Core Electronics Forum

Mechanical question: create friction/constant friction

Hi there, I’m working on building a joystick from scratch, but hitting the limits of my mechanical know how. One of the reasons I’m doing this is because pretty much every joystick you can buy, not to mention instructions for DIY joysticks, have springs that return the joystick to the center. I would like to make one isn’t auto-centering (maybe with a bit of pressure at the middle) but rather has more or less constant friction and stays where you put it.

When I 3d print the gimbals I could just glue something on there so that it doesn’t move very smoothly, but I wonder if there’s some mechanism or component I could search for that would be a better solution. What do you call something that’s the size of a spring but instead has two pieces sliding over one another to create friction?

I was going to follow a design using magnets and hall effect sensors rather than pots. I’m not sure whether a very stiff pot would make this easier; and how to stiffen it up so to speak?

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The magic words you’re looking to google are “friction hold”, here’s some results I got:

http://www.cw-industrialgroup.com/Newsroom/News/Friction-hold-joystick-offers-´put-and-stay´-opera

I think you’re on the right track. Most designs just use a moderately stiff bit of metal, and a bolt to clamp it down and adjust the friction. There’ll usually be some sort of fibre material in there (felt was common back in the day) to act a bit like brake pads on a car. They spread the load out more evenly and give a better friction profile than raw metal on metal.

For something that’s going to wear long term, you need some spring in your system to keep the force fairly constant as the material wears down. A setup a bit like carbon brushes in a DC motor commutator is a good way to go (but with much stronger springs).

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Hi Colin,

Just to add to Oliver’s suggestion, if you wanted a hard-wearing surface, think about printing in TPU or Nylon. Nylon is very hard-wearing, and hard TPU even more so. NinjaTek Armadillo comes to mind. Someone on reddit had success smoothing their TPU prints with a heat gun, so that may be the key to getting something with a smooth action:

PTFE may also be suitable for this, but is nigh-impossible to print with (resists temperature like a champ, and doesn’t stick to itself :/) So you might consider printing a support piece for a small ring of PTFE tube glued into a slot. I designed a horizontal drybox/spool holder with something like that.

-James

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You can get sheets of PTFE actually.

I had a job once where we were making a huge number of steel wheels for brick kiln carts that ran on rails. There were multiple PTFE seals in every one. Spent a couple of days in front of an arbor press punching them out.

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Hi Colin
This site may be worth checking out. All sorts of Joysticks and I noticed what I think are linear potentiometers which you are also after I think. You may get some ideas from them.
http://www.precisionsales.com/joystick/industrial-grade.htm?gclid=Cj0KCQiAuP-OBhDqARIsAD4XHpfG4pjAbhh7P-e67fnIAxd6YbFZQJ8tzzCopesYcYk3UpE0jgv2k38aAsphEALw_wcB
Cheers Bob

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Hi Bob,

Good find. I found a couple of sites like that - here’s one that has some great hardware. The downside? They sell to industrial equipment manufacturers. It’s more of a ‘send us an inquiry and how many of our $1500 components you’re interested in’. I think they’d be great but a bit beyond the reach of a hobbyist at the moment.

That said some more ideas/stuff to search for there.

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Hi Colin
Yes that site I linked is probably like that but you might get some ideas.
I noticed that at least one has the choice of spring return to centre or friction. If you investigate more closely than I did you may get an idea on how they do that. I get the impression you can get any configuration you want and different combinations but I only got as far as an initial look.
Cheers Bob

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Hi Colin,

Might be worth looking at some nice consumer gear as well.

Virpil/VKB make some very nice sticks if you’ve got the coin and aren’t happy with thrustmaster-grade performance.

Cool project nonetheless, are you trying to emulate a specific plane or something like that?
-James

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Hi James,

Ooh, those are some beautiful pieces of hardware! Ironically perhaps, I’m trying to simulate one of the most low-tech aircraft, a glider. To properly develop the muscle memory it would be nice to have something that replicates the response (and position relative to the body) of the real thing, hence the DIY. One of those fancy VKB joysticks with all the missile-arming switches and so on may or may not have a more realistic response, but that’s a bit of a massive investment if it’s not perfect.

Interestingly, some of those high-end joysticks have a brake lever on them which is the next bit I’m trying to kludge up; the glider has the elevator trim as a lever behind the joystick as well. Once again, I can handle the electronic bits but figuring out springs and hinges is the trick!

VKB have some awesome mounts which I will look into getting. In the end I’m going to bolt all this onto a low-end flight sim chair setup, so mounting it all properly is yet another mechanical challenge.

In any case I’m here for a reason, I enjoy the challenge of the project! Once I’m done I’ll come back and post a summary. For comparison there is a company selling a complete rig, right now it’s $2k USD with insane shipping costs (>$1000!). So let’s see what I can do on my own first with your help!

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Hey Colin,

i have that same cheap ‘lawn-chair’ style chair! I have been racing Project Cars 2 in VR with it for close to 18 months now, with zero issues. It is very big however, in the way that I’m 179cm tall (almost 6’) and yet my head is between the red ‘seat belt’ holes. i bought it at my local JB-HiFi store for $499. Next Level Racing F-GT Lite Cockpit | JB Hi-Fi (jbhifi.com.au) My review is still there under the same handle.

I love the fact it folds down with my entire wheel and pedals, so I can store it out of the way when I’m not using it. It’s very sturdy for all my runs through Bathurst :smiley:

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I know nothing of how a glider is controlled, but I am imagining levers attached to rods or cables attached to movable wing surfaces. Simulating that requires more than friction. Friction is a constant resistance to movement regardless of speed. Moving an object that weighs something also has inertia, more resistance to fast movements and some overrun. Another factor that may come into play is forces on the object to be moved. That would give a variable resistance to movement.

I may have this wrong, just throwing ideas into the mix to get knocked down.

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Hi Alan,

Yes, you’re correct of course; as you say, the feel and response of the controls varies a lot just with airspeed. There’s a limit to how far I can and will take this in terms of realism!

Having said that, constant friction is a pretty good approximation. The controls are in general very light (thumb and forefinger is enough!) so one doesn’t have to counteract much in the way of inertia. To first order the big difference with an off-the-shelf joystick is that the glider controls don’t automatically re-center themselves as well as being a bit stiffer.

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