variable rack and pinion

[josh2417]

Hi,
This is my first post in this forum. We are building our fsae car for the first time. one of my friends suggests we use a variable rack and pinion instead of the fixed ratio. We fixed the ratio as 6:1 for the fixed ratio rack.While the idea sounds good, i couldnt find many teams running this setup. Am i missing some important factor here? Any help will be helpful
Thanks in advance. Cheers.

[josh2417]

Hi,
This is my first post in this forum. We are building our fsae car for the first time. one of my friends suggests we use a variable rack and pinion instead of the fixed ratio. We fixed the ratio as 6:1 for the fixed ratio rack.While the idea sounds good, i couldnt find many teams running this setup. Am i missing some important factor here? Any help will be helpful
Thanks in advance. Cheers.

[Zac]

I might be wrong here, but I don't think there are many suitable variable ratio steering boxes available on the market that would be a good fit for these cars, which is likely why you don't see many teams running them.

But if you really want to play around with variable ratios, you might want to look at the stuff connected to the steering rack.

[BMH]

I had actually been looking at trying to utilize a variable rack and pinion setup, but ultimately decided to just put it on hold. I was unable to really find any for our application, so you would need to have your own rack cut to be able to have a lightweight, simple variable ratio steering rack.

[dazz]

Depending on your setup, you could design a 'variable ratio rack' if you use two universal (cardan) joints.

Remember, they are NOT constant velocity...

How far do you turn your steering wheel from lock to lock? +/- 90 degrees?

[Joji]

why dont you consider going for a variable steering arm?
you can still change the ratio. It is a cheaper solution. Or is there any other thing that you need from variable rack?

In addition you can consider steering quickeners..

[josh2417]

Guys thanks for your advice. Coming to the point. We simply plan to have the ratio as 6:1 in the middle of the rack.Towards the ends have something around 8:1. But towards the end, no of turns will increase. Is this compromise justified? All this due to the luxury that a steering system manufacturer is willing to help us out with the machining. My major doubt has been that, we are simply making things complicated.

[josh2417]

dazz
about 30 to -30 with ackerman. floor mounted rack. connecting behind the upright. we probably might have to use two cardan joints since we are using floor mountings.

joji
i think varying the steering arm is a good option, but read somewhere that it reduces the road feel. About steering quickeners, will give it thought surely.
cheers

[Price]

There was a team at FS Germany this year that had a pretty sexy looking adjustable ratio rack. Or at least, to me it looks like it would be fairly easy to change the ratio to a different one.

http : // media. formulastudent. de/FSG11/Hockenheim2011/20110805Friday/18383248_VpSqWk#1428589543_r9fcDZP-L-LB

[josh2417]

price

thanks man. But the link is not active i guess. pls do re post it. Thanks in advance.

[wagemd]

I dont want to sound like a downer, but can you justify the extra weight and complexity? Will it make your car faster?

Since you building your first car, I would suggest spending you time getting familiar with suspension kinematics and basic vehicle dynamics. You will see an infinitely improved return on time investment.

While variable ratio steering might be nice while parking your BMW, it *probably* wont make your car any faster.

For your first car, keep it simple, and in the following years, make it simpler. Finish endurance and go from there.

[josh2417]

wageman

True man. But we just thought bring about a few innovations just to score more points with the judges. We also plan on using an adjustable pedal assembly because our drivers vary from about 6'3" to 5'6".

Frankly are we trying too hard???

[NickFavazzo]

Adjustable pedal box is great, you need to accommodate a huge range of people, not just your drivers (what if a judge sits in the car).

Why not test a few ratios on track and go from there, it is much better to have more track time than fancy parts, if your car can finish enduro well, then that is a great start, you will score decent for finishing dynamic events.

[Mehul Botadra]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NickFavazzo:
Adjustable pedal box is great, you need to accommodate a huge range of people, not just your drivers (what if a judge sits in the car).

Why not test a few ratios on track and go from there, it is much better to have more track time than fancy parts, if your car can finish enduro well, then that is a great start, you will score decent for finishing dynamic events. </div></BLOCKQUOTE>

+1!

Adjustable steering toe on uprights is definitely a better option!

[exFSAE]

"Innovations" ... aka random fancy crap that doesn't have much of a purpose, will not impress the judges. Wouldn't impress me either! Legitimate engineering work will.

You can have a dick-a-thon messing around with a variable rate steering system which will probably net you little or no benefit and just add complexity.

Or, you can get some fundamentals down.. which probably 90% of FSAE teams don't do.

[wagemd]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:
wageman

True man. But we just thought bring about a few innovations just to score more points with the judges. We also plan on using an adjustable pedal assembly because our drivers vary from about 6'3" to 5'6".

Frankly are we trying too hard??? </div></BLOCKQUOTE>

Driver variability is a design problem that does exist, and an adjustable pedal tray is a reasonable solution. If you don't have a big problem that the rack is a solution to, the judges will probably be more likely to penalize you. What they really want to see is that you justified the system.

Being innovative is not a bad thing, and I will go out on a limb and say that it would be difficult to truly "try to hard" on a formula project, but I think your time would be much better spent in other areas...

I'm not even saying don't do the rack, but make sure you have a real reason to do it and that you can convince the judges the weight, cost, complexity downside is worth it (hint: points).

From my formula experience, first year teams are almost always <STRIKE>extremely</STRIKE> extraordinarily heavy. I think the judges would be far more impressed by a 450lb first year car than a 750lb one with lots of gizmos.

[Sormaz]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by wagemd:
Being innovative is not a bad thing, and I will go out on a limb and say that it would be difficult to truly "try to hard" on a formula project, </div></BLOCKQUOTE>

I have to disagree. One must know the difference between "trying hard" and "working hard"

[wagemd]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Sormaz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by wagemd:
Being innovative is not a bad thing, and I will go out on a limb and say that it would be difficult to truly "try to hard" on a formula project, </div></BLOCKQUOTE>

I have to disagree. One must know the difference between "trying hard" and "working hard" </div></BLOCKQUOTE>

I guess that's what I was trying to convey by "truly", but I'll agree to that...

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:
wageman

True man. But we just thought bring about a few innovations just to score more points with the judges. </div></BLOCKQUOTE>

Variable steering is not an innovation, it has been done since the advent of steered vehicles.

If you want to stand out from other teams in design, I recommend that you actually learn how to justify design decisions with real data and follow a process to implement these decisions. Such activity would easily put you in the top 10 teams in any event.

[josh2417]

We figured we ll run a few ratios before determining what is best for the car. As for the trying hard part, i just meant to say that we are just too excited and dream to get the best car possible( sure everyone who does it for the first time will testify).

As for the changing the toe on the uprights. We just wan to make sure its simple this time. We plan to use shims outboard. Then finalize the values and get the uprights for the competition. As Pat Clarke has pointed out we dont want to see broken rod ens!!!

Thanks guys for your help.Really appreciate it.

[Adambomb]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
If you want to stand out from other teams in design, I recommend that you actually learn how to justify design decisions with real data and follow a process to implement these decisions. Such activity would easily put you in the top 10 teams in any event. </div></BLOCKQUOTE>

+1

A common thread for people starting out with FSAE is to try to come up with some random doo-dad to "stand out" with the judges, which usually manifests itself as a solution to a problem that either doesn't exist at all or is very poorly defined at best. It's hard enough to get a bare-bones car "just right." Focus on the fundamentals, if you manage to get them 75% right you're pretty much guaranteed top 10.