Steering Gearbox

[Mehul Botadra]

Hi,

I've been through innumerous FSAE posts regarding the usage of universal joints for the steering column. Now the primary problem we are facing is that the rack is way behind the front axle line, almost close to the front roll hoop. The rack is 10cm away from the front roll hoop. Mounting the rack above is not an option because of packaging issues. The maximum angle that I could come up with was 66 degrees. That angle is unacceptable for a universal joint. I thought of using a Constant Velocity joint because that allows a larger degree of power transmission. Bevel gears was also an option but I've read a lot about gears skipping at high forces. Also supporting the vertical shaft was a problem.

I've read a lot of people using 90 degree steering gearbox. It'd be great to have a better insight into it as to how you'll do it. Thanks!

[RollingCamel]

There was a thread before about it and someone was complaining that the gears weren't rigid enough and may skip, or something like that.

What about double UJ? Could give you 70 degrees.

[Mehul Botadra]

Exactly. I tried that too. Doesnt give me the required angles since the shaft becomes too small to be attached to the Universal Joint.

[oz_olly]

Just use something like this:

http://www.tea.net.au/welcome.aspx?page=12

We have used a very similar product when we had a rear mounted rack. Down side large mass high above ground level but what does that matter http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[The_Man]

If you can't really change anything else. Go for a double Universal Joints. It is always a good idea to have 2 Universal joints for uniform steering response.

33 deg per joint is not the best but I have seen bigger angle joints function in the past. The old 118 NE had such a double Universal Joint in its steering, you can use that it worked out to be the perfect size for us.


Originally posted by Mehul Botadra:
Exactly. I tried that too. Doesnt give me the required angles since the shaft becomes too small to be attached to the Universal Joint.

What is the required angle you are looking for?

[Mehul Botadra]

Around 31 degrees. That is the maximum considering manufacturing errors for those apex joints. They give really good response and transmission.

[RollingCamel]

Didn't you say that you need 66 degrees?

[Mehul Botadra]

I said I got 66 degrees. It need it to be lesser. I got 31 degrees on one U.V. I need it close to 31 on the other one as well.

[BillCobb]

Does FSAE require a solid connection for steering control? (I forget). If not, consider "steer by hose" (2 small hydraulic motors). I'd actually recommend brake pipe instead of hose, but you get the idea, I hope...

[Mehul Botadra]

Thats a little hard to comprehend!

[The_Man]

Originally posted by BillCobb:
Does FSAE require a solid connection for steering control? (I forget). If not, consider "steer by hose" (2 small hydraulic motors). I'd actually recommend brake pipe instead of hose, but you get the idea, I hope...

Steer-by-hose! Is there anywhere this has been implemented? Personally hydraulic coupling for the steering is not very appealing.

@Mehul: Surely you can tweak out 4deg more for the steering. If you are just looking for alternatives a bevel gear might be the way to go. A professor of ours told us that it was not a good idea because bevels are very prone to backlash which can grow over time. The ones that are suitable will be very expensive and not to size so you'll have to make your own in which case it is difficult to make them accurately enough.

[Mehul Botadra]

My primary idea was to use bevel gears at such steep angles. The problem there was wearing out obviously, even hardening doesnt help. There is a tendency that the gear might just skip because of heavy turning like most of our inexperienced drivers would do. So bevel gears is out of the question. Besides a housing would be required to support the vertical shaft and would cause major template problems!

[BillCobb]

Steer by hose has been in use in quite a few applications. Open your mind up a notch or two. Even my John Deere rear steer lawn mower uses a hydraulic rack fitment. Or maybe you were thinking reins and a bit and bridle (Rope steer, anyone?). Do you need a picture? A motor on the column and a motor and the rack pinion. Do the plumbing. A really clever design would use a motor on each knuckle and avoid the nuisance of tierods, lash suppressors, cv joints, rod ends and angle stipulations. Did I mention that nuisance steering column and brackets, leg movement freedom and complete tilt and telescope steering wheel placement? Ratio the motor/pump displacements according to your overall steering ratio needs.

Don't like the taste of hydraulic fluid? Steer by wire baby. Guess what: The plane you fly over here on is already using it. Must not be safe if they use it on airplanes. Very few survivors to sue.

I hope you realize that your car's brakes are stop by hose (or are you still using that 2x4 on the tire treads)...

[Mehul Botadra]

Steer by wire not allowed in FSAE! That would solve almost every problem in Earth! Hydraulic motor, I'm a bit doubtful. Anyway I'll perform a feasibility test! Thanks!

[BillCobb]

Do a search on eBay for "outboard hydraulic steering". There are several flavors of a steering wheel motor and a slave rack for use in controlling outboard motors in boats. One hose. You would need a relay rod to tie both knuckles toether. Manual steering.

