Power Steering using Raspberry PI for track car

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Power Steering using Raspberry PI for track car

Post by Project-RX8 » Fri Oct 12, 2018 10:54 am

Thoughts...?? ;) Stupid idea?

Ok hear me out.

So... As we know the power steering on our cars can be very troublesome.

It either works, doesn't work, it twerks and interferes with driver input.

Having erratic power steering is one thing but for a track car you don't particularly want a system that may correct driver input.

I have been building a track car and the power steering has also been playing up, done all the usual fixes. One min it's fine the other it's gone, when it's gone it's savage heavy and becomes hard work.

At first it was safer to pull the fuse so i knew where i stood, no power steering but it was just too heavy and half way round the Nurburgring i was tired and aching which took the fun out of it and made me take it easy.

Following Clive's idea i converted to a manual rack and yes it's a big difference over power steering not working and with the conversion i wouldn't say the steering feels heavy as such but the best way to explain it is, you can't turn the wheels quick enough so any tight corners you run wide.

So I had an idea...

The RX8 is not hydraulic, and has an electric motor that could be very easy to control.

The power steering must have a sensor that detects the position of the rack and the amount of movement, this would be a ranged signal.

The motor will also have a range of movement.

So if you could feed the input signal from the sensor and send it as an output signal to the motor you could not only determine how much movement you want from the motor from steering wheel input but you could also specify the amount of torque (help) the motor provides.

I believe the motor has a plus and minus signal, not sure about the sensor or where it is, is it the one on the steering shaft and part of the rack?

The motor would fry the Raspberry PI and the cabling if you tried to wire it directly so you would need some kind of box that provides the power to the motor from the battery that acts upon the signals from the PI.

So the way i see it working is the signal from the sensor goes directly to the PI as an input, the output from the PI goes to a box that also is capable of powering the motor at the amps required.

If i did try this i would also build in an led and a kill switch, the led to indicate the PI is on and a kill switch so if it did break you can kill the PI turning off any assistance. You would also need to make sure the whole thing including wires and terminals are probably insulated from moisture as water is a conductor and could possibly bridge pins.

The theory is there, it shouldn't be that hard to get working in basic form.

You can get it working and calibrated on a bench and fine tune the amount of torque and movement while in the car.

It would be perfect for a drift car because you could flick the front wheels to full lock with minimal input from the steering wheel.

WARNING... If anyone wishes to take this idea further it could be very dangerous so do so with extreme caution. This might not be suitable for road use as you will be using cheapish components to control the steering that might be sensitive to vibration and moisture or poor programming. You would need to be fairly confident what you are doing and test thoroughly. It's is purely an idea that could be a great answer to the issue if executed well.

p.s. another solution to improve turning speed could be to simply change the gearing (the cog) of the steering shaft. I didn't disassemble the rack enough to see what would be involved and it's probably out of my depth so would need some help changing, welding of the gear.

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Re: Power Steering using Raspberry PI for track car

Post by 13Black » Fri Oct 12, 2018 11:27 am

Not sure on the drift application myself - apply all your lock (too much) to initiate and there'll probably be far too much scrub angle on the front wheels and it'll just plough forwards.

Interestingly also, once you've got the back end out, it's basically not possible to keep up with the wheel as it will naturally flick lock to lock during transitions by itself - you basically let off the accelerator and let go of the wheel and it'll do it all for you until you're at full angle again:





It's an interesting project though - ideally I'd have it slightly stiffer but not full-fat manual rack.
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Re: Power Steering using Raspberry PI for track car

Post by warpc0il » Fri Oct 12, 2018 11:32 am

It either works, doesn't work, it twerks and interferes with driver input
So... As we know the power steering on our cars can be very troublesome.
IMO This is a maintenance issue not down to the design
It either works, doesn't work, it twerks and interferes with driver input
Only if it's damaged or not properly maintained.

The system you describe is similar to the first generation of power steering systems and results in zero feedback, due to the lack of road speed compensation.

The Mazda system employs both a position and torque sensor, while the EPS control module also receives both vehicle and engine speed from the PCM.
Screenshot (12).png
Screenshot (12).png (203.93 KiB) Viewed 97 times
If you need very different behaviour from the steering, for a specific purpose, such as drifting, then this may be of little value to you, or you might just need to change the mechanical geometry, e.g. increase the length of the steering arms, such that the angular gearing between steering wheel and road wheels is increased.
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Re: Power Steering using Raspberry PI for track car

Post by StreetDragster » Fri Oct 12, 2018 11:38 am

I have also not found the eps to be troublesome at all in track use, in fact it's been rock solid. Not really sure what you would benefit by going to a manual rack aside from a bit of weight saving, reduced complexity and larger arms

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Re: Power Steering using Raspberry PI for track car

Post by Mazda Rotary Parts » Fri Oct 12, 2018 11:59 am

There is another alternative, apparently many kit car guys use these now and I have seen one of these mounted under the dash of an RX-7 FD so it would fit adapt to an RX-8 .

(Word of warning though to use this unit, for safety you must fully convert the rack to manual as per my race car thread)

After my manual steering conversion on the race car I was going to use one of these but then realised it would put around 7 kilo back in the car so I stay with the heavy while going slowly steering.

Here we go, you can even get one with the adjustable unit.
If you look on the internet you will even find the wiring diagrams to mount this as a stand alone unit,

https://www.ebay.co.uk/itm/Vauxhall-Cor ... :rk:3:pf:0
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Re: Power Steering using Raspberry PI for track car

Post by PeteH » Fri Oct 12, 2018 12:45 pm

Tuning the electronic power steering is a massively complex job. There are Vehicle Dynamics engineers employed full time at car manufacturers who do this and only this. The control strategy is way more complicated than you could ever imagine. It involves such esoteric things as inertial compensation of the rotating parts of the motors, and compensation for the back emf of the motor, and battery protection strategies, epas motor protection strategies. And that's before you even get onto the basic tuning of the relationship between the handwheel torque and the epas assistance (which is hugely non-linear, and very sophisticated). It has very little to do with rack position, by the way, except to protect the rack when at full lock.

I don't want to rain on anyone's parade, but I wouldn't go anywhere near epas tuning.

I too had no issues at all with my epas system when on track. It was always perfectly behaved. If you do have issues then are you using a race battery? Epas can demand huge currents, and I would be reluctant to run an epas system with a race battery (although I think Clive did used to).

I have also made a manual rack, but only to save weight and facilitate using an aftermarket ecu. I'd much prefer to keep epas if at all possible.
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Re: Power Steering using Raspberry PI for track car

Post by 13Black » Fri Oct 12, 2018 2:48 pm

Race b82rez with EPAS here, for many months, without any perceivable downsides so far on tracc.
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