Drive motor options

[Liftoff]

Nice work nick. Could be it was as you said Ellis, some type of sintered steel... strange material to work with!
It's also most probable my fault as well as I drilled them without coolant and the two that cracked clearly overheated!
That material has got some sort of case hardening tho, I could cut through the central part relatively easy with a black HSS drill and reamed to a good finish. The ends were a different story!

I was also drilling slightly larger holes than you were Nick, 6 and 5mm. The 5mm holes came out fine, but the 6mm holes were at the limit a 10T mod 1 gear can take!

20140207_090836.jpg

[overkill]

Hi Ellis! You reminded me how slack I've been so I tried out some new drill on the drill gears. It worked brilliantly, see the details here: http://www.robowars.org/forum/viewto...?p=85652#85652

[Ellis]

Sounds like they are sintered steel (the one you linked looks like it), like drill gears, which are equally impenetrable with a cobalt drill. Nick, in Aus, intended to mod loads of drill gears to make more rugged drill gearboxes but found the same thing as I did, simply not drilling. He ordered a carbide drill and reamer from US, don't know how that went, will ask.

I think the way they do it is they mold and compress fine powder to form the gear and then to make it at all viable they harden it to hell and back, or it may just be very hard from the casting. Either way, I'm quite sure the gears from places such as Technobots and Beltingonline are "proper" machined gears from steel and not cast. Likely to be more expensive but at very least they'll be practical; they can be welded too.

[Liftoff]

Update: finally found some free time and got the motors and escs rigged for a trial, looks fine running on no load and looks quite powerful. One thing I noticed,full fwd to full reverse the motor will come to a stop in a fraction of a second (with a big jerk), but you have to give it a reverse command again to spin in rev. Well, I'll see to that when I get the programming card and have everything connected...

Gearboxes almost done, had a problem with the pinion gears which I just couldn't drill through! Dont know what material they were made from, for me its some type of cast steel or similar. Tried with a cobalt drill, no success, so I machined a new face on the lathe, no swarf came out, just a golden powder...tried to drill again, with some success...again golden powder instead of swarf. I bored about 3/4 of the length of the gear and then again, the drill refused to cut any further...like trying to drill a piece of hardened steel.
I the end I found that the gears had cracked the gears are made of some type of steel for sure as its magnetic and flies yellow sparks when ground, like these:
http://www.modelsport.co.uk/hpi-pini...roducts/363296

I ordered a new set from a different shop and I'm sure these are normal steel and the hole size is correct so I dont need to drill anything... after that the boxes should be done...

[Liftoff]

Any idea from where I could get some laser cutting on acrylic done, at a reasonable price? I'm being asked silly prices locally for a couple of pieces 64x34mm 10mm thick...

EDIT: No longer required - alternate method suggested

[Liftoff]

Great, thanks again Trev. Ordered the remaining parts I needed (bearings, silversteel shaft, loctite, drills and reamers). Will go on with building the boxes as soon as I have everything...and keep you posted

[mightymouse]

Chris,

0.2mm on diameter is perfect. When drilling pre-drill to within a couple of mm of finished size. If the reaming drill has to do too much work it may cut oversize and ruin everything.

Get the ream holes dead size for the bearings and loctite 603 or similar will hold them in the plates without needing retaining plates.

The gears should Loctite well but if not make a small collar and loctite that to both the gear and axle as well.

Trev

[Liftoff]

Thanks for the tips Trev, will surely come useful.
For the idle shaft will use silver steel as that comes ground to size (6mm), I just cut to length with no need for machining. The output cant be made from silver steel though, for ease of machining I'm using a 1/4" drive extension turned down from the original 8.2mm to 8mm. That is because I need a square drive to couple the gearbox the the wheels.

One question regarding reaming before I purchase any drills, how much smaller should I get the the hole drilled? The final sizes of reamed holes shall be 14mm, 12mm, 8mm, 6mm, and 5mm. Would say 0.2mm in dia less be ok?

[mightymouse]

Chris,

been trying to reply all weekend but home pc refuses to connect, work pc is ok.....

If you are making this set-up without a mill then follow a few simple steps;

1; Bolt the 2 side plates together and drill the shaft holes together to ensure they line up.

2; Drill the bearing holes as near to finished size as you can so the reamer cuts dead size.

3; Fit the bearings with Loctite - I prefer 603 - but make sure none gets in the workings.

4: Use silver steel for the shafts and loctite again for your gears.

trev

[maddox10]

I would use simple 2K glue. But that loctite is ok.

[Liftoff]

and best done with a TIG.

Wish I had spare money to have one!

You mentioned metal glue Mario, did a quick search on the subject and found this:

http://www.loctite.sg/sea/content_da...g_Compound.pdf

Looks exceptionally strong and can be installed on interference fit items, will get a some and lock every thing with it.

[maddox10]

It's finicky work,welding such small things, and best done with a TIG.

The solution with the dowel will work, in combination with some good metalglue.

[Max]

@ Max

I see what you mean, and I think its possible to do with a small modification to the shaft. If I increase the shaft diameter from 6mm to 10mm I could put a 3mm dowel axially to act as a key...

That's exactly what I meant- should work well I think.
With the pinion gear I'd use some thread lock or bearing fit adhesive as well as the press fit then should be fine.

[Liftoff]

I'm afraid of welding tiny parts Mario, got a habit of fusing small things into one single part! Yes I thought about getting spare shafts, can use the 6mm silversteel shafts for the gear cluster, but for the output gear it has to be machined to size because of the square drive. That's why I'm using a 1/4" extension for the shaft, the material should be strong enough (chrom-vanadium), the problem might be as Max pointed out, the gear slipping on the shaft... welding is out of question for me - just dont feel at ease welding tiny things where you just cant go wrong!

@ Max

or a pin going thought the shaft or drill half a hole down the axel and half on the gear and put a bit of rod into the hole

I see what you mean, and I think its possible to do with a small modification to the shaft. If I increase the shaft diameter from 6mm to 10mm I could put a 3mm dowel axially to act as a key...

something like this:
gearbox4.jpg

[maddox10]

On the NTM's, just weld it on the shaft. The NTM shafts are cheap.
And to make the shafts yourself, just buy silversteel of the right diameter, and go for it.