Minibot motors

Does anyone know how to attach an 3in. long axle directly to the tetrix motor, no gearbox at all?

Is it legal to remove the gearbox from the P/N 739023 Tetrix motor, and use the motor (without the gearbox) on the MINIBOT ?


Yes, that’s pretty much the only way to get up in less than 3 seconds.

I saw a team put shaft collars onto the remaining gear and then tinker around with that, but it kills the gear.

PVC and (lots of) PVC cement?

It doesn’t say you can’t. I saw team 16, 148, and 118 at the Alamo regional with these modified motors and the officials didn’t say anything.

It is legal to remove the gearbox and use the Tetrix motor alone.
From the Q&A…

Tetrix Motor/Gearbox
Posted by 2011FRC2775 at 01/13/2011 05:10:19 pm
In regards to to R47 and R93 Is the Gearbox on the Tetrix motor considered to be integral to the motor? Can the gearbox be removed and/or modified as long as the motor itself is not changed.

Posted by GDC at 01/16/2011 11:47:05 am
No, the gearbox is not considered integral to the motor. Yes, the gearbox may be removed and modified.

Modify Gearbox:
Remove Gearbx:

Off the shelf collars would not be legal. We made them by machining a bolt.

Does anybody have a link to the motor curves of the motor without the gearbox?


Back to the original request now:

Yes, we do. I suppose you want us to tell you?:stuck_out_tongue:

Here is an example, you can experiment from here:
Take a Tetrix metal shaft. Carefully drill a hole with a #40 drill bit into the very center of one end. Press this onto the motor shaft carefully, to avoid damage to the motor (meaning: Hammering is bad).

Some tips:
Hot metal expands, which may make an interference fit easier to assemble.
Long shafts under radial load must be supported at the far end.
Latex tubing is not very abrasion-resistant.
Rubbing alcohol makes a fine lubricant for assembling rubber onto metal.

Good luck.

Thanks. I just found this, which has speed and current in addition to power and efficiency.

The gear ratio is 52:1, so the motor free speed is something >8000 rpm.


Do keep in mind the motor gearbox is almost laughably inefficient (hovering around 50%)

R92, S. Indicates “mechanical fasteners” are allowed. A shaft coupler/collar mechanically fastens two shafts together…there were several examples of minibots that passed inspection with such couplers/collars this weekend.

Pretty sure they changed that to “mechanical hardware” in an early update, might wanna check the current version manual.

Nope, they changed it from “mechanical hardware” because all sorts of people were getting confused. It reads “mechanical fasteners”.

Yeah, I just discovered that as I was comparing the test data with and without the gearbox. I was wondering if it’s even the same motor.


The correct read on R92 is
S. Mechanical fasteners (e.g. screws, bolts, etc),
I would be hard pressed to include COTS shaft couplers in that definition without direct GDC guidance on the subject. Something manufactured from the allowed materials would be OK.

Do you have a lathe with a drill attachment and someone that knows how to use it?

Do you have a drill press?

We would have had difficulty with drilling a proper hole or press fitting the aluminum round bar without both machines and some expertise…

If no local expertise, find a local team or machine shop that will lend you a hand to make the parts and assemble them to your specifications.

There are many teams that try to get by with hacksaws, vises and power drills and don’t know what a gear-puller or a press fit is.

To me, it’s not very sporting to get you to try to imagine what the right machine shop tool is if you have not been trained in a motor machine shop nor have access to one.

Now it might be that you have a motor expert mentor and machine shop and you asked here before asking the local team mentors: but I find that unlikely.

Good luck.

(I would not advise you to try to make the hole in the cylinder or try to attach it to the motor without the proper tools).

Right, Update 3 changed hardware to fasteners…But “etc” is so esoteric, Al! I do agree that someone considering purchase of shaft coupler should check with the GDC though.:slight_smile:

Inefficient?- it all depends on perspective…

@$30 a pop and a tendency to quickly burn out when bumping into a stop- the motor with gearbox* is very efficient *at generating revenue.

The first reason we got rid of the gearboxes is the motor sounded so much better (i.e., not that sound of impending doom) when relieved of their gearboxes. We’ve had 5 motors: 2 with gearboxes have already burnt out.