Pump My Ride - Ninety on air

[mad_pete]

How was the ride ?

[Turbocharger]

On 4/4/2020 at 1:32 PM, MECCANO said:

Turbo C,

So when you say they p38 springs are more like a commercial vehicle spring, could you fit a rear bag and piston to a front top hat?

Yes, and swapping the pistons and top pieces is an interesting route to tweak the characteristics a little. Disco 2 bags are crimped on though.

On 4/5/2020 at 7:41 AM, Badger110 said:

Will the airbags give a smoother ride overall?  A recent journey in the back of mine made me realise that the dogs feel everything when we travel and although they seem unaffected, if it’s a fairly straightforward swap down the line, I could be very interested in doing something similar.

They're not magic - it's a spring so doesn't provide skyhooks. They help to separate out the spring rate from the ride height though, so you could run a soft spring without one end being droopy when laden. The car on top of the spring/shock makes a huge difference, clearly.

A lot of 'feeling every bump' is down to the damping though, and it's very hard to get any numbers on damping characteristics or rates. The best I've found is Gwyn Lewis who's characterised four different shocks, no numbers but 'by feel' is sensible. (I've got Fox 2.0 IFPs on the front of mine and very very pleased with their high speed damping particularly, but they replaced some knackered ProComps so hard to get a proper back to back.

Gwyn says: (from eg here:https://gwynlewis4x4.co.uk/product/challenge-old-man-emu-5-5-inch-shocks-four/)

Quote

Procomp :- A budget shock better suited for use on a lighter weight trialer / offroader. The valving in these is soft, they will give a soft boaty ride on road, not recommended if your Land Rover is a heavier one or used for towing.

Bearmach 11” :- These are priced more like the budget Procomps are but they offer much better valving and build quality. The valving is more comparable to the Pedders, these will give better road manners than the procomps.

Pedders :- These are a quality Australian shock. We recommend you use the Pedders shocks if you want more of a comfort ride, they are better suited to a standard weight Land Rover or one that is carrying little extra weight. The valving is softer than the OME Sport but still able to provide very good road manners.

Old Man Emu Sport :- These have powerful valving which provides very good road manners, even on a heavier Land Rover without Anti Roll Bars fitted. They are available with a medium and firm sport ride. We recommend these for the best road manners but on a Land Rover carrying little extra weigh they do ride a bit hard.
These are the shocks I designed my Challenge Kit around some 20 years ago. 

 

[elbekko]

I have TerraFirma shocks on my P38, they give a very good ride (including off-road) and still firm enough for road use.

And yes, you very much notice the difference between air and coils when driving off-road. So much less jarring.

[Turbocharger]

 

I've done a little more playing at the weekend and got some characteristics for the various springs. The key to getting a decent mix of ride and handling will be to match the natural frequency that the car had on coil springs - this will ensure the shocks are working in something like the envelope they were designed for too. Natural frequency should be between 1 and 2 Hz, and the rear slightly higher than the front (because bumps hit the front end first, usually 🙄).

I used a natty free app MyFrequency, which uses the phone's accelerometer data. You can see on the trace when the axle hits bump stops (or a dangling shock absorber 😱), and the low frequency analysis is a little imprecise, but the method is consistent at least.

• The front suspension came out at 1.6Hz (300Tdi, auto box, Milemarker on the bumper, 6 point cage, red & white RR front springs)
• The rear suspension came out at 1.7Hz (same powertrain, some tools and old paint tins in the back - this frequency would go up slightly if unladen)

The frequency changes slightly at different ride heights - the lower piston is often shaped and there's more air doing the springing if the bag is extended. I've found the RR bags need about 60psi to hold the Ninety up, and the Disco 2 bags nearer to 80psi because they're a smaller diameter.

For the front axle, I've found:

• P38 front airbag
  • 1.9Hz at normal ride height
  • 1.6Hz at +50mm
• P38 rear airbag -
  • 2.3Hz at -50mm
  • 1.8Hz at normal ride height
  • 1.9Hz at +50mm 
• Disco 2 springs - (still to fit)

For the rear axle, I've found:

• P38 front airbag
  • 1.7Hz at -50mm
  • 1.6Hz at normal ride height
  • 2.0Hz at +50mm
• P38 rear airbag - (still to fit)
• Disco 2 rear airbag
  • 1.9Hz at -50mm
  • 1.6Hz at normal ride height
  • 1.8Hz at +50mm
  • 1.9Hz at +120mm

So if all these measurements are +/- 0.3Hz, it looks like we're in the right ballpark with any of these springs so I'll select based on what I can package and what will give a balanced setup.

