pushing a gear on a fp
 

ok so my team has pressed 2 gears on one successfully the other we got on but it bent and then the bushing exploded so we got a new motor and removed the sun gear from it but now we are having trouble pushing the gear on with out bending the shaft

any hint on how to get the gear on??

Re: pushing a gear on a fp
 

If you can heat up the gear a bit without heating up the motor, that will help. also, you shouldn't be using the can or mounting holes to hold the motor while pressing. You need to put the corner of a plate under the back end of the armature to support it. Also, make sure your press is in good order (not real sloppy) and have someone hold the motor straight while the other person slowly presses the gear on. A bit of oil on the shaft may help as well. If you still can't get it without bending the shaft, the press fit may be to tight and you may want to ream out the gear half a thou or so and try again.

Re: pushing a gear on a fp
 

All sounds like good advice to me.

I've pressed on a lot of gears in that shaft size in recent times. Another thing to notice is that sometimes the shafts are oversize and the gear is way under. Sanding a running motor with emory paper (cover holes to prevent dust from entering motor) is a decent way to fix this. Otherwise, it's almost impossible to press on straight.

Re: pushing a gear on a fp
 

Back in the late 90's I used to work in the PowerWheels Plant as an Automation Engineer that assembled these same motor gearbox assemblies and I can support your troubles in pressing a gear onto the shafts of these motors. I was derictly invloved in the design of the machine that pressed on these gears so I can give you some do's and don'ts. First, you must support the end of the shaft so the motor bearings do not take the axial load of pressing the gear onto the shaft and it goes for the removal of a gear as well. The bearings in these motors are very intolerent to axial loads. Second, I would not recommend sanding the shaft dia smaller for two reasons. First, the ribs on the shaft diameter were intended to deform the gear material during the pressing of the gear onto the shaft to provide interference between the two parts to prevent slipping under loading conditions. Secondly, during your sanding process, you mentioned blocking the motor holes to prevent debris from getting in the motor, by blocking the holes you are blocking the air flow used to cool the motor internels, which is necessary even for short durations, to extend the life of the motor.

The process we used to press the gear onto the shaft was to lay the motor on its side in a vee block, support the non gear shaft end with a fixed anvil, support the gear with another vee block so its centerline is matched to the motor's and then press the gear onto the shaft with a quick pressing motion. This may sound easy, but we struggled with this for quite some time due to the variables in the motor assembly and the gear manufacturing tolerances, but we were trying to do this in a 2.5-3.0 second time frame per assembly.

Hopefully this helps!

Re: pushing a gear on a fp
 

Refer to the white paper here on CD that pertains to Nothing But Dewalts.

We (Team 47) have a fixture that aligns/guides the pinion from the Dewalt on to the shaft of the FP (we have the hole opened to exact size by wire EDM +0.0000 -0.0000). we then use an Arrbor press to press on.

It is very important to correctly support the motor and the shaft. Bad support means a bent shaft or damaged bearing/housing.

I am sure that we posted pictures if this fixture (Josh Murphy) did that a few weeks ago. If they are not up I will get them posted.

Re: pushing a gear on a fp
 

Thank you for correcting me. I should have noted that my advice was based only on personal experience and anecdotal evidence.

So, how can this advice be applied to teams using a vice? or an arbor press?

Also, I have noticed some gears I was pressing on to FP shafts (I have used them outside of FIRST applications) have a bore of .122ish. Is this still large enough for it to work with the spline? I was never able to get ones with that small of a bore pressed on without bending the shaft if I hadn't sanded them first. Is this because I didn't have a method of keeping the two aligned on centerline? If they were aligned, would that still work with that small of a bore?

I would really like to know the proper way to do this, thanks for your reply.

Re: pushing a gear on a fp
 

Hello Adam,

My comments were to confirm your difficulties in working with these motors and caution you on their sensitivity. They very inexpensive (aka Cheap!!) and very hard to work with. The gears that were designed to be used on these shafts were a Powdered Metal Material and very fragile during the pressing on the shaft and we found it very difficult to press the gears on consistantly. During our trials on the machine specifically designed for this purpose, we had buckets and buckets of bent and broken motors and gears. As I mentioned earlier, we had the motors on their side in a Vee Block to clamp them in place during the pressing operation. We then aligned the gear to the motor centerline for the pressing operation. We actually used a steel disc with holes in it to hold the gears during the index of the machine. Picture a Ferris Wheel where the gear is loaded at 12:00 position and then indexed to the 6:00 position for the pressing operation. When the gear is aligned to the motor shaft we used a pneumatic cylinder (3.5" dia bore double piston) that had a pin that was slightly smaller than the gear diameter, mounted to its rod that would push the gear out of the hole in the disc and onto the motor shaft. During the pressing process the motor would move slightly axially to contact the motor shaft to the stop anvil that would take the force of the pressing action.


