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It's a misconception that brushless motors are all super fast. Many many examples are significantly slower than traditional brushed motors. The big-gun brushless outrunners are almost inconveniently low revving.
I imagine a 16:1 p60 banebots gearbox would handle a brushless up to say 1kw peak power, beyond that the torque involved might be a bit risky? Never worked with them so don't know how tough their insides are.
The Ntm 4248 motor does around 12000rpm at 5s and 1300w, good for the given weight and size of the motor. Thats almost half the speed of a gimson or banebots so it's not going to over rev a gearbox.
The problem I'm seeing is that it will probably need a custom gearbox as I have yet to find a 10:1 ish box. If I still don't find one will have to build my own :-|
Another plus I can think of is the relatively cheaper price of the esc when compared to a brushed one.
I think a few people are coming up against the same problem (I know I am) i.e it's easy enough to get hold of a decent motor, but then trying to find an off the shelf 'box to fit is nigh on impossible.
That's very true David, however it's not too difficult to construct a simple gearbox with 10;1 ratio me thinks...I mean the motor speed is not that fast so the no of gears required is low and normal off the shelf bearings will do.
Have to start looking at some gear selling shops to get an idea of dimensions etc tho...
I fitted 2850 Kv Brushless motors to Gimson GR02 24-1 gearboxes, all it took was drilling 2 3.5mm holes at the right spot.
Well my reason for switching to brushless was a bit more unusual. I took Huntsman to RoboGames 2012 and during it's second fight agaist Last Rites it had all 4 motors fail due to popped out brushes and shattered magnets. Then at our Nationals in 2012 my Vendetta failed in the finals for simalar reasons. So I chucked a wobbly at the world of complex brushed motors and went brought the brushless setup. I wanted cheaper motors that are made with less parts and smaller magnets, and therefore less likely to have mechanical failures from shock.
I chose the because NTM 42-30 750kv because on 4-cell they should hit 10800rpm. With a 10:1 reduction and 100mm wheels that is a calculated 5.65m/s. Under load it's probably half that and would therefore take 1.7 seconds to drive across our 4.8m wide arena which was simalar to my previous robot. I do all my calculations in m/s because we only drive a few meters before hiting the other side of the arena, in a few seconds, so miles or kilometers per hour isn't relatable. So 10mph sounds slow, but 2 seconds across an arena sounds decent, and it's actually the same thing.
If I had to build my own gearbox, would it be ok to use helical gears? Main reason I'd consider them is space, I could use narrower helical gears having the same contact area a wider spur gear would. But not too sure about the extra forces generated by those gears..... any one who built their own boxes used helicals, or knows of some reasons not to use them?
Have a look at the toughbox gearbox options on http://www.andymark.com/Gearbox-Transmission-s/55.htm
Thanks for the link Chris, that's what I had in mind, something down that line. The problem with their boxes is they are quite large for the space I have. But still, got some ideas from their assembly drawings. I could build mine much smaller and probably lighter without the need for helical gears...
Helical gears have an inherent disadvantage , because these load the bearing also longitudal, not only axial. That can be solved by using 2 next to each other in the herringbone setup.
But for our application just straight gears will do nicely.
Hmm, that will defeat the purpose of a light and compact setup if I had to use herringbone gears. I could maybe use helical gears and thrust bearings...but probably its better to keep it simple and do as you said...go with straight gears, any recommendations on who sells loose gears at a reasonable price, preferably within the EU not the States?Quote:
Originally Posted by maddox10
Technobots has a suitable range of gears, and are very dependable.
Christmas shopping time!
Just need some advice before I start ordering stuff... I'm about to order gears for the gearboxes, motors and escs.
The motors I'm going for are these:
http://www.hobbyking.com/hobbyking/s...dproduct=16231
These spin at around 13500rpm on 4s. The diameter of the wheel/track is 80mm, I'm thinking of gearing it down with a 12:1 ratio.
Did some research of available gears and I'm looking at two stages of 6:1 using 5mm wide 0.7mod gears with 10 and 60 teeth.
Any suggestions if this is suitable and strong enough for the above motor?
The NTM motors have a lot of torque, I would opt for mod 1 gears. Z12 to Z 36/Z12 to Z48.
The 12/36 double gear is one you can buy at www.Conrad.com , order number 240320 - 62
, making life easier.
Two 6:1 stages makes for 36:1, not 12:1. Stage ratios are multiplied to get the overall reduction. That setup would get you a bit over 3mph!
