servo controlled wastegate

[MWP]

Would a servo or other device open the gate much quicker?

Servos can be slow depending on the gearing, but would still be much faster than the normal system.
A solenoid would be almost instant.

... but all of this is not about how fast you can move the gate, its about when you open it.

[The Witzl]

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.

the force of the gas on the wastegate would be pretty substatial i thought?

[big_zop]

Check with Pete on how it all works, he may tell you if you catch him on a good day. I am pretty sure that he is doing his thesis on the wastegate and since he is electrical, should be about the control of it rather than jsut relying on the Motec. So if you wait for him to finish it then borrow it from the faculty. by the way, what year are you in?

In regards to heat, have a look at Rex to see where it is mounted for yourself. i have some pics from th 06 comp and the servo is no more than 15cm away from the top of the manifold (pm if you want them). i know that it really only has to last for the competition which is no where near as much exposure as a car.

As for positioning the servo in the cabin, be very wary about what is does to the length of the actuator as in order for it not to bend is has to be quite substantial (the pics have it bigger than the oil feed line!) and at that length it may provide its own issue. Not too mention that the hole in the firewall needs to take into account the non linear nature of the servo actuation and i dont know how a cop is gonna feel about a pretty big rod heading almost straight at the passenger. And you have to listen to it moving all the time!

As for the design of the SAE wasegate, the butterfly is mounted in the middle of the shaft, so it requires much less force to open since one side is working with the servo as it rotates.

[Mos]

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...

Yeah, they are just a dc motor with a feedback pot.. but.. how does the RC controller get it to do what's needed?
Pulses are really easy to send via radio, especially when you use time division to multiplex the channels on the one frequency. The receiver then splits up the pulses and sends them to the correct servo. The servo controller (inside the servo motor assembly) takes the pulse and determines where the arm should be sitting and moves the motor until the correct position is reached, all based on the length of the pulse. There is no feedback to the RC controller - it just assumes that whatever it told the servo happened.
Things may have changed since I last researched servo motors, but that's my basic understanding of how they work.

Have a look at ZN409 - not sure if it will help but it might give ideas.
http://www.jaycar.com.au/images_uploaded/ZN409.PDF

Mos.

[brett_celicacoupe]

modify a JZ throttle body (TRC) to have a arm on a balljoint instead of the brass butterfly and youd have a robust, powerful unit. they also have a TPS on them so you would have feedback

[BMWTurbo]

http://www.rc-cam.com/


http://www.rc-cam.com/servotst.htm

A useful link...

[The Witzl]

modify a JZ throttle body (TRC) to have a arm on a balljoint instead of the brass butterfly and youd have a robust, powerful unit. they also have a TPS on them so you would have feedback

I think this is a good idea - the servo control on these units would have to be strong enough to close off airflow at full noise after the turbos, so in theory it should have enough grunt to control a wastegate.

Good thinkin' brett.

[JustCallMeOrlando]

Wouldn't most fly by wire TB's be suitable? They're designed to stand heat and can block the airflow at full noise as well? Might be expensive, but who knows, maybe the components themselves are cheaper?

[brett_celicacoupe]

I think this is a good idea - the servo control on these units would have to be strong enough to close off airflow at full noise after the turbos, so in theory it should have enough grunt to control a wastegate.

Good thinkin' brett.

i have been playing with one of these a fair bit. depending on how you drive them you can get torque or speed. half stepping them gives loads of torque. you only have to excite one of the fields to hold the shaft in whatever position

strong enough to close off airflow at full noise after the turbos
Good thinkin' brett.

dont forget there is equal area either side of the shaft so moments should be cancelled


a wastegate is different in this respect

Wouldn't most fly by wire TB's be suitable? They're designed to stand heat and can block the airflow at full noise as well? Might be expensive, but who knows, maybe the components themselves are cheaper?

still too hot for one of these. they have bearings on either side of the shaft so the grease would melt out. i have thought of using one for an exhaust bypass around a muffler. ie divert exhaust flow through muffler near cops, open straight through pipe when you want to gas it so close to the engine will be a bit hot though. your also going to collect heaps of heat having it partially open. fully open and fully closed shouldnt get too much heat however

[JustCallMeOrlando]

still too hot for one of these. they have bearings on either side of the shaft so the grease would melt out.

Wouldn't that be a function of hot close it is? You can make a longer rod and have the rod as the sole link between the servo and the wastegate, separated by a headshield.

[Ribfeast]

What about this? It is designed for exhausts:

http://www.quicktimeperformance.com/QTEC/index.php

[wilbo666]

What about this? It is designed for exhausts:

http://www.quicktimeperformance.com/QTEC/index.php

High Torque DC Gear Driven Motor

Sounds like my windscreen type motor idea

Which besides the failure mode doesn't sound bad to me lol

Cheer
Wilbo

[rxbenny]

Sorry to be a dusch but I dont understand why this is better than using a electronically controlled boost solenoid.

[MWP]

Sorry to be a dusch but I dont understand why this is better than using a electronically controlled boost solenoid.

Its not...
Well, direct control may be a little faster acting, but thats the only difference.

[Ben Wilson]

Theoretically, it should allow a lot more precision in boost control. In reality...