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.

The ext chassis is 15mm longer IIRC. Not a lot, but enuf.

Well, 15mm would make sense. That's actually quite a bit really; over 1/2 inch.

So, I guess from the responses here, either the Futaba or Hitec would be good. The JR probably would work, but I think I'll stick to a torque/speed spec that I know work well.

Go Futaba.

I just called my LHS and the Futaba is the only one they have in stock, so Futaba it is!

Hitec 5245 is what I had.

This is the JR I am using now. Best mini servo Ive found.
http://www.jrradios.com/Products/Tec...dID=JRPSDS3421

I ended up getting the Futaba S9650. It is a hair narrower than the Hitec, but several mm longer. As such, the servo mount didn't need that little spacer that the Hitec did.

Put the new servo in last night and it runs great, and is quieter than the Hitec. And it seems to center much better too. I could never seem to get a consistent center with the Hitec, even when new, but I just thought it was the tire resistance or something.

Another thing about the Hitec 225MG: When I took it apart to troubleshoot, I found the power PCB is just floating around the servo case. It is encased in some heatshrink tubing, but the only thing keeping the board in place was the stiffness of the motor, pot, and servo wires. So, on hard landings/jumps, I'm sure that little PCB was smacking against the case, which isn't good for the components! Poor design. Hopefully, Hitec fixed this poor engineering choice in the newer model, but I'm not going to be another guinea pig!