Ergonomic design vs weight

Hi all,

We’re making a portable product and are trying to develop some high level concepts of what it may look like. The thing is, the weight is hovering between 8-14lbs depending on how much engineering resources we throw at it. What I’d like to find is a resource of sorts that shows different portable ergonomic designs classified according to weight.

For example: At what point does a pistol grip device get too heavy? How light does a product need to be to eliminate a handle and introduce a hand grip?

While I know I can go through iterative design concepts and figure out these values for myself, I’m sure someone has done this before and hopefully had the foresight to write it down.

Specifically it probably depends on what you are doing i.e., “just” carrying an object vs. carrying it and making precise adjustments to it at the same time (e.g., a camera, a weapon, etc). Held close to the body? Or at full extension (as in carrying a suitcase)? Of course, none of that takes into consideration how long is the user going to carry it? We’ve all tried at some point to hold our arm extended perpendicular from the body. The average weight of the male human arm is between 11-12 pounds.

A portable device is one that can be carried for at least ten minutes without resting.

For single handed carrying < 4.4 kg.
For use held away from the body < 2.3 kg
If manipulated with precision < 400 g

Someplace to start. Source: Ergonomics of hand-held devices for industrial use

Hand Held Tool Ergonomic Standards

See > Hand Held Tool Ergonomics Standards

Realistically once you get past 3-4lbs for a handheld device you are in the danger zone - especially depending on the way it’s designed to be used. When you say a pistol grip I get the assumption that you’re holding it away from the body and manipulating it. If your use case is for burly construction workers being the primary demographic, and for short amounts of time you’re OK with more weight, but try it for yourself - grab a 15lbs weight and walk around with it like it was your product. You can quickly see how fatigued you get.

Thanks for the replies.

I can’t go into too many details of what is being developed. The device will be required to be positioned to measure targets at varying orientations. The required precision would be similar to that of a flashlight. It would not have to be pushed away from the body, but that capability would certainly be nice.

Pistol Grip - One of the concepts I’ve been envisioning is an inverted pistol grip configuration with thumb controls and a display on top of the stick. The weight of the device would be under the stick and somehow (varying configurations) the load would be brought to the forearm. The goal would be to move of the center of mass closer to the elbow to reduce fatigue. So really what I’m trying to figure out is the comfortable limits of moment at the elbow.

Picture - A similar application of what I was mentioning. Instead of a strap over the forearm, I was thinking of having the user interface extend back from the top of the stick and rest with a pad on the users forearm. I feel that would make grabbing and using the device easier.

Just some thoughts…

Resting that much weight on the forearm just beyond the wrist might become uncomfortable, especially since this would be picked up and carried/used for some time. The strap looks to position itself just below the elbow - the upper forearm - and as you mentioned it is a much stronger area than just aft of the wrist. What if your support were similar but not as cumbersome as a full strap - something like a half-support, wider and ambidextrous in it’s attachment method to the device?

Positioning of the screen off the axis of the pistol grip will have a big impact on how much the user needs to move the device away from his/her face to see the UI - adjustable screen would be great, as I’m assuming there would be a regular group of users, but not just one?

Balance from end to end should work in your favor, allowing the downward weight of the measuring end to create upward push at the user end.

Neat product pictured - reminds me of the stuff Rob Seigel (The Hack Mechanic) uses.