I built a Pro10 car...

Melbatoast · October 30, 2009, 11:38:00 PM

Well, it's in progress anyway. Despite ther being good reasons to not get a link car, I bought John's CRC and got the 3-link rear end setup, which arrived today. It's very trick, easy to install, and should work well. The nerf wings are for a wide car, but obviously could be trimmed to 200 if necessary (or just order 200mm wings). Protoform 905 body fits over the shock towers with room to spare.

The kit was something like $100US, and seems not too unreasonable considering you get the nerf wings, a new pod bottom plate and right side bulkhead, shocks, links and everything else you need to bolt it on. The only issue I have is droop control, because there is a lot of droop and no way to limit it. I'm going to email Stranahan about it, but it would be pretty easy to figure out how to set up a system like on a touring car.

I think the new CRC 12th scale shocks would work too, although I'm okay with the Associated parts on it now.

Still gonna hold off on electronics, hopefully I'll get one of the Black Diamond ESCs if/when they're available. I'm also not going to do the damped, A-arm front end, because it's not as elegant as the rear end, and I do believe ROAR mandates a kingpin front end for WGT, if that's the direction the class goes.

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Tom · October 31, 2009, 12:12:45 AM

Droop is a very different thing on a pan car than a touring car. You're probably concerned about nothing.

Melbatoast · October 31, 2009, 10:59:02 AM

You're right, he says he leaves it a max droop. If I want to reduce it, just use internal shock limiters.

haddow · November 02, 2009, 04:57:01 AM

looks like you could still limit droop by shortening the the extened length of the two side shocks and then setting a flat ride height with pre-load? Droop in a 12th scale carpet car (angle of rear pod unloaded compared to main chassis plate) is an importnat consideration so if it is a significant amount then maybe its worth figuring out?

jody

Melbatoast · November 02, 2009, 09:17:12 AM

Thanks - I fixed it last night, using internal travel limiters made from spare ball cups with the ball cut off. It's got about a chassis plate's thickness worth now, which seems like a good place to start.

jarrodH · November 03, 2009, 01:27:31 AM

in that first picture, what about movin the side links above the carbon fiber plate, to where the spacer is, and put the spacer below..

those links have a huge angle on them.. would think that havin them flat would be better. but the angle might help plant the rear on acceleration..

Shawn68z · November 03, 2009, 01:01:52 PM

Quote from: jarrodH on November 03, 2009, 01:27:31 AM
in that first picture, what about movin the side links above the carbon fiber plate, to where the spacer is, and put the spacer below..

those links have a huge angle on them.. would think that havin them flat would be better. but the angle might help plant the rear on acceleration..

Jarrod: by having the forward part of the link up higher then the rear part gives you a bit of rear steer. I found it allows the car to turn alot smaller of a radius on a tight track without the car pushing mid-corner.

Shawn.

Melbatoast · December 13, 2009, 03:34:21 PM

Progress resumes.

I tried to rig up a normal A-arm front end for outdoors using ball links and turnbuckles and stock upper arms, but it looked super trashy, and mounting shocks was very difficult without hacking up the car.

A while ago Stranahan built a front end using Losi Mini-T parts, which looked really sexy but he says was too weak. Inspired by that, I've used Associated TC3 lower arms (Shaver has tons of spares), and B4/T4/SC10 knuckles, caster blocks and axles (same diameter as standard pan car bearings). A standup servo mount is used for the shock and camber link - I think it will have to be raised a fair amount to get a better angle on the shock, but that's just a detail. The whole deal has to come up off he chassis plate about 5mm for decent ride height.

I think I can use Mini-T pivot blocks out of the box and get the proper track width, which will make aligning everything a lot easier. As it's mocked up now the track and wheelbase are identical to a normal wide CRC pan car. And, it would take about 5 minutes to go back to the stock front end, there will be no change to the plate except drilling holes for the pivot blocks.

This thing will be fun.