Trying to do this consistantly with an arbor press could be done with some fixturing to align the motor centerline to the gear centerline during the pressing operation. If you had a vee block and mounted a plate to its end that had a hole in it to guide the gear while it is being pressed onto the shaft by a pin that is being pushed by the Arbor Press Ram should work with a high success rate.

Again hopefully this helps.

Re: pushing a gear on a fp
 

I'm not sure about keeping everything on center, but I know a way that has worked for me in the past. From my limited experience in pressing gears onto Fp's the pinion gear, if kept square(or perpendicular to the shaft), will auto center itself when being pressed on to the shaft.

So the setup I have used, consists of a v-Block with the screw clamp and a parallel. You put the Fp in the V-Block and tighten the screw clamp down onto the motor enough to hold it against the block. then place the parallel under the motor and against the block to support the shaft. when set into an arbor press everything should be square and easy to press on the pinion.

Re: pushing a gear on a fp
 

Ive had no problems with this method of pressing on the pinions.

Place the gear flat on the bottom of your arbor press (Note, this is with a lever actuated press with very little slop--not a hydraulic press, some of which have a LOT of slop).

Place the motor shaft down on top of the gear, with the shaft on top of the hole in the gear. Level the motor roughly by eye. very gently and slowly apply pressure with the arbor press to begin pressing the gear onto the shaft. You may have to bend the tabs for the leads down a slight bit to make sure you're pushing only on the shaft where it exits the rear bearing.

Every few seconds remove pressure and watch for the motor to "spring" back. If it moves you're not aligned straight. Move the motor/gear under the center of the ram until you no longer see any spring.

Continue pressing and checking until the gear is where you need it.

The above method should come out centered, as you're relying on the bore of the gear being perpendicular to the face of the gear, and you're referencing the face of the gear off a flat surface.

For anyone who hasn't done this often, these are a VERY tight fit. You will in all likelihood feel like you are going to break the motor while doing this. Just go slow and make sure you have everything perpendicular and you should be fine.

Re: pushing a gear on a fp
 

i really have come hate these things even with there wight and power just give me the big cim back

there way to fast 30,000 rpms
there way to hard to mod
they have the really really bad leads
they have heat problems (not a big deal throw a fan at it and a heat sink)

all these makes me wonder how they can run at 24 volts (a common mod by most dads with a tech background)

-grumpy colin

Re: pushing a gear on a fp
 

~15,000

Really, between the AM planetery, the dewalt gearbox, banebots products and many other COTS gearboxes for motors with a 3.2mm shaft, there are more mounting options than any other motor.

They are kind of weak, that's why it's important to put proper strain relief on the wire to protect them.

They can make a lot of heat when stalled, but when they are used in proper applications it's never a problem.

They run pretty well at 26 Volts as well; worked awesomely in my 12lb battle bot.

Re: pushing a gear on a fp
 

I'm sorry to revive the thread but are there any other effective ways of pressing gears onto the fp shafts?

We have a 20 ton shop press and it makes it very easy to bend the motor shaft.

thanks, Vivek

Re: pushing a gear on a fp
 

How much slop is there in the ram?

If it's like our hydraulic press and it has a lot of slop, you're going to constantly be fighting it to get a straight press.

Re: pushing a gear on a fp
 

Well, it is a lever press and I don't have anything to compare to but it seems like it has very minimal slop. The surface of the ram is pretty rough though.

thanks, Vivek

Re: pushing a gear on a fp
 

While it is a bit hard on the manual mill's quill and chuck - the method I like to get everything lined up and the gear in place:
1. make sure the bore of the gear is properly sized
2. mount a sacrificial Al block in the vice
3. mount the drill chuck in the spindle with a small center drill with a tip smaller than the 3.2 mm shaft
4. peck a divot in the Al block - less deep than the length of the shaft extension out the back of the motor
(then without moving the table of the mill)
5. remove the drill bit and open up the chuck until the outside edge of the chuck is ~ the same size as the outside of the gear
6. set the backend of the FP shaft in the Al block's divot and the gear loosely on the other end of the output shaft
7. press the quill down until it contacts the gear and holds it in place - then use your fingers to align the gear with the chuck teeth
8. press a bit more and the gear should slide onto the shaft without buckling the shaft

For small motors, big mills, and robust chucks - I don't worry too much about the stresses - for smaller equipment I would proceed with caution - could take the load off of the chuck by constructing at stepped shaft that will seat on the bottom of the chuck to align and press with.