Mod .7 sounds a bit small to me (roughly the same as what's in a drill gearbox), and I'd be even more cautious at just 5mm wide. I'd expect to use mod 1, 10mm wide, or similar.
How silly of me! You're right! This will make my life much easier as I can select smaller gears with a larger modulus making the whole gearbox smaller.Quote:
Originally Posted by Ellis
Thanks to both of you, spared me a log of grief ;)
Will have a look at Conrad tomorrow Mario, hope they have decent prices as the gears I found aren't exactly cheap!
Had a good look at Conrad and found the same items for a lower price from the UK http://www.rapidonline.com
Going for 10 and 35 teeth gears with two stages of 3.5:1 for a final drive of 12.25...that will fit in the space I got, the 48T gears will be too large and will require quite a lot of work to fit in.
I estimate the weight of the motor and gearbox to be around 340 gr each, that's a weight saving of 110 gr over my current setup...I desperately need to shed off weight!
Christmas presents finally arrived, slightly belated but that doesn't matter now!
Been doing some sketches for the gearbox in the meantime, I'll upload them and as this is my first attempt to building one please feel free to point out any flaws etc which can be noticed
Attachment 4228
Gearbox details:
2 stages with 10t and 35t mod1 gears.
Gears interference fit on shaft.
Shaft material: chrom-vanadium (a 1/4" drive extension turned down to size)
Bearings: MR126 ZZ 6 X 12 X 4Mm, 6700 ZZ 10 X 15 X 4Mm
Side plates 7075t6 Aluminium 64x41x4mm
Grease : Rocol Aerospec100
The gearbox output shaft will bear no side loads as the drive wheel is supported by its own bearings.
Attachment 4229
Attachment 4230
I'm confused as to where all the gears are mounted, presumably the first gear is attached to the output shaft of the motor, the second 2 gears are on a separate shaft both attached to te shaft with a grub screw so they rotate at the same speed. Then I don't get where the last gear is connected? Is it on a separate shaft inline with the motor's shaft but only supported on one end?
The motor pinion is just below the final stage shaft. The final stage shaft has a bearing in each plate and is supported on both sides.
Thought it would be confusing with just a drawing, 3d is better! Let my try to explain...
The first 10t gear is press fit on the motor shaft. It's not supported in anyway other from the motor bearings (looks solid enough as its got 3 bearings inside)
This 10t gear drives a second gear cluster (35t and 10t). These gears are press fit on a 6mm Crv shaft and turn together (driven by the 10t gear on the motor. This shaft is supported at both ends by two 6x12x4mm ball bearings.
This gear cluster in turn drives the final 35t gear. This gear is press fit on the output drive shaft. The output shaft is supported at both ends on ball bearings. One side is 6x12x4mm, the bearing on the other side is larger in diameter (10x15x4mm) because of the square portion of the shaft.
Here's a couple of pics from different angles...does it make sense?
Attachment 4231Attachment 4232
Chris,
Perfect sense and well engineered. I am assuming there is another support plate wheel side not shown on the model?
Trev
Hey Trev yes there's another plate, the drawing is on pg6 of this thread...its supported on both sides. My thinking behind all this is to get it built without the need of complex machining (milling etc) I got no access to. My intention is to drill all holes on a pillar drill, then ream to size to get the bearings fitting properly. The gears will heat them up and press them on the shafts, should not slip I think?
Looks great,just a quick tip if you bore oversize by accident very easy even on a miller, centre dot all around the the hole and using bearing fit adhesive sets like rock. Good look bearing fitment tolerances are very small
Personally I wouldn't trust a press fit on the final gear, for the gear on the motor it is fine as there is little load on it, the gear cluster shouldn't want to spin on their shaft as there is no load on that axel it shoudo just spin freely but the last gear has lots of torque and will want to slip on the axel- it may work but it could easily fail, I would go for something like a keyway, or weld it to the shaft, 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 if you see what I mean- but like a keyway.
Grub screw on an angle grinded flat would hold,ceros uses roll pins
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.
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!
@ MaxI 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...Quote:
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
something like this:
Attachment 4234
That's exactly what I meant- should work well I think.Quote:
Originally Posted by Liftoff
With the pinion gear I'd use some thread lock or bearing fit adhesive as well as the press fit then should be fine.
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.
Wish I had spare money to have one!Quote:
Originally Posted by maddox10
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.
I would use simple 2K glue. But that loctite is ok.
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
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?
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
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
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 :D
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 :angry: 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...
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.