Differential steering

[Danjr1]

Has anyone ever tried using a differential with individually-activated brakes on each output shaft to achieve steering?

[robotwars]

Re: Differential steering

I did it on one of the old pay to drive robots years ago!!!

Worked ok actually !

[Danjr1]

Re: Differential steering

I'm just speccing up a heavyweight. the issue would be finding a diff suitable!

[maddox10]

Re: Differential steering

Firestorm did it, and did it well. But it wasn't a cheap, easy or light drive-system.

But they used smaller motors in stead of brakes to control the turning ratio.

Suitable diff. The Old Litton/diff setup Roger Plant sold was fine in that respect. You can find simular sets in disabled 3wheel scooters.

Or else look here

[Danjr1]

Re: Differential steering

im thinking dirt cheap! its just pie-in-the-sky thinking at the moment but im thinking a diff with mini moto disc brakes on the output shafts, activitated by 3-4 high powered servos on each side. 1 motor powering the diff with twice the amount of power of the bosch 750. ideally, id want a open diff (same kind of appearance as a lego technic diff)

[mattsdragons]

Re: Differential steering

ive got an old diff so if you want it, you can have it. i doubt ill ever use it

[maddox10]

Re: Differential steering

im thinking dirt cheap!

Who doesn't? Oh, I see.

its just pie-in-the-sky thinking at the moment but im thinking a diff with mini moto disc brakes on the output shafts, activitated by 3-4 high powered servos on each side.

so, 8 servo's working in 2 groups. Main question, what does a high power servo cost?

1 motor powering the diff with twice the amount of power of the bosch 750.

Mag C40, Perm 080 (if you find them) Black Max, Cheap???
If you want cheap, powerfull and dirty, car starter.

ideally, id want a open diff (same kind of appearance as a lego technic diff)

Get out the dremel then.

[PJ-27]

Re: Differential steering

I was thinking car starter motor too, would be perfect.

[Ellis]

Re: Differential steering

They're single direction aren't they?

[PJ-27]

Re: Differential steering

Apparently it's not easy to, but exactly why I don't know. I thought they just had advanced magnets so spun faster one way than the other, like drill motors. They are series type motors though so will keep spinning faster and faster until the destroy themselves and draw a serious amount of current!

But, very powerful, loads of torque and dirt cheap.

[maddox10]

Re: Differential steering

Depends on starter motor, more modern ones could be timed PM motors, but old school starters are series wound.

If you take a series wound starter motor as it comes, and reverse polarity, you also reverse the field of the electromagnets, resulting in net no change whatsoever.

To make a car starter reversing, you need to seperate the field windings and the stator windings, and make sure you reverse the polarity on 1 of the 2.Another issue is that the body is electrified, that to has to be adressed.

Also, car starters are ment for short bursts of very heavy torque production. Not for continious running, and this is reflected in the construction. Very low internal resistance for example.


The Fiesta starter we used in Project One was rated 800W @12V, but could easely draw over 250A , making it to hot to handle in a few seconds.

Next bit of problem. You need a very rare kind of speedo to control it.

All in all, I would suggest using a car starter for weaponpower or such, not drive. I tried, and didn't like the result.
Project II Hex'em, therefor, used a Bosch 750.

[widow_twanky]

Re: Differential steering

I'm just speccing up a heavyweight. the issue would be finding a diff suitable!

Maybe if you looked on ebay for a transaxle for a mobility scooter you would find what you are looking for. (Make sure you get the faster ones, the 4mph ones aren't too good for us!!)

The only problem you have with these is they're 20:1 in a single stage making the input gear quite small. These can break if you run them against a brake which apparantly is the major cause of failure. So it's either a big bag of input gears or Kenny and some tool steel.

http://www.ebay.co.uk/itm/mobility-scoo ... 3a6a67db18

[widow_twanky]

Re: Differential steering

oh and trev had a sort of linear actuator powered thingy powered by a bosch 35W motor (which you get with the car seat when you buy it) on the front wheels of mighty mouse which seems an awful lot less faffing about than using a braked system. Didn't have a really good look at it but might be worth speaking to him.