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Need new motors? Grind a gearbox? Adding teeth to a pinion?
#146785
HI all,

I recently acquired a dune racer which has the Gear Box shown below. I believed this is a 7R gearbox but not 100% sure and am hoping someone here can charm in on this. I think this gear box can accept pinion gear of 16T 32P. If my guessing is correct, would 775 motor upgrade works if I buy these parts off amazon? or do I need to buy another gearbox that compatible with 775 motor?

775 Traxxas motor:

https://www.amazon.com/Traxxas-Titan-Motor-10-Turn-Volts/dp/B001SETT0Y/ref=sr_1_1?s=toys-and-games&ie=UTF8&qid=1502727582&sr=1-1&keywords=titan+775+motor

Pinion Gear:

https://www.amazon.com/Traxxas-3946-16-T-Pinion-Gear/dp/B0006O5L3Q/ref=sr_1_1?ie=UTF8&qid=1502727104&sr=8-1&keywords=32P+16T+pinion+gear

Here is the gear box picture:

Capture.JPG


Thanks
#146849
The pinion gear you linked to is for 5-series motors (the specs are not very clear, but the Q&A is), and won't work

what is the bore diameter on this pinion gear? will it fit the traxxas titan 775?
Answer: no it will not its bore hole is 3mm and the Titan 775 shaft is 5mm,let me know if you need any more help


Try:
https://www.amazon.com/HobbyStar-Pinion-Hardened-Steel-5-0mm/dp/B014U2OI6K/ref=sr_1_3?s=toys-and-games&ie=UTF8&qid=1503092293&sr=1-3&keywords=16t+32dp+5mm
or
https://www.amazon.com/Axial-AX3842-Pinion-Steel-Motor/dp/B008JXKJKG/ref=sr_1_2?ie=UTF8&qid=1503092373&sr=8-2&keywords=16t+32p+5mm+pinion

The motor you linked should work. Likely fine at 12V but I think you'd want to upgrade to relays and larger wiring for 18V+ (though someone commented that they've successfully used them at 18V). These will pull more current at startup.
It would be nice if Traxxas actually had real specifications for their motors.
#146875
Thanks for the info. I am thinking of upgrading the gearbox from stock (16T) to gearbox with 21T like this one:

http://www.mltoys.com/Power-Wheels-Mustang-and-C7-Corvette-Gearbox-p/00968-2821.htm

This is possible right? or I am stuck with the gearbox with 16T pinion gear?

And then get the Traxxas titan 775 with either the pinion gear from Amazon with 5mm bore:

https://www.amazon.com/HobbyStar-Pinion-Hardened-Steel-5-0mm/dp/B014U2NVO0/ref=sr_1_3?s=toys-and-games&ie=UTF8&qid=1503286161&sr=1-3&keywords=21t+32dp+5mm

or this from mltoys:

http://www.mltoys.com/product-p/775-pinion.htm

I have the motor heatsink from hobbyking so that should ease out some motor heat. I plan to run 18v for my kids' dune racers and maybe upgrade to steel first gear for longevity (maybe later after 18v experimentation on upgraded gearbox and motor)
#146886
You can buy the Corvette gearbox (21-23T) and use it with no problem. However, if you are putting in an aftermarket motor, you should buy a 22T aftermarket gear for it (not 21T). This is just like the 15-16-17T range; the one in the middle is the normal pitch, where the 15/17 are custom-built to still mesh with standard gears and are smaller diameter than the normal 15 or 17T ones would be. The 21/22/23T has the 22T as the "normal" size.
#146898
Yes, I'd imagine he is.
18v on stock is fine, beyond that you'd want something like http://eastcoastpowerup.com/ provides.
Keep your terrain in mind, when ordering too much $ in parts for stock, because if it's all hilly grass and mud, with some roughhousing 65 pounded(s), a torquey motor in high pinion with large diameter drive tires may not have the end result you desired.
#146900
Well here is my situation:

1. 2 kids with 2 dune racers
2. No MUD, just roughly about 90% grass with hills that goes up to 35-40 degree angle (I have walkout basement so front yard is higher than back yard) and 10% driveway ride
3. Running at 12v 12aH when going up the hill portion of it seem to slow down a lot and wire is getting warm (guess this is expected with stock motor) for riding so many rounds like this

My goals: How to make the dune racer be more efficient at riding on grass and hills?

