| Author |
Message |
Mike prince (Quadra)
Member
Username: Quadra
Post Number: 4
Registered: 1-2008
|
| Posted on Thursday, January 10, 2008 - 7:27 pm: |
  |
Paul
The motor has a 25-1 reduction gearbox and at 24 volts the output shaft runs at 200rpm. So I calculate that the motor is running at 5000rpm, does that sound about right.
Mike |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 667
Registered: 10-2004
|
| Posted on Thursday, January 10, 2008 - 8:15 pm: |
|
Mike,
Yes that does sound about right. So, you need a tacho that produces about 7V at full speed. Our MFA 280/1 part number 1401-007 or 1401-008 with a mounting bracket gives 8400 rpm at 12V so at 5000 rpm you get 5000/8400 x 12V = 7.14V which is spot on.
You will also need to retain the motor so that the body does not spin as well which I'm sure you can sort that out either using our motor mount as a basis or make a bracket of your own.
Hopefully that gives you a solution.
Regards
Paul |
Mike prince (Quadra)
Member
Username: Quadra
Post Number: 5
Registered: 1-2008
|
| Posted on Friday, January 11, 2008 - 7:21 pm: |
|
Paul
I have looked at the motors suggested and they seem fine. I have two options with regard to mounting, the first is to attach a tacho motor directly to the end of the shaft somehow and make it fit within the chassis (which shouldn't be a problem). Or I could mount the tacho motor on top of the large motor (more space here) the only issue with this is that I would then have to join the motors with a small belt via some pulleys,(would you use a toothed belt or a smooth belt?)this would mean that the tacho motor would run in the reverse direction to the main motor, does this matter? I assume not. I could very easily make a bracket up to mount both motors together and the main motor has some pre-tapped holes in the emd of the main casing that I could use. i could buy two pulleys of the same overall diameter and then drill one of them out to fit over the 8mm main motor shaft. I assume that once I have done all this then I will need to order a speed controller with the extra tacho board, is this correct. I am just trying to get a feel for total costs. At the moment I think my parts list looks something like this:
1 VTX speed controller
1 Tacho board
2 Tacho motors
1 Plunger throttle pot
4 Small pulleys
2 Belts
can you thing of anything else that I have missed, for controlling the motors.
Thanks again Mike
P.S do I need a tacho motor for each main motor or just one to send the signal to the tacho board? |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 668
Registered: 10-2004
|
| Posted on Sunday, January 13, 2008 - 6:30 pm: |
|
Hi Mike,
I would use a toothed belt as less worry about tension and belt slip. Simply reverse the tacho motor polarity to compensate for reverse direction.
Sorry, I had forgotten you were going to run the main motors in parallel and only use one speed controller. This means only one tacho motor and as long as you do not get wheel spin, I can't see any immediate problems. Two speed controllers and two tacho motors can give improved results for skid steer robot applications but really is an overkill for you.
As for the shopping list, you will need wire (power and multicore), connectors, ignition switch, batteries, maybe a battery voltage monitor, I think that's about it.
