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Tuning a freshly-built Womp?


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#1 btk

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Posted 14 December 2017 - 07:33 PM

I just built two new identical brass Womps with PS 16Ds and natural rubber tires. 1” diameter by .8” in the rear and 13/16”x1/2” in the front. The fronts roll on the track. One side is set-screwed to the axle and the other is free. I’ve done the following so far:

- Flattened the chassis
- Made sure the axles are square
- Tilted the guide up at (roughly) a two degree angle
- Set what appears to be a good guide height.
- Adjusted for a smooth gear mesh
- Set a hair of side play in the back and maybe 3/64” in front.

Predictably, and I expected this going into the project, they handle... well... let’s just say that “poorly” would be a charitable description.

They skip out of the slot when faced with even the prospect of a turn ahead. Sometimes they just go straight. Other times they do a cartwheel that would make Mary Lou Retton proud (except for the landing, of course).

Off the line, the front wheels hop off the track and bounce a bit unless you really baby the throttle.

I know there’s more that should be done, but wanted to tap into the crowd of Womp enthusiasts here to ask:

After the car is initially assembled, what’s on your checklist to make it driveable?

Thanks!
Brian Keifer




#2 Samiam

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Posted 14 December 2017 - 11:22 PM

Replace the 16-D with a JKMB.

 

Add a huge chunk of lead to nose.


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#3 Ramcatlarry

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Posted 15 December 2017 - 12:29 AM

The guide flag 'ride height' should be adjusted to have the braid flat on the track and still allowing the front tires to roll.  Every track has a slightly different depth of the braid in the track.

Some rules require tire sizes that you must use, and others allow you to resize the tires smaller to fit the car. Womps normally have 5/8" diameter front tires.

FLATTEN the braid.

Do not use the flag braid as springs - you have to add nose weight to compensate. Just turn the tips of the braid down a little.


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#4 btk

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Posted 15 December 2017 - 01:08 AM

I figured lead would be my next step.   Thanks, Sam and Larry, for confirming my instincts.

 

Replace the 16-D with a JKMB.

 

What's your reasoning for a mini brute over the 16D?  Not doubting you at all, just interested to learn how the two differ and what makes one better than the other in this application.

 

Also, for what it's worth, I'm starting at 9/33 for my gearing.  


Brian Keifer

#5 John Streisguth

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Posted 15 December 2017 - 03:34 AM

I would imagine with those tire sizes, you have way too much clearance. Get smaller tires so that you have no more than 1/16".

 

The body thickness has a huge influence on how the cars handle.  Once you have the tire size set up correctly, try running the car with and w/o the body.  You will probably see a huge difference.  If you are running one of the 30's-40's bodies, try a Kremer (Porsche) body.  We used to race folded laminated paper modified bodies on them, those bodies are "soft" and help dampen the vibrations

 

For guide height, with the car in the slot, press down on the guide flag shaft and see how much the rear tires lift off the track. You don't want them lifting more than just a little bit.  And make sure you reduce any wobble in the guide to the minimum possible without binding the rotation.

 

And running a mini-brute motor isn't a bad idea...most motors will overpower these cars.  Experienced racers like that...not so good for beginners.  The mini-brute is a good balance for what the chassis can handle.


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#6 Brian Cochrane

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Posted 15 December 2017 - 05:41 AM

Go with the smallest tires possible



#7 Samiam

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Posted 15 December 2017 - 08:00 AM

What's your reasoning for a mini brute over the 16D?

 

 

A 16-D is way too much power for these little cars. As John said, the Hot Thumbs can handle it but it takes a lot of trigger control to use all that power. We ran Hawk Retros in these cars with Legends bodies. They were quite a hand full on Port Jeff's Hillclimb. The marshals got a work out. We are going to try the JKMB to calm them down a bit. 


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#8 Tim Wood

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Posted 15 December 2017 - 09:54 AM

16-D work fine on a Kingleman track, JK-MB work great also for Legends bodies, just add a lot of weight. Hawk 7 motors work great with Kramer bodies, again add a lot of weight. I would screw down both front wheels with minimal side play. These are all ran on a Kingleman track. 16-D are the hardest to handle as Sam said but they will make a driver out of you quick or you will be straightening your chassis a lot.



#9 John Streisguth

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Posted 15 December 2017 - 10:10 AM

A 16-D is way too much power for these little cars. As John said, the Hot Thumbs can handle it but it takes a lot of trigger control to use all that power. We ran Hawk Retros in these cars with Legends bodies. They were quite a hand full on Port Jeff's Hillclimb. The marshals got a work out. We are going to try the JKMB to calm them down a bit. 

Sam, back when the Fast Tracks hillclimb was still in Columbia NJ, we ran womps with mini-brute motors and folded lexan dirt mod bodies.  Those motors were a good match for the handling capabilities of the chassis.  We also found that the thickness of the lexan had a big effect on the handling.  I think the standard bodies were 010 thick and the cars chattered a lot.  Going to an 007 thick material got rid of the chatter.  It's probably because these chassis have the bodies mounted directly, and they are smaller so naturally stiffer than a larger body of equal thickness.  If i were running races with the legend bodies, I would allow the windows in the bodies to be cut out so that they can flex more. 


