About two years ago I tried to implement kind of a elementary robot (platform with motorized wheels).

Each wheel+motor at the low end of a vertical axis. The axis able to spin more than 360 degrees with no phisical limitation. Obviously, this last dictates for slip rings to convey power and sensing to/from wheels.

My search in the web at that time gave many options but all of them extremely expensive.

My questions:

a) Do I have any other option?

b) Has anyone be able to produce homemade slip rings, reliable enough? I presume that I would need, ground, power and three more lines per wheel.

My bot/paltform should be small and light. It would be built to try some ideas on motion control, mapping and distance calculations.

Any reply will be much appreciated.

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

You could try etching a PCB and use small brushes with soft springs!

 

Placing the motor in the wheel is not often done as it adds to the unsprung mass of the system ( if your bot is lucky enough to have suspension otherwise it dont matter)

In your case a quick redesign is needed..

Keep the motor body and encoder stationary and
couple the rotor shaft to wheel rim :wink:

Attached Images

untitled_499.jpg (6.5 KB, 986 views)

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It may seem like a good idea at the time but.. never stir your cold coffee with a soldering iron.

 

Is your platform likely to spin round and round several times? or is it just going past a 360 degree rotation and then back in the opposite direction eventually?
If so a flexible cable that winds around the shaft is all that might be required. You will need some mechanical means that takes the strain after, say, 2 full revolutions, to avoid the cable being overstressed.

If you think this is a silly idea consider this: many smaller wind turbines use a wrap around cable to convey the power from the alternator to the supporting mast. This is far more reliable and cheaper to make than slip rings. It s unlikely that the wind keeps changing round in the same direction.
Your robot platform also most likely will never have to spin round and round like a wheel.
If you can find a junked printer, they use a very flexible printed cable to the print head which might be used for your robot platform. Possibly good for two full revolutions over a reasonable diameter support shaft.

Klaus

 

Tansis, could you please hexplain a little bit further. I can't grasp de the whole idea. I will appreciate that.

Klaus, I am afraid that wheels could turn twice times more than 360º and then the cable will not suffice. My idea is to avoid a potential problem from the beginning.


Any comments on the proposed link itself :?: Gracias.

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

My drawings are awfull I must admit ,
Have a look at these links...

http://www.electricmotors.machinedes...ticleDraw.aspx

http://www.carvariety.com/home/detail.php?show_id=453

Sadly both these applications use specialist motors but the principle is the same and can be implemented with any motor, the motor body is stationary (bolted to the suspension or directly to the chassis of the robot) and the rim carrying the tyre turns around the oustside of the motor.

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It may seem like a good idea at the time but.. never stir your cold coffee with a soldering iron.

 

[quote="atferrari"]Tansis, could you please hexplain a little bit further. I can't grasp de the whole idea. I will appreciate that.

Klaus, I am afraid that wheels could turn twice times more than 360º and then the cable will not suffice. My idea is to avoid a potential problem from the beginning.



So it seems that I misunderstood your question. What I read out of it is that you wanted to spin a platform that travels on wheels.

Now you say its the wheel rotation you are worried about. Feed power to the wheel motors as Tansis suggests ( motor housing with windings stationary and a PM rotor with wheel attached to shaft).

If, later on, you want to mount something on top of your moving platform that also rotates you could consider my suggestion.

Klaus

 

Hi Tansis,

I've got your idea. Implementing that, without special motors seems quite difficult. We shall see. :?:

Gracias

__________________
Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

A few ideas:
1) use copper tape on an insulated shaft (like an old paper roller from
a printer), and the grounding wipers (sometimes available from the
same donor printer) or brushes (rip up some cheap DC motors that
have removable insulated brush holders). Brushes will carry more
current and last longer than the wipers (generally have more contact
area), but need a preliminary seating.
2) If you have access to a small lathe, the whole thing is just finding
some proper material - PVC or something similar for a base, and
rings turned from copper pipe. You could probably buy a tiny lathe
for what vendors want for finished slip-ring assemblies - at least the
ones I have looked at, which for the most part are aimed at military
and large indutrial applications.
I could probably come up with a few more, but one of the above
has always worked for me.
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