Installing the Aluminum Servo Horn provided with Hitec Servos

First things first, if you plan on using a Hitec servo with your T1M Mini, you're going to have to make a few minor modifications to get the servo to work properly.  Xray provides in the kit two servo horns, one for Futaba servos, and the other for KO, JR, Airtronics, and Multiplex servos.  So what's the difference? - the number of teeth on the output shaft (spline), which translates to overall diameter of the output shaft.  Futaba servos use 25 teeth, and therefore have the largest diameter output shaft.  The rest use 23 teeth resulting in the smallest diameter shaft. Well then along comes Hitec and much like Goldilocks, decided that the Futaba servos were too big and the rest were all too small but 24 teeth seemed just right.  So as a result of that kind of thinking, all Hitec servos and servo horns use a non-standard 24-tooth spline.  Or maybe they thought of it first and everybody else is off their rocker?  Either way, just remember, all servo horns are not alike and they must be mated to their proper servo or there will be some stripping factor going on, or they won't fit at all.  Guaranteed.  I know, my KO, JR, etc. servo horn stripped out on my first test drive (and it's the smallest, so you'd think it would fit even tighter over the Hitec servo, but that's just not the case).

So the two servo horns provided in the T1M kit will not work.  Hitec provides several servo horns with its servos (all of which appear to be for airplane use) and their digital servos even come with this really cool blue anodized aluminum servo horn.  The servo horn is predrilled with 4 holes and the 2nd to last hole is even tapped for a M2 screw.  In comparing the length of this servo horn with the ones provided in the kit, it appeared that the 2nd to last hole was going to be a perfect fit, and it was. 

But here's the next problem, the servo horn is tapped for an M2 screw and the rod ends and pivot balls in the kit all use M3 screws.  So this is what you have to do.  Drill out the tapped hole with a 3/32" drill bit and then tap it with an M3 tap.  I didn't have an M3 tap, but I do have a 4-40 tap.  So I tapped it with the 4-40, just to get some threads going, and then "tapped" it again with a spare M3 screw.  It wasn't easy.  M3 screws are larger in diameter than 4-40 screws, so the fit was tight, and the threads were all wrong, but once the screw went it, it came out a little easier.  The screw showed some wear on the threads from the "tapping" but will suffice.  I thought I could just use a 4-40 screw to tie the linkage to the servo horn, but since the 4-40's are smaller than M3 screws, and the pivot balls were designed to accommodate M3 screws, there would be too much slop in the steering to even be drivable.  I had to use the original M3 screw.  And if you've got an M3 tap, that will work even better.

I removed the tie rod completely from the dual ackerman servo saver, so I could have more room to screw the servo horn into the pivot ball and rod end.  Again the fit was pretty tight, but the screw threaded through without any problems.  Now I had the servo horn connected to the tie rod and the fit was good with no slop.  I reattached the linkage to the servo saver, and loosely positioned the new servo horn on the output shaft of the servo.  I clicked on my radio and car, got the servo all centered up on using my trims, and then installed the servo horn with the wheels as dead straight as I could get them.  With everything tightened down, I cranked the wheel a few times back and forth to make sure there wasn't any rubbing and that was that.  I've got my sweet blue aluminum servo horn to match my sweet blue chassis.  And hopefully the next time I run into something (like a 2 oz. plastic cone) the servo horn won't completely strip out leaving me with a car that only goes in circles (like what happened to me today).

Aluminum Servo Horn Installation