1. Add more torque so these kids can ride up the hill a little easier (hence the 775 motor idea)
2. More speed to push the pw up a little faster

So I guess I could either:

1. Use stock gearbox and motor and just upgrade 12v to 18v setup and be done with it (not sure about going up the hill part since faster speed but same torque)
2. Use the stock gearbox and upgrade to 775 motor with 16T pinion gear with added heat sink to the motor and upgrade the voltage from 12v to 18v (I hope this will give the same speed as stock 550 motor on 12v or better but more toque since I will be on 775 motor) - Do I need steel first gear to be safe running at 18v?
3. Use higher tooth gearbox (like the corvette one above) with 775 motor and 22T pinion gear with heat sink and 18v setup
#146911
Higher-tooth gearbox is going to lower the effective torque at the wheels. It doesn't sound like that's really what you want.

If you're willing to do 18V and want to try the budget route (more work):
Nichibo RS775-7013F motors (4 for $16 shipped from Jameco/ebay) -- see my motor database sticky post for links or search ebay for "Nichibo 7013f"
16T pinion gear ($15-20 for a pair)
Centering rings and/or Spacers (mltoys or make your own)
+6V for 18V total

This should give you 2x the torque of stock and 50% more speed, and the max current draw will be ~50% higher than stock. The motors should handle 18V with no problem. If the stock wiring is warm at 12V, it may get excessively hot at 18V with any motor on that type of terrain, but "warm" to the touch may not be a problem (I'd generally be more concerned about the switches).

Do you need a steel 1st gear with this setup? I'm not sure -- I've only broken 1st gear when I overheated a stock motor (it overheats and weakens the plastic too).
#146918
When I heard 50% more current, I think about heat being added more to the stock pw wire. They use 14 gauge wire right? I am thinking of redoing the harness wire to 10 gauge or something if needed. I don't plan to upgrade the pw to 24v since I don't want to use the front drawer (my kids are still using the front storage) so 18v is pretty much all I wanna go to since 12v is probably too slow to go up the hill.
#146919
Yes, it will add more heat to the wiring. Upgrading the wiring alone won't solve all of the problems because the switches are also a limiter (rated at 30A average, but driving two motors, so it sees double the current vs. most of the wiring). The peak current draw is worst at a start, and that's what I was quoting -- and that is much lower than most of the aftermarket 775 motors (eg. the Banebots 18V will pull 134A @ 18V from a stop, vs. 100A for these -- it turns that extra current into more gearbox-breaking torque if you don't have an ESC or other limiter). You should still expect 50% more currnet when running also since you've got overcome more drag and/or gravity at the higher speed.

To really do the wiring upgrade right you'd want to buy some 30A/40A relays along with the heavier wire.

If you like tinkering, you could do this in steps: get the motors and pinions and just run them 12V (33% more torque vs. stock, same speed, ~10% more current). Then try running 18V and see if it looks like it'll get you the power you want, and the kids can use it while you decide on the wiring changeover. If you buy a 4-pack of the cheap motors and a pair of pinions you're only out about $35-$40 (with another $15 to get two more pinions if you end up deciding to do the same for the other racer). You will need to make centering sleeves for the motor ends -- mltoys sells very nice ones on their page or you can buy a piece of 1/2" PVC and drill it out with a 11/16" drill bit. The 1/2" PVC is exactly the correct OD for the cutout in the gearboxes.
#146920
Hammer-fm wrote:...or you can buy a piece of 1/2" PVC and drill it out with a 11/16" drill bit. The 1/2" PVC is exactly the correct OD for the cutout in the gearboxes.


Do you have picture of how you did this? I am assuming the 1/2" PVC pipe will go between the gearbox and the motor as a spacer? Not sure about the 11/16" dill part.
#146921
I just looked at the specs for the motor you mentioned above on ebay:

Nominal voltage: 12VDC
Voltage range: 1 - 12VDC
Current @ maximum efficiency: 13.52A
Speed @ maximum efficiency: 12,610 RPM
Torque @ maximum efficiency: 93.7 g-cm
Efficiency: 76.0%
Terminal type: 0.19" solder tabs
Shaft diameter: 0.19"
Shaft length: 0.57"
Size: 1.77" diameter x 2.59" depth

It ranges 1-12v. Should I be concern of running this at 18v? I have motor heat sink but not sure if this motor will run hotter than say traxxas 775 one.
#146928
It's a 12V rated motor, mostly due to RPM (at 18V it's 23k RPM; you don't see many motors "rated" for that). It's 50% heavier and substantially larger than the standard 5-series motors, and should dissipate the extra heat from running 18V well enough (esp. compared to the stock 5-series motors). It won't burn much more power at 18V than the standard 18V-rated motors (like the Mabuchi 20k RPM 8514), and will be substantially less than they run at 24V.