[Nick Renold]

Steer by wire is allowed, "steer-by-wire" is not allowed.

Electronic steering systems are not allowed, but mechanical ones are. If you really wanted to go through with an innovative solution for your steering, I would recommend contacting the rules committee.

[Tom W]

The solar car team at UNSW in their car previous to the current one had steer by rope. then again there aren't many corners on their route through the country. The rules got changed for their most recent car that they had to use a steering wheel.

[RollingCamel]

What about worm drive?

Skipping wouldn't be a problem but more friction might be a problem if not in operation but in steering feel.

[Mehul Botadra]

Worm drive will not give me linear motion and it will have to be translated. Obviously the friction is another factor that affects it thoroughly.

[RollingCamel]

Linear motion?? You lost me there..

Yes it has some translation but depending on its size maybe the eccentricity can be dealt with.

[Mehul Botadra]

Linear motion of the rack.

[RollingCamel]

Rack?

Weren't we talking about replacing steering column universal joint?

[Shashi]

Why don't you try moving the rack fore of the front axle and reduce those angles?

[Mehul Botadra]

@ Rolling Camel
Yes, we're replacing that to transmit the power from steering wheel to the rack. The rack has to move linearly to move the tire at the steering arm.

@ Shashi
Screws up the geometry. Besides larger steering arm allows us to apply more force. Yes its a compromise, but then we have to check for suspension bump steer as well.

[Mikey Antonakakis]

You could always try what we did last year... top-mounted rack with steering rockers. We needed better mounts on the rockers, and stronger rockers, and the geometry wasn't exactly designed into the system, but on the race track I thought it worked just fine. Certainly better than having two u-joints to have to constrain laterally. Give it some thought.

[Mehul Botadra]

And you'll didnt face any template issues because of rack on top?

Rack on top has a major disadvantage of force transfer from the ground to the steering since it is closer to the UBJ, which might not give the driver enough feel to turn the wheel. Nice suggestion though!

[RollingCamel]

Originally posted by Mehul Botadra:
@ Rolling Camel
Yes, we're replacing that to transmit the power from steering wheel to the rack. The rack has to move linearly to move the tire at the steering arm.

I don't care about the rack and pinion. You want to transfer rotary motion from you steering wheel to your column either by UV, bevel gears or worm drive.

[Mehul Botadra]

Exactly, you have convert rotational motion into translational motion.

[RollingCamel]

By, translation you mean that the either the steering column or the steering wheel is not in plane with the chassis mid-plane. So either the rack and pinions' pinion or the steering wheel off plane.

If you are going with custom r&p then you're problem seems to be solved. Woodward and companies can manufacture it for you. If the distance between the worm and worm wheel centers isn't that huge then you could adjust the driver position to accommodate it.

That is if you want 90 degrees angle.

Other problems in this idea is reduction ratio....

There is more problems than solution...

[Mehul Botadra]

Nope. You're not understanding. See the steering wheel moves in rotation. The rack will move in translation. You have to connect the two motions. Get it?

[RollingCamel]

Whats the pinion gear for then?

I'll recheck your posts because I'm certainly missing something. You are not running a typical configuration?

Steering wheel>Steering wheel shaft>UV>Steering column> R&P.

[RollingCamel]

You want to use steering gearbox with linkage in order to to put the gearbox forward and decrease the angles? Why add complexity and more compliance?

For Apex double UJ the max is 35 deg per joint so it just might work. If you are worrying that UJ's variable speed especially at its limit, then you might want to settle for a compromise.

[Mehul Botadra]

Perfect. Thats the typical combo we're running. What is the motion of the rack like? What kind?

[RollingCamel]

The rack it self moves linearly/translatory or right and left to put it simply.

[Mehul Botadra]

Exactly. So arent you converting rotation to translational motion?

[RollingCamel]

Yes, using a pinion.

[Mehul Botadra]

Bingo!

[Finisher]

Hi Guys
I read before that you use an APEX-UJ...right? If so would you tell me where you ordered the component. Most resellers here have price minimum limit of at least 500$...

Many Thanks
Sven

Steering&Chassis
Highoctane Motorsports Erlangen/Germany

[RollingCamel]

Pegasus Auto Racing

[Finisher]

THX

Steering&Chassis
Highoctane Motorsports Erlangen/Germany

[Wesley]

An interesting graph:

h t t p ://e n .wikipedia.org/wiki/File:UJoint2.png <- for a single U-Joint

If you run two, you can achieve constant velocity, but you MUST phase the two by 90º or it will be an additive vs subtractive effect.

[Mehul Botadra]

Yup! Thanks!

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