I have a complete Aim setup (Evo4S, GS-Dash, Smartycam HD, brake pressure sensor, and throttle position sensor). I made my own steering angle sensor using a 2K potentiometer, appropriately-sized pulleys, using the string concept with a second pullet wheel connected to a pair of badge lanyards serving as the retraction mechanism, which worked well for a few months, but then the retraction mechanism failed, plus it was a nightmare getting the string wrapped around the shaft while simultaneously holding the pot's shaft at the center of the pot's range while applying preload from the retraction mechanism. I felt like I needed an army of a half dozen miniature people to get everything synced up, but by some miracle, I got it reasonably close, only to have the thing fail.

Aim sells a pulley-type steering sensor for about $140, so I'm kicking myself for not going this route in the first place, but since I have the mounting bracket built (probably have 20 hours invested in that thing), and with the potentiometer mounted on it, it theoretically should be pretty simple to attach a small toothed pulley to the shaft of the pot, and (this is the part that has me stumped) a larger diameter toothed pulley around the steering shaft. I've already cut the patch cable, so I'd have to buy a new one if I went with the pre-made Aim SAS, which is another reason to just take what I've already built and modify it to use pulleys and a belt instead of the string approach.

With that long-winded intro, my questions are simply,

1. Where would I find a toothed pulley that would fit around my 17 mm diameter steering shaft?
2. If I found such a thing, how would I fit it around the shaft (this question applies if I purchased the AiM SAS as well)? Does the shaft come apart at the U-joint's fork? Or is there such a thing as a split pulley that comes apart in two halves?

Thanks in advance.

 

 

Thanks, Peter, it's good to know that split pulleys are available. However, the Aim kit says its pulley is designed for a shaft with a 7/8" (or 22mm) diameter. So I'd have to find a split bearing with an i.d. of 17mm, and an o.d. of 22 mm. Seems like a tall order... I know Van Svenson has built his own SAS for his 944 race car using a pair of pulleys, so it's clearly possible, and I've reached out to him, but haven't heard back yet (only been a few hours, though).

 

A note on what I think I understood from your current setup - you don't need to have it centered at assembly (unless it's a rotary problem). You can take care of the voltage range in the calibration.

It's been a looooonnnnnggggg time since I've used the pulley setups, but I never really like them. I always found them to skip a bit once in a while then be off until they were re-calibrated. I went to using string pots on the shaft (really easy) or linear sensors on the rack.

 

Thanks, Matt - you are correct - it isn't necessary to have the pot exactly centered at assembly. Aim walked me through the calibration procedure to center the voltage within the range.

Interesting comment on the pulley approach. I have no problem sticking with the string approach. I built something similar to what's shown in this video:


except I used two pulleys on the pot's shaft - one for the retracting reel's string, and one for the string that's wrapped around the steering shaft. Also, mine is mounted on a fairly elaborate mounting bracket which is attached to two unused threaded holes in my cross member. It took a lot of trial-and-failure to get this bracket configured so that it was "aiming" the pulleys pretty squarely at the steering shaft. I didn't see any other place to mount the bracket.

My main concern with sticking with the string approach is the uncertainly of exactly what type of retracting reel would hold up under this application. This one looks pretty good, and has gotten great reviews:


But I wonder if it has a little bit too much force, since all it has to do is provide enough return force to prevent the string from going slack when turning the wheel in the opposite direction from which it is wound around the shaft. Also, for this application, the retracting reel is always extended, because it always has to exert some return force on the shaft of the pot via the pulley to prevent the string going to the steering shaft from going slack. I'm not sure if commercially available retracting reels are designed to always be under tension. I must be the only person in the history of the world who has ever built anything like this, so I have to use my judgement on a lot of aspects of it.

Then there's the mounting. The thing that makes it challenging is because the rotation of the pot starts in the center of its range (when the wheel is pointed straight ahead), there has to be "preload" on both pulleys to allow the shaft to turn in either direction without breaking the string (ask me how I figured that out...). So I have to pull the string out of the reel and wind it around its pulley a couple of times, and do the same thing with the string that winds around the steering shaft that's attached to the other pulley at its other end. And I have to make sure I wind the strings in the right direction so that the retracting reel applies force to the pot's shaft in the correct direction, depending one which direction I wind it around the shaft (ask me how I discovered THAT). I need to figure out a way to temporarily hold the pulley that the reel's string is wrapped around until I get the string wrapped around the shaft...

Anyway, sorry about the long email, but as you can see, I've bought myself a lot of frustration because I was too cheap to shell out the $255 for a SAS from Aim (plus I thought it would be relatively simple to make one, and that is actually a pretty stiff price for something that is pretty simple in principle). I feel like a walking billboard for this t-shirt:

https://www.walmart.com/ip/I-TRIED-IT-AT-HOME-science-project-funny-Cotton-Unisex-T-Shirt/575555877?wmlspartner=wlpa&selectedSellerId=2115&adid=222222222271216437 54&wl0=&wl1=g&wl2=c&wl3=235338088219&wl4=pla-387619936965&wl5=9028308&wl6=&wl7=&wl8=&wl9=pla&wl10=115781661&wl11=onli ne&wl12=575555877&wl13=&veh=sem&gclid=Cj0KCQiArenfBRCoARIsAFc1FqdzM99xJV TLoavXJVd6dg0wdunILYXkdW7mP9tdPOeGnjTRfMCiGYgaAkZmEALw_wcB

Thanks for any inputs you or anyone else here may have. In particular, a recommendation as to a retracting reel to buy would be extremely helpful.

 

Here's a shot of mine using the AiM 10" string pot. Same idea as yours, but the "bought" solution. I've tried lots of rigged up setups over the years, but I've found it's better to pay up front than have the frustration of failure with the time and expense it takes to get to the track. When I said string pot, I never thought of making up my own. No reason it wouldn't work, but would take a lot more fab than this.

You've got some stick-to-it-ness though!

 

Hi Matt,

Not seeing a picture. I've had problems posting pictures on Rennlist lately, so maybe there's something going on with the site.

Yeah, I'm in one of those situations where I have so much time, and a modest amount of money, invested in this project that I don't want to bail now and have all that time and effort go down the drain. If I could turn back the clock, I would probably just buy the Aim SAS, but it's kind of too late now.

I thought of a way I could hold the retracting reel in place with the pot at the midpoint of its travel, which will allow me to wrap the string around the shaft and attach it firmly to the other pulley (after wrapping it around the pulley a couple of times), without having to simultaneously hold everything together with my teeth (kidding...). Sometimes it helps to just talk these things out. I'll order that heavy-duty retracting reel tonight, so I should have it in a couple of days. Wish me luck!

 

I'll try again.

 

Thanks - ah, the luxury of not having to mess with two pulleys. Also, I didn't see an obvious spot where I could mount mine, so I had to build a pretty elaborate bracket, but I would have had to do that even with a "store-bought" SAS. I'll try to post a picture of my setup when I get home, but as I said, I haven't had any success posting pictures on this site lately for some reason.

 

 

I used this string type - it cost about $100 shipped from China and it is very good quality.

 

Here are some pictures of the SAS I built:

Edit: Sorry, I've lost my ability to post pictures on this site for some reason. I deleted a bunch of my previous images, thinking that maybe the problem was that I exceeded my capacity, but no luck. Very frustrating. Oh, well...