The PVC pipe isn't a spacer for the depth; it's for centering. The stock motors come with a plastic collar on them -- the orange piece of plastic shown in this picture here. We're trying to replicate that, but for a 7-seires motor. The OD is 0.84"; the ID is matched to the motor (smaller on a 5-series than a 7-series). This collar ensures the motor stays centered and the gear-to-gear spacing is consistent. Otherwise the motor end (which is 17.5mm) is only secured laterally by the two screws and it'll wander around, which may damage your gears.

Imagestock motor by [url=https://www.flickr.com/photos/28511405@N02/]

I can make up a few more spacers and take a picture of an example installation tomorrow -- don't have anything around right now.
#146930
Hammer-fm wrote:I can make up a few more spacers and take a picture of an example installation tomorrow -- don't have anything around right now.


That would be great thanks. Is the relay doable for easing out the heat to the wire? ESC is very interesting but I am still new at modding so won't risk it unless I can find a tutorial somewhere with wiring diagram and such for dune racer :)
#146948
Ok, I mocked up one with one of the rejects I had lying around -- reject because it's not symmetrical. It turns out that even the reject will work fine if you pay attention to detail, but if you can get the drill centered it removes any issues.

First, I take a piece of standard 1/2" PVC pipe -- outside diameter is 0.840" +/- (spec; mine measured 0.844" -- close enough). Somehow clamp it so that you can drill through it with an 11/16" drill bit (0.6875" -- the same diameter as the hub on the end of the motor where the shaft comes out). I built a crude jig that would hold the pipe, and drilled a 2" length of it (not shown).

Image

Then cut it into slices about 1/8" long (0.125-0.150"); it should fit inside the gearbox, as shown. It should not stick up above the protrusions that the motor rests on, which are to space the motor out from the case for ventilation. If you were not able to get your hole centered (as with this reject piece), it doesn't matter. You just need to make sure that you rotate the spacer so that the "offset" part affects the spacing to the screw holes, as in my picture (the too-thin and too-thick parts are closest to the screw holes). Think of it as ensuring that any offset of the spacer -- and thus the motor -- is tangential to the gear so that it doesn't change the motor/pinion-gear-to-first-gear spacing.

Image

This how it ends up on the motor -- you can either install it on the motor and then put the motor into the gearbox, or install the ring on the gearbox and put the motor in. If you are using a large gear (20T+), you will need to install the ring before you put the gear on.

Image

And lastly, installed in the gearbox. Sharp eyes will note that this is a 17T gear, which you should not use unless you purposely offset the spacer hole and rotate it to space the motor further from the gear so as to accommodate the larger diameter. Let's not go there right now 8-) . I only had a 17T lying around...

Image

A lot of people have had success without the spacer. I think it's good insurance. It's a robust way to ensure you've got proper gear-to-gear spacing and that it won't wander on you even if you're the motor hard.
#146959
Many thanks Hammer. I will give this a shot. I have a couple options to try out. For now I will just do some experiments by first to try stock motor at 18v to see what happens. I'm tempting in doing some experiment on upgraded 550 motor, but this could end up wasting my time so who know i might go with 775 motor directly.
#146978
Well, now reading thru the post, you've got me interested in trying some of this out, Hammer, where can I order the 16T pinion gears you mentioned? I searched on fleabay, and come up w/quite a few but looking thru the shaft diameters, don't see any matching the Nichibo motor, Thanks!
#146988
Hi Digg7,

There are two links further up in this thread to gears (both Amazon). The two key features you're looking for is 32P or 32DP (pitch) and 5mm bore (the same as the shaft on all of the 775/755-series motors). You should be able to search for "16t 32dp 5mm pinion gear" on ebay (this brings up the hobbystar one and a few sets; "16t 32p 5mm pinion gear" also gets a few more options)
#147160
No real difference. Technically the tooth spacing is specified as a pitch at the diameter (not circumference), or "diametral pitch" -- a 32-tooth gear with a 32dp would measure 1" in diameter at the centerline of the teeth. Thus the 'dp' abbreviation. However, many vendors simply shorten it to 32p/24p/etc, which I why I suggest searching for both.
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