I put together this overview of body powered terminal devices from my applied / user view.
Janet and John break this down
You don’t have to “decide” which one to get, if you just roll a dice or if you have a tight budget, things sort themselves out all by themselves. I bought a few of these on eBay.
Quick decision
If I was to get “just one”, it really would be the V2P Prehensor [link]. If I was to get just one and for real hard work including chemicals and biohazard, it’d be the Hosmer #5, possibly the all steel (no nitrile cover) version, or a work hook where I’d put springs instead of rubbers (as in photo below). If it has to look like a hand, the Becker Mechanical Hand is the one to get – it fits regular hardware store work gloves [link], it has an obscenely great precision grip [link], it is very robust, and can be also fitted with cosmetic gloves if need be.
Table columns – properties
- A Appearance rating (subjective) [link]: 1 technical, attracted positive comments 2 anthropomorphic / hand-like, attracted positive comments 3 technical 4 anthropomorphic / hand-like
- B Grips: 1 precision 2 wide / flat precision 3 wide bore opening 4 stable cylinder grip 5 adaptive 6 not really a cylinder grip 7 adaptive finger grip
- C Grip angle [relevance of issue: link]: 1 ideal for typing 2 ideal for many ADL 3 almost ideal 4 requires significant compensatory motion
- D Grip surface tuning [various applications: link]: 0 cannot be tuned 1 hard to tune 2 moderately easy to tune 3 very easy /cheap to tune
- E Grip power adjustment: 0 not possible 1 possible via different rubbers 2 possible via built-in mechanism
- F Ideal applications (subjective / own experience): 1 typing 2 kitchen work 3 laundry 4 box lifting 5 wood work / mount appliances / power tools 6 bicycle riding 7 precision work (repair computers, watches, etc) 8 touch/shake hands 9 appear like a hand 10 steering wheel car driving
- G Cost [USD]
- H Weight [g]
- I Maximal opening [cm]
- J Grip force [N]
- K Mount: 1 UNF 1/2-20 2 Otto Bock ~16mm bolt
- L Where to order: 1 USA 2 Europe 3 Worldwide 4 Fillauer-problem/issues [cf. link; Fillauer does not sell to real users nor has it any interest to do so], so maybe better elsewhere, such as eBay etc.
- M Frequent problems: 0 none 1 joint wiggle 2 screws 3[ other
- N VO (voluntary opening) or VC(voluntary closing)
Comments about properties
Grip force is by far not the only dimension or property that defines whether you get a good grip experience. Grip type/s (i.e., precision, cylinder, ..) and angular device constraints [relevance of issue: link] vice versa the type of application or use case that you have are at least as important if not more. Furthermore, a lot of physical raw device closing force can be avoided by clever surface modification with soft or non-slippery grip surfaces, so adding these to a device may be a relevant aspect as well. So while the V2P prehensor lacks a massive maximal grip power (the TRS Jaws XFS is better that way), the gripper surface can be tweaked by adding good grip covers from ubiquitous cheap hardware store materials – and as it turns out, the everyday use in my experience ends up actually being better.
Steering wheel gripping for car driving is one of the most important applications in terms of responsibility. There is not a lot of room for error there. Neither is it desirable to experience a grip that digs into the steering wheel spokes, as that may prevent a fast turn of the steering wheel. Nor is it desirable to have a very strong grip that then requires too much effort for loosening the grip in case a sudden steering wheel motion becomes necessary. I personally place 2-3 soft covers on my steering wheel so it is slightly compressible. That allows me to grasp that steering wheel from its side, i.e., laterally, by way of any parallel oriented gripper surfaces. These then squeeze the soft covers a bit which provides for good stabilization, while the grip force that I apply then is low to moderate. With that, the steering wheel can swivel a bit while being gripped for shallow curves such as when driving on a highway. Also the grip can be opened easily and rapidly due to low grip forces and parallel gripper surfaces on pass / curved roads. When one drives and requires the prosthesis to actually support the other arm, which is the case when the other arm needs to be protected from overuse, then this can be a factor.
For bicycle riding, I find the option to open and reposition the gripper during the ride important. It helps me to reduce back strain / back pain and also it helps to use different handle bar parts such as on a road bike’s drop bar. The fixed mounts that are sold are not nearly as comfortable.
