Build Thread The most interesting Team Associated SC10 in the world

[Spksh]

I literally holyshit SAID, “I’m not the only one!?!”.. I fully appreciate your methods sir. Back 20+ years ago, when press-parts carbs would develop tune sabotaging air leaks, I layed down the sealant the exact same way as you illustrated above.

I had to chuckle at the pimp-o-licious, overachiever, wheel reinventing that was your servo mount plight.. I’m guilty of the same shenanigans, and with a damned steering servo as well-no less..

Making sure that the next crazy person who's rebuilding this in 20 years gives me the nod of appreciation when they see the details.

 

[Spksh]

I’m stuck in Dallas and missing my baby

 

[Beer_Goggles_RC]

incredible thread, just got around to going through the whole thing. can't wait to see it finished

 

[Spksh]

incredible thread, just got around to going through the whole thing. can't wait to see it finished

Thank you! I love discovering all the weird workarounds and fixes the previous owners did to keep their baby going.

 

[Spksh]

I’m jet lagged to heck, so I printed labels and reorganised my hardware in a slightly different way.

 

[CertifiedMike]

I’m jet lagged to heck, so I printed labels and reorganised my hardware in a slightly different way.
View attachment 259192

Makes my OCD happy!

 

[Spksh]

OK, I've been thinking about this for a week and it's still eating me. I'm just not happy with the stock servo mounts. Let's talk about why.

First, these little guys are soft, and a couple holes are stripped out, but that's curable with thread lock. My biggest problem is with the geometry. If you've got one of these, you'll know that it's injection molded and the holes for the screws are all aligned - their centers are all on the same plane.

This is the front elevation for a standard servo. Pay attention to the measurement between the centers of the mounting holes. That's 50.5mm, and it's the same across all servos I've had my hands on.

Now this is the top-down look at the mounting holes in the SC10 chassis. This would be in some kind of weird imperial/SAE nonsense fractional inch measurement on the original plans, but 47mm is what I measure with my calipers. You'll notice that 47mm is not 50.5 mm.

So what gives? If the mounting brackets have their chassis mounting holes in the same plane as the servo mounting holes, how does 47mm end up equaling 50.5mm?

Well, we cheat - the #4-40 screw major diameter is slightly less than the diameter of the mounting holes in the servo ears. That means the screws don't have to line up with centers of the mounting holes in the servo, they can sit up against the inner edge of the hole, buying you the critical few millimeters you need to line up with the holes in the chassis.

Now I think they maybe did this deliberately. Maybe a little to account for tolerances in the servo, but I think mostly so that you can squeeze the servo mounting brackets up against the servo body and give it some resistance to lateral twisting. I think there's also a little pinching included when you tighten down on the chassis screws, giving us extra grip on the servo.

The problem that I have with this chassis is that the pinching, coupled with screws that maybe weren't tightened down enough, caused the holes to oval out. I'm concerned that screws don't have enough holding power already.

I think this gets even worse if you decide to use those cute servo washers that have a shoulder. These force the servo mounts out to that 50.5mm center, which makes them bend and apply even more pressure to the (thin) chassis.

I think a better strategy is to account for the real-world geometry by offsetting the chassis mounting hole.

...which I did with the custom brackets I was talking about a few posts back. I got around the layer adhesion problem ("self-tapping" into 3D prints tends to split the layers) by using threaded inserts. A little heavier, but way more secure. And now, with the rear-entry servo lead change I made, actually fit this low-profile servo.

I'm debating if I should use this opportunity to design a full-width monolithic mount like the aftermarket aluminum ones you see everywhere.

Or I could just use servo tape like a normal person .

 

[Littlemotor]

OK, I've been thinking about this for a week and it's still eating me. I'm just not happy with the stock servo mounts. Let's talk about why.

First, these little guys are soft, and a couple holes are stripped out, but that's curable with thread lock. My biggest problem is with the geometry. If you've got one of these, you'll know that it's injection molded and the holes for the screws are all aligned - their centers are all on the same plane.
View attachment 259225

This is the front elevation for a standard servo. Pay attention to the measurement between the centers of the mounting holes. That's 50.5mm, and it's the same across all servos I've had my hands on.
View attachment 259226

Now this is the top-down look at the mounting holes in the SC10 chassis. This would be in some kind of weird imperial/SAE nonsense fractional inch measurement on the original plans, but 47mm is what I measure with my calipers. You'll notice that 47mm is not 50.5 mm.
View attachment 259227

So what gives? If the mounting brackets have their chassis mounting holes in the same plane as the servo mounting holes, how does 47mm end up equaling 50.5mm?

