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Thread: Duuuuuuuude's ProStock...or maybe ProMod

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Old 11-13-2009, 10:09 PM   #21
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Originally Posted by Sharkey View Post
i doubt thats going to work very well, not enough gear reduction. the stock axial axle is 2.94:1, with my drag car i run 5.42:1 (currently) and i calculate top speed to be 105mph. that much gearing will likely just cause a lot of heat. however if you can mount a spur gear to the pinion you might come up with something that works well.
I thought about that, mounting a spur to the pinion shaft of the axle, or something similar, however I haven't come across anything I could use to hold it all. I'll have to look through my little box of gears and see what I have.
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Old 11-14-2009, 12:00 AM   #22
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I think I found a solution! Pics and details tommorow!
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Old 11-14-2009, 02:22 PM   #23
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So I searched around my parts last night looking for a gear that would fit and lock down on the pinion shaft of the axle. I had several old TMaxx tranny gears but couldn't find anything compatible that would fit on the motor to drive it.

I came across a bag of broken Axial parts and pieced together the center trans dif, then drilled the center out to 5mm and installed a set screw. The other end I cut off flush with the gear. I was pleasantly suprised to find that I had drilled the holes straight! No wobble!

I then took the lathe motor mounts, drilled and tapped a couple of 3mm holes into the side and bolted it down to the chassis. Added a 18t pinion and set the mesh. Everything looked perfect.

One the second run it was obvious that I had lost some speed so I swapped pinions. The next run munched the plastic gear on the axle.

At this point I'm pretty well out of usable parts, so I decided to try belt drive. I grooved the plastic gear to hold a big o-ring, and swapped the pinion out for the spindle that drives the lathe. Got everything lined back up and tried it out.

It worked very well. The o-ring acted like a slipper, but I didn't want to make it too tight and put tons of sideload on the motor or axle. Still not very fast though.







I'm thinking I may have to call this one done. For everything I've gone through I could have just slapped a big motor and battery in my B4 and been faster.

I had the idea to do the micro switch thing but with two batteries and two switches to make it a dual stage kinda thing, but I'm thinking I've already reached the point of diminishing return with this drivetrain.
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Old 11-14-2009, 02:30 PM   #24
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if you could put the big gear so it goes into the motor plate you could put it tighter if you end up with it slipping to much, but great idea i really like it
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Old 11-14-2009, 02:39 PM   #25
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if you could put the big gear so it goes into the motor plate you could put it tighter if you end up with it slipping to much, but great idea i really like it
Thats a damn good idea.

But...

I'd have to move the motor mount inboard further, and I'm nearly out of motor adjustment already.

Also I'm drilling all these holes by hand, and frankly, I'm astonished they've been as straight and true as they have been. I'm pretty damn good at eyeballing this stuff, but it has its limitations. To keep the motor plate square AND align the hole for the gearshaft would simply be too much to ask from me.


I'm currently looking on ebay for pinions that fit a 5mm shaft. There are tons, but I need to find a big one. Something in the 20's at least...
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Old 11-15-2009, 11:38 AM   #26
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For everything I've gone through I could have just slapped a big motor and battery in my B4 and been faster.
So I took that assumption and ran with it. Here's how I'm standing now...





I bolted the entire rear half of the B4 onto my chassis, tires are old bald Slash units glued onto Losi truck rims. Stock spur (89t or so, haven't counted) with a 26t pinion.

I don't have an official speed on it yet, but just bombing around the street it feels faster. Runs way cooler too. I may try the EZrun again on 3s and see how it goes. Ride height in the rear needs dropped some.

Still really stable and it'll turn corners too.
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Old 11-15-2009, 01:17 PM   #27
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EZrun on 3s netted me 43.7 mph. Half a dozen passes and everything is still only warm, so I'm thinking I've got room for some more gearing.
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Old 11-19-2009, 10:13 PM   #28
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Looks like I've gone as far as I can. I hope to get another couple runs in tomorrow if I can find some flat ground and expect to do a wee bit better than the 43 I got last time. We'll see.

And since you can't have a rat rod without a crappy paint job, here it is.

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