High Torque Steering Servo For Clod Buster

[Rob Buckle 1]

Happy New Year All,

I've been looking into high torque steering servos as I'd like to improve the steering of my Clod Buster. I am aware that using twin servos, one mounted at each gearbox will probably result in the best steering performance. However, while I intend to modify the Clod in some respects, I will be retaining the original 1-servo-for-both-gearboxes steering for aesthetic reasons.

I am leaning towards the Futaba S3305 because I know Futaba is considered a quality manufacturer and also because my existing radio/servo gear is Futaba. This servo returns a torque of 9kg cm compared to my existing Futaba FP-S148 that returns a torque of 3kg cm.

In reading about the S3305 I stumbled upon the following text:

This servo can produce high-current draw from your batteries. If using NiMH or LiPo batteries, make sure they are capable of delivering sufficient amps.

I will be using LiPo in the very near future. Therefore my question is: is it still okay for me to go for the S3305?

Cheers,

Rob

[commiedoor 18]

mate ! ebay is full of them ! read the specs and get the one with the most lb of torque ..i just bought 2 MG995 Hi-Speed & Torque Metal Gear RC Servos for under 30 bucks posted .. if in doubt use the this forums search funtion !

[Rob Buckle 1]

Hey Commiedoor,

...if in doubt use the this forums search funtion!

I did a fair bit of reading prior to starting this thread, including using the search facility, but didn't come across a reference to my specific question. Of course the possibility exisits that I may have missed a reference.

...read the specs and get the one with the most lb of torque...

The Futaba S3305 does not return as much torque as alternative servos. Nevertheless it is 3 times as powerful as my existing servo which I would have thought would be ample (?).

The text quoted in my previous post was from the specs for that servo. Therefore my original question remains unanswered: will LiPo batteries deliver "sufficient amps" to drive this servo adequately?

Cheers,

Rob

[terry.sc 16]

The S3305 will have enough torque for a standard Clod, after all a standard servo is manageable in there. A S3305 will also take less power and be much more accurate than the cheap Towerpro servos. They certainly have more torque than the MG995s do whatever it says on a web page. I used to run MG995s in my crawlers, I now use Savox, Hitec and Futaba servos as they are actually up to the job and you do get what you pay for.

This servo can produce high-current draw from your batteries. If using NiMH or LiPo batteries, make sure they are capable of delivering sufficient amps.

This is aimed at flyers and nitro powered cars, where the radio gear is powered by a tiny nimh or lipo pack the size of 4 AA batteries. Nothing to do with electric cars, although you will have to take the extra power drain of a high torque servo into consideration. Most ESCs have a limited power output to drive the radio and a high torque servo of any make will need more power than the BEC circuit in the ESC can supply. I would recommend getting a separate 5A BEC to supply power to the servo, find them by searching ebay for UBEC.

[Rob Buckle 1]

Thanks Terry,

This is aimed at flyers and nitro powered cars, where the radio gear is powered by a tiny nimh or lipo pack the size of 4 AA batteries. Nothing to do with electric cars, although you will have to take the extra power drain of a high torque servo into consideration.

Yeah, I'd figured the servo would drain the battery quicker. I'll first see how things go using 1 LiPo battery. If need be I can always use 2.

Most ESCs have a limited power output to drive the radio and a high torque servo of any make will need more power than the BEC circuit in the ESC can supply. I would recommend getting a separate 5A BEC to supply power to the servo, find them by searching ebay for UBEC.

Ah, didn't know this. I've taken a look on ebay and seen the item in question, but admit I'm a little confused about where exactly they fit in, in the wiring scheme of things. Normally power for receiver, motor(s) and/or servo(s) is drawn from the battery through the esc, correct? If so, then the UBEC must presumably bypass and draw power from the battery independently from the esc because you noted that the esc on its own will provide insufficient power to a high torque servo...so far so good? If so, then don't we now have two parts (esc for motor(s) and UBEC for steering servo) looking to be connected directly to the battery?

What about the LiPo discharge protection circuit I have? Does having a UBEC cause any issues with that?

If I use 2 LiPo battery packs in future (not saying I will, just want to be covered if I do) for either longer run time (most likely) or twice the power (less likely but still a possibility) do I need to consider a UBEC with a rating greater than 5A?

[terry.sc 16]

A separate BEC fits between the battery and the receiver, you disconnect the red wire in the servo lead from the ESC so the ESC only powers itself. A diagram is included with the BEC.

As for the lipo cutoff the servo won't make that much difference if you still operate the servo after a cutoff in the ESC has activated. If you are using a separate lipo cutoff then you connect both the ESC and BEC to the cutoffs outputs.

[Rob Buckle 1]

Thanks Terry,

If I can kindly ask for clarification on one last thing:

If I use 2 LiPo battery packs in future for, say, double the run time, should I consider purchasing a UBEC with a rating greater than 5A? Is it the case that a value greater than 5A provides an additional safety margin?

[terry.sc 16]

Adding a second battery in parallel makes no difference to the power the motors and servo asks for, it just means the truck runs for twice as long.

Using a higher rated BEC won't make any difference to the servo power as long as it's powerful enough, but it's useful to get something higher rated so the extra power is there just in case. For my crawlers which need servos capable of lifting the whole truck on occasion I am using 10A BECs just to make sure that the very small numbers of times it actually stalls when a wheel is wedged in a crack and needs the extra current it has the extra power there for it. Using a 5A BEC would make no difference for 95% of the time.

[Rob Buckle 1]

Terry,

Thank you very much for all the information. I've ordered the servo and will now go get a UBEC. I suspect there'll be a bit of head scratching when I finally get all the various bits together and am trying to connect them all up, as I'm about to dive into LiPo (vs NiCd), LiPo protection circuit, ESC (vs MSC) and BEC for the first time, but I'll deal with all that at the time.

Thanks again,

Rob