The Disco 2 bag is seriously long - they're a crimped design so harder to play with pistons, change bags etc, but...

 

Thanks to Andy for some prior experience - this really is the most useful way to learn anything!

On 4/7/2020 at 1:20 AM, landy_andy said:

... thought you'd like to see these pics.... I made them way back in 2005.

They use commonly available HD Firestone bags... if you want more info drop me a PM.

Thanks Andy - really good to see the experience of someone who's been through the pain before. Looking at the frequency stats I'd say this was quite a soft ride (depending on the shocks you used) but the background suggests this was an offroad truck so that's probably ok? The lower piston isn't shaped so those force charts (top right graph) are nice and flat in the middle area.

I'm keen to avoid the kind of extended bump stops you've used so packaging a short compressed length between the upper spring chair and the axle mount will be a challenge, and then getting the most travel available from the bag and any matching shock absorber.

[Turbocharger]

 

On 4/5/2020 at 11:26 AM, robertspark said:

If I ever get my 90 finished (now have a chance + instruction from swmbo as furloughed over virus).

<snip>

(Lots of cleverer stuff than watching me bolting bits together like a curious monkey)

<snip>

Looks like we're working on similar projects! Keep in touch, keen to learn by your mistakes rather than my own 😉

On 4/5/2020 at 4:22 PM, robertspark said:

got some pressure sensors (each corner) which I did consider may be useful to determine an off-road situation where one wheel may be loaded but then it's what you do with that information because it would probably be useful with more information such as a 9 axis gyro, accelerometer and magnetometer.... Speed sensor.... Steering angle.... And all of a sudden the code is very complex... and what you want to do with all this info .... Automatically by microcontroller....

Yes, it's possible to make this very complex indeed. Pressure sensors at each corner, 9 axis in the car, maybe a vertical accelerometer on each unsprung mass, add some extra chambers onto each corner which you could activate with their own solenoids... The microcontroller can probably deploy any logic you like - but what's actually desirable?

There's a good chance active interventions could be the wrong thing, or the right thing at the wrong time - we know adjustable (passive) shocks etc just gives many more degrees of freedom for any amateur to make it worse. I'm keen to make it self-level, run on the road at a slightly lower height and be liftable for offroad/lowered for the garage. Then to look at how to make it cross axle better with a sensible level of complexity. If I wanted skyhook ride I'd just buy something with a significantly lower unsprung mass. This is never going to be a limousine. 

 

[Turbocharger]

Some more playing with Disco 2 rear airbags on the front axle yesterday evening - whichever bags I go for, I'm inclined to cant the lower pedestal back a little so that the angle at full droop is less extreme. 

The minimum length of the springs is going to be very important - I can see why Robert had those extended bump stops - there's 160mm package volume for the spring at full compression to the bump stop, and I'm keen to design it as if the 50mm bump stop was removed, or at least substantially compressed. (Spring cup is upside down to take the air spring piston, as a static mockup)

The Disco 2 airbag looks like it'll compress to 140mm, but the bag is overhanging the lower piston - that's not actually an issue once there's any pressure in it because it rolls back like ... (try to avoid a foreskin comparison here).

I made a video of it inflating at moderate height - and with the rear pedestal settling and scaring the bejeezus out of me. The Disco2 bag is crimped top and bottom so it appears to have a very long length when it's off the car, but the effective travel when it's inflated isn't much more than the P38 bags.

 

 

Edited April 9, 2020 by Turbocharger
Edit for pics

[Mo Murphy]

An interesting thread John, I'll keep an eye to see how you progress. 

Good luck with your experimentation 👍

Mo

 

[maverick]

Don't forget to carry your puncture repair kit

its a right bugga when you bust a bag

 

Edited April 15, 2020 by maverick

[WesBrooks]

I was thinking a pair of springs would be easiest?
My plan was to have the manual override and external connection so you could pump individual bags with a tyre pump or similar. I get the impression that's nothing novel.

