servo controlled wastegate

[brett_celicacoupe]

if you can find something to survive the heat, or find some way of relocating the servo then you should be fine.

maybe you could mount a gear on the WG shaft and attach a stepper motor

stepper motors can be driven to output LOTS of torque if needed. best of all, if it does fail, there wont be any torque and the wastegate will just stay open

the ones on the TRC TB's look pretty durable and heat resistant

[kewp]

i guess it would be possible to mount the servo inside the cabin and have a cable running to the wastegate, but that would probably need an even bigger servo to overcome the resistance of the cable...

[30psi 4agte]

FWIW i have seen a servo controled actuator on a rally car..... So it can be done but with what components .......... I am of no help here guys..

[mrshin]

I kind of dig this idea, I want to do it on my car... Except I've got an external gate. Might give me something to play with/look at/pull apart later on...

[The Witzl]

i cant really see a hobby servo having enough grunt, or being able to take the heat.

I'm actually looking at sourcing servos at the moment, and they are all rated at about 55*C max.temp..... so mounting near a turbo = DEATH.

Further to that, i think your estimated torque requirement is WAAAAAY too low.

[MWP]

I'm actually looking at sourcing servos at the moment, and they are all rated at about 55*C max.temp..... so mounting near a turbo = DEATH.

I would think any where in the engine bay would = death for that temp.
Would want a servo rated for far higher temps than that.

[Mos]

The disadvantage would be the extra electronics you would need to drive the pwm, although it wouldn't be that difficult.

Correct me if I'm wrong, but I believe "standard" RC servos work on pulse width as well - 1-2mS range with 1mS being end of travel in one direction and 2mS being end of travel in the other direction.
If that is the case, your electronics need to generate this pulse width repeating every.. 10mS or so (I think)? - to do straight PWM is easier, even with a dodgy saw tooth ramp generator and an opamp/comparator.

I haven't designed or built servo control loops, but have been involved in some at a keen observer level. The hardware will be the easier bit, to get the servo loop to do what you want will be the most time consuming though it sounds like you know what you're doing. As part of my work I provide training for equipment that contain analog motor controllers that control both speed and torque and the amount of analog electronics is astounding - more modern designs do all that in dedicated motor control ICs and offer much more precise control. I'm sure you're aware of it, but if you set up all your op amp circuits with trimpots all adjustements will be interactive (tweak one pot, get ready to adjust the other 20 ).

Will be cool to see you do it, good luck with it!!
I'll chime in if I can think of a suitable actuator.

Mos.

[kewp]

hmm, i'm not really sure if rc servos are operated by pwm? I always assumed the were just normal dc motors with a pot for position feedback...
And yer, if anyone else can think of a suitable actuator, then post it up, cos i agree that an RC servo will be out of it league in this situation. I had a brief look at solenoids and it's difficult to find any that would output nearly enough force...

[kewp]

http://cgi.ebay.com.au/2x-Servo-MG99...QQcmdZViewItem

this is 2 servos for $25, metal gears, ball bearings. 2 of these working together would produce of maximum of 15kg force with a 2cm servo horn. That would be plenty to operate the wastegate. It would just be a matter of keeping them cool. I'm thinking I could mount them behind the pod heat shield and make them drive a cable back to the wastegate.

Oh yeah, if anyone has a 4agze or other suitable map sensor they aren't using, send me a PM

[XR Pilot]

I've seen something similar fitted to an aircraft engine, using a servo of some description (guessing it was a custom piece) - apparently it is a quite common practise on light aircraft using turboed engines

EDIT: RC servos are most definately PWM.

[The Witzl]

kewp - i think you need to grab yourself a wastegate actuator and see how tough those bastards are to move.

Then you might get an idea of what you need in terms of power from the servo

[LeeRoy]

So what would the benefits of an electronically controlled wastegate be anyways? I'm sure there are some good benefits to be had but would it really be that much different to a spring/pressure actuated gate?

On a side note how quickly does a wastegate actuator open the wastegate in a standard style setup?

[kewp]

kewp - i think you need to grab yourself a wastegate actuator and see how tough those bastards are to move.

Then you might get an idea of what you need in terms of power from the servo

I know what it feels like with the standard wastegate actuator in place, it is very hard to move, but seeing as the stock actuators will be removed then the only force will be the gas pressure, and i've already worked out what force that will be... these servos will easily hold it.

[MWP]

So what would the benefits of an electronically controlled wastegate be anyways? I'm sure there are some good benefits to be had but would it really be that much different to a spring/pressure actuated gate?

Normal gates open slowly as the pressure increases which gives slow spool times.
A good system will keep the gate shut until just before the required boost pressure is met.

[LeeRoy]

So the wastegate opening slowly would also help create boost spikes. Would a servo or other device open the gate much quicker?