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View Full Version : [Question(s)] Alternative to wheelchair motor for payload of 50kg/110lbs



garagelane
09-11-2013, 11:35 PM
Hi,

Been spending a lot of time going through various threads, tutorials, spec sheets etc to find some suggestions for motors/servos that are suitable for a max payload around 110lbs. The availability of spare wheelchair motors in Australia is minimal therefore would love some suggestions for readily available alternatives.

Would be aiming for a speed around 3-5mph, max 30 degree incline. Config is two wheels and caster. Wheel diameter is yet to be determine but looking at 200mm+ or 8 inches. Happy to take further advice on this. Robot height will be around 5'6"

karstetter
09-12-2013, 02:23 PM
Treadmill motors?

garagelane
09-12-2013, 11:52 PM
Thanks for the suggestion. I've had a bit of a look but unfortunately they're availability is about scarce as the wheelchair.

Are there any general motor recommendations for this weight? eg. ampflow, npc etc. Would prefer under $200-$300 per motor

darkback2
09-13-2013, 12:14 AM
You may be able to get away with a CIM motor and a gear box (http://www.andymark.com/CIM-motor-FIRST-p/am-0255.htm). Trossen used to sell them a while back, but they are pretty much a FIRST robotics type deal...Those bots weigh in at about 150 lb when fully loaded and some of them move pretty quickly. A lot of the AM gear boxes allow you to mount multiple motors on one gear box...

Hope this helps.

DB

tician
09-13-2013, 12:43 AM
There are also the banebots P-60 (for RS-300, RS-500, and RS-700 series motors) and P-80 (for CIM) gearboxes that are kinda scary maxing out at 35 lbf-ft and 85 lbf-ft, respectively.

garagelane
09-15-2013, 10:38 PM
Thanks for the tips. I've been checking them out.

It's for use for a guide/telepresence robot concept so the motor will be running constantly as the robot covers quite a bit of territory over a few hours. In some cases driving at a constant speed for 5-10mins at time to reach a destination.

Hopefully these motors would be ok.

jwatte
09-15-2013, 11:53 PM
As long as you don't overvolt/overload the motors, I think you'll be fine.
I'd be more worried about battery capacity. Several hours of driving takes a *lot* of juice!

garagelane
09-16-2013, 12:29 AM
Noted on the overload :veryhappy:

Regarding the juice, you're spot on. That's where most of the weight comes from. Would be looking at a 60-80AH deep cycle battery AGM at least. That's around 20-25kg (55lbs)

tician
09-16-2013, 01:35 AM
I've been known to harp on about them, but LiFePO4 batteries can be pretty nice (not quite drop-in) replacements for lead-acid. Generally a longer life, much lower weight, and a bit harder to kill by over-discharging. Got a 4S 20Ah prismatic pack in the lab's omni-wheeled rover to power the rover's motors, a DARwIn-OP via tether, and eventually the brain (couple laptops for now) controlling it all. Unfortunately, I am the only grad student in the lab and there are way too many projects using way too many different pieces of hardware to have had a chance to do any stress testing on the new battery (instructional robotics, humanoid robotics, machine vision, agricultural spectroscopy/spectrometry, etc.).

jwatte
09-16-2013, 10:46 AM
I would like to second the recommendation for LiFePO4. Safer than LiPo, good high-discharge and fast-charge capacity, very long lifetime, and much more lightweight than lead-acid. Also lighter-weight than NiMH. Draw-back: A little more expensive than LiPo, and also needs balance chargers, which lead-acid don't.

tician
09-16-2013, 02:47 PM
The 4S 100Ah prismatic pack (without any charge/discharge protection) from the devil I know (http://www.batteryspace.com/lifepo4cellspacks.aspx) is $610 plus ~$40 FedEx Ground shipping (might add a $40~$60 per package HazMat fee; did not for my 20Ah, but who knows). Supposedly a minimum of 80% of initial capacity after 1000+ cycles at 20A continuous discharge. Charging a pack of that capacity in a reasonable amount of time will probably require a significant equipment investment.

A 12V 110Ah lead-acid from same shop is $200 and about three times the weight. The 12V 7Ah lead-acid in my dinky little APC UPS barely lasted two years with no usage other than the occasional <10 second blackout. The 12V 7Ah lead-acid batteries sitting in the lab as the occasional infrared lamp power supply seem to lose capacity if you even look at them.

escott76
09-16-2013, 03:59 PM
Contact builders of combat bots, they use stuff like this all the time. There may even be some aussies out there with some gently used ones they may be willing to part with. The best place to ask would be the RFL forum on Delphi forums. The NPC's are what I would be looking for.

DangerousThing
04-10-2014, 11:31 PM
The 4S 100Ah prismatic pack (without any charge/discharge protection) from the devil I know (http://www.batteryspace.com/lifepo4cellspacks.aspx) is $610 plus ~$40 FedEx Ground shipping (might add a $40~$60 per package HazMat fee; did not for my 20Ah, but who knows). Supposedly a minimum of 80% of initial capacity after 1000+ cycles at 20A continuous discharge. Charging a pack of that capacity in a reasonable amount of time will probably require a significant equipment investment.

I've already decided to go the LiFePo4 route for SA-Groucho. I'm curious why you didn't get balance modules. They seem inexpensive at around $10 per 3.2v module, or $40 for your pack. And from what I've read they would help to keep the cells in balance during charging.

Am I wrong? I've been so before, so please don't hesitate to tell me. The new lithium batteries are new to me and I'm trying to get the right one without paying too much. I think I need a 24V 100AHr battery and I don't want it going bad on me too quickly.

tician
04-11-2014, 12:26 AM
Very limited (personal) funds and I already have a decent external balancing charger (IMAX B6; only 50W charging, but works well enough).

Was also planning to build my own balance/charger/SMPS board with better over/under-voltage protection/isolation for the battery in the hope of making the battery automatically exchangeable at a ground station in the lab. I know I had a post somewhere (think it was the darsha thread) about the hope to make the battery pack completely self-contained with an internal SEPIC or split-pi power supply, and have the only external access be a power connector for charge/discharge and a smaller comms connector. The SEPIC/split-pi would enable just about any voltage to be applied by an external DC power supply to charge the pack and enable the pack to output almost any voltage to the bot. The comms port was to enable the bot to select output voltage and current limits, and provide battery status to the charger/bot.