Help! Servo choices

[niggle]

I am led to believe that 100oz/in is generally accepted as the minimum torque specification for steering on a 1/8th buggy.

I have a Hitec HS645MG on back order with a supplier here in the UK, it is intended as the steering servo for my new buggy (Swift).

At 133oz/in the '645 should be adequate but I am beggining to wonder if the 0.20s response time will be fast enough. Eventually I would like to compete at club level.

It seems that for a little more cash outlay I could get a coreless and/or digital servo with similar torque but faster response. Apparently these types of servos also have a tighter deadband.

My questions are: -

1. Is 0.02s fast enough for steering (HS645MG) ?

2. Would 107oz/in still be adequate for steering (HS925MG) ?

3. What are the recommended minimum torque and speed figures for the throttle/brake servo? The Swift has a slide carb and four brake discs.

4. Is receiver battery drain considerably worse when using digital and/or coreless servos?

5. Is there any point in using digital servos if I don't have a servo programmer to go with them?

Thanks for your help.

Sorry, that should have read:

1. Is 0.20s fast enough for steering (HS645MG) ?

Not "0.02s"!

[dgrobe2112]

i was fixin to say.. .02.. plenty fast.. hehe..

i run the airtronics 357, which has 125oz torque and .07 speed.. the 925mg from hitec will work great in the steering.. anything over 100oz is fine in buggy..

Digital servos.. i dont reccommend.. with all the vibration in nitro vehicles.. they go out.. i had (2) hitec 5925mg servos burn up..

Battery drain.. depends on the load you are putting on the servo.. if you have your enpoints set.. you should have no problem with battery drain..

.20 speed.. is slow.. for me.. you do notice the speed difference.. alot.. i had the airtronics 358 200oz .10 speed in steering.. and didnt like it.. swapped it for a 357..


for your throttle servo.. the 645mg will work great for that.. plenty of torque.. to pull them brakes..

[zoeybadm]

I would run the 358 Airtronics with 200oz of torque @ 0.10 response time. I run the 358 for steering in all my cars except for the B4 buggy which I use the 357 which has the fastest response time but a little less torque. With buggies I would go with as much torque as you can get and 200oz has a good balance between speed and power. The best of both worlds. If you want more specs let me know.....

[dgrobe2112]

200oz is great.. just was too slow for me.. got the 357 in there.. and have no trouble at all..

[zoeybadm]

Originally posted by dgrobe2112
200oz is great.. just was too slow for me.. got the 357 in there.. and have no trouble at all..

I also run the 357 but only find it useful in the B4. I used one in my 1/8 buggy and did not really notice any improvement...I did notice I was not able to hold as much speed in a long sweeping straight due to less torque...

[Hypedonrc]

The whole box is in Jap.

I run a JR NES-4721 for a steering servo, and the 590 that came with the radio for throttle. the only info I can understand is .22S/60deg. It seems to work well for me, except how much it drain the receiver batt.

[themerritt]

So the JR 650m has 142/oz and .17 sec @ 60 degrees. That is considered slow?

[SkyMaxx]

I run digital servos and they do have some great advantages: strength, speed and great recentering. Their one negative seems to be in the area of power drain and a good battery pack can resolve that.

I run HiTec digitals in my MBX-5 and have not been disappointed yet. I also run their digitals in my MTs. Great servos in my opinion. The HS-5645MG digital hi torque is great for steering duty at 168oz-in w/.18sec speed on a 6 volt system it is a great steering servo.

[niggle]

I run digital servos and they do have some great advantages: strength, speed and great recentering. Their one negative seems to be in the area of power drain and a good battery pack can resolve that.

I use a home-made 1800mAH Rx pack so hopefully current drain should not be a problem.

I run HiTec digitals in my MBX-5 and have not been disappointed yet. I also run their digitals in my MTs. Great servos in my opinion. The HS-5645MG digital hi torque is great for steering duty at 168oz-in w/.18sec speed on a 6 volt system it is a great steering servo.

Hmmm, at 0.18s that's only just faster than the HS645MG, seems the jury is still out on whether 0.20s is fast enough. Is there any point in using digitals if you don't have a servo programmer?

[dgrobe2112]

they usually recenter better.. but i dont like digitals.. .2 speed is fine.. just not for me.. i gotta have the quick response of the servo.. and .10 to .07 is definitly noticable..

[1meathead]

358 for steering and 357 for throttle

[mattyk6]

I've always been under the impression that for 1/8 buggys, you want at least 130 oz of torque.

That being said, I do run a 645 in my Storm and absolutely love it.
Matt

[niggle]

I'm gonna go for the HS945MG for the steering.

153oz/in, 0.12s response time. Coreless, but not digital.

Thanks to all for the valuable advice.

[uDi_MP7.5]

Whoops guess I got in a bit late.

Comparing servo specs over different brands is like doing the same with engines, it does NOT work. Those specs are only good for comparing different servos from the same brand.

For all those 358 fans, drop it next to a Futaba 9350 digital or something and see how it compares, I think the 9350 would slam it. If it was possible to make a servo that milked a true 200oz at .12s or whatever airtronics outrageous claim is, all companies would have something comparable. Anyone stopped to think about that?

Hitec is even further down the line, the higher end products rated similarly (to say 5945/5925) should blow them away. The hitec's also seem to have a (much?) higher failure rate than other brands.

As for digital servos, i've got a pair of 9451's doing duty in my buggy for now (futaba digital, .1s /120oz claimed) and it is going great - fast and has a lot of holding power - and torque is nothing without that imo. As long as you run good batteries, juice is no issue - and as long as the endpoints are all set right, and there is no linkage binding etc, they shouldn't die any quicker than an analogue.

udi

[zoeybadm]

Then please explain why all the top drivers use Aitronics 358 and 357 and would switch for nothing else in the world....expensive yes but in the long run Airtronics is the way to go.

200oz w@ 0.10 is extremely fast for 200oz.
125oz @ 0.06 is even faster for throttle.

When I use the 125oz @ 0.06 in my B4 it seems like the steering is wired into my brain and the response is lighting fast and can hold a line really well. Better than any other servo I have run in my cars.

I run the 200oz Air in all my cars for steering except my buggy.
For throttle I use the 125oz with lighting response and I have never had a problem.

I have used JR, Hitec, and Futaba in the past but found their life to be short along with the quality. Moreover, the performace was not really there. Airtronics has always been the best servo IMO and I would not change unless something magical came down the servo production line.