Well, we cheat - the #4-40 screw major diameter is slightly less than the diameter of the mounting holes in the servo ears. That means the screws don't have to line up with centers of the mounting holes in the servo, they can sit up against the inner edge of the hole, buying you the critical few millimeters you need to line up with the holes in the chassis.

Now I think they maybe did this deliberately. Maybe a little to account for tolerances in the servo, but I think mostly so that you can squeeze the servo mounting brackets up against the servo body and give it some resistance to lateral twisting. I think there's also a little pinching included when you tighten down on the chassis screws, giving us extra grip on the servo.

The problem that I have with this chassis is that the pinching, coupled with screws that maybe weren't tightened down enough, caused the holes to oval out. I'm concerned that screws don't have enough holding power already.
View attachment 259228

I think this gets even worse if you decide to use those cute servo washers that have a shoulder. These force the servo mounts out to that 50.5mm center, which makes them bend and apply even more pressure to the (thin) chassis.
View attachment 259229

I think a better strategy is to account for the real-world geometry by offsetting the chassis mounting hole.
View attachment 259231
View attachment 259230

...which I did with the custom brackets I was talking about a few posts back. I got around the layer adhesion problem ("self-tapping" into 3D prints tends to split the layers) by using threaded inserts. A little heavier, but way more secure. And now, with the rear-entry servo lead change I made, actually fit this low-profile servo.

I'm debating if I should use this opportunity to design a full-width monolithic mount like the aftermarket aluminum ones you see everywhere.
View attachment 259234

Or I could just use servo tape like a normal person .

Been here before lolz…

I’m old, and hard headed.. I still like my rubber servo grommets, and non-shouldered countersunk washers w/12.9 flat heads..

 

[Spksh]

Been here before lolz…

I’m old, and hard headed.. I still like my rubber servo grommets, and non-shouldered countersunk washers w/12.9 flat heads..

Of course this isn't new knowledge for you .

I always worried that the rubber grommets would affect steering feel. Do you notice any movement?

 

[Littlemotor]

Of course this isn't new knowledge for you .

I always worried that the rubber grommets would affect steering feel. Do you notice any movement?

ZERO difference. And I sleep much more super bueno knowing my $200+ servo is rubber isolated.

 

[Spksh]

ZERO difference. And I sleep much more super bueno knowing my $200+ servo is rubber isolated.

Nice. Of course that means I might have to design new brackets anyway, because the grommets add depth.

(This is my “oh no!” face.)

 

[Littlemotor]

Nice. Of course that means I might have to design new brackets anyway, because the grommets add depth.
View attachment 259236

(This is my “oh no!” face.)

What I do NOT use are the sleeves. Not once in 40yrs lol.. What can I say-I like to party..

 

[Spksh]

What I do NOT use are the sleeves. Not once in 40yrs lol.. What can I say-I like to party..

Interesting! Do you just not crank down too hard on the screw?

 

[Littlemotor]

Interesting! Do you just not crank down too hard on the screw?

I go until the rubber distorts, then back off. I’ll find a pic..

 

[Littlemotor]

One I had on hand that was easy enough to find.. I compress the grommet, but back it off from distorted.. I can find/take a better one of one of my vehicles if it’ll help your brainstormin’..

 

[Spksh]

One I had on hand that was easy enough to find.. I compress the grommet, but back it off from distorted.. I can find/take a better one of one of my vehicles if it’ll help your brainstormin’..

That’s a great example, thanks!

 

[Littlemotor]

That’s a great example, thanks!

Nuthin’ to it suh!!!

 

[Spksh]

Man, there is some capital-D Discourse on the internet about whether to use grommets or not. This feels like the "battery memory" thing back in the day.

 

[Littlemotor]

Man, there is some capital-D Discourse on the internet about whether to use grommets or not. This feels like the "battery memory" thing back in the day.

As with literally anything anyone can argue about.

What I can say is that there is absolutely ZERO harm in running them (provided your linkage is not suffering), and ZERO benefit to NOT running them (provided your linkage-you get it )..

People are gonna argue..

 

[Spksh]

(provided your linkage is not suffering)

My doctor has me checking my linkage every day.