actuation motor for seat design
actuation motor for seat design
(OP)
hi folks,
I've been trying to spec a motor for a seat project I'm working on.
It needs to move a 100kg person up and down at 45 degrees by about 400mm. The actuation would be via a toothed rack cut into one of the motion guides, so I've estimated i'd need a pinion with about 300 Nm torque. The motor itself needs to be quite slim, and as light as possible.
So far, the best option I've found is a 480 watt 4-pole item from Maxon: http://www.maxonmotor.com/maxon/view/product/motor...
This motor runs nominal load at 4350 rpm, so I'd need two stages of worm gear reduction (built into design of motor unit). However this wouldn't give me enough torque - not including losses, at a 263:1 reduction it would give 254 Nm, and with two worm gears, I'm looking at 30% or more in mechanical losses, is that correct?
So my question is, could I run more current through it to get more torque, and also, is there an alternative motor out there that anyone can think of? The Maxon motor is very expensive (around $500 I think) but it's very light (800g) and has a very small diameter, which is ideal. I get the impression that its more designed for automation though, and I don't really need that level of precision.
My alternatives at the moment seem to be adding some kind of spring balance to the mechanism, which would add a load of complexity, or more heavy-duty motors, which are more like 2500g, which is way too heavy.
thanks in advance - as you can probably tell, electronics are not my forte.
I've been trying to spec a motor for a seat project I'm working on.
It needs to move a 100kg person up and down at 45 degrees by about 400mm. The actuation would be via a toothed rack cut into one of the motion guides, so I've estimated i'd need a pinion with about 300 Nm torque. The motor itself needs to be quite slim, and as light as possible.
So far, the best option I've found is a 480 watt 4-pole item from Maxon: http://www.maxonmotor.com/maxon/view/product/motor...
This motor runs nominal load at 4350 rpm, so I'd need two stages of worm gear reduction (built into design of motor unit). However this wouldn't give me enough torque - not including losses, at a 263:1 reduction it would give 254 Nm, and with two worm gears, I'm looking at 30% or more in mechanical losses, is that correct?
So my question is, could I run more current through it to get more torque, and also, is there an alternative motor out there that anyone can think of? The Maxon motor is very expensive (around $500 I think) but it's very light (800g) and has a very small diameter, which is ideal. I get the impression that its more designed for automation though, and I don't really need that level of precision.
My alternatives at the moment seem to be adding some kind of spring balance to the mechanism, which would add a load of complexity, or more heavy-duty motors, which are more like 2500g, which is way too heavy.
thanks in advance - as you can probably tell, electronics are not my forte.





RE: actuation motor for seat design
300Nm on a pinion driving a rack where the pinion is, lets say ~25cm diameter = 2400N force.
Either your pinion is rather bigger than I imagine or one of us did some math wrong someplace.
RE: actuation motor for seat design
RE: actuation motor for seat design
Also what about a cast metal counter-weight that conforms to the rack? Might be simpler than springs and generally works great if what-must-go-up always has to come down and vis-verse.
Keith Cress
kcress - http://www.flaminsystems.com
RE: actuation motor for seat design
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: actuation motor for seat design
The pinion will only be small - probably more like 3cm diameter, rather than 25, with a small gear pitch.
How does torque on a rack and pinion setup translate to vertical force? because 24,000Nm of torque sounds like rather a lot.
itsmoked - I need it to perform the movement in 30 seconds or less.
I can't use a counterweight, because it's an aviation seat, so weight is critical - hence the rumination around spring balances etc.
RE: actuation motor for seat design
300Nm with 25mm pinion = ~24,000N Force. (Use pinion pitch-radius as the moment arm).
Where'd you come up with this 300Nm estimate, anyways?
RE: actuation motor for seat design
To be honest, I can't remember exactly.
Though using this (ignoring friction coefficients) I get just under 300Nm. https://servotak.eu/tools/engineering_calculator (radial force on pinion)
If I include a reasonable friction coefficient of 0.8, I get a radial force on pinion of 500N.
System inclination is 48 degrees and speed required is 0.013 m/s
RE: actuation motor for seat design
RE: actuation motor for seat design
A controller solution can be had for less than 10% of the cost of the motor, so it's not a massive diffidence, especially given the benefits.
RE: actuation motor for seat design
I'm curious, what controller did you find? The one thing that has kept me away from the brushless motors in our product is the size and cost of the controller.
RE: actuation motor for seat design
RE: actuation motor for seat design
I was just going to use an Arduino for the prototypes, and a basic rack mount supply
but one of these will run three at once http://uk.rs-online.com/web/p/products/4184045/?gr...
RE: actuation motor for seat design
I'd toyed with the idea early on. But there's not really enough space to get a motor and drive to a jackscrew, certainly not without adding a lot of weight and complexity. I'd put a motor by the passenger's feet, which connected to a jackscrew via a driveshaft, but it needed universal joints and spur gears to transmit the power to the right place.
The pinion and rack works because the toothed rack can be cut into one of the guiderails for the movement, plus having the motor as part of the moving structure means the motor housing can be used to add strength to the seat base for the 16g crash test.
RE: actuation motor for seat design
RE: actuation motor for seat design
Radial force is great if you want to separate the pinion from the rack, but it's not what you want to push your seat...
RE: actuation motor for seat design
I'm confused now (easily done)
I thought radial force is applied in the direction of rotation, and axial force would separate the pinion from the rack? But there's little axial force if I use straight-cut teeth.
RE: actuation motor for seat design
Radial = force trying to separate the pinion & rack. (Primarily because of the pressure angle of the teeth)
Axial = force along the axis (shaft)
Tangential = the bit that moves the rack. The one you want.
RE: actuation motor for seat design
You are indeed a little confused if you think that the controller you linked to will control three motors:
A "brushless DC motor" is essentially a three phase AC motor and that controller has an output for each one of those 3 phases to one motor.
Keith Cress
kcress - http://www.flaminsystems.com
RE: actuation motor for seat design
Probably back of a napkin stuff for you, but it's been a while since I've had to work out anything like this, and rather a lot of other crap has filled my brain since. Plus I have a screaming baby in my ear today.
However, just to check I'm not going crazy here: I need to move 1000N, 48 degrees upwards at a speed of 0.02 m/s with a 24mm spur gear.
Depending on the coefficient of friction (I'm not sure what lubrication I'll be using yet) I'm getting a tangental force on pinion of around 1400N.
I must have been using the wrong forumla before, because it seems I only need a torque at pinion of about 16Nm (rather than the 290-odd I previously had.