Regards
Paul |
steve Hutchinson (Exup)
Member
Username: Exup
Post Number: 1
Registered: 1-2008
|
| Posted on Tuesday, January 22, 2008 - 8:04 pm: |
|
Hi! I was wondering if you would be able to help with the selection of a speed controller for the following application? We are currently building an electric powered racing car for a school project. We are looking for a speed controller to help control this vehicle. It is 24v dc from two large car batteries, forward only, regenerative breaking is not needed, the car runs at between 23-26 amps in normal operation but may draw up to 70amps when setting off etc the car can travel at speeds up to 40mph. A soft start may be an advantage but is not essential, compact (light, cost effective and programmable would also be desirable! thanks for your help! Exup. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 681
Registered: 10-2004
|
| Posted on Tuesday, January 22, 2008 - 9:17 pm: |
|
Steve,
Sounds a good project to be involved in. The 70A is the main factor in recommending a controller. The 4QD Uni Series 8 24V 80A 1514-824 or 1514-825 for the boxed version. You mention programmability, what features are you looking to be able to program as the only model we currently have is the 4QD Pro 150 but is significantly more money that the Uni 8 and I doubt if it would be cost effective for your application? |
steve Hutchinson (Exup)
Member
Username: Exup
Post Number: 2
Registered: 1-2008
|
| Posted on Tuesday, January 22, 2008 - 11:18 pm: |
|
Hi again! Thanks very much for the advice! The race is four hours long and you are allowed two sets of batteries. If you use the batteries up too quickly it means your race is over. Running the car at around 23amps allows the batteries to last the full two hours. We are using a fourteen speed gearbox so are always close to 23 amps but the controller will allow us to run exactly at this optimum current draw. Controlling the speed of acceleration is one thing we would like to look at as well as being able to limit the current draw. ie set at 23 amps so the kids cant go faster when they are out of sight! A programable controller would also be more interesting for the kids. Thanks very much for your prompt responce and advice! |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 683
Registered: 10-2004
|
| Posted on Thursday, January 24, 2008 - 7:31 pm: |
|
Steve, As the higher current is only seen during the acceleration period, you could get away with a smaller controller as most of its time is spent at 23A. Current limit is typically in place at all times which means that it would also limit the acceleration current. So it may be worth considering a speed limiter rather than just a current limiter. Our only programmable speed controller is the Pro 150 and uses a relatively simple plug in programmer. We used to supply a controller that could be programmed via a PC but whilst expensive, it would have had the capability to do what you want. You could also use the serial input function that is available on some of our controllers but that could be quite involved.
Not sure we can really meet your exact needs.
Regards
Paul |
Ccworth555 (Ccworth555)
Member
Username: Ccworth555
Post Number: 1
Registered: 1-2008
|
| Posted on Sunday, January 27, 2008 - 3:59 pm: |
|
I have some purchasing and technical questions regarding the specifications of motor speed controllers and channel mixing devices / methods.
I’m in the process of building an RC ‘agricultural’ skid steer robot which is not for fighting.
There are to be two large diameter wheels which will be driven independently in order to perform skid steer and two trailing jockey wheels. In fact just like a powered wheelchair working in reverse.
The gearing will be arranged such that maximum motor speed (at 12v) will produce a machine speed of around walking pace. I would like to achieve good proportional speed control from zero to maximum forward and reverse speed for each driven wheel.
The machine will be quite heavy at around 450kgs including batteries. Assuming adequate traction, I would like the machine to be able to climb 30 degree slopes.
I would like to purchase from you an array of AGM batteries, motor speed controller and the 6EX 2.4GHz SS Futaba RC set. I would like to have the right hand stick operate exactly like a wheelchair joystick and so I assume I will require some method of channel mixing also.
I’ve already sourced the two motors (12v) from a new heavy duty caravan mover. The details are as follows below. I’m unable to find the ‘make’ of the motors.
Caravan mover model: Powrtouch heavy duty model 3.
Manufacturer: Powrwheel Ltd of Dorset.
Description: PM Geared Motor.
Model: BH-PT1, 12 volts DC
RPM: 3750
Duty: S2
Amps: 50. (each motor)
I would appreciate all the advice you can relay regarding the specifications of all the remaining electrical / electronic equipment I need so that I can purchase this from you in one go.
Many thanks indeed in advance of your reply.
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 687
Registered: 10-2004
|
| Posted on Monday, January 28, 2008 - 8:54 pm: |
|
Chris,
AGM batteries will depend on the running time you expect to get although they are going to be quite large to handle those currents. My initial reaction is that you are going to be under powered with what is about a pair of 480W motors especially with a 30 degree slope. The S2 rating is likely to cause you problems if you run it for too many minutes at high load but without seeing the S2 ratings we can't be more specific.
Yes you will need a mixing function which can be done in the robot or by using the V-tail mixer function in the radio gear.
As for the speed controllers, I would recommend a pair of VTX controllers from 4QD - our part number 1511-023 or the boxed version 1511-033. You will also need a RC interface 3401-005 which also has the mixer function built in.
After that we stock fuses, connectors, cabling, etc..
Regards
Paul |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 2
Registered: 1-2008
|
| Posted on Wednesday, January 30, 2008 - 1:18 pm: |
|
Paul,
Many thanks for your prompt response.
Regarding the AGM battery array, I had planned for 4 off 26Ah batteries along with a 14.4 volt – 50 Amp ‘alternator’ continuously charging them as per a car system.
