Servo for CRT.5
 

My second Hitec HS-225MG (66oz-in & 0.11s @ 6v) gave out today for no apparent reason. Voltage is present at the servo board, but no go - even with the gears unattached. The motor spins if I apply voltage directly to the terminals, so the driver board is toast. Normally, I'd just get a replacement servo board, but seeing as how this is the second servo that went bad with not much use, I would rather just get another one.

This is on the stock non-extended chassis, so it needs to be a mini servo. After research, my choices are:

Hitec HS-5245MG. 76oz-in & 0.12s @ 6v. About $46

Futaba S9650 63oz-in & 0.11s @ 6v. About $58

Obviously, the Hitec is a little more powerful, but a tad slower. But I am tending to lean toward the Futaba simply because Hitec has been giving me grief. Plus, the Futaba case is a tad larger (still fits though) which means things probably aren't quite so cramped inside and may be a little more reliable.

Any thoughts? Or, is there another alternative?

skip the small boys get a 7955tg

And how do you propose I fit that in there? It has to fit on a stock CRT.5 chassis, and I have no intention (or desire) for an extended chassis.

Brian your running the original CRT.5 chassis? I got the OFNA extended chassis just so I could use a full size servo (Hitec 645MG). I have also used a Spektrum Z590 servo, just put the hitec in there because it is a better servo and I had it, both threw the tires around with ease. The extended chassis isn't much bigger, just enough to use a real servo.

Yup, the original chassis. I realize the servo choices would be far more open if I just get the longer chassis, but I really like the way it is now. If it gets much bigger, it'll be 10th scale. If I wanted 10th scale, I'd get 10th scale, but I wanted 12th scale. :smile:

I'm with you Brian. I'm runnin the original short chassis on my .5 too. I like it small like it was originally intended.

I have been running the digital hitec servo with no problems. It's fine for the little guy. Of course I pretty much only run mine on flat parking lot so it's not really jumping or anything and that's easier on the servo.

I can say that the JR is a tough little bugger though. I burned up 2 of the digital hitecs using them as brake servos on my 1/8 truggy and then I got the JR and it has never failed. The electronics inside seem to be able to handle more power than the hitec.

Which hitec servo are you running? Like I said, I'm kinda leary about them, but maybe the newer 5245MG is better/more reliable than the older 225MG's I had.

I just looked at the JR site and the only digital mini seems a little low on the torque (51oz-in @ 6v), but the 0.06s speed is nice (although I probably wouldn't notice the difference between 0.12s and 0.9s in reality).

The ofna ext is only a fraction longer. If you mounted the servo vertically could you get a full size servo?

Mine is not that much longer. Just enough for the full size servo.

BG- I've had excellent service from both Futaba and JR. I'll be in the market to replace a Hitec 645 in a Revo pretty soon and my choices are narrowed down to both Futaba and JR servo's only. I too have had nice service from Hitec but a few have just crapped out as you mention.

Do you really need more than 51in-oz of torque?? I was running a JR8700G in my SC10. JR8700G specs are 49.3 oz/in @ 4.8V torque and .09 sec/60° @ 4.8V. This servo EASILY turned the wheels lock to lock on any terrain and driving condition. I had no complaints but more complements and questions from others on the servo than anything. I know its only 2WD but the truck is probably close in weight and larger in size. I feel that the added speed makes up for the lack of torque. Just my opinion and experience.


EDIT: Just saw that your 51oz/in is at 6v. I was running the JR8700G at 6v also so my number are slightly higher.

Nitro: Don't know exactly how much torque is required, but the 66oz-in that the 225MG provided was perfect, so I was shooting for around that same value. Anything in that vicinity would probably work though.

I tried all kinds of mounting positions, even some that were never done before. A full size servo is just too big. Even if I cut the ears off and come up with another mounting scheme, there is just too little room.

So your chassis is that much shorter than mine?

http://i189.photobucket.com/albums/z...5/DSCF8135.jpg

If I lay a standard size servo down right up against the steering bellcrank, and cut the servo mounting ears off, I have about 1mm between it and the pinion. Not to mention I'd have to really contort the servo wire so it doesn't touch the diff/pinion.

Thats a big difference! Snell looks to have a good 1-2cm between servo and pinion.

Crap, that's a big difference then.