scynox

small linear actuator for raisable axle

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hello guys,

I made a raisable axle using a small linear actuator. it works fine and raises suspension by almost 1.5 stud and suspension still works which is nice. problem is the linear actuator's internal clutch. it pops up due to suspension press force if I manually press suspension for too long

800x624.jpg

another angle

800x600.jpg

principle is moving suspension's connection to axle's interior or outside to create a different angle on suspension which makes the wheel arms to raise or lower the wheel. suspension is not fixed, it moves and suspension shall work in low or high mode which is a requirement (I want it that way).

now if I press suspension (half stud 6L beams or wheel) then the LBG #44809 (the shock absorber and frictionless pin is connected to it) shall move towards interior (middle of axle) which shall press the 3L red beam to forward. it is going to force the linear actuator to pop forward, and it does unfortunately.

obvious answer would be to change direction of linear actuator, which is going to be ugly but possible. yet the same problem shall be there. this time pressing the suspension shall push the actuator's arm to inside.

my questions?

* I think I shall stick with this design (using small LA) because of compactness and it really does not pop up frequently. it rarely does when applying full force. I am thinking of changing direction (linear actuator shall be at opposite side) but shall this help? is actuator's internal clutch (or internal parts) have more force to prevent the arm to go backward or forward?

* funny part is, I used linear actuator for fun and I trusted its internal clutch, holding power. it does not have much power it seems. It only needs to go forward 1.5stud at most and it is enough for suspension.

alternate 1: worm gears with axles with stoppers?

alternate 2: using linear actuator to create a more powerful but shorter movement and apply the power to the LBG pin through a beam (where in image LA is connected)

 

what do you suggest? is small LA really that weak or did I break it during tests?

cheers

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if you move the links back toward the (gear end of the) actuator 1 stud, so the links are at 90 degrees to it when at its shortest there will be almost no force transferred to the actuator when the suspension is compressed.

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You have not broken the mini LA during the tests. It can't deal with extreme forces. I have been expirimenting with adjustable suspension too lately and I personally don't like a worm screw setup as they will cause a lot of play in the setup and cause axles to twist slightly. I tested this on a 1:8 scale chassis which seems a larger scale then you are working in. If it really rarely pops I think you should stick with your current design and change the geometry like Aerolight sugested. The advantage of your setup is that you did not use two seperate mini LAs for each axle individually which could cause the LAs to go out of sync if only one would pop.

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@Aerolight, 90 degree is dangerous. LA cannot push it (maybe?), the #44809 should be able to slide easily but in 90 degree it might be locked there. the small bushes on yellow 9L axle are there for this reason, to create an angle to allow small LA to push (pull the #44809 even at corner). also another factor: linear actuator, it is not 1 or 0, and it shall have between values. at between values the problem is still there, maybe less but consider low ride position (actuator expanded at almost max possible, not entirely), at this point it also causes pop because of the force. there shall be another problem. perhaps you can see the half bushes, yellow and LBG on yellow 9L axle. they prevent wheels to scratch over suspension arms (red 4x2) I cannot make it 90 degree unfortunately. 4x2 beam placement scratches wheels of 8070 (or 42096, smaller porsche set) without bushes which I think is for this scale. I shall test more though.

@T Lego I have done 1:8 already, it works fine but with two small LA, one is definitely not enough but the movement is slow and long so out of sync should not be a problem at that scale (I can live with 1-2mm diff). principle is very different and it is not something like above (I raise entire arm plus suspension). I could not manage to pop in that yet but I also did not build the car. it is for later. above just came to my mind today for a smaller scale car/pickup :D

temporarily I opted to go for my alternate #2 temporarily, at opposite direction. suspension falls when wheels are not on ground but it presses when it is on ground (and stops depending on LA position). I could not pop it up but the angle of LA arm scares me, it bends a little and I dont like it, I should find a better way.

thanks for answers.

