We have a handful of 775Pro motors with pinions on them, and we are stumped as to how to get them off.
You can also purchase a gear puller set, they were made specifically for this purpose, and they come in handy in various situations. Here’s a set from Harbor Freight. I’m unsure if the smallest is small enough, so you should spend more than 30 seconds reaearching to find one that fits your needs.
When I had to do this last year I used our bandsaw to make a notch in a metal ruler. The notch was just wide enough to fit around the motor shaft. I placed it between the motor and the gear and then set the unit in a vice with the motor on the bottom so the assembly was supported by the ruler. I next took a bolt that was slightly smaller than the shaft diameter and pounded it with a hammer to press the motor shaft out of the gear.
NOTE: Make sure you have something soft under the motor, otherwise you’ll trash the motor contacts when the motor falls out of the gear.
I have that set for automotive projects, beyond being very large they are not what I would describe as “Harbor Freight’s best offering”
Fair, I’ve used micro ones for this type of application before, and I also propbably would find a better source than harbor frieght if I had the time.
Another way to get them off is by using an arbor press and basically pressing the shaft out for the pinion. It’s more work to setup the work holding, and is only really necessary when they’re REALLY stuck, but it has never failed me.
If you don’t want the gear a little chisel work can crack it right off, or if you aren’t that brave dremel a groove first.
I like to use a a nut splitting tool like this one for this.
If you don’t mind buying something, gear pullers for RC cars usually work well on 775/550/Bag sized motors for FRC. Here’s an example from Amazon. Link
Cut a groove in a steel plate (thin enough to fit under the pinion). Find a pin that fits inside the pinion. If you don’t have a press, carefully set it on a vise and use some means of pushing the pin through. Be sure to have someone holding the motor so it doesn’t fall on the floor.
Has anyone found a pinion gear puller that works on the 775?
During our week 6 competition in Livonia, we smoked the two 775’s on our elevator practicing our hab 2 climb. We had brought two spare motors but did not have extra pinions besides what was already on the robot. While our robot was on the field playing defense, I fabricated this home made pinion puller out of 1x1x1/16" aluminum square tube, a 10-32 socket head cap screw, and a nyloc nut. I drilled a hole thru both sides and then notched one side with a hacksaw. Once the motor was hammered into place, grip the nut with needle nose pliers before tightening the bolt to press out the motor shaft.
After the second pinion was removed, you could see the tube start to deform. This works if you are in a bind, but a permanent solution would be preferred.
I’d love to know if there is a similar solution to pulling pinions off of CIM/Neo style output shafts.
Use a vise or press to gently crush it.
We cut a thin strip out of the thickest steel we could fit between them motor body and the gear. We then set that on a vice and used it to hang the motor from the gear. Get a small rod that is slightly smaller than the motor shaft and use it to hammer the shaft out of the gear. This way you put minimal force on the bearings during gear removal. Just make sure you have something soft to catch the motor when it drops.
The small gap between the pinion and motor body makes this a real challenge to pull for sure; my experience has been mixed due to the difficulty of having something that is both strong enough and thin enough to fit and provide the support needed. There is enough variance that in many cases you’ve got to decide what you want to keep.
Splitting the gear is a reasonable option if you want to save the motor and other attempts to remove the gear have failed (mostly due to the mentioned difficulty in finding something that is strong and thin enough to support the operation).
My experience has mostly trended towards fried motors where I feel compelled to pull the gear as a salvage operation. Since the motor is scrap at this point, I put it pinion gear down in an open vise and give the back end a few whacks with my BFH. You’ll easily drive things to the point where you end up with a substantial gap between the gear and the motor and be able to get a thicker support plate in there to get some force onto the operation.
I always try to use an arbor press rather than a hammer but if you’re only looking to save one part…
This video was very informative and I plan on making this with our mill. Probably won’t work for 775 but neo, cims, minicims are good for this
If you have access to a machine shop, it’s really rather easy to make a gear puller using a bit of box tube, a bolt, and a nut. Cut the tube, mill the slot sufficiently thin, drill the hole, weld the nut (which we’ve found is more reliable than tapping the hole), and turn down the end of the screw to just under the size of the motor shaft (pictured screw isn’t turned down as it’s already thinner than a CIM shaft).