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How to: Improve Servo throw

U

Uli

Quarry Creeper
Joined
May 26, 2008
Messages
277
Location
Clarkston
Many unprogrammable Servos don´t have enough throw. Most are not near the 180°. The easy fix are a couple of resitors.
Testobjects: 2xHV300 by Turnigy(MKS)
First unscrew the servo. Desolder the motortabs. Be careful, they are quite fragil
4458452852_5d685a81ca_o.jpg

Gently pull everything apart...
4458453186_5036ba68ec_o.jpg

Now solder extra resistors to the two outer potentiometer-contacts and reconnect the wires there.
4457676373_13f44f1c05_o.jpg

The HV 300 does about 110° von 900µs-2100µs impulse-length.To reach 180° each poteniometer-tab needs an extra 1.6kOhms, not more!


For any servo:

wanted servo throw (180° for example)
--------------------------------------- x 4,7kOhm(pot) = new total resitance(incl. pot)
momentary servo throw in degrees

The potentiometer resistance has to be subtracted from the new total resistance and divided by two. This will tell you the resistance of the resistors you will need. I used two in series to get that value I needed.
This is not a difficult mod, but be careful to set your steering EPA to 50% or so when you turn your rig back on. Carefully increase the EPA until you reach 180°. Going to far will destroy your servo.
"thumbsup"
Uli
 
A servo stretcher will only work, if the servo resolves the stretched signal. But since the HV 300 does just a 110 degrees between 900µs and 2100µs impulse length, you´d have to have a PPM-signal between 500µs up to 2500µs, which is no real option, since most servos(at least the digital ones) don´t work below around 800µs and above 2300µs anymore. Also, this mod is cheaper and definately works with any servo that has a regular poteniometer as a position feedback. Last, you carry less electronics that might fail. "thumbsup"
 
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It´s no trouble. It´s saving money modding a 533oz titanium-servo that merely cost $65. And it doesn´t even need a BEC.
Anyway, I´m just the do-boy who did the mod. I´m not using it, I don´t play with supers, yet... :roll:
 
12V "thumbsup"
It is larger, since the motor is one big hunk. The power´s gotta come from somewhere. Since they probably can´t afford putting as much research in the motor and case-heatsink topic as the leading servo companies, it´s just that little bit bigger. Anyway, can´t beat the price.
 
EvilTwin v2 said:
I question any manufacturer that uses non-standard measurements in order to make their product seem more than what it is.



12 volt? Really???
Click to expand...

What are non-standard measurements? Metric units (used by most of the world) or the voltage. This is a high-voltage servo, designed around a 12v system, orginally for robots, but then transitioned to larger planes and now crawlers have found the amazing power it puts out. I've seen plenty of people that say that the 533oz-in is a little underrated...

Can't beat the power for the price. I'm looking at picking some up with my new build.


As far as the topic, what would the point of 180* of steering be if between 90* and 180* with a 1" servo horn you are only getting another few mm of travel (with the way most people mount their servos), and some axles can only handle 110* to 120* of rotation at extremes, most get around 90* of travel anyway.
 
I'm going to have to give some serious creativity points on this! Have a few old servo's laying around I'll try it out on just for kicks. "thumbsup"

I can see the point some people have with "what good is 180"...but I can't count how many times I've wished some of my servo's had just a bit more throw (which I'm assuming could be gained by adding the proper resistance value ie:needing >90, but <180). Especially when adding length to the servo horn is not an option.

Also, who said this 180 mod is limited to just steering applications?

I, for one, think this is pretty good thinking on someones part, love these kind of tweaks on the cheap! "thumbsup"
 
whats the difference in doing this, or buying the stretcher, and changing the EPA's on my radio?
 
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WarMachine said:
I'm going to have to give some serious creativity points on this! Have a few old servo's laying around I'll try it out on just for kicks. "thumbsup"

I can see the point some people have with "what good is 180"...but I can't count how many times I've wished some of my servo's had just a bit more throw (which I'm assuming could be gained by adding the proper resistance value ie:needing >90, but <180). Especially when adding length to the servo horn is not an option.

Also, who said this 180 mod is limited to just steering applications?

I, for one, think this is pretty good thinking on someones part, love these kind of tweaks on the cheap! "thumbsup"
Click to expand...

I think it's a good mod, and I commend the OP for posting it, the mod is less than $1 for 2 servos, which is way less than a servo stretcher.

I think for steering 120 is sufficient, beyond steering, this is a great mod!
 
@all: thanks.

slobin3d said:
whats the difference in doing this, or buying the stretcher, and changing the EPA's on my radio?
Click to expand...

Some radios don´t have the EPA´s needed. Especially the low budget ones. Then, even with a good radio plus a stretcher the servos don´t move as far as desired, not because the stretcher won´t put out a proper signal but the servo can´t resolve it anymore, thus still not travelling the wanted amount. This makes the mod reasonable, besides the fact of its cheapness.
Uli
 
So then, if you were to mod a mid-grade servo (160oz) to get more throw, then you can essentially gain steering torque.
Increase throw - Move your control arm up the horn a hole or 2 - Steering is now closer to the fulcrum(torque), but still has the same/maximum steering movement at the end of the throw.

Sounds like a nice little mod for us 645/5645 guys.
 
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