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9 hours ago, T Lego said:

I have been expirimenting with adjustable suspension too lately and I personally don't like a worm screw setup as they will cause a lot of play in the setup and cause axles to twist slightly. I tested this on a 1:8 scale chassis which seems a larger scale then you are working in.

Have you tried to use a pneumatic system to  lift a 1:8 scale model before, to create some kind of Air Suspension? I experimented with my old pneumatic cylinders yesterday, but they lose too much preassure before reaching the neccecary power (1kg per cylinder)

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2 hours ago, Gray Gear said:

Have you tried to use a pneumatic system to  lift a 1:8 scale model before, to create some kind of Air Suspension? I experimented with my old pneumatic cylinders yesterday, but they lose too much preassure before reaching the neccecary power (1kg per cylinder)

Not on a 1:8 scale car but on a much smaller one. I had issues with micro leaks in the cylinders. Within two minutes after pressurizing all pressure was lost gone.

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1 hour ago, T Lego said:

Not on a 1:8 scale car but on a much smaller one. I had issues with micro leaks in the cylinders. Within two minutes after pressurizing all pressure was lost gone.

Damn, I guess it was a cool idea but not suitable for a 1:8 scale car.

Even if I would run 2 seperate pneumatic systems with 2 small cylinders per wheel I bet the car would still air down on its own in less than a minute due to leaks :sceptic:

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When the links are at 180 degrees the actuator cant move them, at 90 degreases however the force from the actuator is maximised. Due to the force direction you might be able to get away with moving the links  back one and use a axle with 2 90 Degree connectors and a half stud shim to make the 2.5 stud link length you need. (while the links would only be held together with friction only a downward force on the wheels would cause them to pull apart).

If we could see more pictures there might be a way of simply moving the suspension connection pin out 0.5 studs.  

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1 hour ago, Aerolight said:

When the links are at 180 degrees the actuator cant move them, at 90 degreases however the force from the actuator is maximised. Due to the force direction you might be able to get away with moving the links  back one and use a axle with 2 90 Degree connectors and a half stud shim to make the 2.5 stud link length you need. (while the links would only be held together with friction only a downward force on the wheels would cause them to pull apart).

If we could see more pictures there might be a way of simply moving the suspension connection pin out 0.5 studs.  

thanks for the answer but I really did not get what you mean. here is the design with all other things removed. how do I turn the (red) links 90 degrees? I dont get what you mean.

800x464.jpg

this is not steering, either both red links move towards inside or towards outside (pulling or pushing shock absorbers), at the same time, not one by one. it is meaningless then.

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Whenever I dabble with this sort of thing I either make it so that the top suspension mount is on a piece that can rock into one of two positions and come up against a stop so there is no load on the actual mechanism, or I’ve used a 24? Tooth cog (the one with the four pin holes in) and mounted the top of the shock in the pin holes and then driven the cogs with a worm.

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@Aerolight thanks for the idea. I have not built in real but here is what I fear (direction also matters, I cannot move towards south in below image because dark brown axles shall hit each other before end):

800x392.jpg

since LA shall pull the red T beam, it ?might? pull the axles as in blue arrow direction and connectors might pop. unfortunately the T beam does not stop at something I can backup behind. It moves around 1.4? stud, with lego it becomes unstable to back it up to prevent movement further (for example LA pulling connectors on the #44809 connection). not sure of course and it depends on the weight of car because car's weight shall push it back. even if the axles move a little then the suspension shall be clogged and disassembling might be required. in original design I might even add a gearbox to raise front or rear of car which would solve out of sync problem if LA pops up but solving left-right sync problem is messy, perhaps impossible.

I hope I got your idea correctly.

I feel it is not different from the original issue, we only empowered the push/pull power of LA due to different angle by lowering the link length.

@MinusAndy does it ever become out of sync? for example when raising car or playing with suspension, like pressing? what if you mistakenly cause worm to skip a gear on big 24Z gear, would not all suspensions become out of sync? how do you prevent that?

 

thanks for the answers.