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#10 Half Fast

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Posted 15 December 2017 - 11:17 AM

All good advice from guys that know what they are doing :good:
 
Cheers

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#11 Foamy

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Posted 15 December 2017 - 12:31 PM

With a flat chassis, rear tires should be 13/16. If you are allowed to bend the chassis, bend up the rear to make the axle on the same center as the motor shaft.


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#12 Tim Neja

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Posted 15 December 2017 - 03:24 PM

I don't know Foamy---I've seen some of your "chassis bends" :shok:  :crazy: in the past!! Not sure a womp could survive that!!!!  :dash2:  :laugh2:  :good:


She's real fine, my 409!!!

#13 gc4895

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Posted 15 December 2017 - 05:02 PM

Jk mini-brutes are the bomb! Our most popular racing series uses these with flexis, LMP bodies on our flat track. Its what racing is all about.
Mark Bauer

#14 gc4895

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Posted 15 December 2017 - 05:03 PM

Jk mini-brutes are the bomb! Our most popular racing series uses these with flexis, LMP bodies on our flat track. Its what racing is all about.
Mark Bauer

#15 gc4895

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Posted 15 December 2017 - 05:03 PM

Jk mini-brutes are the bomb! Our most popular racing series uses these with flexis, LMP bodies on our flat track. Its what racing is all about.
Mark Bauer

#16 btk

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Posted 18 December 2017 - 09:45 AM

I had a chance to get to the track Friday night and tried a few of these suggestions.  Bending up the rear of the chassis and adding weight (18g so far) behind the front axle made a world of difference.  It's definitely still a driver's car, but I'm going to try a Mini Brute and see how it goes.

 

You guys are the best!


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Brian Keifer

#17 btk

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Posted 19 December 2017 - 09:24 AM

Got the bodies mounted last night.  Still need to trim a bit more, but this is what they're going to look like Christmas morning...

 

The bodies are Caveman's rally bug.  Brian was great to work with and shipped them to my home raceway.

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Brian Keifer

#18 Brian Cochrane

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Posted 19 December 2017 - 10:17 AM

Should be fine



#19 btk

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Posted 19 December 2017 - 04:35 PM

Now that I see a photo of the car I can see that the front tires are not nail polished.Put nail polish on the front tires so they don't grip the track.When it comes to womp cars,you don't want the front tires to grip the track,you need them to have no grip .This helps the car to turn and gets rid of the chatter...

 

Interesting!  I'll have to steal a bottle from my wife.

 

Is there a particular shade that works best?  :laugh2:


Brian Keifer

#20 MG Brown

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Posted 19 December 2017 - 05:02 PM

Now that I see a photo of the car I can see that the front tires are not nail polished.Put nail polish on the front tires so they don't grip the track.When it comes to womp cars,you don't want the front tires to grip the track,you need them to have no grip .This helps the car to turn and gets rid of the chatter...

 

Either that or make the front wheels independently rotating.


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#21 btk

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Posted 19 December 2017 - 05:10 PM

 

Either that or make the front wheels independently rotating.

 

They already are.  The lefts are set-screwed to the axle and the rights are just held on with a spacer soldered to the end of the axle.

 

Does that eliminate the need for the polish or would it still help?  I've seen TonyP mention coating fronts with CA as well.  Is there a difference?


Brian Keifer

#22 MG Brown

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Posted 19 December 2017 - 05:38 PM

Does that eliminate the need for the polish or would it still help?  I've seen TonyP mention coating fronts with CA as well.  Is there a difference?

 

 

My feeling is that using nail polish or CA on the tire surface (if now independent) would gain little or nothing. Caveat being that this is just my feeling- I have never done back to back tests.

 

What you really need are some RED or BLUE rear tires. LOL

 

IMG_9409.jpg

 

IMG_E9369.JPG

 

 


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#23 hjames

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Posted 20 December 2017 - 04:32 AM

Narrow up the rear tires a bit. I like to run around .700 wide, ymmv. !
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#24 btk

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Posted 21 December 2017 - 10:15 PM

I had some time to test them this afternoon.  I was the only one on track, so I was able to get some video of the sometimes spectacular de-slotting that they're prone to in corners.  I'd like some advice on how to adjust them to minimize (or at least decrease) this behavior.

 

It looks like under braking/cornering the nose is dipping down and the outside front wheel is hitting the track a bit sideways.  This, in turn, causes the rest of the car to pop out of the slot and start tumbling.  Is this where the nail polish/CA comes in?

 

Since I was the only one there, I was able to prop my phone up on the track to get some slow-mo video of what's going on that hopefully will help the more knowledgeable among us see what's going on.  I put a few videos in a YouTube playlist.  Thanks to anyone who takes the time to watch. =)

 

https://www.youtube....qI70rbw6SWF1Yde

 

Fun fact:  Within minutes of uploading it and well before linking it here, the clip titled "Topless Womp Gymnastics" had seven views.


Brian Keifer

#25 btk

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Posted 21 December 2017 - 10:19 PM

Narrow up the rear tires a bit. I like to run around .700 wide, ymmv. !

 

What effect(s) should I expect to see from narrower rears?


Brian Keifer





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