 

Edited April 15, 2020 by WesBrooks

[elbekko]

5 hours ago, WesBrooks said:

I was thinking a pair of springs would be easiest?
My plan was to have the manual override and external connection so you could pump individual bags with a tyre pump or similar. I get the impression that's nothing novel.

 

Yup. Bags are pretty compact to carry when not inflated (and really only for worst-worst-worst case scenario that's like a .0001% chance of happening), and as you say a couple push-fit schrader valves in the toolbox solves the rest.

[maverick]

I had one go bang when competing in cork with no spare bag

blooming long drive back when riding on just a Cpl of poly bump stops fastened together

bought two spare bags after that

That was many year ago though when I was young and foolish

[WesBrooks]

Is the schematic available for what is potted in resin? Is it the MOSFETS/Transistors and a controller to drop the PWM shortly after firing? All 12V logic signals?

[WesBrooks]

4 hours ago, WesBrooks said:

Is the schematic available for what is potted in resin? Is it the MOSFETS/Transistors and a controller to drop the PWM shortly after firing? All 12V logic signals?

Haven't found a schematic yet but I think this is the 'valve driver' and according to an EAS manual I found online the signals it expects are 12V logic and it creates the PWM to drop the current draw shortly after the valve has been activated.

 

[Snagger]

On 4/5/2020 at 3:56 PM, FridgeFreezer said:

I think they're a common failure but not a common cause - if there's a leak in the system, the compressor runs flat out and burns itself out and people blame the compressor rather than the 50p bit of pipe with a hole in it.

I think the other cause is that they’re usually not serviced, even by garages, so the air filter clogs and the pump has to work harder to get air.

[robertspark]

It is avalve driver and just gets 12v input logic at low current and opens and closes the valves according to the logic.  It contains the MOSFETs.

 

No internal information is available as to what the resin block contains but it's something which you could easily reuse to drive your valves correctly so the coils are not overheated with 12v dc

[elbekko]

IIRC there was a guy years ago on rangerovers.net that was designing his own driver block, and had some good info up about it.

[FridgeFreezer]

It's very similar to the injector current limiting circuit on the Megasquirt, not surprising as injectors are just a solenoid. There's probably a driver chip that will do it for you TBH, although you've got the microcontroller and LR have given you a timing diagram so it's not hard to mimic that at all.

[WesBrooks]

As far as I can see the graph is detailing what the potted driver block does. I was hoping that the flyback diode was in the valve block or directly on the solenoids. I should be able to check this with a multimeter. Other point of interest would be of there is any transient voltage suppression on there.

It's probably best if I assume there is no protection in the block and double up atbthe processor end.

[FridgeFreezer]

Just 'cos I got bored and googled it, there's any number of driver chips that do this - DRV120 or LM1949 first on the list.

[missingsid]

Can't remember from the begining now, but did you look at Disco 3/4 bags? They have integral shock and the bottom mount is a single horizontal bolt in sheer. Would this help your articulation bag angle?

[WesBrooks]

Anyone looked into whay pots are inside the height sensors?

Look to be about 1.4kOhm track resistance. Polymer pots are recommended for low noise over carbon track but I guess these may predate polymer pots?

[WesBrooks]

I sacraficed a knackered sensor to satisfy my curiosity. It is a custom pot. It's roughly 1.37kOhm 180 turn, but wired in such a way that it can be run on onside or the other.

I don't think there are any physical limits, rather than this one is broken as there wasn't any obvious bits inside.

As shown in thw above photo: Left wire goes to the top left two contacts on outer ring. Centre wire to the centre of the outer track. Right wire to the inner (wiper) track.

[WesBrooks]

Ok so I can find plenty of near 360 degree pots, but no 180 degree. That and there being very few high IP rated items make me think the most cost effective method will be to work with P38 sensors if I can. Back sensors don't look a problem, but front may need some CAD and printing to get working.
The fact that there are few 180 pots isn't insurmountable, but it reduces the resolition of sensing for body height.

 

[Ed Poore]

Why not get a pot that's double the value but only use half it's travel?

I wouldn't worry too much about the IP rating. If you go for a standard shape pot (classic bulkhead mount ones) then I doubt it'd be that difficult to make up an IP rated enclosure for it. If you could find a suitable bearing you could glue the pot shaft to the inner race of the bearing thus sealing it out. Nice little 3D printed housing for prototyping.

[Bowie69]

As above, just use a regular swing pot, way easier.