Newsgroups: comp.robotics
Path: brunix!uunet!magnesium.club.cc.cmu.edu!news.sei.cmu.edu!bb3.andrew.cmu.edu!crabapple.srv.cs.cmu.edu!e4.ius.cs.cmu.edu!hbb
From: hbb@cs.cmu.edu (Ben Brown)
Subject: Re: Micro Motor Hints
Message-ID: <CAFK7J.EGt.1@cs.cmu.edu>
Keywords: Motors etc for small bots
Sender: hbb@e4.ius.cs.cmu.edu (Ben Brown)
Nntp-Posting-Host: e4.ius.cs.cmu.edu
Organization: CMU Vision and Autonomous Systems
References: <C9sr4x.F98@math.uwaterloo.ca> <2211viINN8si@uwm.edu> <1993Jul15.153306.7471@webo.dg.com> <1993Jul17.125203.1402@phx.mcd.mot.com>
Date: Mon, 19 Jul 1993 21:11:40 GMT
Lines: 47

In article <1993Jul17.125203.1402@phx.mcd.mot.com>, schuch@phx.mcd.mot.com (John Schuch) writes:
> In article <1993Jul15.153306.7471@webo.dg.com> pmalenfa@kitkat.webo.dg.com (Paul Malenfant) writes:
> >In article <2211viINN8si@uwm.edu>, rick@ee.uwm.edu (Rick Miller - Crazed Newbie Roboticist!) writes:
> >|> Anyway, I thought it would be nice to start a list of DOs-n-DON'Ts for small
> >|> motor purchasing/handling/use to prevent overentheusiastic newbies like me
> >
> >Has anyone ever tried using a die/tap to put threads onto a shaft?
> >I've never used one of these tools.  Do you need more clearance than
> >the motor permits?  Is the shaft too hard to be cut?  Will the wheel
> >be too crooked when it is screwed on?
> >
> 
> Threading a small motor shaft is damn near impossible. The best/easiest solution
> is to use something like a Dremel tool and grind a flat on the shaft. You then run 
> a set screw through the collar of your wheel to this flat. This should hold very
> well however severe vibrations can bake the set screw back out. I'd put a drop
> of LocTite on the screw after tightening it.
> 
> John
> 
> 
I've used Loctite products successfully to hold gears and wheels on
small shafts. Drill or ream a hole a few thousandths of an inch bigger
than the shaft. (A number drill will often do the job.) Clean the parts
with alcohol, etc. Apply the adhesive to the leading edges of the shaft
and hole, and slide the parts together with a turning motion to 
distribute the adhesive. (Chamfers on the leading edges will help
the adhesive to flow into the gap.)

The Loctite cylindrical-parts-bonding adhesives (available in auto parts
stores and eleswhere) are rated at 1000s of psi shear strength, and 
my experience is that a properly assembled joint meets this spec. So,
for a shaft of radius R and length L, you can expect the joint to 
transmit

	Torque = (approx) 1000 psi x R x L x (2 x pi x R).

For example, if R = 1/16" (1/8" diameter) and L = 1/4",
Torque = 6.13 pound-inches = 98 ounce-inches, which is a lot more than
a typical small motor (say R/C car size) will produce. 

If you need to remove the gear/wheel, support it on two plates (or one
plate with a slot for the shaft), and press or tap the shaft out with 
a hammer and punch. Don't pull against the motor--you'll likely destroy
the bearings.

	Ben
