thought. Remember to get sol/sol operated 5/2 valves. The one your looking at needs a constant 12v to remain in state (It is a sol/spring) If
you remove the voltage it will switch back. You can get them to move both ways at a solenoid signal I.e a sol/sol unit.
[Edited on 3/12/12 by TPG]
..Which was nice..
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