Playing around with toys but cannot figure how to connect an axe to a motor shaft

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Grossel

Well-Known Member
Hi all.

I'm just fouling around and tries to put a motor in a simple toy car.
The problem I face is fairly easy to explain: Both the motor shaft and the axe that leads to the wheels has a diameter of 3mm.
I got a set of heat shrink tubes, but I doubt that they have enough mechanical strength to lock the two axes.

I've also got an idea of using a metal tube and make use of the expansion coefficient so that it will lock onto the motor shaft and axe.
But I'll have som problem with making the connection tight since I do not have a proper mechanical workshop avaiable.



Any ideas?
 
How about a stand-off for a 3mm screw with a set-screw on each side or small holes drilled and nails glued into place. E
 
You want one of these: https://www.electro-tech-online.com/custompdfs/2012/09/5Css5CPDF5C80506079.pdf

There are couplings available that will compensate for straightness. When using most of those, the output end usually needs to be supported.

Anyway making one would depend on a couple of tools. One is called an "Over reamer" as in over/under reamer. "under" reamers are used for "press fits" while over reamers are used for slip fits.

Me, being used to US standards, you can buy say 0.124", 0.125" and 0.126" reamers for 1/8". So, if you had a 0.125 precision shaft the shaft could be pressed into a 0.124" hole and would slip into a 0.126" hole.
 
Hi Grossel,

your problem wasn't mine when I was young (which was about 60 years ago).

I used a cardanic drive for one drive wheel. (With toy cars you don't necessarily want the same behavior as a race car).

If you don't know what a cardanic drive is just take a look underneath a truck (lorry in English).

There is a drive axle going all the way underneath the truck from the gear box into the differential. The connection is NOT straight and therefor the cardanic drive connects the gear box and the differential.

Both drive axles are just connected by slipping one into the other using "mouse-teeth" (literally translated from German to English).

If you want to use heat shrink tube make sure both axles are completely free of oil or grease and don't move the connection while cooling.

Just consider both parts have to be perfectly inline for a fit with tube. Otherwise the connection will shake lose when operating.

Boncuk

This toolbox contains a cardanic drive. It's the fourth item from left bottom.
 
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Hi all. Thanks a lot for enligthen me in mechanical parts.

I'm not that familiar with english names of mechanical components, but I google as I learn more (r was it the other way aroun). Only thing I cannot get is what a "slip fits" is. It may not be important for this case, but good to know. I may considering bying a set of reamers (it's always nice to have enough tools, even if used just once).

I will try heat shrink tubes and see how that works, but I doubt they will last for long.

I also liked KeepItSimpleStupid's suggestion, I just need to find out where to buy it from.
 
One cheap way would be to use a short piece of extension spring, inside dimension just smaller than the shaft, and "screw" the spring onto the shaft ends. E
 
canadaelk said:
One cheap way would be to use a short piece of extension spring, inside dimension just smaller than the shaft, and "screw" the spring onto the shaft ends. E
Click to expand...
Hi. That sounds as a good idea. I have to thaught about that. I think I would need to glue the ends of the spring so that the shaft cannot rotate around the spring.
 
Mikebits said:
The coupler idea mentioned by KISS is the best way to go.
Click to expand...
Possible. However, since it's a toy (don't build this for lasting very long) and since there is a fair chance that I have a spring somewhere I will try this.
What problem I expect to face is that I cannot find a spring that is enough rigid to withstand the motor torque.

Using the heat gun is last resort, as the heat may damage the toy as well.
 
Mikebits said:
The coupler idea mentioned by KISS is the best way to go.
Click to expand...

Hi Mikebits,

either you have superview all the way from California to Norway or you hold back information you got about the project.

The coupler you suggested will work fine under the provision that power source (motor axle) and target (drive wheel axle) are mounted in an absolutely straight line with no angular offset between them.

Here is another image of a cardanic drive. The function is self explanatory.

Boncuk
 
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That's nice to be sure, but more costly, harder to get, and I don't recall Grossel mentioning that there was an offset.
 
Hi, no offset is not an issue in this particulary case. However, It would be nice to know how where to get an angular cardanic drive to future projects
 
no offset? id use metal tube, break line has been my recent fav, lots of choice for diameters and soft enough to work with, and some 5min epoxy to make it all stick(the dry hard stuff).

..but thats just my ghetto approach to things..
 
doggy__ said:
no offset? id use metal tube, break line has been my recent fav, lots of choice for diameters and soft enough to work with, and some 5min epoxy to make it all stick(the dry hard stuff).

..but thats just my ghetto approach to things..
Click to expand...
Epoxy, if you're talking about the same two component as I think of, that is the same as I use to prevent my car from rusting.
However, to using break lines I need to know how to apply those on an axel. Isn't break lines just weaved metal so it's soft? Will it sustain if it is subjected to torque?
 
nono, there are break lines out there that look like metal tubes, no rubber or anything, im sure for a battery rc car it will sustain,
all i can find is a pic of the endpart, but you can see what the line looks like all the way through
https://www.northernautoparts.com/Images/Uploaded/AGS/AGS_brake_lines_316.jpg

epoxy:
i think you are talking about stickey tack?
here is best example of what i get looks like
https://www.tfw2005.com/boards/atta...er-glue-plastic-fusion-epoxy-glue-15277_l.jpg

however i just remember the picture of the type i get, it is for plastics, and i find that when it drys it hardens pretty tough, unlike in the example pic, the stuff i actually get is clear, an in blue packaging,

i cannot gaurente that this will work, its just cheap method and what i would try to do ...
 
@Doggy__, I'm still not sure I got the concept about break lines. Are they supposed to tighten when the screw is screwed toward where it cover the axle and motor shaft?
 
screw tighten would work, better than epoxy even, just as long as you keep everything centered.
 
Hi Grossel,

the part can be found with lots of different axle diameter drills and maximum angles to transfer mechanical power up to slightly less than 90 degrees.

You can find it at model shops where they sell car and ship models. Minimum drill diameter should be 2.5 going up to 8mm.

I suggest to look at ebay. I searched there and got a bunch of different "cardanic drives" within a few seconds, some of them under one $.

Boncuk
 
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