Device overview – table
Adapter (all devices weighed with adapter for my own wrist unit): 57g
Device | A Appearance rating | B Grips | C Grip angle | D Grip surface tuning | E Grip power adjustment | F Ideal applications | GCost [USD] | H Weight [g] | I Maximal opening [mm] | J Grip force [N] | K Mount | L Where to order | M Frequent problems | N VC VO |
TRS Jaws XFS | 21
|
2 3 4 | 1 2 3 | 22 | 2 | 13 2 3 4 5+ 6+ 4 | ~1200 | 605 | 75 | 1.9-6.9 | 1 | 1 | (2) 4 | VO |
Otto Bock Hand | 4 | 1 6 | 2 | 25 | 0 | 16 2 3 6 8 9+ | ~1200 | 511 | 55 | 1.8 | 2 | 3 | 37 | VO |
Toughware Equilux | 3 | 2 3 | 1 2 | 3 | 1 | 18 2+ 3 4 5+ 6 10 | ~2300 | 318 | 80 | 1.8 VO
>10 VC |
1 | 1 | 0 | VC VO |
Toughware V2P | 3 | 2 3 | 1 2 | 3 | 29 | 110 2+ 3+ 4+ 5 6 10 | ~1210 | 275 | 68 | 1.0-2.2 | 1 | 1 | 311 | VO |
H0smer #5 | 3 | 1 6 | 1 2 | 312 | 1 | 1+ 2 3 4 5 7 10 | ~500 | 281 | 90 | 3.9 | 1 | 1 4 | 313 | VO |
Hosmer Work Hook | 3 | 1 3 | 1 2 | 314 | 1 | 1 2 3 4 5 6 7 | ~700 | 368 | 80 | 2.7 | 1 | 1 4 | 315 | VO |
Hosmer Work Hook with backlock | 3 | 1 3 | 1 2 | 316 | 1 | 1 2 3 4 5+ 6 7 | ~700 | 407 | 80 | 2.7 | 1 | 1 4 | 317 | VO |
Becker Mechanical Hand | 2 | 1 6 7 | (1) 2 | 218 | 219 | 120 2 3 4 5 6 7 8 9 | ~650 | 520 | 70 | 4.1 | 1 | 1 | 0 | VO |
Otto Bock Movohook 2 Grip | 3 | 1 6 | 1 2 | 321 | 2 | 1 2 3 4 5 10 | ~1800 | 358 | 80 | Lever setting 1 1.7 setting 2 3.0 | 2 | 3 | 322 | VO |
TRS Adult Prehensor
[IMAGE]
|
3 | 1 3 | 2 | 3 | TBD | TBD | ~2200 | TBD | TBD | TBD | TBD | TBD | TBD | VC |
If cost estimates are too far off, drop me a mail, so we can see where it hangs.
Footnotes
- The TRS Jaws attracted by far the most frequent and most positive unsolicited comments even from the unlikeliest commenters.
- TRS Jaws can be grip tuned but takes away from its raw elegance. I used soft padding and textile, but finding easy to fit textile can be a bit of a search.
- The typing tasks are best performed by placing a pen into the device.
- TRS Jaws is my first choice for bicycle riding. Using garden power tools is a perfect use for this device, as the strong cylinder grip keeps a tool handle stable.
- Grip surface tuning of a prosthetic hand usually means to place soft pads underneath the rubber/PVC or silicone glove.
- The typing tasks are best performed by placing a pen into the device.
- I have two of these, both of which exhibited strange mechanism issues long time ago. I only wear these on rare occasions so when my prosthetist said he could not fix it, we decided to let that be. As they don’t “heal” that is what they are. But possibly these aren’t very heavy duty.
- The typing tasks are best performed by placing a pen into the device.
- The current shape for he rubber mount is not ideal to add many more rubbers there. So the maximal grip force is quite limited here. That is remedied to a degree by the ease by which soft surface padding can be added. But some double grip force would be nice.
- The typing tasks are best performed by placing a pen into the device.
- V2P: frequent loss of factory issued plastic covers. Is solved by user through own grip pad modification [link].
- Typical materials that work very well are silicone tubes cut to length.
- Hosmer#5: rubbers tend to age and tear, but are cheap and easy to replace.
- Typical materials that work very well are silicone tubes cut to length.
- Hosmer#5: rubbers tend to age and tear, but are cheap and easy to replace.
- Typical materials that work very well are silicone tubes cut to length.
- Hosmer#5: rubbers tend to age and tear, but are cheap and easy to replace.
- Grip surface tuning of a prosthetic hand usually means to place soft pads underneath the rubber/PVC or silicone glove.
- The Becker Mechanical Hands have a base plate screw to adjust grip power, straight-forward for the Becker Imperial and with instructions for the lock grip.
- The typing tasks are best performed by placing a pen into the device.
- Typical materials that work very well are silicone tubes cut to length.
- Otto Bock Movo 2 Hook: lever issues see [link], joint problems see [link].