Steel cables in replacement of rack & pinion

[TonyTheTiger]

Hey all,

I have heard about one team in this year's Michigan Competition using steel cables instead of rack & pinion for the steering system. Does any1 have pics for that and know if the design judges liked that design?

[TonyTheTiger]

Hey all,

I have heard about one team in this year's Michigan Competition using steel cables instead of rack & pinion for the steering system. Does any1 have pics for that and know if the design judges liked that design?

[Lorenzo Pessa]

I don't know if Delft was in Michigan but you can find this useful.
h t t p :/ /w w w.youtube.com/watch?v=-MpQi82ZW2M
@0:32

[RollingCamel]

Lorenzo you can link directly now.

[Perito]

I remember a similar system on Roma "Sapienza" fsae car at FSAE Italy 2008.

I don't know exactly what is happened with judges, but I've heard during the event that the system could be defined like a "steer by wire", so it was not conform with the rules.

Anyway, the car was allowed to participate at the dynamic event.

[TonyTheTiger]

thx guys. that video is very helpful http://fsae.com/groupee_common/emoticons/icon_smile.gif

[JDS]

Pretty sure the wire in "steer by wire" is referring to electrical wire, not mechanical, so it wouldn't really fit the "steer-by-wire" as it is intended to be defined.

[Perito]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Pretty sure the wire in "steer by wire" is referring to electrical wire, not mechanical, so it wouldn't really fit the "steer-by-wire" as it is intended to be defined. </div></BLOCKQUOTE>

This is the interpretation of rules that I've ever considered. In fact it was strange for me that this system was not regular, expecially for the reason that I've heard.
Maybe someone of Rome could explain better what is happened, if something is happened.

[Ben K]

That seriously doesn't look like it is worth the danger factor of losing your steering if something breaks. Also--cable stretch causing toe compliance....not so good. I'd rather stick with a good ol' rack+pinion.

Ben

[PatClarke]

Just a tip TTT,

If you are even remotely considering a wire and pulley steering system, I would float it by the Rules Committee before you get too far advanced in the design!

Cheers

Pat

[TonyTheTiger]

sure, we are going to stick with rack and pinion for 12'. Just thinking ahead for 13'

[Dr Tron]

someone explain to me an advantage of this system... aside from the fact that its different from anything any other team is doing....

lighter... maybe although the proposed system i saw in the youtube dident seem to be terribly light

more accurate... i would tend to doubt it considering the amount of cable stretch as opposed to the kind of stretch you would see with a traditional rack and pinion

better feel... i also doubt it due to the compliance in cables

if someone wants to think outside the box on steering systems i would say look at making a manual steering box fesible

[TonyTheTiger]

hmm...if the cables are always stretching when the wheels are turned, then where does the compliance come from?

[Kirk Feldkamp]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TonyTheTiger:
hmm...if the cables are always stretching when the wheels are turned, then where does the compliance come from? </div></BLOCKQUOTE>

Uhh.... the cables? Is this a chicken and the egg question?

[AxelRipper]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">if someone wants to think outside the box on steering systems i would say look at making a manual steering box fesible </div></BLOCKQUOTE>

I'd say try to adapt the EPS off of an ATV would be a fun job... I can only imagine the amount of camber that our chief engineer would try to run then.

[onemaniac]

Pretty sure MIT has done cable steering a few years ago. Google it if you're interested

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kyle "steering and suspension":
someone explain to me an advantage of this system... aside from the fact that its different from anything any other team is doing....

lighter... maybe although the proposed system i saw in the youtube dident seem to be terribly light

more accurate... i would tend to doubt it considering the amount of cable stretch as opposed to the kind of stretch you would see with a traditional rack and pinion

better feel... i also doubt it due to the compliance in cables
</div></BLOCKQUOTE>
Most aeroplanes (almost everything up to Jumbos) have "cable and pulley steering". Also roll and pitch control. I would guess they do so because of lighter weight, and more accurate and better feel. Note that bad R&Ps have a lot of slop and stiction. Also reliability is important on planes (because you can't just "park them" when something goes wrong), and that hasn't stopped cable and pulley systems. Most speedboats also have cable steering. It is not a radical idea...

