Low frequency driver for Sim Shaker - Page 1
Forum section: electronics / projects

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: August 28, 2024, 06:02:56 am
content: Hi all,I am in the process of designing my low frequency sim shaker that will attach to the underside of my seat frame. This is for my A320 simulator on XPlane.Please refer to the attached basic design file.The aim is to provide a low frequency signal that simulates any actuator sounds or engine vibrations etc, to this shaker, via the two leads of the coil.Based on my limited research, this would necessarily be a high current (to induce a strong magnetic field), amplifier, using a power transistor like a 2N3055G to amplify the source signal to a high current signal to the shaker coil.It is quite possible that a basic sub-woofer amplifier circuit should do the trick, but an not sure.I have access to a 12VDC5A power supply, thus far. Any nudge in the right direction would be appreciated.

author: moffy
author_rank: Super Contributor
timestamp: August 28, 2024, 07:01:01 am
content: It is best to start by choosing your transducer then you can work out what power/current/voltage you need.

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: August 28, 2024, 07:21:44 am
content: Okay, so the max power I would want to use to drive this is 50W.Depending on the number of turns and the resistance of the copper wire, I could create a coil that has a DC resistance of say 4 Ohms. I'll be using 0.5mm diameter wire which typically has 1.6 x 10-8ohms/m. This means I would use a length of approx 50 m to create a coil with DC resistance of 4 ohm.Using i2r gives us a current of 3.5A. I'll be using a 12V power supply that is capable of delivering 5A, so looks like I'm covered there.So, I've now defined my high level design.12V, 3.5A, giving us 42W of power.Not sure what to do next.

author: moffy
author_rank: Super Contributor
timestamp: August 28, 2024, 10:00:40 am
content: Your idea of using a subwoofer amplifier is sound(no pun intended), and 12V fits right into the area of car audio, so a class D 12V subwoofer driver, make sure it's low frequency response is suitable and go for bi-amping as well say 200W at least should do.

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: August 28, 2024, 10:09:05 am
content: Superb! - okay the search for that amp starts now.Thanks mate.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 28, 2024, 12:11:11 pm
content: Yes, I recently used a single board Class D amplifier to resto-mod an old guitar amplifier. Easy job, it works well.Sure-electronics AA_AB32996, but you may need a bigger version.Takes 500mV audio, frequency 20Hz ~20 kHz.I found it necessary to use a regulated power supply to avoid exceeding its supply voltage rating in quiet periods.Sounds like you have an interesting project there.

author: Andy Chee
author_rank: Super Contributor
timestamp: August 28, 2024, 01:04:49 pm
content: I think I've still got one of these in my shed of stuff:Bought mine ages ago from Jaycar bargain bin. Used it while playing Quake 1, but the novelty quickly wore off, and it's been in the shed ever since.

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: August 29, 2024, 07:45:01 am
content: Quote from: mag_therm on August 28, 2024, 12:11:11 pmThanks, I never considered using a Class D amplifier. I was only thinking of a Class B push-pull.I've found this OTS product:https://fosiaudio.com/products/tda7498e-subwoofer-amplifier-receiver-mini-hi-fi-class-d-professional-integrated-amp-for-sub-bass-shakers-220w-x-1-power-supplyI think it should do quite nicely as it should be able to drive 2 sim shakers easily. Perhaps I'll make them both 8 Ohms and drive them in parallel so that the amp sees an effective 4 ohm impedance (please note I'm aware that I'm over simplifying the impedance to a DC resistance).What are your thoughts on this?

author: moffy
author_rank: Super Contributor
timestamp: August 29, 2024, 11:11:40 am
content: Something to consider is if 20Hz is a low enough frequency for your shaker, I would have thought that vibration could go lower.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 29, 2024, 01:03:15 pm
content: About the 20 Hz limit: If budget permits, you could initially try component sub woofers (already matched to the amplifier) before doing the actuators.Test to see of the turbulence, clunks , ballscrews, pumps etc can be simulated well enough with a minimum of 20 Hz.My project was simpler, modifying old tube and transistor class B PA's down to suit bass guitar (Low E 43 Hz).I used old stock component speakers and a plywood dual speaker kit. The advantage of the kit is that the big holes are already cut.

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: August 30, 2024, 09:32:43 am
content: I cant say for sure whether anything lower than 20Hz would be reproduced properly by the amp. I would imagine that even if, for example, a 'thud' of the landing gear came through, I dont think the active filter would be able to filter out, what it would encounter as a singular instance of a varying DC voltage.I'm fairly confident that part of that signal would get through and the shaker would respond. Having said that, it would also depend on the inertia of the shaker.Mind you all I've stated above could fall flat on its face - I'd have to do an actual experiment.There is an alternative school of thought that use microcontroller to interface with the host PC (via USB) and read events directly from the sim software - called DataRefs. when the microcontroller reads a signal that, for example, the landing gear has come into the locked position, the micro could generate a 'thud' signal. Doing it this way is a cleaner, more controlled design without having to depend on an mp3 sound of the thud to activate the shaker.The latter design is out of scope for me at the moment as I'm focussing on my sub-woofer amp method of generating haptic feedback.One day though, I would love to be able to design a sub-woofer amp that can amplify a 5 or even 10 Hz signal - it may be just a case of tinkering with the active filter?

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 30, 2024, 11:52:48 am
content: About the haptic driver sketch in your post#0:Speakers evolved into into a configuration with the hard magnetic circuit surrounding an annular airgap.This part is heavy and is regarded as being at rest. The voice coil in the annular airgap is light-weight and configured as a short solenoid ( Len < Dia)The voice coil is connected to the speaker cone to couple the vibrations to the air.I think this arrangement has occasionally been used for obtaining mechanical oscillatory motion, with the voice coil replaced by a mechanical piston.The parameters used for speaker design are still based on the parameter set by Neville Thiele and Richard Small.(Confusingly they only apply to "small" signals, that is the linear mode of the speaker.)It might be worthwhile to read about these to get an idea of what is involved.This ref is a concise read:https://en.wikipedia.org/wiki/Thiele/Small_parametersHere is a step by step woofer design using TS:https://www.stradivariaudio.com/woofer-design/For an amplifier in the 0 to 20 Hz range, you could look at servo amplifier designs which are basically high power operational amplifiers, can be Class D too.(search for "servo amplifier" on EEVBlog)

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: September 01, 2024, 01:36:03 am
content: Thanks, I'll do a bit of digging on servo amps.

author: _Airbus_A320_SIM
author_rank: Newbie
timestamp: September 01, 2024, 01:47:06 am
content: Right...so a servo amplifier is a servo driver. I could use a H-Bridge to drive the servo.The servo drive could open up so many possibilities:(1) I could attach an eccentric cam and use it to generate vibrations simply by rotating at differing speeds(2) or attach a crank and use it to as you would a crank.