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Melbatoast · December 13, 2009, 11:08:05 PM

Well, I was inspired and finished it off. Getting the pivot blocks aligned was a bitch and despite measuring 3 dozen times one of the holes I drilled was still off somehow. Managed to get the arms aligned with some creative trimming and spacer-ing, so it's OK. Mini-T blocks were no good, by the way, so I used TC3 parts, split in the middle to narrow them.

I'll have to run numbers through the roll center and camber gain calculator but it looks OK to me at least, and it's all aligned.

With the shocks layed down that far I need far heavier springs on there - CRC shock springs are the right diameter and should be OK with a couple coils cut off.

I'll bring it along next weekend for some constructive criticism.

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haddow · December 14, 2009, 04:41:39 AM

how much caster does that setup have?

When you move the front end through its suspension travel what is the camber gain/loss it looks as though it could have big camber differences at the bottom and top of the suspension travel.

Looks cool though and as you know its fun making modifications. I will say that other than the small bearings, the new CRC stock front ends is really good as is.

Tom · December 14, 2009, 09:46:47 AM

Good point about the caster adjustment, as well as the reactive caster aspect.

It does look like it has in the ballpark of the correct camber gain looking at the geometry.

As you mentioned though, what about roll center?

Melbatoast · December 14, 2009, 02:38:24 PM

I eyeballed the camber gain again and it looked to be way too much, compared to the Pro Strut setup. So, I lengthened the upper arm by moving the attachment to the outer hole on the caster block and it's very close by eye, now, which is to say not much. I also increased the height of the shock tower by a couple of mm, making it the upper arm closer to parallel with the lower.

I have to figure out the calculator because the numbers I'm plugging in don't make sense, although the model looks fine. I guess I could measure it easily enough.

There's very little caster with the blocks I have in, I'll have to adjust it using different blocks. I don't remember if I have 22 or 25 degree SC10 blocks. I believe 22 would mean 0*, 25 means 3*, as I think the SC10 is 22* static with the big front kickup. I don't know how much I'll need, I would guess 3* is a good start. There are 30* blocks, too, which would match the stock front end static caster, 5*. There shouldn't be any reactive caster with this setup.

Obviously still a work in progress and I'll have no idea how it works till I drive it, but still fun.

Melbatoast · December 14, 2009, 04:47:53 PM

Figured out the calculator. I have to raise the mounting point for the upper arm by about 7-8mm but it's otherwise OK. With the arm raised, assuming I measured correctly:

Roll center is -11.5mm.

Camber gain is 0.5* for 5* of arm travel.

Melbatoast · December 18, 2009, 01:30:06 AM

I must be on holidays...

Major revision as far as components go, if not concept. The way I had to make the lower arm pivots on v1.00 was really ugly, and not at all stable - hacked up TC3 pivots.

So, I was able to use an Associated B4 pivot block and TC5 arms, which makes for a perfectly positive and strong mount. I had to grind on the stub axles a fair amount to get them to seat further into the steering knuckles, but that had the great benefit of improving the scrub radius a bunch.

I changed the shock tower to something that allows the shocks to mount a little more vertically, which helps a lot, too. I think it was getting into regressive spring rate the other way.

I haven't put it through the model yet but I think it's improved in camber gain and hopefully stays about the same as far as roll center goes. I don't think a foam tire needs much gain, probably .15/5* is what I'm after.

Melbatoast · December 20, 2009, 12:33:25 PM

The car is pretty much ready to test, most of the loose ends are tied up. Just waiting on the electronics.

It uses almost 100% Associated parts:

-TC5 arms

-B4/T4 pivot block

-TC3 hinge pins (block and arms sleeved to 1/8")

-B4/T4 knuckles, caster blocks and stub axles

-RC18R shocks

-CRC angled servo mounts from a 3.2 Carpet knife, for the shock towers

Here's a picture of the model, using tires trued to 61mm. The roll center is very low, which I'll counteract with stiff springs. That should make the tire stick - a long of roll lever should shove the outside tire into the ground. That's my theory, anyway.

I'm still not sure about the camber gain, I think that's too much for a foam tire. An easy change. And if it doesn't work at all, the stock sliding kingpin setup just bolts right back on.

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