How to stop wheels spinning off their output shafts and Brushless drive

[Danjr1]

Good afternoon,

Two questions:

My bot's wheels keep spinning on the output shafts so I'm planning to take the inside shoulder off all my wheels and drill through the wheel hub, 3/8 unf nut and motor shaft to either install a bolt or split pin. My question therefore is whether to use a bolt or split pin? My gut is going for a nut and bolt but wanted to see what more experienced roboteers might think.

Second question is related to brushless drive. I've seen some sensored motors on Hobbyking that produce 350w and, through a 20:1 gearbox on 80mm wheels, would run at 15mph. Thing is that these motors are rated at 2s so I'm wondering whether this could potentially work even if the voltage is very low compared to what's been before?

Cheers

Dan

[maddox10]

I wouldn't recommend drilling trough the output shaft of a drill. Seen it before, and it will give a nice weak point that will snap.

On brushless drives. 350W/7.4V= 50 amps. 50amp esc's needed...

But I think it will work nicely. After all, Hannibalito3.2 drives on 3S with 28mm diameter unsensored brushless motors.

[Danjr1]

Unless people know of another method to secure a wheel to a 3/8unf thread, I'm gonna have to do it for Portsmouth.

[RogueTwoRobots]

Do you not have reverse thread screws for them?

[Danjr1]

Yeah but hasn't really helped. What I might try is putting a little grease on the reverse screw head so that the washer between the wheel and the screw doesn't grip

[Garfie489]

Might sound abit basic, have you tried putting more washers on? - Defector has 6 on each side.

[Danjr1]

Will give it a go. Two washers with grease between them sounds like it could work.

[Ellis]

Don't grease them. You want the complete opposite: the normal thread and the reverse thread bolt need to be locked hard to each other. The idea is if one starts to rotate the other locks up. Try some low-mid strength thread locking compound and crank them up hard.

[Danjr1]

Cheers Ellis!

[Ellis]

I wouldn't use much on the wheel's threads (if any) as if the gearbox goes it'll be a massive struggle to remove it, but the reverse threaded bolt could benefit from some. The suggestion above of sturdy enough washers, so tightening up doesn't flex them, is a good one.

edit: although 6 is overkill lol

[RogueTwoRobots]

A tip for if you do put threadlock on the reverse thread screws. Sometimes, as you might expect, they're a pain to try and undo with a standard Philips 2 screwdriver when threadlocked, risking chewing the head and rendering the screw buggered (to use a technical term). If you have a cordless drill with a hammer function, use that. Does a great job of breaking the bond and undoing the screw. Saved many a reverse threaded screw with that technique, just make sure to exert as much downward pressure as possible onto the screw (i.e. have your bot on the floor with the screw head pointing up)

[RogueTwoRobots]

And as Ellis said, avoid putting threadlock on the wheel's threads. I used to do this as a backup in case the reverse screw came loose, but it becomes a nightmare if you need to take the wheel off but can't lock up the gearbox for whatever reason. Usually results in butcherment of either the chassis or the wheel, depending on the mounting method used.

[leorcc]

Blue threadlock 242 should be fine. It is the kind that doesn't get rockhard but you can still use a normal tool to loosen them again if need be.

[Danjr1]

Cheers guys, will give it a go for Portsmouth.

[PJ-27]

The reverse head screw doesn't often screw all the way into the output shaft, it'll lock and still protrude ~6mm from the end of the shaft.
To make sure the reserve screw locks against the wheel you either need a nut that much longer or to make up the gap with washers.
Remember flimsy washers will bend in on themselves before you get any meaningful torque on the screw so use beefy ones. Also any left over thread lock from the manufacturer will give the impression of torque, whereas in fact it's just all gummed up in there.
Shaft pins don't work, the punt of torque those gearboxes put out will snap near anything you put through there.

Also +1 what Ellis said, don't forget you have to actually remove the wheels!