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Old 02-26-2012, 12:29 AM   #381
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Default Re: Super Experiment... :&

Proud of you, A.

You were the first to make a gutsy move (buying parts yet to ever be produced), and you saw it through to a proper conclusion. This thing is off to a good start, and you deserve the credit for that.

Beginning at 1:25, it's on it's nose, and it shows the cam effect of all the scrub. I can't help but wonder if it would help to widen the axles a bit, and reduce the wheel offset.
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Old 02-26-2012, 08:22 AM   #382
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Proud of you, A.

You were the first to make a gutsy move (buying parts yet to ever be produced), and you saw it through to a proper conclusion. This thing is off to a good start, and you deserve the credit for that.

Beginning at 1:25, it's on it's nose, and it shows the cam effect of all the scrub. I can't help but wonder if it would help to widen the axles a bit, and reduce the wheel offset.
Hummm... looks like I have to do some research. I'm not sure what scrub and cam effect is.
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Old 02-26-2012, 08:31 AM   #383
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Hummm... looks like I have to do some research. I'm not sure what scrub and cam effect is.
Eric give us the complete run down on your observation
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Old 02-26-2012, 02:37 PM   #384
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Well from what I read, for our purpose we would want zero scrub since we primarily go slow and to get the most efficient steering. If I understand correctly, zero scrub would be when the center line of the tire (when viewed front he front) is inline with the pivot point of the knuckle. So if this is the case, every essentially every RC Crawler on the marked has slight degrees of positive scrub.

So for example, the stock EXTM with the long wideners, when you remove them and put a short stubby hex on it the scrub is reduced closer to zero giving you smoother more efficient steering and better stability.

I should be completely wrong but that's how I understand it.

So if you found a wheel and were able to get the clearance for a negative scrub that would make the rig less stable.

If I understand it correctly, slight positive scrub will increase stability but decrease steering efficiency. But too much positive scrub will decrease stability and greatly decrease steering efficiency.


Some one please clear this up for me if I'm off.
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Old 02-26-2012, 06:19 PM   #385
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Well from what I read, for our purpose we would want zero scrub since we primarily go slow and to get the most efficient steering. If I understand correctly, zero scrub would be when the center line of the tire (when viewed front he front) is inline with the pivot point of the knuckle. So if this is the case, every essentially every RC Crawler on the marked has slight degrees of positive scrub.

So for example, the stock EXTM with the long wideners, when you remove them and put a short stubby hex on it the scrub is reduced closer to zero giving you smoother more efficient steering and better stability.

I should be completely wrong but that's how I understand it.

So if you found a wheel and were able to get the clearance for a negative scrub that would make the rig less stable.

If I understand it correctly, slight positive scrub will increase stability but decrease steering efficiency. But too much positive scrub will decrease stability and greatly decrease steering efficiency.


Some one please clear this up for me if I'm off.

Pretty much how I understand it as well. At zero scrub the tire pivots in place, at positive or negative scrub, the tire actually rotates toward the front or rear of the vehicle in an arc (when viewed from above) which is where you lose efficiency; the tires are moving against the tread pattern.
If you look at the XR10 steering, the kingpin is on an angle, to theoretically line the pivot point up with the middle of the tire without having to have such an offset wheel.

The "Cam effect" is when due to the scrub the vehicle moves laterally (which is sometimes wanted, sometimes not.) So if you look at the video at the section E was referring to, when you turn the front wheels from full lock left going right, the whole crawler moves to it's left (toward down hill) which causes the need for a reverse to line back up.

A zero (or near zero) scrub set-up will fix that.
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Old 02-26-2012, 06:47 PM   #386
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Pretty much how I understand it as well. At zero scrub the tire pivots in place, at positive or negative scrub, the tire actually rotates toward the front or rear of the vehicle in an arc (when viewed from above) which is where you lose efficiency; the tires are moving against the tread pattern.
If you look at the XR10 steering, the kingpin is on an angle, to theoretically line the pivot point up with the middle of the tire without having to have such an offset wheel.

