GRU help

[offacup]

Okay... here is my problem:

I just got my Great Planes GD-600 GRU. Opened it up and proceeded to install it in my truck. Got the motor mounted and was about to install it into the truck when I noticed the output shaft on the GRU is too big for the stock pinion.

I've seen a few ppl using GRU's, so I know that it's possible. But how do I get a pinion on there??? Do I just drill out the stock pinion, or is there a pinion that will fit the GRU shaft???

HELP!!!

[Badmuthatrucker]

Your easy option is to drill the pinion. No one makes Tamiya .4 module pinions with a bigger bore.
Or, you could get the output shaft turned down to 1/8". That would be better, as pinions don't last for ever and you wouldn't need to drill out every one before you can use it.

[offacup]

i was kinda hoping someone made a pinion, or if anyone changed the output shaft on the GRU instead...

But I knew that my last resort would be to bore out the pinion or shave down the shaft. I'm probably gonna go with the shaft but, do you know the best way to grind it down evenly???

[cartronicshn]

I would recommend turning down the shaft over boring the pinion, the pinion would be to weak after imho, to turn down the shaft i took apart the gd600 and put the shaft in my drill press and used a file making sure the the shaft was spinning true and measuring on the pinion as i went along, then i just filed a small flat spot for the pinion grub, hope that helps.

[Flowmastered87GL]

I turned down my pinion shaft... but bent it when I got in a bind

Good thing these GRU's are cheap.... and I had a spare

I never thought about drilling out the pinion... I would consider trying that personally if I had easy access to all that stuff without taking my rig apart again.

[offacup]

^^^ So your GRU shaft bent before the pinion gave up??? Interesting, maybe I'll try doing the pinion first. Since it's cheaper to purchase a new pinion and they're available locally.

Thanks for all the insight guys...

[cartronicshn]

Originally Posted by Flowmastered87GL

I turned down my pinion shaft... but bent it when I got in a bind

Good thing these GRU's are cheap.... and I had a spare

I never thought about drilling out the pinion... I would consider trying that personally if I had easy access to all that stuff without taking my rig apart again.

Originally Posted by offacup

^^^ So your GRU shaft bent before the pinion gave up??? Interesting, maybe I'll try doing the pinion first. Since it's cheaper to purchase a new pinion and they're available locally.

Thanks for all the insight guys...

I turned my gru's shaft as described before and have been running a jrh outrunner and 3s lipos once in a while for about 3 years now, and when i get in a bind i might hear gears slipping/skipping in the tranny, axle shafts skipping on the dogbone, but so far i haven't even slighty warped the gru's shaft.

[offacup]

^^^ Thanks... I'll keep that in mind, but I guess I can try boring out the pinion first and see how long that will last...

Being that I can get them locally and it is cheaper than purchasing a new GRU...

Then I'll try turning down the shaft after I break a pinion... I'm tryna source out another Axial AE-2 ESC or Castle ESC so I can run my 2s Turnigy lipo, but until then I think I'll be okay running the truck with the modded pinion and DTX 5000 NiMh pack on an XL-5 ESC...

[Flowmastered87GL]

Originally Posted by offacup

^^^ So your GRU shaft bent before the pinion gave up??? Interesting, maybe I'll try doing the pinion first. Since it's cheaper to purchase a new pinion and they're available locally.

Thanks for all the insight guys...

Yes but I did a kinda half-assed turning of the shaft so that may have something to do with it.

I had the GRU hooked to a 55T motor with a pack plugged straight into it.

I ran the pinion shaft against a spinning dremel disk until a pinion slid over it. Its not perfect, but it worked... so that may very well have something to do with my failure.

[rcjeepbuilder]

I used the hpi wheely king gear reduction unit and it went in way easy..And their cheap!!

[offacup]

Originally Posted by rcjeepbuilder

I used the hpi wheely king gear reduction unit and it went in way easy..And their cheap!!

Where'd you order yours from???

[Flowmastered87GL]

Originally Posted by rcjeepbuilder

I used the hpi wheely king gear reduction unit and it went in way easy..And their cheap!!

They have a TON of reduction though... like 7.4 to 1 or some crazy high number!

[offacup]

R u happy with wheelspeed to torque ratio, though??? Right now with a 60T on a 5000 7.2Nimh pack it's still too fast for my liking...

[Flowmastered87GL]

I have a GD600, a 55T motor, 6 cell nicad pack and 16T pinion. My speed is just about where I want it... maybe slightly too slow. I could not even imagine going with more gear reduction unless you are running like a 27T motor (or even less)