Looking at some brushless servo - thoughts? Longer runtime? - RC-Monster Forums

Gee

Low on servos these days so I was looking at new ones to get. I stopped at this deal on tower.
http://www3.towerhobbies.com/cgi-bin...1&I=SE3226&P=K

It has two brushless servo and a rx. I could use all three items. The thought was that the brushless servos should use less then digiatal right?

Bashing with a brushless setup I never really paid much attention to the little things that are also hooked up to the lipos. But with the nitros I run started to take notice a little more. A 6v hump pack doesn't last that long. I get a fairly significant amount out time more out of a DX3R on the truggy below then I do from the 4PK on the XL.

The two setups
STRR
DX3R - SR3100
HiTec 5998TG steering
" " 5645mg throttle
.28

Sav XL
4PK - RS604F
HiTec 5955TG steering
Trx 2070 throttle
.32

There is a some weight different in the two and the Savage running 40's is going to take a lot more then the other. Well everything added together is the factor but will the brushless servo make a difference that will be noticed? Does the Futaba 4pk use a lot more power then the Spektrum dx3r? I've been meaning to swap the radio setup to see if what the differce it.

Mentat · 06.13.2009, 07:55 PM

Nice, and on easy pay too.

Overdriven · 06.13.2009, 09:38 PM

Assuming the 6v batteries are the same, and all endpoints are set properly I can't see why one would draw more than the other to the point its that noticeable. The only other conclusion I can come to is one of the 6v packs is weaker than the other or because the savage is heavier the steering servo is drawing more working harder to turn the wheels and the brake servo is working more often/harder to stop the truck.

A friend and I experimented once hooking up an amp meter to the steering servo in a T-Maxx. With the truck stationary we tried going lock to lock wheels on the ground and off, and noticed significantly less draw with wheels off the ground. The rate at which we sawed the wheel back and forth also affected amp draw, slower saw=less draw. We also tested the effects of bad endpoints, steering binding issues, and big tires (each tested individually) and saw amp spikes over 1amp (about twice normal readings) in each case. Another interesting find was upgrading from a TRX2055 to a 200oz JR? (i forget exact model/specs) saw a significant decrease in amp draw under normal conditions.

Gee · 06.14.2009, 01:43 AM

Yeah, 3 pay is nice. That's about the only reason I order from tower anymore. Their shipping started getting slower and slower. They do have a great selection of item where the description actually tells you the dimension. Good place to use for research when looking for alternative parts. You know I tried telling my LHS owner he would get a lot more of my money if he had a 3-pay or if his wife started wearing more revealing outfits. He wasn't interested in the hassles and that he's already brought the other up with her. Neither is going to happen.

The battery is usually the same. I have two charged up before I start. I put the same one in first and keep the second for a reserve. The more I thought about this. It's not that the battery is dead. It more that it seems like the steering performance is lacking. So i swap batteries earlier then I would have to with the lighter STRR. Probably is just the truck. Didn't know if just cuz the Futaba RX requires 6v that it would consume that much more the others. I forgot I picked up a digital VA tester (volt and current indicator) a while ago. I will have find it and do some testing. Thanks for input OD.

I did pick up a rx lipo (7.2v 2300mah) while I was at the LHS earlier today. It should be a considerable improvement over the 1600mah nihms.

That V/A tester I have belowe should draw a lot while it in use should it? If I hooked it into the lipo so I could keep an eye on the volts. It's not going to make the pack drain a lot faster while I am running the RC would it?

http://www.hobbycity.com/hobbycity/s...rent_indicator)

Overdriven · 02:46 PM

For the testing I mentioned in my previous post we simply made a harness that allowed a standard multi-meter to be used, inline with the servo for amp readings, parrallel for voltage readings. The VA meter you linked is only acurrate to .5amp, and from my experiments I'd say is not accurrate enough. Of the half dozen servos I tested, average amp draw was between .2-.5amps with spikes averaging .5-.7amps under normal conditions. Big tires, binding and other forms of increased strain on the servo typically raised those values by .2-.5amps. These values would be hard to measure with a device that's only accurate to .5amp, but it would able to be used on a running vehicle instead of the static testing I did.

If your reciever lipo doesn't help response, double check the tx settings, particularly expo before blaming the servos. I'm not familar with the savage does it use a servo mounted servo saver? If so I'd switch to a mgt servo saver, they are about the tightest readily availinle one I've found and work well on the maxx trucks I've had.

Overdriven · 02:56 PM

I just reread your post. I'd try out your va monitor and watch the volts more. Servo torque drops off quite a bit as the voltage drops. Take a look at servo specs @ 4.8 and 6V and you'll see what I mean. If you really want to get technical with this time how long it takes for the voltage to drop to a certain level. The va meter should draw less than a servo would so I doubt you'll notice much difference in runtime.

Gee · 06.16.2009, 03:43 PM

Thanks. It doesn't show the amp most of the time too low I suppose. I do have it hooked so I could keep on eye on the volts. With the lipo installed all my problems or questions above are now gone or forgotten. The lipo lasted the whole time I was out running this time. It was around 8 or 9 tanks and it voltage went from 8.4 to 7.6v

Here's a different but similar question that I may as well keep in this thread.

Any ideas why Futatba has thier brushless servos listed as using only NiCd batteries with them?

Here's a link to thier brushless servos. Only one of the servo say anything about lipo or Nihm the others say NiCd only. Maybe they haven't updated the template they use for servo description since 1975. lol
http://www.futaba-rc.com/servos/brushlessservos.html
BLS351
BLS352
BLS452

Were the ones I was looking at. I sent a e-mail to futaba tech support. I've never gotten a fast response before.

lincpimp · 06.16.2009, 03:53 PM

They mention nicd as an alkaline cell will not be able to output the current needed to run the servo. This is old news as most people use rechargeable nimh packs that can handle servo loads just fine. If you are trying to get max performance out of servos with alkalines you are barking up the wrong tree.

Gee · 06.16.2009, 04:50 PM

So they just haven't updated the information on the pages. Maybe to say NiCd or better battery required. Some of the description on Tower also had the NiCd required. It makes sense the way you put it. Thanks. The Mashers are mashed into the smallest box I could find. They should come back to shape after they are baked. lol Went out yesterday.

lincpimp · 06.16.2009, 06:05 PM

Thanks, your servos went out sun night!

Gee · 06.25.2009, 04:00 PM

Reply from Futaba about NiCd required batteries for thier servos

Thank you for your recent e-mail.

As far as the NiCd warning. That servo can produce high-current draw from your batteries. Most NiMh and LiPo cells were not designed for high discharge currents just high capacities. If using NiMh or LiPo batteries, make sure they are capable of delivering sufficient amps, 1 to 2 amps per servo.

Sincerely,
John G.
Product Support Lead Technician
Futaba Programming Technician
Great Planes Model Distributors
www.realflight.com
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