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On 6/8/2020 at 12:29 PM, scynox said:

 

800x600.jpg

 

cheers

 

On 6/8/2020 at 12:56 PM, Aerolight said:

if you move the links back toward the (gear end of the) actuator 1 stud, so the links are at 90 degrees to it when at its shortest there will be almost no force transferred to the actuator when the suspension is compressed.

 

I agree with this, and that would be my suggestions as well.   Try getting rid of the grey half-bushings in the photo above, and move the LA back (towards the gear) at least 1 stud.  1.5-2 studs may even be better.  When the suspension is loaded, it will force the already retracted LA to want to retract more, which of course it can't do.  

 

4 hours ago, MinusAndy said:

Whenever I dabble with this sort of thing I either make it so that the top suspension mount is on a piece that can rock into one of two positions and come up against a stop so there is no load on the actual mechanism,...

 

I agree with this as well, and that's a good design.  I did something similar on my Piper Super Cub and the retractable landing gear in the floats.  See video below starting at about 4:02.  The mini LAs retract the landing gear, but the over center pivot (red 3x3 arch pieces) transfers the weight of the model from the LAs to the frame.  The landing gear was strong enough to support the weight of the plane despite only using two mini LAs for all four wheels.

 

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15 hours ago, dhc6twinotter said:

I agree with this, and that would be my suggestions as well.   Try getting rid of the grey half-bushings in the photo above, and move the LA back (towards the gear) at least 1 stud.  1.5-2 studs may even be better.  When the suspension is loaded, it will force the already retracted LA to want to retract more, which of course it can't do.  

I agree with this as well, and that's a good design.  I did something similar on my Piper Super Cub and the retractable landing gear in the floats.  See video below starting at about 4:02.  The mini LAs retract the landing gear, but the over center pivot (red 3x3 arch pieces) transfers the weight of the model from the LAs to the frame.  The landing gear was strong enough to support the weight of the plane despite only using two mini LAs for all four wheels.

read my posts above, it is already answered why I cannot remove half studs.

in the plane there is no suspension so it is on its weight of plane. according to here the press force applied to shock absorber is around 1.2 kilo but not directly to LA so obviously less than 2.4kg yet still something, not just weight of car/plane/whatever. I also have a similar scale and at 2kg-ish the LA retracted forcefully just like in the post linked. it means pressing the suspension really applies 2kg force in my design.

here the bushes gone and T beam is moved back to max possible. right position is fully retracted (secure position), left position is HALF retracted (most problem position). How do you plan to protect the LA to be popped up in half retracted position? you guys only think binary like on-off but I want to use at various positions, it is LA, it can stop at any position. forcing to use only low or high mode is very dull and also not fun at all. also depending on car weight maybe the weight itself shall force it pop up, assuming I put heavy stuff like battery etc.

800x395.jpg

by the way my temporary solution is exactly like what you did in the plane. it works quite fine, it is even in pics (between suspensions and differential). I think I shall stick to that design, it is best in this scenario and it allows almost every position safely.

cheers guys. thanks for help

 

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If you want it to work at any height with the same range the only way would be a camming system, possible but would defiantly take more space.

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Posted (edited)
9 hours ago, scynox said:

in the plane there is no suspension so it is on its weight of plane. according to here the press force applied to shock absorber is around 1.2 kilo but not directly to LA so obviously less than 2.4kg yet still something, not just weight of car/plane/whatever. I also have a similar scale and at 2kg-ish the LA retracted forcefully just like in the post linked. it means pressing the suspension really applies 2kg force in my design.

here the bushes gone and T beam is moved back to max possible. right position is fully retracted (secure position), left position is HALF retracted (most problem position). How do you plan to protect the LA to be popped up in half retracted position? you guys only think binary like on-off but I want to use at various positions, it is LA, it can stop at any position. forcing to use only low or high mode is very dull and also not fun at all. also depending on car weight maybe the weight itself shall force it pop up, assuming I put heavy stuff like battery etc.