The Delft system ref'd above does NOT seem to have many advantages over conventional R&Ps. I think the main advantage of cable systems comes when you have long transmission distances to cover. Think about all the "U-jointed steering shafts" and "bevel gearboxes" that would be needed from the cockpit to tail and wing tips of a WWII bomber. Easier with cables? Yes IMO.

For an FSAE application another advantage (not used by Delft) is the ease of incorporating variable ratio steering, via cam shaped pulleys. Also a cable/pulley system can be manufactured with lower tech tools than gear-toothed R&Ps.

Are the advantages worth the potential flack? Maybe, maybe not. But never say never! (I can think of one situation where I would use it.)

Z

[Bemo]

I remember the car at FSAE Italy in 08 using cables instead of rack and pinion for steering. In my opinion the major advantage of their system was packaging. The cables were acutuated above the cockpit and ran down on the sides of the car. So there weren't any parts of the steering system within the driver's compartment (especially no steering rack) except the steering wheel. Maybe they also saved some weight, but I guess that wasn't the major reason for going that way.
I can't tell if they had any trouble with it in scrutineering, but I'm pretty sure they were allowed to take part in the dynamic events so the scrutineers must have been convinced that the setup was rules compliant.
When looking at it, I was pretty sure that compliance must be a problem of that system. The cables were quite long and were running around a couple of courners.
Unfortunatly I didn't have the opportunity to talk to one of those guys about it so I can't tell how well it worked for them and if they had any problems with reliability. Perhabs someone from that team is around in this forum and can help.

In my opinion (and at least I was a scrutineer at FS Austria this year ;-) ) using cables for steering actuation is absolutely rules compliant because the steer-by-wire rule clearly refers to electric steering actuation. But directly asking the rules commitee never hurts.

[Perito]

Here is a picture of the Roma Sapienza cables:

http://imageshack.us/photo/my-...s/12/filisterzo.jpg/ (http://imageshack.us/photo/my-images/12/filisterzo.jpg/)

[Z]

Perito, Thanks for picture. Looks like the cables are doubled up for safety, which makes sense (one can break, the other still works).

Bemo, Most of the compliance can be taken out by preloading the cables with a spring (don't know if the Roma car does this?). Easy way is with a small coil spring somewhere in the cable run, with spring preloaded in compression. A badly designed R&P, one that doesn't press the rack against the pinion (common), can have a lot of "backlash/freeplay", which is worse IMO than a bit of "springy" compliance.

Cable and pulley systems are also common in the "materials handling" industry. They are smooth (low friction), precise (no backlash), easy to build, cheap, etc... compared with the alternatives.

Note that in the Roma car the worst part of the design (IMO http://fsae.com/groupee_common/emoticons/icon_smile.gif ) is the sliding rack, which has significant stiction, bulk, and weight. This could be replaced by a half-pulley on a short vertical shaft, driving a "Pitman arm", which then connects to the steering arms. This would have less friction and weight, and would make variable ratio easier.

Note also that many FSAE cars now have a horizontal steering shaft going forward to a 90 degree bevel gearbox, then down to a floor level R&P. The R&P is redundant and can be replaced by a Pitman arm at the bottom of the vertical shaft from the bevel g'box (now with ratio ~ 3:1).

Z

[Dr Tron]

the problem with a pitman arm after a 90 degree is that you have alot of moving parts and motion right below the drivers legs.

As far as most planes I was under the impression that many (back in the day with large distances between controls and controlled) used hydraulics, and currently i thought it was mostly control by wire... as in electronic.

It is my firm belief that if wires were the way to steer automobiles then at least one car company or race team would use it, thats not to say "no one is doing it" is a reason not to do something.

for delft it was pretty much a rack and pinion with cables as opposed to geared teeth

i designed a rack and pinion for my team and it had no way of lashing adjustment which did lead to some slop however it was under 4 degrees and with the next generation lashing adjustment will been in place and its not overly complicated at all and i was able to manufacture most everything myself and i am by no means the best guy in the machine shop