Minibot motors

[Chris is me]

Or you can do away with the transmission altogether.

Other than being ridiculously long and complex I don't see what's wrong with the above solution that 1322 posted.

[Chickenonastick]

We were attempting to design a minibot with surgical tubing rollers, but couldn't find the sweet spot for the rollers to actually work.

[Mr V]

Originally Posted by Ether

Tom, you said the 10.4:1 mod was easy. Would you be willing to post a bit more detail how you did this? Thank you!

Here is how we make 10.4 to 1 gear boxes.

We make a spacer out of legal material that fits between the gear on the output shaft and the output end bushing that makes that gear mesh with the input gear.

Then you must machine the input end of the output shaft to fit in the bushing and provide the proper thrust clearance.

The input gear stays on its' original idler shaft with the original spacers and there is no need to modify the case. This keeps the machined lip that keeps the end plate square.

The down side to this method is that the output shaft is a precision polished piece and you can't replicate that surface finish. That means accelerated wear of the input end bushing.

In our prototype boxes there is noticeable wear, however that includes a number of minutes of run-in time and dozens of runs between the different wheels and frames we tried. That set is getting retired since we have more transmissions than motors, having let the magic smoke out of a couple.

We also tried the rod wheels w/o the trans and we are not going that route. Yes the direct drive gave us our record time but was no where near as consistent.

[Tom Ore]

If you look at the four shafts in the gearbox, there is a 10 mm center distance between the first three with a total of 40 teeth in the mesh. The first pair of shafts have a 10T / 30T combination, the second pair has a 15T / 25T combination. All three of these shafts have a 12.5 mm center distance to the output shaft. The final reduction is a 10T / 40T combination or a total of 50 teeth in the mesh. Since all three shafts are 12.5 mm from the output, the final reduction gear can be placed on any of the first three shafts and still mate properly with the output gear. To make the 10.4:1 ratio, attach the output gear directly to the input gear. This leaves a stack of 4 gears with only the first and last actually being used. You have the 26T helical input gear, the 10T gear, a 25T gear, and the 10T output gear. The transmission ratio is then 26/10*40/10 = 10.4:1. The advantage of this arrangement is that the only modification required is to attach the input gear and output gears together. The gear box and spacers do not need any modification - the spacers just need to be moved around a bit. The output gear has a very thin spacer under it - we moved that from the third shaft from to the first.

[JOClarke]

Does anybody know what size the screws that connect the tetrix motor to the transmission plate are? The really small, short flat head phillips screw. We have lost some and it is an expensive venture to buy more tetrix motors/gearboxes just to get the screws. We are definitely more careful when pulling the motors now.

[joeweber]

Last night I was able to grind down the shafts and use them in direct contact with the metal pipe. It did work but it still was under powered and just the slightest drag would smoke the motors. The couplings are the aluminum slugges that go inside the tubes, we drilled the center to fit the motor gear and the shaft than drilled setscrews into it. I think we will stay with our original design (design #7) even though it is not the fastest, it is fast and solid.

[Bill_B]

Originally Posted by JOClarke

Does anybody know what size the screws that connect the tetrix motor to the transmission plate are? The really small, short flat head phillips screw. We have lost some and it is an expensive venture to buy more tetrix motors/gearboxes just to get the screws. We are definitely more careful when pulling the motors now.

those are M2.5 on my motors

[DonRotolo]

Originally Posted by joeweber

I place rubber electrical tap over this shaft which is legal but there is nothing else small enough that is legal.

*cough* latex tubing *cough*

Originally Posted by Captaindan

but a 3sec robot is possible with proper engineering it is totally up to the builder/team

THREE seconds? Goodness, we're down to one point three seconds now.

Originally Posted by JOClarke

Does anybody know what size the screws that connect the tetrix motor to the transmission plate are?

I agree with above, I get 2.5 mm x 0.45 pitch (which is standard). McMaster has them for about $4 a box of 100, depending on length.

[Bill_B]

Originally Posted by Tom Ore

... The advantage of this arrangement is that the only modification required is to attach the input gear and output gears together.

So these two gears are on the same shaft (1st) and the other gear is gone? Connection via roll pin? welding?