The "Cam effect" is when due to the scrub the vehicle moves laterally (which is sometimes wanted, sometimes not.) So if you look at the video at the section E was referring to, when you turn the front wheels from full lock left going right, the whole crawler moves to it's left (toward down hill) which causes the need for a reverse to line back up.

A zero (or near zero) scrub set-up will fix that.
Precisely.

It looked like the rig wanted to "side step" off the edge... and it looked like A had to be very gentle with steering to prevent that.

With the balance that precarious, that effect was perfectly illustrated by the vid.

What do you guys think? Should we look into mitigating all this?
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Old 02-26-2012, 08:05 PM   #387
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I've been working on a wheel design that would give us a zero scrub, I just didn't realize that's what it was called. The only down side to this is that we'll have to make custom axle tubes that are longer to compensate for an even narrow track width. I think I'm at the minimum track width before it start's hurting performance.

E you might be able to easily make the rim portion utilizing your lathe. I can get the hub and the front and rear plates.

I just didn't have a way to perfectly cut the groove to hold the bead. I was thinking about getting a small turn table to bolt on my drill press then with a cutting bit I could just spin the plate to cut my bead groove. That was just my thought.

The other upside to this would be the knuckle would be completely protected by the wheel. not that that's much of and issue.

I'm going to get some more wheel time then I'll decide for sure.
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Old 02-26-2012, 08:46 PM   #388
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I lost count of how many times I watched that vid... and I think you're right. The width seems to be perfect for the conditions you face (to this untrained eye). Setting the Ks into the wheels a bit might make a real difference in those off camber turns.

I just need a baseline, as I mentioned earlier. What is the rig at now?

Your camera man got some very useful shots. You can thank him for me... this was very informative.

Get on the wheel thing, guys. The shop stands ready to help. If we come up with a solid baseline width, and a couple options in hubs... we'll nail this down.

And, A... I agree. Run the wheels off that thing. Get a feel for what you like, and what you don't... get vid when you can, and we'll refine all this to fit your situation.

We are going to learn a lot soon... I could not be happier with the direction this is going.
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Old 02-27-2012, 07:32 AM   #389
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Okay, I'll add my 2 cents. With the 3.2's (2.375 Wide X 15MM offset) and the no offset hubs, the axle tubes are too short. I'm using the Axial high steer knuckles with shorter arms than the MT which give s it more turning radius. Even with this setup, the tires will hit the shocks and lower links. My scrub is almost 0. The only way that that this can be eliminated is longer tubes. If I go to a more offset hub, I will get more scrub. If I narrow the wheels, I will get more scrub. Maybe find a 17 MM with 0 offset and a longer hub would be the Money Way. I prefer not to go to the larger wheels without spending an arm and leg.
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Old 02-27-2012, 08:07 AM   #390
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Okay, I'll add my 2 cents. With the 3.2's (2.375 Wide X 15MM offset) and the no offset hubs, the axle tubes are too short. I'm using the Axial high steer knuckles with shorter arms than the MT which give s it more turning radius. Even with this setup, the tires will hit the shocks and lower links. My scrub is almost 0. The only way that that this can be eliminated is longer tubes. If I go to a more offset hub, I will get more scrub. If I narrow the wheels, I will get more scrub. Maybe find a 17 MM with 0 offset and a longer hub would be the Money Way. I prefer not to go to the larger wheels without spending an arm and leg.
Agreed. We are all at 250mm (outboard bearing face to face). At 1:54 it's obvious that there is no room for more width on A's rocks. Although upcoming K weights will settle things a bit, the inside wheels float more than once in the vid. The width seems right, so...

Although I can cut to any length, there is a big consideration here. The time spent to get to this point, multiplied by my shop rate, creates a number that, if stated out loud, would immediately cause a majority here to decide I was a liar... and a few to knod their heads knowingly. However...

We have +30mm waiting right here. No new dimensions, notes, parts, fixtures, or even thought. (2) long tubes.

We have 280mm on tap. Can we work with that? I sure as hell can.

D, did your rig seem more graceful when you cut the scrub? More precise?

