Im building a 4WD robot capable of 100lbs total. Using the DC calculators I need 4 motors capable of the following: About 100rpm and 900oz-inch, I can’t find that motor on this website and don’t want to spend 8000$ for a platform already made. NPC motors perhaps? Or other direct DC motor companies? Someone help me find a seller for these specs please.
Regards
Do you have something in between? I mean, a fully built DC motor that can be used with 8 inch wheels with the same specs?
I saw a video on youtube where they have to un-mount the whole thing and add grease inside the gears, is this what you mean by greasing? youtube.com/watch?v=ZLLQXDcXAKE
I know it uses a gearbox but its hard to believe 4 7$ dc motors will carry 100lbs around. Does the gearbox magnify the small motor’s power that much? What is the catch compared to 180$ npc motors?
If I buy the motor you suggested can I use the Pololu 18v15 motor controller with it? (I already own one) I see the specs for the motor is 15A stall current.
I see the shaft diameter is 1/2" on these motors, can I find a hub and 8 or 10 inch wheel easily for this size of shaft?
Here’s an example
northerntool.com/shop/tools/product_18845_18845?cm_mmc=CJ--551338--551877-_-Product%20Catalog
Maybe consider adding it to your store?
I’m trying to do the calculations with the motor you suggested, here are the specs on your website:
• Operating voltage: 5v - 15v
• No Load RPM: 7750
• Stall Torque: 29.16 oz-in 205.9 mN-m
• Shaft Diameter: 0.13 in (3.2mm)
How do I do the math for the 1:64 ratio you suggested? I want to make sure I’m buying the right motor/gearbox for my 100lbs robot on this thread. Also, what type of grease can I buy at canadian tire for these gearboxes? Is this good?
My original requirement was 100rpm and 900oz-inch so 1/4 of 1866 oz-in is only 466 oz-in, is this still good? Also, is the greasing a one-time process? or does it need to be re-added?
I guess I don’t understand why you would suggest two Pololu 20A single motor controllers, even if you connect one DC motor to each the stall current on the 550 motors is 85A and those motor controllers can’t go higher than 20A.
how long would it take to receive the gearbox/motors? I see you have nothing in stock… 2-3 days? or 2-3 weeks? Also, the robotshop.com/productinfo.aspx?pc=RB-Ban-71&lang=en-US cim motor with a gearbox looks very powerful, or am I wrong?
Hi starguy,
Welcome to the RobotShop Forum. Consider the RS555 motor with P60 Gearbox. The required gear ratio would be ~64:1 to get roughly 900oz-in and roughly 100rpm.
Hope this helps,
Hi,
Not sure what you mean by “in between”. With the torque and rpm you require, that is the best option. You only need to add grease and attach the motor; The gearbox is already assembled. It will be very difficult to find less expensive and/or smaller motors with the same specifications.
Sincerely,
That’s quite thorough, but yes. It won’t take too long to do that.
Gear boxes reduce the rpm and increase the torque by the gear ratio. If you start with a motor which can produce 0.1oz-in at 10,000pm, and connect it to a 67:1 gear system, the output will be 0.1x67 = 6.7 oz inches at 10,000 / 67 = 149rpm. The motors themselves usually cost less than $20. The NPC system starts out with a beefier DC motor and adds a lower gear ratio, nevertheless, the gearing system is what costs the most money, especially in NPC’s case where the input power is that much greater. Planetary gears provide the highest efficiency (lowest power loss due to internal friction which generates heat).
Hope this helps,
If the motor’s stall is 15A and the Pololu 18V15 can provide 15A continuously, then the two can be used together.
Sincerely,
We don’t carry any 8-10" diameter wheels at this time, so if you find one, you may need to make a custom interface between the 0.5" hub and the wheel.
Sincerely,
For $10 each that looks like a great deal. We will certainly take your suggestion into consideration. That has four mounting holes whereas the hub we carry has six. You would need to make a simple adapter plate (preferably out of metal) to connect the two. Use CAD to mark the locations of the holes and print it 1:1 scale (or CNC it if you have the capability).
Sincerely,
• Operating voltage: 5v - 15v
• No Load RPM: 7750
after 64:1 gear down, the output rpm would be ~7750 / 64 = 121rpm
• Stall Torque: 29.16 oz-in 205.9 mN-m
after 64:1 gear down, the stall torque would be 29.16 * 64 = 1866oz-in
Note that you should NEVER operate anywhere close to stall torque - this will cause irreparable damage to the motor (locked shaft). Consider the maximum continuous torque to be ~1/4 stall.
That grease looks like it would do well - the general idea is to reduce friction and therefore reduce heat which also lowers efficiency (and also makes the gears louder).
Hope this helps,
