Sturmey Archer drums mounted backward

[The Speaker Guy]

Hi
Think I can glean the answer from previous posts, but the question was not quite asked this way:

Do SA drum hubs have equal braking force if mounted backward?
For the front of a tadpole, is it ok to mount each drum with the brake plate facing inwards?
I know car brakes are self energizing due to asymmetric mounting and hardware, is this true of SA?

A side question is : are these easy enough to adjust to get equal left and right braking force?

Thanks!

 

[amberwolf]

diagram of drum hub, maybe helpful?

http://www.ihpva.org/Projects/PracticalInnovations/BuildingStubAxleHubs.html

 

[gogo]

As illustrated in the graphic amberwolf posted above, this is a 'single-leading-edge shoe' brake. What will change is which shoe is the 'leading-edge shoe' part, so the internal mechanicals should be ok if everything is symmetrical inside the hub. [edit] The internals aren't symmetrical -see below.

The torque arm, however, will be 'backwards', so you will have to account for that. There are ways to deal with that, but the brake cable mounting to the torque arm is another complication to account for.

Do you understand the force vectors and are you comfortable with minor fabrication?

 

[The Speaker Guy]

Yes, comfortable with fabrication. Picture below is quad I have built. It has tubing bent and gas welded. There's a U joint in steering I made with hack saw and drill press!

We've put many hundreds of miles on this in 3 years, worn through about 7 tires so far. Bike tires don't like the loading this puts on them.

it has a Magic Pie in right front wheel, and a 48V/10Ah battery.

 

[gogo]

That quad looks fun.

If the symmetry allows, you might try drilling out the rivets on the torque arm and flipping it over? The brake cable mount won't have the same geometry, so be careful to account for that.

 

[flangefrog]

I might be misunderstanding what you're doing, but why not simply use the drum brakes that come in a left and right version?
http://www.sturmey-archer.com/en/products/sd-hubs

 

[gogo]

What flangefrog said, unless you want axle out both sides?

Do SA drum hubs have equal braking force if mounted backward? Should.
For the front of a tadpole, is it ok to mount each drum with the brake plate facing inwards? Should be.
I know car brakes are self energizing due to asymmetric mounting and hardware, is this true of SA? They appear to be simple, non-energizing type.

A side question is : are these easy enough to adjust to get equal left and right braking force? I don't know.

 

[bobc]

If you look carefully at the actuator which pushes the shoes (the bit that's twisted by the external arm) ( it bears on 2 small steel pressure pads that slide onto the diecast shoes) you'll see that it's asymmetric.
This is because the one that's longer is meant to be the one furthest from the shoe hinge pin (nearest to the outside of the drum) so that both shoes actually receive the same actuating torque.
Pretty much the only thing you can get wrong with these is to fit 180degrees out so the shorter side is on the outside.
Probably needs a diagram, but if you look at the parts it should all make sense

 

[gogo]

bobc, good catch! I'd never done a force analysis that detailed. So, the shoe that inherently provides more braking force during hub rotation gets less pressure from the 'actuator'.

I stand corrected, a drum will not behave identically when flipped, due to asymmetry.

My motorcycle hub's actuator is symmetrical about its axis of rotation. In other words, it could be rotated 180 degrees and would still work the same. Sturmey's non-symmetrical actuator seems a bit 'fussy'.