M, if you want to start at 280mm, turn in your short parts. I'll replace them, n/c, and cut them into 2.2 parts.

Last edited by ekd; 02-27-2012 at 08:23 AM.
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Old 02-27-2012, 05:18 PM   #391
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Agreed. We are all at 250mm (outboard bearing face to face). At 1:54 it's obvious that there is no room for more width on A's rocks. Although upcoming K weights will settle things a bit, the inside wheels float more than once in the vid. The width seems right, so...

Although I can cut to any length, there is a big consideration here. The time spent to get to this point, multiplied by my shop rate, creates a number that, if stated out loud, would immediately cause a majority here to decide I was a liar... and a few to knod their heads knowingly. However...

We have +30mm waiting right here. No new dimensions, notes, parts, fixtures, or even thought. (2) long tubes.

We have 280mm on tap. Can we work with that? I sure as hell can.

D, did your rig seem more graceful when you cut the scrub? More precise?

M, if you want to start at 280mm, turn in your short parts. I'll replace them, n/c, and cut them into 2.2 parts.
At this point ,I would like to play around with it some more. Gracefullness is one of a kind. It's all in the way you drive. I don't have the speed that "a" has so I'm always graceful. Do seem to have some push, but that will go away in time when I install another ESC.
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Old 02-27-2012, 08:05 PM   #392
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I was referring mostly to very low speed manners. The stockers flop around a lot in situations like seen on the vid.

You went from a lot of scrub to near zero, and if you didn't see any drastic changes (especially bad ones), I feel good about cutting up the parts I have been saving until we got the good look we just had.
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Old 02-27-2012, 09:28 PM   #393
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So had an interesting thought, once this season is over I'm going to finalize my gear box design. And work up some numbers for a proper width of these axles.

Plus my laser cutter should be cutting aluminum by then for a proper cut gear box.

I should have enough wheel time by then to know exactly what needs to be adjusted.

Right now all I can really see is the width so I can fix the scrub.

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Old 02-27-2012, 09:46 PM   #394
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How wide is that rig?
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Old 02-28-2012, 06:10 PM   #395
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it's 13.5 inches to the outside of each tire with about 1 inch of positive scrub.

I've got and issue with the long tube idea, let me ponder it and I'll respond shortly with a diagram. That will be the easiest way to explain.
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Old 02-29-2012, 11:34 AM   #396
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it's 13.5 inches to the outside of each tire with about 1 inch of positive scrub.

I've got and issue with the long tube idea, let me ponder it and I'll respond shortly with a diagram. That will be the easiest way to explain.
30mm = 1.2"... pretty close!

Looking forward to your thoughts.
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Old 03-04-2012, 08:42 PM   #397
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Default Re: Super Experiment... :&

Here's the base issue, It will require some unique bent links or deferent link mounts altogether. I know you're thinking, just move the mount to the outer side, but then the wheel won't turn much past 45 degrees...

Here's a quick illistration.
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Old 03-04-2012, 09:41 PM   #398
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Are we talking about extending 15mm on each side to get the +30mm or just extending the short side?

I think that the links I am making (even though they are BEEFY) will still clear the motors with full triangulation at the chassis side with just using bent rod ends all while providing awesome steering angles.
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Old 03-04-2012, 09:47 PM   #399
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We were talking about slaping on a long tube on the short side. That would be quick and easy but not the best way to acomplish this.

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Old 03-05-2012, 04:45 AM   #400
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Here's the base issue, It will require some unique bent links or deferent link mounts altogether. I know you're thinking, just move the mount to the outer side, but then the wheel won't turn much past 45 degrees...

Here's a quick illistration.
Quote:
Originally Posted by monkeyracer View Post
I think that the links I am making (even though they are BEEFY) will still clear the motors with full triangulation at the chassis side with just using bent rod ends all while providing awesome steering angles.
Let me know what dimensions will work with 2D bends. It seems to me, though, that we'll all eventually have to go M's route, and use 3D links (or maybe long mounts?) to get those last degrees. It's where #3 is headed.

Can't wait to see M/M #2.
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