ok so here is how you swap the metal gear from a mg90s and put it in a hxt900, and the hxt900 gear in the mg90s.
ok so i realised i probabily went into too much detail for most people and i probabily made heaps of mistakes soo, main points are
The mg90s cap stays with the metal gear so you get a blue black servo, (because of the bearings)
When reassembling keep the "V" on the varible resistor centered with the mark on the biggest cog, like before you removed it.
I reckon you should test before and after, to check they actually work,
please ask i probabily havent explained it very well what dont you understand, sorry in advance for the spelling, probabily.
so start with the control arms and arm screws out, then take all the four screw off the back of the two servos, try to use a good driver, we dont want to damage them now, ok so i find it useful to try and keep the screws still in the case to help hold it together, if you are not so familiar with exactally what cog goes where it is very useful to have a 3rd servo sitting there with the cap off so when you get the 2 your working on apart you know exactally what goes where in what order, ok so start with either one probabily the 90s,
now when you go to take the cap of each servo i found the pin ( the pin that holds 2 cogs in place next to the main (big) cog/big shaft, so two things the big shaft connected to the varible resistor, i know its got a different name, and the small "idler pin"/ support pin, which goes between the top cap and the base,) im sorry if im being too simple but i dont know how much detail to include, so on the 90s when you take the cap off the pin usually gets stuck in the cap(what ive found) so best to get pliers straight away and pull it out carefully, keep its orientation(i dont know if it matters but i did to be safe), put it back into the two cogs watch you dont drop them out, also try not to remove their black grease so you dont have to add more,
pop those cogs out on the pin lay them down, do some gentle force is required to remove the main cog(biggest one), lay that down, also remove the one below now if there is any grease on the little varible resistor/sensiometer?, you should remove it so im told as it can work its way in not that ive ever had problems, i found only on the hxts had some on the top, so when you first pulled the big cog off the varible resistor may have came out, try to hold it in while removing the main cog as you dont want it out and you can damage the wires, so, now everything is removed from the servo, when you pushed the v.resistor back in keep its orientation ie, dont spin it around. push it as far as it goes. now do the same with the other but on the hxt900 the main cog is on a lot tighter than on the 90s, now important, there is a little v in the v.resistor which should point to the end when centered but the main cog has a little mark/area on the side the same as the top of the servo, they both have to point in the same direction otherwire you wont have full throws and your servo will bind, it is hard to explain so i will find a photo,
sooooo, you are now going to put the metal gear in the hxt 900, ok so starting with the "V" centered away from the "pin" put the cog that goes on the main shaft below the main cog on, then get the "pin with the 2 cogs on it put that is with the correct cog order look at you 3rd servo or google pic, now get main cog and check "V" is still all good, now get the main cog with the little plastic (nib/bit its black) backing the same way as the "V" away from the pin. put it on , now, get the mg90s cap and use that get it all siting nicely, put the cap back on and dont bother doing the screws right up just yet, test it, if its all good then you done do it up, also i test all my servos before and after the mod, just to check, like i know one of my 90s' was a slight bit jitterey before i modified it so, when it was doing it afterwards i knew i hadnt recked it,
so now to do that same with the other servo.
also if the gear bind loosen the case (power off) check the "pin" is sitting nicely in the cap lightly tighten up and try again
now i did this becasue i wanted the metal gear for the hxt900, so i havent decided what to use the plastic 90s servo's for yet.
i hope this helps someone i will have to open a hxt 900 up tomorrow as i cant find any photos on the net,
ok so i realised i probabily went into too much detail for most people and i probabily made heaps of mistakes soo, main points are
The mg90s cap stays with the metal gear so you get a blue black servo, (because of the bearings)
When reassembling keep the "V" on the varible resistor centered with the mark on the biggest cog, like before you removed it.
I reckon you should test before and after, to check they actually work,
please ask i probabily havent explained it very well what dont you understand, sorry in advance for the spelling, probabily.
so start with the control arms and arm screws out, then take all the four screw off the back of the two servos, try to use a good driver, we dont want to damage them now, ok so i find it useful to try and keep the screws still in the case to help hold it together, if you are not so familiar with exactally what cog goes where it is very useful to have a 3rd servo sitting there with the cap off so when you get the 2 your working on apart you know exactally what goes where in what order, ok so start with either one probabily the 90s,
now when you go to take the cap of each servo i found the pin ( the pin that holds 2 cogs in place next to the main (big) cog/big shaft, so two things the big shaft connected to the varible resistor, i know its got a different name, and the small "idler pin"/ support pin, which goes between the top cap and the base,) im sorry if im being too simple but i dont know how much detail to include, so on the 90s when you take the cap off the pin usually gets stuck in the cap(what ive found) so best to get pliers straight away and pull it out carefully, keep its orientation(i dont know if it matters but i did to be safe), put it back into the two cogs watch you dont drop them out, also try not to remove their black grease so you dont have to add more,
pop those cogs out on the pin lay them down, do some gentle force is required to remove the main cog(biggest one), lay that down, also remove the one below now if there is any grease on the little varible resistor/sensiometer?, you should remove it so im told as it can work its way in not that ive ever had problems, i found only on the hxts had some on the top, so when you first pulled the big cog off the varible resistor may have came out, try to hold it in while removing the main cog as you dont want it out and you can damage the wires, so, now everything is removed from the servo, when you pushed the v.resistor back in keep its orientation ie, dont spin it around. push it as far as it goes. now do the same with the other but on the hxt900 the main cog is on a lot tighter than on the 90s, now important, there is a little v in the v.resistor which should point to the end when centered but the main cog has a little mark/area on the side the same as the top of the servo, they both have to point in the same direction otherwire you wont have full throws and your servo will bind, it is hard to explain so i will find a photo,
sooooo, you are now going to put the metal gear in the hxt 900, ok so starting with the "V" centered away from the "pin" put the cog that goes on the main shaft below the main cog on, then get the "pin with the 2 cogs on it put that is with the correct cog order look at you 3rd servo or google pic, now get main cog and check "V" is still all good, now get the main cog with the little plastic (nib/bit its black) backing the same way as the "V" away from the pin. put it on , now, get the mg90s cap and use that get it all siting nicely, put the cap back on and dont bother doing the screws right up just yet, test it, if its all good then you done do it up, also i test all my servos before and after the mod, just to check, like i know one of my 90s' was a slight bit jitterey before i modified it so, when it was doing it afterwards i knew i hadnt recked it,
so now to do that same with the other servo.
also if the gear bind loosen the case (power off) check the "pin" is sitting nicely in the cap lightly tighten up and try again
now i did this becasue i wanted the metal gear for the hxt900, so i havent decided what to use the plastic 90s servo's for yet.
i hope this helps someone i will have to open a hxt 900 up tomorrow as i cant find any photos on the net,