Desert Fox Pinion Troubles
 

Hey folks,

Newb here so my apologies in advance if I sound like an idiot....


I bought a Desert Fox from Hobby King for my kid. The guy at the hobby store was in the process of swapping out the motor for a 4 pole brushless motor, so we bought the rig as-is and took over the process. It's super fun, for 2-4 minutes then we strip the gear. I spent a long time last night working on a good mesh with paper between the gears until it felt right, and then we ran it for a few minutes this AM and it was great until I tried to run it in reverse to whip the car around (see above note about sounding like an idiot....). I recall running these as a kid and being able to do that - but this time it immediately stripped out the gear. I have spare gears (this is not the first one we have ruined) but before I go through the process of replacing it again and destroying another one I thought I would seek advice from experienced people. So I have some questions:

1. Is this common?
2. Did I mess up by hitting reverse at speed (on loose dirt)?
3. Given that this is NOT the stock motor, is it possible my pinion gear is improperly matched?
4. Is there a place I can go to have someone help me get this right (Los Angeles)?

Thanks for the advice/assistance.

1. It shouldn't be. If the new motor, pinion, and spur gears were installed correctly.
2. Are you running it in a mode where you can go from forward directly to reverse? Then, maybe. But it should be set for forward/brake/reverse, where you initially get brake on the first pump of reverse before it actually goes into reverse.
3. Yes. You need to know what the gear pitch of the spur gear is, and match the pinion gear to it. Is it 48 pitch, 32 pitch, Mod1? What? It's crucial to have these two items matched.
4. First, I'd try going to Hobby King's website. They seem to have all the documentation, and even discussion forums. Or you could phone them. Otherwise, there are several RC race tracks in So Cal. Orange County RC comes to mind. Look up hobby shops in L.A.

Sounds like you know the paper method for setting gear mesh, so you're doing something right. Did you remember to put loktite on the motor mount screws? That's important too.

I'm pretty sure the spur gears are 0.6 module on the Desert Fox and Vandal.

I recently figured this out and am starting to understand my issue. It seems that most cars run a 42p pinion and that my car runs a 48p METRIC, or .6 module. Those pinions do not seem very common, and I recall the guy who sold me this car grabbing the pinion off the wall quickly - acting very much like the pinion he gave me was standard. When I look at the mesh, the gears barely interact. And looking at the stripped gears, they only seem to be stripped at the edges of the teeth. Both things seem to tell me that the pitch is off and not biting. Am I reading this scenario correctly? I've since ordered two .6 steel pinions, one in the stock 17T and one in 19T and a handful of stock spur gears to play with (because I burned through three today!). I think I'm on the right path now.

Thanks for chiming in.

I think you are on the right track. Most common pitch gears on 1/10 scale platforms are 48p. You'll have some models/people using 32p gears for "heavy-duty" applications needing gears with more surface area. A lot of 1/8 scale platforms use Mod 1 gears. There are companies, like you found out, that use the "metric 48 pitch", 42p, Mod .6, or 0.6 module...all the same thing. I think Tamiya, and Redcat are among the heavy hitters using that pitch of gears.

If you have new gears , and some verniers , give this a go .
http://www.scriptasylum.com/rc_speed/gear_calc.html
You should be able to work out what pitch you have by counting the teeth and measuring the diameter .
" Metric 48 P " .... I saw that on the Hobbyking website ...lol .

What really irks me is having to "dig deep" on the www to find the gear pitch on a particular RC. Drives me up the wall when trying to help someone. At least with the more "common" brands in RC I know where they stand in terms of gear pitch.

I agree mate !
Gear pitch is a spec that should be listed in every manual .