 

I'm not entirely sure I understand what the suspension has to do with the LAs.  The forces being exerted on the LA is the same, regardless of whether or not shocks are used (well unless you drop something, in which case shocks might help).  My original plans with the plane design was to include a couple of stiff shocks on the main wheels.  These shocks would have replaced the grey 7L beams in the landing gear mechanism seen in the video.  The rest of the mechanism would have stayed the same, and the weight of the plane would have still been on the plane's frame, rather than the LA.  I abandoned the shocks because I quickly realized the plane was too heavy for only two shocks, and I didn't have time to work out a different solution. :classic:

Sorry, I didn't see any comment about you wanting to have various positions.  I assumed it was just an up or down scenario.

Do you have to use an LA?  Why not just use a rack and worm gear?  Then you don't have to worry about internal clutches.      

Lego set 8297 Off Roader has motorized adjustable height suspension.  It might be worth a look for some inspiration.  

Edited by dhc6twinotter

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Posted (edited)

This might work with some light modifications (allowing the actuator to extend to go though its full range would make it effectively stronger anyway though). Not Sure how to get the elbow perfectly stiff and the eyelets ideally should not have friction but here is the basic concept. 

49994598676_b4e5509d5d_b.jpglego cam actuator by michael waterfield, on Flickr

 

Edited by Aerolight
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13 hours ago, Aerolight said:

If you want it to work at any height with the same range the only way would be a camming system, possible but would defiantly take more space.

we have cam already :) and it does not take too much space at all. in fact instead of the T beam I can put two technic cams in opposite direction and rotate it which can extend to 3L and retract to 2L. unfortunately the movement is little, half stud per wheel, not enough to extend the suspension.

still a very good idea and can be applied for compact suspensions which I shall try for sure. not at this scale but maybe smaller wheel/tire options and different setups. thanks for reminding this.

12 hours ago, dhc6twinotter said:

I'm not entirely sure I understand what the suspension has to do with the LAs.  The forces being exerted on the LA is the same, regardless of whether or not shocks are used (well unless you drop something, in which case shocks might help).  My original plans with the plane design was to include a couple of stiff shocks on the main wheels.  These shocks would have replaced the grey 7L beams in the landing gear mechanism seen in the video.  The rest of the mechanism would have stayed the same, and the weight of the plane would have still been on the plane's frame, rather than the LA.  I abandoned the shocks because I quickly realized the plane was too heavy for only two shocks, and I didn't have time to work out a different solution. :classic:

Sorry, I didn't see any comment about you wanting to have various positions.  I assumed it was just an up or down scenario.

Do you have to use an LA?  Why not just use a rack and worm gear?  Then you don't have to worry about internal clutches.      

Lego set 8297 Off Roader has motorized adjustable height suspension.  It might be worth a look for some inspiration.  

when you press the suspension it creates an additional force which is applied to LA. at that point LA pops up (due to the additional power applied to suspension). it only happens when you are testing suspension for example.I already said it in first post. LA pops up when I press suspension. it does not pop up when vehicle is stationary.

I prefer the machinery to work in every position, not only in up/down situations. just personal preference. that is the challenge and fun. it is nice to watch it running slowly and smoothly and also working on every position. just like the wheel of the plane but not entirely functionality wise. your plane wheel must be on or off, just like a car door but a car height can be adjustable at various positions. when you put a steering wheel or HOG to your car, do you only turn it to max or do you want to steer half perhaps? same principle

Do I have to use LA? not really but just for fun.I trusted its internal parts to provide me enough resistance to stabilize the suspension. I was wrong, that is why I created the topic.

I looked at 8297 already. I am just testing compactness. I am not saying it is bad but I am testing different ideas.

1 hour ago, Aerolight said:

This might work with some light modifications (allowing the actuator to extend to go though its full range would make it effectively stronger anyway though). Not Sure how to get the elbow perfectly stiff and the eyelets ideally should not have friction but here is the basic concept. 

lego cam actuato by michael waterfield, on Flickr

 

you can use #22961 to make it better.

also for your previous example technic cams can be used since they provide 2.5stud beams.

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