# Tray Bot Arm Motors

So I’ve seen tray bots with two motors allocated to the arms and bots with only one motor allocated to the arms. Is there really a consensus on which is better and why?

Well if you use two motors you will be short one motor else where on the bot. probably from the drive. A simple 2 bar can be done with one motor and a nice gear ration. A 100 rpm motor and a 1:7 torque ratio is plenty fast and wont burn out if built correctly.

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My team uses 1 motor arm with a 1:15 gear ratio. And it works great! It never burns out and it has enough torque to lift our robot off the ground

We use two motor 1:10 ratio for the arm and has plenty of torque and speed

curious as to how you achieved this ratio?

12 tooth gear connected to 60 tooth gear driving a 36 tooth gear connected to a 18 tooth sprocket linked to a 12 tooth sprocket with a 12 tooth gear driving a 60 tooth gear with the arm attached.

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woah thats complicated. you’re probably losing a good chunk of your power to friction

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oh yeah, there’s a ton of friction but two 100 rpm motors don’t feel a thing especially with rubber banding on the arm.

but if you have 2 motors why do 1:10? 1:7 should be plenty fast with even 1 100 rpm motor

We don’t have high strength axles and we have a transmission

So the consensus I’m getting is that a single motor arm system works just fine, but using the two motors I assume is much faster. Is that speed worth the loss of the motor from the drive? does the 3 motor drive configuration end up being significantly slower than a four motor one?

A 3m drive is probably not going to be significantly slower than a 4m drive, but you do lose pushing power/torque. I would use a single motor. If you band your arms, you likely won’t need a large ratio because they would help the motor out greatly when lifting cubes to score into towers.

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reduce as much weight and friction as possibly on your arms and I promise that a single 100 rpm motor with high strength axles geared down 1:7 is fast, has enough torque, and really simple. to build.

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We are using a single 100 rpm motor with a 1:7 torque ratio. It lifts perfectly and never burns out. We also banded the arms to allow them to rise more easily and hold its position when risen.

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1 motor is definitely enough to lift the arms. Even if it isn’t you can always fix it with some rubber bands

Would a one motor lift geared 1:15 be strong enough to lift a six bar?

Yea should be. Depends on the quality of the 6 bar but using screw joints and with proper bands, I’m sure you’d be fine.

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I don’t have long enough screws for screw joints would I still be ok?

You can use shorter screws and standoffs. The screw in the joint shouldn’t move, it should be held still with keps nuts, so attaching a stand-off to lengthen the joint shouldn’t be a problem.

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2 inch screw is not expensive at home-depot or Lowe’s.

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