Will the motor speed controllers be ok with a car alternator output with the batteries acting as a buffer and reserve ?
I take your point regarding the two off 480W motors possibly not being man enough for this heavy robot. Also that there may be a ‘duty cycle’ concern with the S2 rating as caravan movers are probably only specified for occasional use.
I would like to plan for a normal running speed on the flat of around 2.5 kph (0.7m/s) with short duration ‘sprints’ of about twice this equating to walking speed.
Certainly climbing a 30 degree slope can take place at crawling speed, say 0.3m/s.
Bearing this in mind, could you recommend a specification for a pair of 12v motors that may be suitable ?
-
Working on an assumption that I commence using the 480W motors then upgrade to larger 12v motors at a later date, do you think that it may be expedient to initially purchase a pair of higher specification speed controllers ?
Say for example the 4QD Pro 120Amp or a speed controller specification to match the two larger 12v motors that you would recommend ?
Would the higher rated speed controllers function acceptably initially with the smaller 480W motors ?
-
Finally I have two detail questions regarding the Futaba 6EX 2.4GHz RC set.
Having the right hand stick mixed to behave in the same manner as a powered wheel chair, is it possible to position a ratchet on the vertical (forward / reverse) stick action ?
Usually I think that there is a vertical ratchet on the left hand stick for throttle operation. I’d like to have this on the right hand stick also so I can set the robot ‘hands off’ to crawl along at a given speed in a straight line.
Secondly, please could you tell me how the receiver behaves in the event of a transmitter signal loss, does it return all channels to their neutral position or do they simply remain locked in the position they were in when a signal was broken ?
Many thanks for your valuable assistance.
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 692
Registered: 10-2004
|
| Posted on Wednesday, January 30, 2008 - 8:46 pm: |
|
Chris,
A few questions for you:
What will drive the alternator to charge the batteries?
Will the batteries be in parallel?
I will respond on your other points in a later post.
The Futaba set has a ratchet on the vertical axis of the left hand stick but it has always been possible to move the ratchet to other axis so I see no reason why this model should be any different.
Only one channel (throttle) has a programmable failsafe channel which can be programmed to return to neutral. The other channels I believe behave like a standard FM receiver where the pulse width may go out of range so additional external failsafes may be appropriate.
Regards
Paul |
ian reddall
Unregistered guest
|
| Posted on Wednesday, January 30, 2008 - 12:14 pm: |
|
We have an application requiring a electrical drive system. We are manufacturing a hoist which will have a gross weight of approx 300kg running on castor 200mm dia.We have tested the force required to move the hoist at 12kg. We require a suitable dc motor, speed controller etc.
this is for an industrial application therefore must be robust enough for the environment. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 694
Registered: 10-2004
|
| Posted on Wednesday, January 30, 2008 - 8:56 pm: |
|
Ian,
Just a few questions for you:
Are you intending to motorise the 200mm diameter casters?
What is the desired speed as motor power will be a function of the force and speed?
Do you need to be able to vary the speed and if so how?
Do you require any positional feedback?
Regards
Paul |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 3
Registered: 1-2008
|
| Posted on Thursday, January 31, 2008 - 1:29 pm: |
|
Paul,
Thanks for your reply. I'll answer your questions:
1. A small diesel engine will drive the alternator to charge the batteries almost 100% of the time.
But if the engine shuts down I need to extract the robot using battery power only, running for say 15 mins.
2. The 4 off 12v 26Ah battries will be in parallel as the complete robot system is 12v.
If you suggest larger motors then perhaps I require more that 104Ah in the battery array ?
I look forward to hearing your comments regarding the other issues also.
Many thanks for your help.
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 695
Registered: 10-2004
|
| Posted on Thursday, January 31, 2008 - 7:44 pm: |
|
Chris,
Diesel engine, for a moment I thought you had discovered perpetual motion!
Just a tip, we would never put lead acid cells in parallel due to the risk of a battery failing and the other batteries dumping all their energy into the failed battery. We have experienced a number of lead acid battery failures where the plates short out due to mechanical shock.
So, the generator will charge the batteries and provide sufficient power to run the motors. This means you just need enough energy to run the motors for 15 minutes. Assuming full load of 100A, that would be 25Ah/0.6 = 42Ah'ish, your 104Ah sounds more than enough. We will be shortly introducing a new range of SLA batteries.
