Gearbox/servo backlash documentation


This is just for general discussion. IMHO, it would be awesome if anyone selling servos and gearmotors for robotics applications mentioned the level of inherent backlash in the particular products.

For example, most or all regular metal gearhead motors ( and RC servos ) have a degree of backlash in them that makes them unusable for precise closed loop positioning applications, whereas they are fine for locomotion or open-loop positioning applications.

Places like servo-database or Pololu RC servo search provide a ton of parameters to search for, but backlash is rarely mentioned. Hitec seems to advertise their Karbonite gears to be really low backlash high strength, but obviously they do not give any numbers for repeatability.

Has anyone seen an online test/benchmark/measurement of backlash specifically between different servo product families ?

For finding reasonably priced low-backlash DC gearmotors i’m most likely stuck with just buying a set of different RC servos and just testing them out ( and ditch the built-in electronics ). Any recommendations ? I guess i’ll try Hitecs karbonite gearset digital ones first.

I don’t suppose there are separate low-backlash gearsets on sale anywhere for small DC motors ? I know i could get some really expensive zero-backlash harmonic drive ones from Maxon but that is just well outside the budget.

On a related note, i wonder why nobody in hobby range is trying to build harmonic drive gearboxes, is it just because the tech is all covered by patents and licenses are really expensive ?