Gears

shrewdPanther46
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Re: Gears

Postby shrewdPanther46 » November 16th, 2017, 5:31 am

SPP SciO wrote:Just wanted to share some info that may not be helpful for elite teams but may help a team trying to get started -

My students spent a lot of time experimenting with a variety of plastic gears and simple 6v hobby motors. Limited success, mostly because they found it really hard to make all the pieces cooperate, so everything that “worked” was less than ideal. I sprung for this: https://www.servocity.com/970-rpm-econ-gear-motor and they used it to directly drive a wheel. I don’t have any time data to share but it’s much quicker than anything else that they tried. Getting it to run straight was a challenge they quickly figured out how to solve.

In general as a coach I’ve found that if you lack the tools (and knowledge and skills...) to scratch build something well, it’s worth looking at a single vendor for off the shelf supplies. Looking through the servocity site for example, my students can shop for all the parts they’d need, and I can order them knowing it’s money well spent since all the pieces are compatible. The mixing and matching, especially if you don’t have bins of spare parts, is an expensive and time consuming process.


Glad to hear that your students have found success. I'm just curious, how would you connect such a motor directly to the wheel? If the wheel is placed directly on the motor shaft, wouldn't it be necessary to use to separate motors (assuming the optimal 4 wheels, 2 wheel drive in the back), one of them being synchronous (but since its synchronous is compatible with AC, idk how this would work) ? I am curious as to what your plan is.

Also, I was wondering how your students were able to get their vehicle to run perfectly straight with so much ease. From what I have done, no matter how accurate you think your vehicle is, it will never go perfectly straight, resulting in the need for "dynamic" steering...
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Re: Gears

Postby SPP SciO » November 16th, 2017, 6:34 am

shrewdPanther46 wrote:Glad to hear that your students have found success. I'm just curious, how would you connect such a motor directly to the wheel? If the wheel is placed directly on the motor shaft, wouldn't it be necessary to use to separate motors (assuming the optimal 4 wheels, 2 wheel drive in the back), one of them being synchronous (but since its synchronous is compatible with AC, idk how this would work) ? I am curious as to what your plan is.

Also, I was wondering how your students were able to get their vehicle to run perfectly straight with so much ease. From what I have done, no matter how accurate you think your vehicle is, it will never go perfectly straight, resulting in the need for "dynamic" steering...


The wheel they're using has a hub which fits directly onto the motor shaft (which is 4mm) with a set screw. A motor mount keeps it screwed onto the chassis. "Perfectly straight with so much ease" is definitely an overstatement - What I meant is, straight enough to get the centerline bonus over the course of the run. There's definitely room for improvement, for the sake of accuracy (but if a car systemically drifts a certain amount you can adjust for this a little when testing). They have a three-wheeled vehicle, with the one drive wheel centered, and the braking system on the back axle.

Major caveat - I'm in no way advocating this as "the" solution - my students have a long way to go before they're competition-ready and it's a guarantee that the design will change over time. It's quite possible that we'll realize soon why 4-wheeled, gear-driven vehicles are the norm.
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Re: Gears

Postby rajofin » November 16th, 2017, 6:50 am

Can you point me to the hub that you are talking about? Seems like I do not know enough to find one that could directly make wheels rotate without using gears.

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Re: Gears

Postby shrewdPanther46 » November 16th, 2017, 7:28 am

rajofin wrote:Can you point me to the hub that you are talking about? Seems like I do not know enough to find one that could directly make wheels rotate without using gears.


Any wheel hub that fits over the diameter of whatever the motor shaft diameter it is. You can look for one, or create one. Finding parts that are compatible is definitely a challenge for this event, so I suggest you take the time to choose wisely.
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Motor and Axle

Postby TheWingsOfFire » November 16th, 2017, 1:13 pm

What are some ideas on how to actually transfer the motor's power to the axle? Which gears do I use?

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Re: Gears

Postby retired1 » November 16th, 2017, 3:18 pm

Since he is talking about a 3 wheel vehicle, as he mentioned using servo city, it is not difficult to come up with the hub attachment that will fit the wheel and the axle of whatever rpm motor you think will work best for you. It avoids gears very nicely. Using their structural material and attachments , it is not terribly difficult to get the buggy to go rather straight. It will take quite a bit of testing to get it accurate enough to medal in many states.

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Re: Gears

Postby samuel.barlow003 » January 3rd, 2018, 8:40 pm

What size of axle should I put the gears on?

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Re: Gears

Postby shrewdPanther46 » January 4th, 2018, 5:53 am

I doubt it really matters...
I think ours are 1/4 inch. Just make sure its compatible with your parts.
Technically, a wider axle means more rotational inertia-1/2*m*r^2 (or moment of inertia whatever you guys refer to it as), so theoretically, it would be harder to start and stop the car from moving lol. But I really don't think it matters...
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Re: Gears

Postby ASdaBEST » January 8th, 2018, 3:12 pm

I'm using a 1/2 inch thick threaded axle for my battery buggy and I had a hard time finding spur gears that work with my pinion gear for my motor. Also, the pitch of the spur gear and pinion gear must be the same to work, right? If anyone knows a good website for gears, please share it.

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Re: Gears

Postby shrewdPanther46 » January 8th, 2018, 3:24 pm

yup same pitch is needed. I suggest finding a local hobby store, it will always beat out some random online service.
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Re: Gears

Postby retired1 » January 10th, 2018, 2:56 pm

In my opinion, a 1/2 inch shaft is excessive and as you see finding gears to fit can bee a problem, as require much heavier gears.
Both of these add weight which will cause both a slower car and a longer stopping distance.
1/4" is more than enough if you do not abuse the car. I am using 4 mm for a prototype and it works fine other than doing a header down a stair well. To do over, I would probably go with 1/8" .
Most people will go with banebot wheels as they have a lot of options. They are relatively more expensive tho. Servo city wheels will work quite well when matched up with their motors, gears and mounts.

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Re: Gears

Postby shrewdPanther46 » January 11th, 2018, 4:58 am

Yea, I agree. The main thing with finding parts is just making sure everything is compatible.
salty

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Re: Gears

Postby MadCow2357 » March 3rd, 2018, 11:55 am

I know some people mentioned traxxas gears, but I looked on the website and found nothing compatible with my 1/4" threaded rod axle. I am thinking of 3d printing the gears, but that is probably not the best option out there. Ideas?
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shrewdPanther46
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Re: Gears

Postby shrewdPanther46 » March 3rd, 2018, 2:23 pm

OOF dont 3d print your gears the PLA will get rekt

My suggestion: find a local hobby store and just pay them a visit. Im sure you will find something there. Thats what we did, and we are using a 1/4 inch drive/front axle as well. As windu said, plastic is better as it is much lighter (trust the OP experienced dudes lol). I didn't realize until I tried it.
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Re: Gears

Postby MadCow2357 » March 3rd, 2018, 4:14 pm

Thx so much, you just saved me a ton of time by telling me this. I was ready to spend a whole day on learning how to make thread in Tinkercad. :P
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