I can't see a problem with the alternator as long as the speed controller can handle the alternator output voltage.
A controller can be used with smaller motors but controllers with current limit may not be able to be turned down low enough if at all to protect the motor under heavy load or stall conditions. Use 24 or 36V motors and you will be able to get away with a lower rating controller and wiring but that may well mess up your alternator concept.
Hopefully that has addressed your questions but if not, just post again. |
Chris Chellingsworth (Ccworth555)
Member
Username: Ccworth555
Post Number: 4
Registered: 1-2008
|
| Posted on Friday, February 1, 2008 - 10:56 am: |
|
Paul,
Thanks for your prompt reply and advice regarding not running 12v batteries in parallel.
If I put an appropriate fuse in each parallel link, can I avoid the ‘discharge into a damaged battery’ issue ?
I would still like to seek your advice regarding an appropriate pair of 12v motors & controllers (I do need to stay with a 12v system unfortunately). I would gear the motors for the appropriate groundspeed.
The robot parameters are:
# Weight 450Kg max.
# Wheeled skid steer.
# Normal running speed on the flat of around 2.5 kph (0.7m/s)
# Sprint running speed on the flat 5 kph – only occasionally for 5 mins.
# Climbing 30 degree inclines, crawling speed 1kph
# Maximum continuous moving (with diesel engine topping up batteries) would be 2 hours.
(Then stationary engine running to implement battery charging / topping up can take place. I think that the 50 Amp alternator may not keep up with the probable demand from the pair of 12v motors)
# Extraction of robot using just batteries, duration 15 mins.
Q. Can you recommend a 12v motor pair ?
Q. Can you recommend the appropriate speed controllers for the above ?
Q. Can these speed controllers above handle the 14.4v that is usually produced by a car type alternator, albeit smoothed by the battery ?
Q. Would the speed controllers that you recommend above be suitable in the interim with the 480w 12v motor pair I already have ?
Q. Is it possible to let me know when your new battery range will be available to purchase ?
Many thanks
Regards
Chris |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 697
Registered: 10-2004
|
| Posted on Monday, February 4, 2008 - 9:00 pm: |
|
Chris,
A fuse would be a safety measure and certainly worth considering. The only immediate problem I can see with a fuse is when you charge the batteries and then reconnect them in parallel, there will be a current rush as the battery voltages balance out which may pop the fuse.
As for a 12V motor, we do not have anything above 150W in 12V so cannot help. Bosch do make a 12V 400W S1 rated motor which were on Ebay recently and with the right gearing might just give the modest speed you are looking for. Personally I would go for something a bit larger. Would you consider a 24V alternator instead?
12V speed controllers will be fine at 14.4V at the VTX 75 model referred to above will be fine.
Our new batteries should start coming in stock in the next 2-3 weeks.
Regards
Paul |
ian reddall
Unregistered guest
|
| Posted on Friday, February 1, 2008 - 2:58 pm: |
|
Hello Paul
We are looking to drive the castors and need the speed variable upto 4 mph. I was hoping you would be able to supply a speed controller whether it be via a POT or other means, we do not require any positional feed back.
I have looked at your motor options with enclosed spread sheet
MY1020G=20.93kgf @ peak
MY7618M1= 33.54 kgf @ peak
1420-002 = 42.52 kgf @ peak
I would appreciate if you could check the above calculations.
Regards
Ian Reddall
|
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 698
Registered: 10-2004
|
| Posted on Monday, February 4, 2008 - 9:21 pm: |
|
Ian,
I will try and study the spreadsheet later but based on what you have advised so far, you need a final geared motor speed of 171 rpm. Our 1471-103 has a speed of 203 rpm which is pretty close. Its torque is 9.35Nm (0.953 Kg/m). You need 12kg of force at a distance of 0.1m which is 1.2kg/m which is more than this particular motor can provide unless my quick maths is wrong. The Bosch 750W is a great motor and design for industrial use. Using a 19.3:1 reduction, the torque would be approx 42.46Nm or 4.33kg/m which is plenty.
As for a speed controller, a 4QD would be best and we can recommend a particular model once the motor is chosen.
Regards
Paul |
